M30 headgasket bore larger than cylinder bore

[epearce]

Building a m30 and up to the stage of fitting the headgasket. Wondering if i should be concerned if the headgasket bore is roughly 2.5mm larger than the cylinder bore? Haven't replaced many headgaskets and wasn't sure if the sealing ring should sit close to the edge of the cylinder wall.

It is a Goetze vrs kit that is meant to be right for my vin.





Any opinions much appreciated.

Eden

[Mark 88/M5 Houston]

Looks fine to me from your photos.

[slammin_e28]

What M30?

[turbodan]

Looks like it may drop the compression ratio slightly but its not worth worrying about.

[ahab]

According to my admittedly rickety calculations, it looks like about 7CCs per cylinder. Instant B35 volume with slightly less than B34 compression! Could the gasket be M90? Sounds like the right dims but I have no idea if they're unique. I have a couple HGs on the shelf at home, including a Goetze and a few Victor Reinz. I'll measure them later tonight and report back.

[turbodan]

Seems like way too much added volume. If I torture the numbers until I think they make sense I come up with 1.26cm^3.

Assuming a 92mm bore or something close to that I get a circumference of ~28.9 cm. I then multiply this by .25 for the 2.5mm wide gap between the gasket and edge of the bore which is 7.225cm^2, which I think is what you came up with. If my logic holds though this would only be valid for a gasket thickness of 10mm whereas the M20 and M30 are actually about 1.75mm thick, so multiplying the 7.225cm^2 by .175 I get the 1.26cm^3 figure.

That's got to be right. I can visualize a volume of 7ml of gasket maker squeezed out of a tube and I can't imagine being able to fit it all in that space.

[Mike W.]

It's a 3.0 or a 3.3, I'm guessing a 3.3 from the size of the crown not to mention the rarity of a 3.0 beyond US spec E12s, and my calcs get about .48CC volume difference, or not enough to worry about. Often the sealing ring is somewhat larger than the actual bore, and this one looks larger than most, but it should be ok IMO. Head gaskets do have the nominal displacements stamped on them, if there's any doubt look for the stamp. It might be for a 3.5, but I'm not sure it's a full 3MM larger. 3.3 bore of course being 89MM and 3.5 92MM.

Edit. Math correction.

[ahab]

I chose a different version of the maths to get to the wrong answer. Especially when I blew the rounding to get 7cc.

π R² on a 92mm bore = 6647.61mm²
π R² on a 97mm bore = 7389.81mm²

Difference = 742.2mm² X 1mm (guess) gasket thickness = 742mm³

or (as Mike predicted) .742cc

Edit, now that Mike has corrected his math I've no idea what's up!

[Mike W.]

I chose a different version of the maths to get to the wrong answer. Especially when I blew the rounding to get 7cc.

π R² on a 92mm bore = 6647.61mm²
π R² on a 97mm bore = 7389.81mm²

Difference = 742.2mm² X 1mm (guess) gasket thickness = 742mm³

or (as Mike predicted) .742cc

Edit, now that Mike has corrected his math I've no idea what's up!

Well for one thing you used 2.5MM difference from edge to edge for 5MM bore difference and I used 2.5MM bore difference. Plus 3.3 vs 3.5, plus a HG IIRC is about 1.7MM thick. I forget what I did to get the .7MM, but it was obvious when I saw it.

[epearce]

I appreciate everyone's thoughts and calculations.

Engine is out of a e23 735i motronic. 89mm bore, so a b32.

General concensus is it should be fine? I'm putting a b35 head on it as well. So I don't want to decrease compression too much, but a b32 has a 10:1 ratio from factory from my research. So I should still be over 9:1 I think?

I'll check head gasket stamping tonight.

Thanks

[turbodan]

With the 89mm bore I'm coming up with 1.048cm^3, with a 1.75mm gasket thickness and an even 2.5mm gap all the way around between the gasket ring and bore. Should result in a negligible, insignificant drop.

[Brad D.]

You can use my compression ratio calculator and just change the bore diameter cell (in cm) and it will recalculate the HG displacement for you. I get 0.74cc change if it is in fact 2.5mm larger.

[ahab]

I don't have a VR but I measured a Goetze against two Elrings and got 94mmØ for the Goetze and 93.5mm for the Elrings (and the package is labeled as such, see below). The water cutouts or definitely different however. I think I got one of the Elrings as a single HG from Pelican last year some time. Not sure of the going rate but I'd part with one if the mm matters that much. The Elring packaging is marked B35, and apparently good for an E23 735, your car. The weird part is the Goetze came out of package with a VR label on it. I think the VRs Pelican sells come as part of the full head kit. So that's what I can tell you, not sure how useful it is!

All 3


Elring Package


VR head set package


Goetze Package (marked VR)


Edit:

You can use my compression ratio calculator and just change the bore diameter cell (in cm) and it will recalculate the HG displacement for you. I get 0.74cc change if it is in fact 2.5mm larger.

