1986 FLHT 80 inch compression?
Seasoned HDF Member
Joined: Jan 2012
Posts: 15,389
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From: Upstate N.Y.-Rochester Area
Compression
This will be interesting.
I have a '89 FLHS, EVO of course which has a factory compression of 8.5:1. I took 14.7 PSI x 8.5 = 124.95 PSI as a reference, checked my compression myself, and also had it verified by my indie, and obtained 125 PSI both barrels, both times, and I thought "GREAT!"
However in a couple of on-line discussions I learned of other standard compression bikes (At least that's what I believe.) with much higher readings (200 PSI ą 20PSI) and was told that this had to do with cam timing/valve overlap, etc.
I'm still not comfortable with my understanding of the way that it all works, and with the values reported, so this may lead to a better understanding for many of us. Looking forward to the replies.
To sort of answer your question, I now believe that my compression values are low, but since they are even I'm O.K. for now. I am planning for a top end rebuild after this riding season so it's all relative. I'm led to believe that the results of a leak down test indicate a slight valve issue is the prime suspect, but intend to clean up everything cylinder /head related once it is broken down for headwork
I have a '89 FLHS, EVO of course which has a factory compression of 8.5:1. I took 14.7 PSI x 8.5 = 124.95 PSI as a reference, checked my compression myself, and also had it verified by my indie, and obtained 125 PSI both barrels, both times, and I thought "GREAT!"
However in a couple of on-line discussions I learned of other standard compression bikes (At least that's what I believe.) with much higher readings (200 PSI ą 20PSI) and was told that this had to do with cam timing/valve overlap, etc.
I'm still not comfortable with my understanding of the way that it all works, and with the values reported, so this may lead to a better understanding for many of us. Looking forward to the replies.
To sort of answer your question, I now believe that my compression values are low, but since they are even I'm O.K. for now. I am planning for a top end rebuild after this riding season so it's all relative. I'm led to believe that the results of a leak down test indicate a slight valve issue is the prime suspect, but intend to clean up everything cylinder /head related once it is broken down for headwork
Last edited by RaSh; Mar 26, 2012 at 07:06 AM. Reason: Last paragraph added.
Cruiser
Joined: Feb 2007
Posts: 138
Likes: 5
From: Dublin, Ireland.
As Gunslingertom says 90psi or higher is stated as normal in the Harley manual with a difference of no more than 10% between cylinders.
Make sure choke and throttle are wide open and crank engine 5 to seven times.
TC
Make sure choke and throttle are wide open and crank engine 5 to seven times.
TC
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From: Cedar Rapids Ia
My compression is around 140 on both holes for my 86 FLHTC stock everything....so i was told 120-150 is good by my buddy NOOT for my pan/shovel which is tested at 120 on both holes...
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From: Cedar Rapids Ia
i was talking with my buddy noot and he was talking about the same concept with cams...i cant remember which cam he mention i thought it was a sifton which makes either lower or higher compression readings....not sure which is which...when ever i talk to Noot he has a bout a million things he tells me to try which is extremely helpful, but the other small talk is forgotten due to the fact im trying to remember every detail he told me about testing this and that.....hahhaha
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