Maximum bore size for 533 block?

[c_spargo]

Will a 533/733 M30 block go right out to 93.4mm like a 535 block? I know it's 86 to start with...

[Rich Euro M5]

Will a 533/733 M30 block go right out to 93.4mm like a 535 block? I know it's 86 to start with...

There shouldn't be any problems boring the block to the proper dimensions for the early 3.5L pistons. However if you are using a 86mm stroke crank you can't use the early 3.5L pistons. They are designed for a 84mm stroke. The 3.4L used in the E28 is a 92mm bore. The crank to use would be one from an S38B35 with the M30 rods and the early 3.5L pistons. This yields 3453cc displacement. If you want a true 3.5L you could use the M30B34's 86mm crank with rods and custom flattop pistons using the dimensions of the S38B36 pistons. This yields 3535cc. Combine this crank/rod/piston setup with a M30B35 head, intake,and 282 degree cam and you'd have an excellent basis for a FI engine. If you use a M30B34 head you'll end up with ~9:1 compression ratio.

FWIW: Jimmy G. has found an inexpensive source for the pistons, but he needs to research the correct piston to cylinder clearance for them. They're Hi-Perf. VW Bug pistons and are allegedly forged. The silicon content of the alloy impacts the expansion rate. If you bore them out too large, the engine will be noisy and probably fail permaturely from piston slap. Once Jimmy finds this info we'll have a source other than JE or Wiseco. One can purchase 3 sets (4 jug/pistons per set) of these piston/jug assemblies for ~$700, this yields two sets of 6 pistons. In other words about 1/3 the cost of JE pistons. The pistons are 93.4mm diameter and I've been told have the correct wrist pin offset and wrist pin to crown height to be used with the 86mm crank and stock M30 rods.

Rich

[cgraff]

Will a 533/733 M30 block go right out to 93.4mm like a 535 block? I know it's 86 to start with...

There shouldn't be any problems boring the block to the proper dimensions for the early 3.5L pistons. However if you are using a 86mm stroke crank you can't use the early 3.5L pistons. They are designed for a 84mm stroke. The 3.4L used in the E28 is a 92mm bore. The crank to use would be one from an S38B35 with the M30 rods and the early 3.5L pistons. This yields 3453cc displacement. If you want a true 3.5L you could use the M30B34's 86mm crank with rods and custom flattop pistons using the dimensions of the S38B36 pistons. This yields 3535cc. Combine this crank/rod/piston setup with a M30B35 head, intake,and 282 degree cam and you'd have an excellent basis for a FI engine. If you use a M30B34 head you'll end up with ~9:1 compression ratio.

FWIW: Jimmy G. has found an inexpensive source for the pistons, but he needs to research the correct piston to cylinder clearance for them. They're Hi-Perf. VW Bug pistons and are allegedly forged. The silicon content of the alloy impacts the expansion rate. If you bore them out too large, the engine will be noisy and probably fail permaturely from piston slap. Once Jimmy finds this info we'll have a source other than JE or Wiseco. One can purchase 3 sets (4 jug/pistons per set) of these piston/jug assemblies for ~$700, this yields two sets of 6 pistons. In other words about 1/3 the cost of JE pistons. The pistons are 93.4mm diameter and I've been told have the correct wrist pin offset and wrist pin to crown height to be used with the 86mm crank and stock M30 rods.

Rich

Rich,

The running clearance for JE and Wiseco pistons are generally ~2x the spec's for the stock BMW pistons; as you said for reasons of material spec / expansion rates, on a street motor. Different specs for race, etc.

Those bug pistons need to be measured, in order to verify what their actual OD is. Pistons are generally made for a certain bore spec. E.g. Bore of 93.4mm minus running clearance. So if their actual OD is too small, then there is an increased likelyhood of piston slap, as you said.

The specs for BMW's pistons and bores are found in the TIS and Bentley.

-Chris

[c_spargo]

I've actually already BUILT a 92mm bug-piston'ed motor for the M30B34 in my 535i.

Worked excellently, apart from the tiny problem of the shop not getting the cylinder bores right and the pistons slapping away straightaway.