Holy shit! My math teacher would be proud.

[Mike W.]

I appreciate everyone's thoughts and calculations.

Engine is out of a e23 735i motronic. 89mm bore, so a b32.

General concensus is it should be fine? I'm putting a b35 head on it as well. So I don't want to decrease compression too much, but a b32 has a 10:1 ratio from factory from my research. So I should still be over 9:1 I think?

I'll check head gasket stamping tonight.

Thanks

I'm not positive, but I think 9.3:1 was the standard compression ratio for 3.3s. Ours were flat tops and 8.8:1, with what looks like about a 2MM crown I'd guess they are 9.3. Use Brad's calculator to figure out what you'll have.

[epearce]

Thanks again everone, amazing forum.

I appreciate everyone's thoughts and calculations.

Engine is out of a e23 735i motronic. 89mm bore, so a b32.

General concensus is it should be fine? I'm putting a b35 head on it as well. So I don't want to decrease compression too much, but a b32 has a 10:1 ratio from factory from my research. So I should still be over 9:1 I think?

I'll check head gasket stamping tonight.

Thanks

I'm not positive, but I think 9.3:1 was the standard compression ratio for 3.3s. Ours were flat tops and 8.8:1, with what looks like about a 2MM crown I'd guess they are 9.3. Use Brad's calculator to figure out what you'll have.

Ah i see. Using that calculator, presuming a 9.3:1 ratio and including the headsurface removal. I get a ratio of approx 8.9:1. Hopefully it's goes alright and isn't too slow.

With the 89mm bore I'm coming up with 1.048cm^3, with a 1.75mm gasket thickness and an even 2.5mm gap all the way around between the gasket ring and bore. Should result in a negligible, insignificant drop.

Thanks for the calculations. Good to know it won't make much difference, so I don't have much to worry about. I think I will still see if i can get a 89mm headgasket if possible as that is what i asked for when ordering the vrs kit. If I can't then no big deal.

[reggid]

i would worry if you are looking at most performance, people go to alot of effort to reduce crevice volumes like raising the top ring and so forth. the effect is more pronounced than just a smidge drop in CR will lead you to believe

[Mike W.]

Elring Package

That's the problem, it's really listed for any M30 when there were 4 different bores. 86 used on 2.5/2.8, 89 used on 3.0/3.3, 92 on 83+ 3.5s and 93.4 used on 82 and earlier 3.5s. All used different head gaskets. If you think that thing looks oversized on your 3.3 think of what it must look like on a 3MM smaller bore 2.8.

[turbodan]

i would worry if you are looking at most performance, people go to alot of effort to reduce crevice volumes like raising the top ring and so forth. the effect is more pronounced than just a smidge drop in CR will lead you to believe

This gap will behave like a quench area. Won't have any significant effect on the combustion chamber other than the added volume.

[reggid]

i would worry if you are looking at most performance, people go to alot of effort to reduce crevice volumes like raising the top ring and so forth. the effect is more pronounced than just a smidge drop in CR will lead you to believe

This gap will behave like a quench area. Won't have any significant effect on the combustion chamber other than the added volume.

it is a crevice volume you will trap mixture than doesn't burn as effectively which is not good for efficiency. if you would remove that much material from the chamber lowering the compression a smidge then who cares but this is not what i am talking about. The goal is to minimize crevice volumes if you want to maximize performance, emissions and economy. it is not as bad a crevice as the gap above the top ring though. Engine will run ok but its just not optimum and gaskets are cheap if there is a more suitable one i would use it.

it would be worse to run with a gasket that overhangs into the bore like MM does though

[turbodan]

It will trap <1cc of air fuel mixture in a 58cc combustion chamber. That's 1.x% of chamber volume. Probably not going to make a difference.

[epearce]

The vrs kit supplier sent me the correct size headgasket after contacting them. Thought i'd be stupid to not do it properly.





Anyone have any arguments for or against using Hylomar spray on a headgasket like this?

[Mike W.]

Much better. Head gaskets are meant to be installed dry, I had one that someone had sprayed copper seal on and it blew, it acted as a lubricant and the gasket just pushed out. Clean the block and head with solvent and install it that way.

[epearce]

Will do. Thanks mike.

[jdb]

Might want to cafully take the sharp edge off the piston dome where the valve smacked it.

Just a thought,

Jeff

[Brad D.]

Much better. Head gaskets are meant to be installed dry, I had one that someone had sprayed copper seal on and it blew, it acted as a lubricant and the gasket just pushed out. Clean the block and head with solvent and install it that way.

I only use copper spray on MLS gaskets.

[Mike W.]

I only use copper spray on MLS gaskets.

Is additional sealant needed on them? I've never used one, do they have a coating on them?