short stroke 3.2

[gpn]

I have a short stroke 3.2 on carbs track motor I will be tearing down for checking heads etc, and am considering having the jugs machined to accept head gaskets. These are older Mahle 98mm jugs that presently have none, and no matter how much we take care in lapping them in to the heads, there always seem to be some seepage over time. Some thoughts by the experts is appreciated before I send these out. Feel free to contact me through this forum or directly.

Greatly appreciated,

Gary Nichols
Batavia, Ohio
nichols.surveying@fuse.net

[Steve@Rennsport]

Gary,

You'll get lots of opinions on this, but I would not recommend machining your cylinders for gaskets unless your CR is above 13:1 and you are using race gas.

Mahle & Porsche specifically eliminated the gaskets on those cylinders to prevent the cracking & breaking issues that the moderate-compression 98mm cylinders had. These problems were rooted in detonation that fractured the edges of the cylinders between the bores and the gasket grooves. The pieces always fell down and wreaked havoc,........

Seeping is usually due to lack of proper clamping pressure across the range of expansion front cold to hot and back to cold again. This is aleviated using the correct head studs and ensuring the sealing surfaces are flat & true.

[gpn]

Steve,

Thank you for the kind reply. I have also talked last evening to a couple of folks who gave the same answer as you. This is a 10.8:1 engine, so we shall be extremely judicious in checking measurements and componenets when we reassemble. Again, my thanks for your wisdom.

Regards,

Gary

[KTL]

Just to add to the discussion and reinforce Steve's point about the gaskets, i've been corresponding with Charles at LN Engineering regarding my engine build. Long story short is i've decided to downsize my engine from 98mm to 95mm. He offered to buy my 98 cyls to offset some cost. But when I informed him that mine are the CE-grooved Mahle cyls, he said no thanks he can't use those for reasons similar to what Steve said.

That said, my cyls have been in service for quite some time on a racecar engine and their thinner upper walls have held up, aside from one cyl that had some plating chip off. That said, my engine is a sample of ONE. I'd trust the experts on this one. My engine probably just got lucky (until I got my hands on it....)

[lindy 911]

Source some studs from Supertec and be done with your head problems. These are good studs and have great clamping force across the board. As long as you properly warm your engine prior to pounding on it at the track, expansion rate issues should be minimal. Given any thought to a 3.2 crank while it's apart? 3.4 liter; the engine is over square by bore already and a little stroke would do wonders.

[KTL]

Yeah but throw in the 74.4 crank and now your rods and pistons have to change too. That cost adds up in a hurry.

I'd go 100mm pistons and cyls before ditching the lighter 70.4 crank and those good SC-type rods, be they stock or aftermarket.

[gpn]

I appreciate the replies from all who have responded. The engine will come out this morning at the Middle Aged Men's Club (a misnomer, since we are all old now, I am the youngest at 60), and we shall begin teardown in due course over the next couple of weeks. The old girl and I are certainly getting a bit longer in the tooth. As an 80Sc that has undergone many changes since we have been together these past 22 years, I have come to accept leaving things in the present configuration. It's been a 3.2 for about fifteen years. We ran CIS until five years ago, then switched to carbs. It has Carillo rods, twin plug, modified S cams, lightened flywheel, 2100#, well, the list is too long. At the end of the day, this engine has been very reliable, perhaps because I keep it under 7K and have done regular rebuilds from 75 to 100 engine hours. I considered making it a 3.4 several times, but will leave it alone. I no longer do the dozen or so events I used to ten years ago, but she still gets the old heart fluttering at full song. I guess we are just content with each other after all these years, an old shoe and an old foot that fit well together if you will. I appreciate the advice and expertise this forum offers to the enthusiast, and again thanks those that have taken the the time to respond with their personal time and expertise.

Regards to all,

Gary Nichols
Batavia, Ohio