I've picked up this 35K mile '79 733i, and since the head is already off and there's very light surface rust in a couple of spots on the cylinder walls (head's been off for 10 years, rings and such were oiled properly, but the walls got dry in a couple spots), my mind started turning about what else would go in THIS motor. I don't think the tiny bit of corrosion I have will really create any problems at all, just got me thinking those evil HP thoughts...

The trouble with the bug pistons is that they're a nominal 91.93mm, vs the 91.97 of the OEM and 92mm bore (plus whatever wear you have). The next oversize is 94mm, which is supposedly too big for a B34 block.

Starting with a 733 block, however, one could bore directly to a 91.93 piston with proper clearances. Since I also have an 86mm crank from a B34 and the rods to go with it, it seems a relatively easy assembly.

[cgraff]

The running clearance, if I remember correctly (please check the Bentley or TIS for me) is 0.02 to 0.05mm for a stock BMW piston. That means a piston diameter of 91.97mm will be ok for a nominal bore size of 92.00mm.

JE Custom pistons, for instance on an M30 application, have a spec of running clearance of: 0.0035 – 0.0040 inch (0.089 mm to 0.102 mm)

http://www.jepistons.com/pdf/2006-sportcomp1.pdf

I don't know what the spec is for the bug pistons.

-Chris

I've actually already BUILT a 92mm bug-piston'ed motor for the M30B34 in my 535i.

Worked excellently, apart from the tiny problem of the shop not getting the cylinder bores right and the pistons slapping away straightaway.

I've picked up this 35K mile '79 733i, and since the head is already off and there's very light surface rust in a couple of spots on the cylinder walls (head's been off for 10 years, rings and such were oiled properly, but the walls got dry in a couple spots), my mind started turning about what else would go in THIS motor. I don't think the tiny bit of corrosion I have will really create any problems at all, just got me thinking those evil HP thoughts...

The trouble with the bug pistons is that they're a nominal 91.93mm, vs the 91.97 of the OEM and 92mm bore (plus whatever wear you have). The next oversize is 94mm, which is supposedly too big for a B34 block.

Starting with a 733 block, however, one could bore directly to a 91.93 piston with proper clearances. Since I also have an 86mm crank from a B34 and the rods to go with it, it seems a relatively easy assembly.

[c_spargo]

The running clearance, if I remember correctly (please check the Bentley or TIS for me) is 0.02 to 0.05mm for a stock BMW piston. That means a piston diameter of 91.97mm will be ok for a nominal bore size of 92.00mm.

JE Custom pistons, for instance on an M30 application, have a spec of running clearance of: 0.0035 – 0.0040 inch (0.089 mm to 0.102 mm)

http://www.jepistons.com/pdf/2006-sportcomp1.pdf

I don't know what the spec is for the bug pistons.

Note that the bug pistons are 91.93, not 91.97 like OEM cast pistons. Add in 150K miles of wear and a quick straight hone, and clearances get big fast.

[cgraff]

The running clearance, if I remember correctly (please check the Bentley or TIS for me) is 0.02 to 0.05mm for a stock BMW piston. That means a piston diameter of 91.97mm will be ok for a nominal bore size of 92.00mm.

JE Custom pistons, for instance on an M30 application, have a spec of running clearance of: 0.0035 – 0.0040 inch (0.089 mm to 0.102 mm)

http://www.jepistons.com/pdf/2006-sportcomp1.pdf

I don't know what the spec is for the bug pistons.

Note that the bug pistons are 91.93, not 91.97 like OEM cast pistons. Add in 150K miles of wear and a quick straight hone, and clearances get big fast.

I meant the spec for the bug piston's running clearance.
That's what I don't know.

If for instance it's 0.07mm +/- 0.01mm, then a 92.00 measured nominal bore would have been OK. I'm guessing because of the problems, either the spec isn't 0.07mm or the bore has worn past spec clearances, as you say.

-Chris

[cgraff]

The trouble with the bug pistons is that they're a nominal 91.93mm, vs the 91.97 of the OEM and 92mm bore (plus whatever wear you have). The next oversize is 94mm, which is supposedly too big for a B34 block.

