Base gasket leak and other ramblings
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Club Member
Joined: Jan 2007
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From: NE Florida
Base gasket leak and other ramblings
I replaced all of the gaskets (Cometic) in the stock 1990 Evo. The engine runs GREAT. After a 120 miles ride a couple of weeks ago, the front cylinder base gasket has a tiny weep on the front side.
Since I'm going to replace the base gaskets (again), I'm thinking of getting the bottom of the cylinders "trued". I don't want to put it back together and have another leak.
Any thoughts?
Background and ramblings:
I sealed the entire engine with Cometic gaskets. It had less than 18k miles and there were still cross hatch marks very clearly in the cylinders. I checked the rings and they were well within spec and the same gap from top to bottom of cylinders. I cleaned up the heads and re-lapped the valves and installed new valve seals.
I did both compression and leakdown tests after about a 100 miles when I got the bike back together. The compression was 150 front and 148 rear (.030 head gasket). Leakdown at 80 psi held 77 in the front and 78 in the rear. This tells me the engine is in great shape.
Since I'm going to replace the base gaskets (again), I'm thinking of getting the bottom of the cylinders "trued". I don't want to put it back together and have another leak.
Any thoughts?
Background and ramblings:
I sealed the entire engine with Cometic gaskets. It had less than 18k miles and there were still cross hatch marks very clearly in the cylinders. I checked the rings and they were well within spec and the same gap from top to bottom of cylinders. I cleaned up the heads and re-lapped the valves and installed new valve seals.
I did both compression and leakdown tests after about a 100 miles when I got the bike back together. The compression was 150 front and 148 rear (.030 head gasket). Leakdown at 80 psi held 77 in the front and 78 in the rear. This tells me the engine is in great shape.
Seasoned HDF Member
Joined: Oct 2015
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From: Pine Flat Dam/South Bay Area, CA
There's no need to re torque Evo head gaskets. Doing such things can result in pulling the threads for the cylinder studs out of the crankcase.
Seasoned HDF Member
Joined: May 2008
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From: South Carolina
Are the cylinder studs original, installed with the shoulder up?
If so, you may have one or more that have stretched or are pulling loose from the cases.
If so, you may have one or more that have stretched or are pulling loose from the cases.
Last edited by Dan89FLSTC; May 27, 2026 at 01:52 PM.
Thread Starter
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Club Member
Joined: Jan 2007
Posts: 3,567
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From: NE Florida
I should have mentioned that the cylinder studs are new and mounted with the shoulder down.
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Seasoned HDF Member
Joined: May 2008
Posts: 21,208
Likes: 12,796
From: South Carolina
A reputable Harley machinist can true the bottoms of the cylinders, just have the minimum removed.
OEM Harley gaskets are as good as any as long as you don`t need a special thickness.
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