Cold vs. Hot compression numbers.
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,115
Likes: 7,638
From: Poolville
Then why did you state "The spark plug on the rear cylinder is loading up, very black and a bit oily"?
Autozone has a leak down tester you can rent.. at 98k miles it might be time to rering... Leak down will tell you.. and then there's the whole "while your at it" a valve job and shave the heads a little too bump the compression to get a little more out of it without going overboard..
Autozone has a leak down tester you can rent.. at 98k miles it might be time to rering... Leak down will tell you.. and then there's the whole "while your at it" a valve job and shave the heads a little too bump the compression to get a little more out of it without going overboard..
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
The spark plug in the rear cylinder IS loading up... its a new condition, it just started after the carb kit and intake seals install. Prior to that they were both a bit sooty, but dry.
Thanks for the info on renting a leak down tester!!!
Thanks for the info on renting a leak down tester!!!
Club Member
Joined: Aug 2008
Posts: 22,861
Likes: 17,917
From: Lafayette, Louisiana
Originally Posted by GOGOBECK
The spark plug in the rear cylinder IS loading up... its a new condition, it just started after the carb kit and intake seals install. Prior to that they were both a bit sooty, but dry.
Thanks for the info on renting a leak down tester!!!
Thanks for the info on renting a leak down tester!!!
Road Warrior
Joined: Aug 2015
Posts: 1,712
Likes: 410
From: Puyallup, WA
Decreased compression from warm to cold can be due to warm oil being thinner and having less sealing properties than thick cold oil. 10% difference cold to warm on a motor nearly 100k, isn’t that much to be concerned about. Also if your valve guides are dripping oil when sitting, that oil can help seal worn rings a bit.
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Road Warrior
Joined: Apr 2018
Posts: 1,347
Likes: 820
From: Moneta, Virginia
Wouldn't an intake leak anywhere lead to both cylinders being leaned out?
Decreased compression from warm to cold can be due to warm oil being thinner and having less sealing properties than thick cold oil. 10% difference cold to warm on a motor nearly 100k, isnt that much to be concerned about. Also if your valve guides are dripping oil when sitting, that oil can help seal worn rings a bit.
Stellar HDF Member
Joined: Aug 2013
Posts: 3,428
Likes: 3,576
From: Texas
I have a 1996 ultra classic FI with 96000 on the bike with pistons and cam changed 2 years ago to wisco 10 to 1, ev27 cam, after reading this thread I decided to do a compression test. I ran the engine for about a minute then pulled the plugs, held the throttle open, rear was 180 psi the front was half way between 175 and 180, so 177. was going to get it to operating temp, but it hasn't stopped raining.
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trike65
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Sep 6, 2017 03:54 PM
