Cyl temps @ beginning of run Evo Harley

[wjnielsen]

Engine in question is 2001 Harley Sportster; air-cooled aluminum cylinders with (I believe) iron liner cast in. 4 long studs from cases clamp down the cylinder heads, and the barrels.

There's a thing that I've been told, and accepted as true (because it sounded reasonable) was that engines with thru-bolted aluminum cylinders rely on the cyls coming up to temp to give the fasteners that final amount of clamping load.

The reasoning was that the aluminum grows taller than the steel bolt, making the bolts really get their full designed tension after that cylinder gets some heat in it. And this is compounded by our engines being air-cooled, and not having a water jacket keeping the temp of the barrel down to 200-ish degrees.

I was told they should NOT be subjected to heavy load until some heat was in the engine, to avoid annoying base gasket leaks and/or more troublesome head gasket leaks.

This is on top of allowing the pistons to grow with some heat, which reduces piston rock (which can affect how the rings seat in the bores); affecting valve lash with non-hydraulic cams, and other issues.

Riding on the street, I've always let my bike run for a moment, then took off, and rode really gently (like barely touch the throttle in 1st & 2nd) for the first mile, then gave her the whip. But now the bike has been re-purposed for land speed racing and trips to the dragstrip.

So, at the track, how much do you guys warm up these type engines?

Looking forward to hearing the experience from those who've 'been there - done that'.

[HDBD]

So, at the track, how much do you guys warm up these type engines?

Not real well so they add piston clearance

[rustbucket79]

I believe the cylinders run a good deal warmer than 200 degrees, especially the rear one.

What the racers do for warm up I don’t know, but you were right to get decent heat into the engine before you ran it hard.

I measured a Harley cylinder that had just finished in our washer, seems to me it was a good .003” larger than room temperature. I never measured another one that way again, some things we don’t need to know about.

[hoodeng]

The problem with gasket seal in engines that were not warmed up came from the days when the base gaskets and head gaskets were composition.
Early performance through bolt engines switched over to rigid gaskets pretty early on, i built a 98"evo when S&S first introduced their kits for these engines, the kit was supplied with a red composition material with a fire ring, the procedure was to heat cycle the engine, pull the rocker boxes and re-torque the top end, these gaskets were not particularly good and would cold blow if pushed when not normalized. This was know as dry blowing, when stripping down an engine, you could see what looked like pencil lines radiating out from the combustion chamber across the gaskets surface.

Milmeyer bought out a copper ring gasket that installed inside a composition gasket that improved things a lot but still had a composition base gasket, gas sealing was good but you could still get a bit of oil weeping. A number of manufacturers then came out with one piece copper head and base that with a light coating of sealant worked great. For a good number of years now we have had MLS gaskets for head and base, gasket leakage is now very rare.

A lot of drag race engines use bolt on base and bolt on head, a greater percentage do not use gaskets, a smear of sealant on the base and metal to metal or a gas filled ring for the head.

Cheers.

[wjnielsen]

Thanks for the replies, folks!

Been a few years since I put the engine in question together in question together... Don't recall what I used for base gaskets - Yamabond...? Head gaskets are Cometic MLS.

Got the itch to do some racing, and went to the ECTA Spring Fling a few weeks back to see what she'd do. Well, looks like I'm going to have to go back again and again to see if we can do better...

Until ya actually go out and do it, I don't think a guy realizes how many variables you are trying to lock down, or compensate for in racing.

And at the end of the meet, I was wondering if there is a perceptible loss in power by having the heads warm at the beginning of the run, or if by the time I got 1000 feet out the heads would be up to temp and the only advantage would have been just coming off the line. I suspect this is the case.

[MadBill]

Since the thermal expansion of aluminum is about double that of steel (~13 ppm vs. ~7), the clamping load increases as the engine temperature rises, especially with long and/or external(cooler-running) studs.

In the later years of their air-cooled engines, Porsche encountered stud breakage at high engine temps if they were torqued enough to seal cold. Their solution was a special high-expansion nickel/chrome alloy called Dilavar. (Google "Dilivar steel alloy")