Why would it be too big?

S38 B38 was running 94.5mm if I remember correctly. The regular M30 (M90) had a block with 93.4mm nominal bore, with a 0.5mm overbore spec possible. Running 94.00mm should be perfectly acceptable given BMW's tolerances/specs for the block. It's going to be necessary for the machine shop to keep the conicity and out-of-roundness within spec, but otherwise should be perfectly ok.

Hmm....94mm bore....86mm stroke....I'm thinking 3580cc of monster M30...what're you thinking?

-Chris

[c_spargo]

The trouble with the bug pistons is that they're a nominal 91.93mm, vs the 91.97 of the OEM and 92mm bore (plus whatever wear you have). The next oversize is 94mm, which is supposedly too big for a B34 block.

Why would it be too big?

S38 B38 was running 94.5mm if I remember correctly. The regular M30 (M90) had a block with 93.4mm nominal bore, with a 0.5mm overbore spec possible. Running 94.00mm should be perfectly acceptable given BMW's tolerances/specs for the block. It's going to be necessary for the machine shop to keep the conicity and out-of-roundness within spec, but otherwise should be perfectly ok.

Hmm....94mm bore....86mm stroke....I'm thinking 3580cc of monster M30...what're you thinking?

-Chris

I understood that maximum standard bore on an M30B34 block was 93.4 - guess I should have asked around harder first before leaping to conclusions.

[Mike W.]

Will a 533/733 M30 block go right out to 93.4mm like a 535 block? I know it's 86 to start with...

Getting back to your original question, I wouldn't, and I have bored a 3.3 block out to 92. 3.3's start at 89 though, not 86, that's the 2.5 and 2.8 bore.

I do have 145K on it now, but I changed heads when it only had 20K on it and noticed the bores were worn in an odd pattern due to the thiness of the bore and the torquing of the head. You could see right where the head bolts went into the block. That was with a 3MM bore, so I would not even think about doing a 4.4MM bore. This was just wear in the honing, not anything measureable, but observable.

On the other hand, as far as the .04MM piston size difference goes, that's not much at all. I've seen BMW manuals that spec'd at least .004" clearance and I've put together quiet BMW engines with running clearance in the .006-.007 range. No issues. That extra .04MM comes out to be about .0015", for a bore clearance of about .003 if the bores are in good shape. Not excessive at all in my experience.

[c_spargo]

Will a 533/733 M30 block go right out to 93.4mm like a 535 block? I know it's 86 to start with...

Getting back to your original question, I wouldn't, and I have bored a 3.3 block out to 92. 3.3's start at 89 though, not 86, that's the 2.5 and 2.8 bore.

I do have 145K on it now, but I changed heads when it only had 20K on it and noticed the bores were worn in an odd pattern due to the thiness of the bore and the torquing of the head. You could see right where the head bolts went into the block. That was with a 3MM bore, so I would not even think about doing a 4.4MM bore. This was just wear in the honing, not anything measureable, but observable.

On the other hand, as far as the .04MM piston size difference goes, that's not much at all. I've seen BMW manuals that spec'd at least .004" clearance and I've put together quiet BMW engines with running clearance in the .006-.007 range. No issues. That extra .04MM comes out to be about .0015", for a bore clearance of about .003 if the bores are in good shape. Not excessive at all in my experience.

Good stuff - thanks.

I guess if the 3.3 starts at 89, the 92 would go in perfectly anyway. No need to get greedy.

[Mike W.]

One last thought. Check the machine shop prices for boring before you start, it was $200 for me to go from 89 to 92 back in 99, and prices haven't gone down since then.

[Jimmie G]

Allright I have a L block and m106 and a couple of b35 blocks all torn down and have looked them over good and from what I have been able to measure the L block cylinders that are 93.4 bore are the same outside diameter as the b35 and m106. So the m106 and b35 once bored to 94mm will be them same as the L block at 94mm hope this is not too confusing.

