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Old 10-15-2011, 04:01 PM   #1 (permalink)
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Compression?

Is 150 Psi to much in each cylinder? Only reason i ask is because book says 90 psi is normal. The heads have been milled but didnt know if a special gasket was needed for higher compression. I keep blowing head gaskets on the rear cylinder. thanks in advance for the insight.
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Old 10-15-2011, 07:46 PM   #2 (permalink)
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If 150 is too much, man am i screwed! lol

Nope, 150 psi is just fine, of course depending on the build/cam combo.
Which gasket do you use and if stock, did you use and oring on the dowel?
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Old 10-16-2011, 03:33 PM   #3 (permalink)
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If 150 is too much, man am i screwed! lol

Nope, 150 psi is just fine, of course depending on the build/cam combo.
Which gasket do you use and if stock, did you use and oring on the dowel?
the engine is stock bore, andrews 46 cam, and ported heads- shop said they had been milled before to bump compression about 1 point or so.

The gaskets I used were from Harley- I even went to the service dept and asked specifically about that O ring around the dowel pin.. they said with the particular gasket set i had- didnt need the O ring.

Im starting to think its a problem with the cylinder head- when it blew a head gasket before ( late august- which was the first time i rode it ) it was in the exact same spot. Rear cylinder, between the head and jug towards the exhaust pushrod. SO i have been a Harley owner for two months, Rode the bike total of two times, and head gasket has blown each time. Needless to say im a little upset at the shop and the dealership.
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Old 10-20-2011, 06:38 PM   #4 (permalink)
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My 88" stock motor pushed 150 lbs. Now at 95" with andrews 26 cams and a thin gasket it's 180 lbs. Sounds like either the head or cylinder is warped or head not properly torqued.
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Old 10-28-2011, 10:51 PM   #5 (permalink)
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My 88" stock motor pushed 150 lbs. Now at 95" with andrews 26 cams and a thin gasket it's 180 lbs. Sounds like either the head or cylinder is warped or head not properly torqued.
I had the same concerns, but I used the book and followed all the steps in order in regard to torque specs, and assembly... even down to dipping the head bolts in oil before installing lol


Well after some research, it seems there was a service note put out regarding the early EVO motor. Seems that Harley recalled or suggested that the studs be replaced. The service note said the stock block studs had a stop or a collar under the threads on the top side of the block studs. Seems the head bolts would bottom out on the block studs when the studs would stretch over time. Now the recommended repair is to replace the original studs with ones that did not have the collar under the threads up top, but the collar was towards the block.

SO I have bought new block studs, a new gasket kit, and ready to assemble again.

I did in fact take the heads, cylinders to the machine shop to be checked out. I wanted to make sure the head surface and cylinder surfaces were completley flat, with no deviations. They were perfect, says the shop.. so here i go again for the third time. Maybe i can actually ride this thing now rather than dissassemble and reassemble the engine.
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Old 10-29-2011, 07:45 AM   #6 (permalink)
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if your doing the 90 deg tq. tightening deal like the manual says...try this instead.


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Old 11-09-2011, 05:50 PM   #7 (permalink)
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I think i found the problem. The block studs were OEM, so after talking to tons of technicians and reading a service bulliten from harley. I have determined this is the only other thing that can cause the issue im having.

SO, replacing the studs in the block with the 'newer' design with the collar beneath the threads and towards the block. And hopefully it will be all i need to do to fix the problem. Im in the process of reassembly now, hopefully riding next week


Thanks for the advise everyone
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Old 06-23-2013, 01:15 PM   #8 (permalink)
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my 88ci has 63500 miles on it with 150psi compression. Is that normal or has been some work done on my bike.
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Old 06-23-2013, 01:25 PM   #9 (permalink)
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Normal cylinder pressure for stock 88.
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Old 06-23-2013, 06:24 PM   #10 (permalink)
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Before I'd go pulling cylinder heads I'd do a leakdown test and KNOW if there was leakage and where it was coming from. You can also do a leakdown test after assembly so you have a baseline, then one after you break in the rings if you are that picky (or racing).

A compression test raises questions. A leakdown test answers them.


The testers aren't usually expensive. You can even assemble one from parts if you like. Plenty of info for the Googling.
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