New M20 Head Gasket Option

[82eye]

Aha- it's a 'crush to spec' head gasket!


But what's happening with M10 and M20 head bolts and gaskets is that the BOLT isn't
tty (it's way too big) but the head gasket CRUSH is what they're adjusting with the '25 degrees and another 25 degrees'
thing.

i've never seen a head work or gasket diy that didn't include new head bolts. i've done them on both m10's and m20's. can you show me one where it says it's ok to reuse the head bolts ?

[TobyB]

Aha- it's a 'crush to spec' head gasket!

So doing lots of M54s with tty bolts, they get 3/4 a mm or so of stretch. 180 degrees in 2 90's.
VW gets 1.5- 2, and it makes me want to throw up, that 'soft' feeling.
You know what I mean, that 'it's gone soft, now I've stripped it' feeling.

But what's happening with M10 and M20 head bolts and gaskets is that the BOLT isn't
tty (it's way too big) but the head gasket CRUSH is what they're adjusting with the '25 degrees and another 25 degrees'
thing.
If you go too far, you can feel the resistance (which has been pretty constant for the 25 degrees) spike as the head bottoms.
I tend to think of it like the crush washers on spark plugs- you can feel it touch, then crush at a constant pressure, then when
you've re- used them too many times, they bottom and now feel like a Ferd.

'Course, if people are now using M54 stretch bolts (or similar) on E30's, ignore me.
But last I did it, the bolts weren't tty. And yes, it's been 15 years or so, maybe there ARE tty's for the M20?
They weren't when they were new.

t

[digger]

...but M20 head bolts aren't tty... ?

t
just the rods, ma'am, just the rods.

idk for sure, but if you are doing a "snug tight" and then angle tighten with a bolt that is waisted in the middle and a one time use thats normally TTY

[TobyB]

...but M20 head bolts aren't tty... ?

t
just the rods, ma'am, just the rods.

[digger]

Last may when I got my 2.9 stroker going I had lots of problems with my hg leaking. I pulled the head 5 total times and tried every brand. It turned out that I just needed to keep heat cycling and retorquing the arp studs. It probably took about 15 times and I also used the anerobic sealer in a couple spots. I think any of the gaskets would have worked if I stuk with it. So just don't give up on the new hg so easy.

McGyver I have a torque plate for the m20 if your machine shop hasn't got that far yet. What shop are you using for the work?

IMO its the same issue with VC gaskets, periodically retorque until they nolonger "budge" and the leaks will stop.

From a HG perspective this is one advantage to the ARPs as you can keep retorquing, you could argue that the TTY factory style bolts arent as sensitive but anecdotally the same issue with leaky oil return occurs on factory bolts and ARPs from what it seems

[kyleconstantine]

Always curious about the machine shops around here. I went to bison motorworks on someone's suggestion and they did good as far as I can tell. Yeah let me know if you need it I'm happy to lend it out locally. I wasn't cheap and it will be years before I need it again.

[McGyver]

digger , It makes sense that that an NA engine struggles to flow with 20% more volume. I'm definitely going to stick with the 2.7i approach.

Last may when I got my 2.9 stroker going I had lots of problems with my hg leaking. I pulled the head 5 total times and tried every brand. It turned out that I just needed to keep heat cycling and retorquing the arp studs. It probably took about 15 times and I also used the anerobic sealer in a couple spots. I think any of the gaskets would have worked if I stuk with it. So just don't give up on the new hg so easy.

McGyver I have a torque plate for the m20 if your machine shop hasn't got that far yet. What shop are you using for the work?

Oh yeah, I forgot you had that! They already align honed the main bearings. Is a torque plate needed for that step? The block is currently getting magnafluxed. I'll text you about that torque plate!

I went with BMS (Budz Motor Sport) in Plymouth Meeting. They were suggested by several independent sources and seemed knowledgeable. Definitely going to be slow and pricing is somewhat of a mystery, but I'm hoping it all works out fine.

[kyleconstantine]

Last may when I got my 2.9 stroker going I had lots of problems with my hg leaking. I pulled the head 5 total times and tried every brand. It turned out that I just needed to keep heat cycling and retorquing the arp studs. It probably took about 15 times and I also used the anerobic sealer in a couple spots. I think any of the gaskets would have worked if I stuk with it. So just don't give up on the new hg so easy.

McGyver I have a torque plate for the m20 if your machine shop hasn't got that far yet. What shop are you using for the work?

[digger]

Thanks AWDBOB,

Part of me thinks, "might as well go bigger if I need to buy new pistons

with a turbo engine this makes sense as off boost it will be better and the turbo efficiency when chosen can help the top.