So basically they are the same cylinder thickness to start with the L bock is just taken out more when built to fit 93.4 pistons this is what Im thinking but since I didnt build motors for bmw I cant say for sure and could be corrected on this. This is my hunch at this point. I have measured the vw pistons and they are tits on what they say they are I dont have them hear at the house but I think they were like spargos but 2mm larger say 93.93mm which you would think means they should have .002 thds clearence.
I also measured the vw jugs that come with the set and they are 94mm tits on also I was using inside and outside micrometers!

Jimmie

[Mike W.]

Ok, I think the question was on boring a 3.3 block, not a 3.5 block. And I'm not familiar enough with the 93.4 blocks to comment on them. Regardless, how are you measuring the OD of the cylinder sleve without destroying the block? I've heard it can be done ultrasoniclly, but I'm not familiar with the process. And unless you are measuring the liner thickness or OD, you don't have a useful block measurement.

[c_spargo]

Ok, I think the question was on boring a 3.3 block, not a 3.5 block. And I'm not familiar enough with the 93.4 blocks to comment on them. Regardless, how are you measuring the OD of the cylinder sleve without destroying the block? I've heard it can be done ultrasoniclly, but I'm not familiar with the process. And unless you are measuring the liner thickness or OD, you don't have a useful block measurement.

I think the previous poster's comments about deformation at the bolt holes would imply that you're getting dangerously close to it at 94. Do-able, but not optimal. If I was starting at 89, I'd likely only go to 92. How significant could the bore difference be from 92 to 94 in hp?

Since the block itself is cast iron, isn't the material homogenous throughout the block? Or is there a separate "liner" cast into the cast iron?

[cgraff]

Ok, I think the question was on boring a 3.3 block, not a 3.5 block. And I'm not familiar enough with the 93.4 blocks to comment on them. Regardless, how are you measuring the OD of the cylinder sleve without destroying the block? I've heard it can be done ultrasoniclly, but I'm not familiar with the process. And unless you are measuring the liner thickness or OD, you don't have a useful block measurement.

There is no 'cylinder sleeve' in an M30. It's a steel block. All you measure is the bore, conicity, and out of roundness of the bore. There's no other measurements you need.

The cylinder spacing is exactly the same for any M30 block. In fact, it's the same for an M10 (100mm). If you have a 92mm bore, your cylinder wall thickness is 8mm. If it's 94mm, it's 6mm. It's pretty straightforward.

Getting back to the original wall thickness issue, the only BMW engine that's had that issue is the S38 B38. Which has a 94.5mm bore, and therefore a 5.5mm wall thickness. On an aluminum block (with steel or alusil sleeves) that is too thin. On a steel block, it's just marginal. That is why the S38 B38 can have bore wear issues.

Every M30 that I've seen torn down (stock or bored out) has had no measurable issues with excessive bore wear - the only thing would be that they have needed to be rehoned.

-Chris

[Mike W.]

There is no 'cylinder sleeve' in an M30. It's a steel block. All you measure is the bore, conicity, and out of roundness of the bore. There's no other measurements you need.

No, not at all. First off, it's a cast iron block, not that it's terribly important. And I might have been misleading about a sleeve. It's not a removable liner such as I think it was Alfa used to use. (or maybe still does for all I know) but it's not a solid block either, it's got water jacketing. Look down the water passages and you can see how it's cast, like a sleeve, with a top and bottom plate. As I said, I bored an engine from 89 to 92 and it looked like no other I'd seen when I swapped the head, it was obvious the bores weren't round after being stretched by the head bolts. Which doesn't happen in regular 3.5's. Normally there is no evidence of bore distortion. And as far as no measureable wear on the blocks, I've taken apart several, mostly 60's- 70's vintage, where I had to ream the ridge to remove the pistons. That's measurable wear. I did an M10 engine (an extremely close cousin as you know) that must have had .003 or .004" wear on the top of the cylinders.

And are you suggesting all M30 engines share the same casting, from the 86MM bores of 2500-2800 engines to the 93.4 of early euro 3.5's? That would be a chunk of weight alone just in the bores. Please, I know this might sound insulting, but I don't mean it that way, but until you have bored an engine 3MM, then taken it apart, at least to the point where you can see the bores and a wear pattern, take my word for it, they aren't all the same casting.

