It was a decent two days at Road America. The CIS system wasn't perfect. It seemed a bit rich and stumbled on abrupt throttle lift but made good power. Achieved a personal best of 2:47 around the course and felt pretty good about it all. Ya know, if you have brake pads sent overnight they'll throw in a T-shirt. Life is good.

I had noticed some tailpipe smoke but ignored it. The coolant bucket didn't look to be getting lower. Engine temp was good. Started it up to get it off the trailer tonight and the steam was there. Not the insect-clearing fog but more than a whisp. The bucket looks to be a quart or so low. I don't need to visit Egypt. I can accept this doom.

I've done many head gaskets on the car over the years. That's be two different blocks but one set of heads. Among other issues, there was a bit of corrosion on the top of one cylinder and, four years ago, I had it machined off. Pulled all the studs and it was milled on both sides. The heads have been surfaced a few times, too. It should be all nice and flat.

Combined with the 98mm oversized pistons, I'm figuring it's running 12:1 CR. Perhaps it's not a "failure" but a wear item at this point. Probably 20 track days and a few thousand street miles but I'd like it to not happen at all.

So... I'm wondering about what to do. I don't have it out yet but am thinking it through. One thing is to go with fancier gaskets and that seems to mean Cometic. Got a few questions...

Is the Cometic gasket a good approach?
What difference in assembly or torque procedure would that mean?
With a 98mm bore will the 100mm gaskets work?
What thickness should I get? What's stock?
Other ideas?

Thanks for your interest!

 

 

Stock 1mm thick, machined 1.4mm thick.
Obviously those are before crush.

I'd think you could likely get away with the 100mm head gasket without any ill effects.

What was the torquing procedure you used on that last gasket?
Did you monitor the tune for knock at all? Any large amount of detonation will pop the headgasket really quick.

 

If you are used to driving with 12:1, you can get that with S4 heads and an S3 bottom end. S3 cams (and even more so S4 cams) will not hit the pistons.

If the gasket went from Detonation, my advice I think you know (and may have already responded to) - get a higher octane fuel. It Rhymes with Flea BateyHive.

If it went just because of shear combustion pressure, then the cometics should help. I always use Something Simard Mentioned - Hylomar Blue.

 

Think of heads gaskets as the "fuse" in an engine. If you are blowing the 5 amp fuse, you can certainly install 35 amp fuse....but something else might melt.

The stock head gaskets will tell you volumes about what is going on inside your combustion chambers....like knocking, etc. When you get them out, post pictures and I can tell you a boatload about what is going on.

New studs? Used studs? Head torque proceedure turns out to be super important, depending on that answer.

You ansolutely should not angle torque these heads without a digital torque wrench that tells you how much torque was applied by the last 90 degrees of rotation.....extremely important when using old studs.

If the resulting torque varies by more than 20ft. lbs., you need new studs.

If you plan on replacing the studs and plan on using the (20nm + 3 90 degree rotations), buy two sets of studs.....you will ruin the first set and then figure out to do something else on the second set.

 

Thanks for the responses.

I've got two new studs in the mix. Those are regular style and don't seem different. I had a third one for the short stud that was all-threaded but it seemed to just stretch. I replaced it with a ugly but serviceable old stud.

For torque I've used the classic multiple-torque approach and not angles.

I don't have a knock sensor and haven't applied one. I've had broken rings previously and now run a 50/50 mix of premium (91 octane at least) and 110 octane leaded race gas. No cats on the RoW car. Not overly ambitious with the spark. It's 3-4 degrees beyond stock.

I've dyno-tuned the car previously and had it set for 12.5:1 air/fuel ratio high RPMs and WOT. Not sure what it's running now but it smells very rich.

 

When were you in Elkhart?

 

Monday and Tuesday.

 

My "issue" with old studs is that some will stretch and some will not. Years ago, I re-used almost every set of studs. Rare to be able to do that with the same 35 year old studs today.

Porsche designed these studs to stretch and keep the head gasket under tension in all situations. If you torque them and some yield and some do not....both the head and the head gasket is under different pressures from stud to stud....both cold and hot. That doesn't work.

When these engines were new, Porsche decided (with a bunch of other automobile makers) that the best way to get the studs into the proper stretch was to angle torque them. The problem with angle torqueing them is that usually some of the used studs will stretch and some will not. It is very possible to have one stud at 65 ft. lbs., with one right next door at 120 ft. lbs. Clearly, that is not going to work, either.

Like I said, you really need a digital angle torque wrench to be able to interpret what is happening as you tighten down these studs.

 

Are there some good ones under 400 dollars?

 

I keep an eye on if the torque steps are taking unusual amount of angular motion. They seem to be similar enough but I'm not being numerical about it.

I am getting a message about having even clamping force on the studs. Angle versus torque has been discussed. The trick is weather the studs are all made to spec, which favors angles, or the friction at the threads and washers is more even, which favors torques. You're saying to do both and that makes good sense.

 

I think all of the studs that I've found existing in engines were made to very similar specifications.....the problem seems to be expose to coolant, age, and possibly heat, which makes some of them more elastic and some less elastic.

There's no question that the current "batch" of replacement studs are made to a completely different specification and have completely different stretch characteristics. These studs will not get anywhere near 20nm + 3 x 90 degree turns, before they yield and are junk.

The combination of old studs having different elasticity and the new studs being completely different makes getting consistent pressure on the head gaskets very problematic.....I don't think it is possible to mix old and new studs and get positive results.

Keep in mind that consistent pressure (even clamping force all the way across the head) is what keeps head gaskets happy.

Again, once you get your heads off, take some detailed pictures of the head gaskets (especially the fire rings). There will be clues to the cause of your failure, there.

 

you might get lucky and have studs that all are in simular shape. scots, we replaced a few with new, not all and they all seemed to end up with the same torque after angle torquing them. ( I always check with angle torque)

why do you think the engine is at 12.5:1? if only shaving the heads , thats a lot of machining!
I dont think the S4 heads on an 85 would give more than 12:1. (i think we all did the calculations a while ago)

 

Bigger pistons with smaller reliefs, shaved heads and decked block. I ran some numbers and came up with 12:1 compression ratio. The pistons are 98mm '84-series so the smaller valve cutouts. It all adds up.

 

ive used the euro heads, decked block with 100mm pistons and shallow valve reliefs and ended up with 10.8:1. even with the dish in the 85piston, that's only 6CC but the valve cuts we made were only 2cc. (probably more shallow than the 84 euro cuts)

off memory:

heads were 46cc
pistons were 8cc
gasket 1mm (or 7cc)
5liter engine block with decked block and shaved heads.

I know you are fully capable of pluggin in the numbers too, but that 12.5:1 number seems a bit extreme and just curious how its possible to get there.