If NA you would not want the biggest cubes of trying to make power as unless you improve the breathing correspondingly as you just you end up with a mismatch in parts that dont work together that is why 3 to 3.1L doesn't make any more power than 2.8/2.9 and sometimes makes less when used with a stock head and intake with a very mild cam and it just makes more torque

[TobyB]

Corteco head gaskets are quite good, generally speaking.

t

[McGyver]

Thanks AWDBOB, all of that makes a ton of sense to me. It really is a slippery slope.

I originally bought a seta engine with the intent of throwing an 885 head on it and boosting it, but the block wasn't great and at least 1 piston was shot. So then I planned to use the good parts to build a 2.7i stroker. The crank, head, and connecting rods were machined, but then I had to move across country and abandon the block. Now I have a new block (supposedly from the e30 vert that drove down the rocky steps), but I wasn't 100% sure of the block or pistons.

Part of me thinks, "might as well go bigger if I need to buy new pistons." At the same time, the parts I have should feel great off boost and get better at 5-15 psi. Its gonna have a 280/274 cam and I'm going to run it NA for a while, so I'll have Racing Dynamics headers and probably use a custom MarkD chip. Eventually it will run MS2, and then get the turbo.

All in all, it should make really decent power without going to a larger displacement. I'm hoping...

[AWDBOB]

I've got 12 pistons for the shop to choose from, so I'm hoping there are 6 good ones in there. The block seems so have 2-3 thou of clearance compared to the diameter of a random piston and I believe the limit for a rebuild is 4.7 thou. So I'm hoping I can get away with just a hone and the parts I have.

It's good to know the 84.5mm pistons are available. This would allow me to use the other stuff I already have. However, if I need to buy an oversized piston to make the 2.7 work, wouldn't it make sense to just jump to a 2.9 stroker with an 84mm crank, 85mm pistons, and my stock 135mm rods?

Awesome, sounds like you'll be fine with what you've got!

Short:

For me, no. For some, yes.

Long: After building my 3.1L and seeing mediocre results I went to the other end of the spectrum and questioned how cheap could I build one of these 2.7s for and what kind of power do they make? The 2.7 so far has felt incredible in the car for the cost difference (and made almost the same power as a buddies similar 3L M20).

So for me, since I have 325e crank/rods for days and an affordable high quality (but slow, can't have all 3 lol) machine shop, doing a 2.9 requires the same change in ingredients as a 3-3.1L, aka changes the entire build. Vs buying $600 pistons is just buying pistons and the build otherwise stays the same and uses all the stuff I already have in bulk on hand.

If you have 0 parts on hand and need to buy a block, crank, rods, etc etc I could definitely see how it would feel similar to do a bigger stroke option. Also $600 pistons vs $1300-1400 pistons is not a small delta. But I definitely see it both ways. For me, the motivation was way less max effort, and way more "how can i use what i have here to put great feeling engines together on the cheap".

It's also worth nothing that we're comparing the 2.7 with proven results to the general varied results of the bigger stroke detonating M20s out there that have invisible dyno sheets. This of course excludes the outliers like Digger, Rama, Grootys R&R, etc. I spent alllll the money on my 3.1 and it made like 190whp. If a 2.7 that costs a 1/10 of the money makes 175whp, I'll take that option all day long! So definitely some bias at play as well.

Also worth noting that ForcedFirebirds highest M20 dyno was on a 2.5 haha, and that was due to baller cylinder head work.

[McGyver]

I've heard that MLS should always be taken apart so each layer can be sprayed with copper on both sides to prevent leaks. (based on YouTube car shows)

For the cost of a gasket and the time it takes to change one, it seems like composite is the better choice for most m20 applications. Assuming a quality gasket is used.

[moatilliatta]

I'm starting to think MLS leak from between the multi layers of steel... So a perfect mirror finish will still leak..

This is what happens when people consistently buy the cheaper VR gasket...

[McGyver]

I've got 12 pistons for the shop to choose from, so I'm hoping there are 6 good ones in there. The block seems so have 2-3 thou of clearance compared to the diameter of a random piston and I believe the limit for a rebuild is 4.7 thou. So I'm hoping I can get away with just a hone and the parts I have.

It's good to know the 84.5mm pistons are available. This would allow me to use the other stuff I already have. However, if I need to buy an oversized piston to make the 2.7 work, wouldn't it make sense to just jump to a 2.9 stroker with an 84mm crank, 85mm pistons, and my stock 135mm rods?

I appreciate the advice E30SPDFRK! I'll definitely put a little 518 on it when I assemble the engine!