[cgraff]

There is no 'cylinder sleeve' in an M30. It's a steel block. All you measure is the bore, conicity, and out of roundness of the bore. There's no other measurements you need.

No, not at all. First off, it's a cast iron block, not that it's terribly important. And I might have been misleading about a sleeve. It's not a removable liner such as I think it was Alfa used to use. (or maybe still does for all I know) but it's not a solid block either, it's got water jacketing. Look down the water passages and you can see how it's cast, like a sleeve, with a top and bottom plate. As I said, I bored an engine from 89 to 92 and it looked like no other I'd seen when I swapped the head, it was obvious the bores weren't round after being stretched by the head bolts. Which doesn't happen in regular 3.5's. Normally there is no evidence of bore distortion. And as far as no measureable wear on the blocks, I've taken apart several, mostly 60's- 70's vintage, where I had to ream the ridge to remove the pistons. That's measurable wear. I did an M10 engine (an extremely close cousin as you know) that must have had .003 or .004" wear on the top of the cylinders.

And are you suggesting all M30 engines share the same casting, from the 86MM bores of 2500-2800 engines to the 93.4 of early euro 3.5's? That would be a chunk of weight alone just in the bores. Please, I know this might sound insulting, but I don't mean it that way, but until you have bored an engine 3MM, then taken it apart, at least to the point where you can see the bores and a wear pattern, take my word for it, they aren't all the same casting.

OK, I *was* a little bit exaggerating when I said there is no bore wear....But to my point, M30s do not wear the block like other engines do, say for example a US S52. This is a measureable fact, ask any engine rebuilder. Yes, they do wear - everything wears - but they are a strong motor that generally needs rehoning. Like I said before, no sleeve on an M30. I've seen numerous (mostly 1980s) M30 blocks with their original honing intact, which doesn't preclude the fact that there is *some* bore wear but does illustrate how strong the motors are. It doesn't preclude the fact that however, if you do bore these motors out, there can be distortion and the bores wear in oval pattern. Thus BMW has in its TIS specifications for conicity and out of roundnesses.

M30s do use the same casting. I cannot attest to older vs. newer, i.e 1960s vintage 2500 vs 1980s B34/B35 series, which definitely BMW could have significantly changed the casting on. However, If they didn't have the same casting then the heads wouldn't be swappable b/c the water and oil passages wouldn't line up. (That is, it is the same casting, excepting the variance in mounting bosses which are known to differ, but that is all external block adjustments - internally it is the same). Also, how come reputable engine tuners like Hartge/Alpina could bore a 528i (80s) with no problems to 93.4mm? Can you answer that for me? Look through all the literature, if you don't believe me - it's been done before without problems, by reputable tuners.

Also I have bored an engined personally to 93.4mm. So I do know what I'm talking about, so please don't infer that I don't by saying things like what you said above, please. I have not driven/run the motor long enough to have to disassemble it again and then measure the wear. From your description of your particular issue, I do think it's a slightly different problem than 'overboring', as you claim. However, the biggest issue you may have had, is if you bored the motor without a torque plate. What you describe suggests the fact that once the head was torqued to the block, there was distortion, and thus the bore wore. When boring a block one must always use a torque plate, because otherwise you will have some distortion, and thus can have excessive bore wear.

If you bore your engine significantly, then doing so without a torque plate will introduce distortion in the bores when you do assemble the engine and torque the head on. This can lead to the wear patterns you've indicated above.

-Chris

[Rich Euro M5]

However, the biggest issue you may have had, is if you bored the motor without a torque plate. What you describe suggests the fact that once the head was torqued to the block, there was distortion, and thus the bore wore. When boring a block one must always use a torque plate, because otherwise you will have some distortion, and thus can have excessive bore wear.

Which is the reason why I have my machine work done at shops with specific BMW experience and proper tooling.

Rich

[M635CSi]

However, the biggest issue you may have had, is if you bored the motor without a torque plate. What you describe suggests the fact that once the head was torqued to the block, there was distortion, and thus the bore wore. When boring a block one must always use a torque plate, because otherwise you will have some distortion, and thus can have excessive bore wear.

I'm not a big fan of boring cylinder blocks to correct damage or increase cylinder volume but it does work. Installing a torque plate (and other engine parts) is a cute idea but understand that boring the cylinder block increases that which the torque plate seeks to correct. Not all individual M30 blocks have the same cylinder wall thickness. I suspect the benefit of using a torque plate is exaggerated on the M30 block while the effect of thermal load and combustion pressure is ignored.

[Mike W.]

I agree that M30's don't generally have much wear in the block, and the original crosshatching is usually present. Just that I have seen some with significant wear that needed a ridge reamer to remove the pistons. And later ones seem better than earlier ones.

What block did you start with when you bored to 93.4, I didn't mean to imply a standard 92 block shouldn't be bored to that size.

But I still disagree on all the blocks being the same. Just from a manufacturing point of view, they wouldn't want to machine out 7MM of hard cast iron more than they needed to. Also, why do they indicate the bore (indirectly) on the block, using 2.5/2.8, or 3.0/3.3 or 3.5? The M30 is an engine family with similar architecture such as bore centers, deck height and many more things. But those castings have a core and can be the same on the outside but not the same on the inside. I wouldn't even think they would want an extra thick cylinder wall just for heat transfer purposes.

Since we both seem sure of ourselves and our point of view, lets agree to disagree.

[cgraff]

What block did you start with when you bored to 93.4, I didn't mean to imply a standard 92 block shouldn't be bored to that size.

92mm.

But I still disagree on all the blocks being the same. Just from a manufacturing point of view, they wouldn't want to machine out 7MM of hard cast iron more than they needed to. Also, why do they indicate the bore (indirectly) on the block, using 2.5/2.8, or 3.0/3.3 or 3.5? The M30 is an engine family with similar architecture such as bore centers, deck height and many more things. But those castings have a core and can be the same on the outside but not the same on the inside. I wouldn't even think they would want an extra thick cylinder wall just for heat transfer purposes.

Yes, you're right that for manufacturing purposes, BMW is not going to use the same casting and then bore to spec. What they are going to do is cast the block, then machine the required surfaces (bottom, top, front, back, bosses, threads, and then the cylinders). They're not going to cast say 85mm diameter hole, then bore to 92mm. No.....they're going to cast a 91mm hole, bore to 92mm. Or cast a 88mm hole, bore to 89mm.

However, with a 100mm spacing, and 86mm cylinder bore, you still have 14mm wall thickness between the cylinders. It's going to be extra thick there - you can't get away from that. Also, given the fact that the heads are the same between a 525i, 528i, 535i, you know that the interface (coolant passages, oiling passages, head bolt holes, etc) are the same there. Similarly, same oiling pump, water pump, etc isn't going to change the passages there either. BMW won't change the casting for these purposes when they don't have to. They will change the casting for the cylinder holes, as said above.

Now, can you explain to me why when looking up the weights (ETK) of the various blocks between E28s you will see that the 525i block is heavier than the 528i, which is heavier than the 535i? (now, granted this is *with* pistons, which you have to weigh separately to get an accurate measure), but a piston isn't going to make up the weight difference of hogging out more material that a 535i has.

Also, given the fact that Alpina and Hartge both started with 528i blocks and bored them out to 93.4mm and 92mm (depending on 3.5 motors), there doesn't seem that there would be a problem doing the same thing yourself (given the right tooling, etc, etc).

FYI, if people need a torque plate (either made or lent), feel free to contact me.

-Chris

[Mike W.]

However, with a 100mm spacing, and 86mm cylinder bore, you still have 14mm wall thickness between the cylinders. It's going to be extra thick there - you can't get away from that.

Ah, if only I had a nice cad program so I could draw what I'm trying to explain.

But no, I again disagree. You don't have a 14MM wall thickness, the cylinders aren't siamesed, there is water jacketing all the way around the smaller bored cylinders. You can stick a piece of wire in the water jacket on the intake side and see it on the exhaust side. I don't remember at what bore diameter it went away, but it is that way.

Now, can you explain to me why when looking up the weights (ETK) of the various blocks between E28s you will see that the 525i block is heavier than the 528i, which is heavier than the 535i? (now, granted this is *with* pistons, which you have to weigh separately to get an accurate measure), but a piston isn't going to make up the weight difference of hogging out more material that a 535i has.

No I can't. Larger displacement should weigh more due to a longer throw crank and larger pistons. Except I think BMW lists engine weights for complete engines including intake, exhaust and all. But I'm not sure on that.

Now this I don't know, but are you sure Alpina etc started with a 2.8 engine or a 528i car since it was lighter and cheaper?

[cgraff]

However, with a 100mm spacing, and 86mm cylinder bore, you still have 14mm wall thickness between the cylinders. It's going to be extra thick there - you can't get away from that.

Ah, if only I had a nice cad program so I could draw what I'm trying to explain.

But no, I again disagree. You don't have a 14MM wall thickness, the cylinders aren't siamesed, there is water jacketing all the way around the smaller bored cylinders. You can stick a piece of wire in the water jacket on the intake side and see it on the exhaust side. I don't remember at what bore diameter it went away, but it is that way.

See if you can remember where you saw this. Because I've never seen this. Not on the M30s I've seen.

Now, can you explain to me why when looking up the weights (ETK) of the various blocks between E28s you will see that the 525i block is heavier than the 528i, which is heavier than the 535i? (now, granted this is *with* pistons, which you have to weigh separately to get an accurate measure), but a piston isn't going to make up the weight difference of hogging out more material that a 535i has.

No I can't. Larger displacement should weigh more due to a longer throw crank and larger pistons. Except I think BMW lists engine weights for complete engines including intake, exhaust and all. But I'm not sure on that.

Check it for yourself. It's in the block housing subsection.

Now this I don't know, but are you sure Alpina etc started with a 2.8 engine or a 528i car since it was lighter and cheaper?

I can check my literature when I get home.

[c_spargo]

I just went out and looked at the bare M30B34 block in the back of my truck.

The water jacket definately does NOT extend between the cylinders. I even took a long skinny zip tie and tried to slide it down there to see if it was tricking my visually, and it's not.

It would make sense that BMW would use the same casting mold for all these. It would ALSO make sense that they could vary the cylinder bore size when casting to accomodate the model they are building.

The difference in material between an 86mm bore M30 and a 92mm bore can be more or less computed. A napkin estimate results in about an 817 gram difference in weight between an 86mm block and a 92mm block. By the time you take the weight of the pistons into account, they're withing a pound of each other I imagine...

[cgraff]

I just went out and looked at the bare M30B34 block in the back of my truck.

The water jacket definately does NOT extend between the cylinders. I even took a long skinny zip tie and tried to slide it down there to see if it was tricking my visually, and it's not.

It's not the B34 that we're discussing here. We know that the water jacket doesn't extend between the cylinders. Mike was saying that there are other blocks (i.e. 2.5 or 2.8 liter) where it does, and thus there is a limit to boring those blocks below what a B34/B35/M90 would be. That's our point of contention. Thus we're both going back to the lab to get our references.

The difference in material between an 86mm bore M30 and a 92mm bore can be more or less computed. A napkin estimate results in about an 817 gram difference in weight between an 86mm block and a 92mm block. By the time you take the weight of the pistons into account, they're withing a pound of each other I imagine...

800 g * 6 I hope. Because I did the computation myself and got ~3 kg/block difference for about every 3mm in bore diameter difference.

-Chris

[cgraff]

OK, so I checked in some of my references.

1. I was wrong about the engines in Alpinas/Hartges, they used BMW's 3453cc engine then 3430cc engines straight away, and the 528i *chassis*. I initially thought they bored out the 2.8s when the 3453cc M90 motor was discontinued.

2. There were only 4 bores the M30 family came with in production, 86mm, 89mm, 92mm and 93.4mm. There is probably no contention that the 92mm and 93.4mm bore blocks can go up in boring.

3. There are illustrations for the early M30s (i.e. 2.5, 2.8, and 3.0 liters that go up to 89mm) that allude to a water jacket in between the cylinders. However, these are illustrations - not drawings or the real thing. And they use the same illustrations for later M30s B34 and B35, which we know not to be the case.

4. BMW racing used M30 blocks in 1973 that increased displacement to 3.15, 3.3, and 3.5 liters (M52/1/2/3). Output of 340, 355, and 370 bhp, respectively. Last of the 2 valve designs to go racing. In 1974 they went to 4 valve heads, with the same capcities, and 415, 430, and 440 bhp, respectively. The 3.5 liter used a bore of 94mm. I quote "the narrow webs (6mm) between its cylinders (bore 94mm) created no problems." This doesn't mean that they didn't use a new casting; but it also doesn't mean they didn't use the old casting. It's nonetheless, a piece of information....M30 blocks in the early 70s were bored significantly.

5. Given that a wall thickness of a minimum 6-7mm seemed appropriate at the time, I personally do not see how an 89mm or 86mm bore with 100mm spacing could have a water jacket *in between* cylinders. The passages could be larger at the sides between the outside of the block and the cylinders, but I can't see why BMW would allow that, given that they built this motor knowing fully well they were going to increase displacement. I would want someone who has got an early 2.5, 2.8, or 3.0 block that they have sectioned or otherwised shown and measured the wall thickness between the side of the block and cylinder, as well as in between the cylinders to show me the water jacket there.

-Chris

[Rich Euro M5]

OK, so I checked in some of my references.

1. I was wrong about the engines in Alpinas/Hartges, they used BMW's 3453cc engine then 3430cc engines straight away, and the 528i *chassis*. I initially thought they bored out the 2.8s when the 3453cc M90 motor was discontinued.

2. There were only 4 bores the M30 family came with in production, 86mm, 89mm, 92mm and 93.4mm. There is probably no contention that the 92mm and 93.4mm bore blocks can go up in boring.

3. There are illustrations for the early M30s (i.e. 2.5, 2.8, and 3.0 liters that go up to 89mm) that allude to a water jacket in between the cylinders. However, these are illustrations - not drawings or the real thing. And they use the same illustrations for later M30s B34 and B35, which we know not to be the case.

4. BMW racing used M30 blocks in 1973 that increased displacement to 3.15, 3.3, and 3.5 liters (M52/1/2/3). Output of 340, 355, and 370 bhp, respectively. Last of the 2 valve designs to go racing. In 1974 they went to 4 valve heads, with the same capcities, and 415, 430, and 440 bhp, respectively. The 3.5 liter used a bore of 94mm. I quote "the narrow webs (6mm) between its cylinders (bore 94mm) created no problems." This doesn't mean that they didn't use a new casting; but it also doesn't mean they didn't use the old casting. It's nonetheless, a piece of information....M30 blocks in the early 70s were bored significantly.

5. Given that a wall thickness of a minimum 6-7mm seemed appropriate at the time, I personally do not see how an 89mm or 86mm bore with 100mm spacing could have a water jacket *in between* cylinders. The passages could be larger at the sides between the outside of the block and the cylinders, but I can't see why BMW would allow that, given that they built this motor knowing fully well they were going to increase displacement. I would want someone who has got an early 2.5, 2.8, or 3.0 block that they have sectioned or otherwised shown and measured the wall thickness between the side of the block and cylinder, as well as in between the cylinders to show me the water jacket there.

-Chris

Originally the question was regarding borng of a 3.2 liter block from a 533i, not the early 2.5 - 3.0 liter blocks. In the case of the 3.2 liter block we only have to check the casting number, if it's the same as used on the later 3.4 liter engine I think it would be OK to bore it.

Rich

[c_spargo]

800 g * 6 I hope. Because I did the computation myself and got ~3 kg/block difference for about every 3mm in bore diameter difference.

-Chris

Doh! Yup. Forgot the *6 thing. That's what I get for being in a hurry at work...