Evo Leakdown Test Results
Road Master
Joined: Nov 2007
Posts: 1,223
Likes: 3
From: Peoria, AZ
"Rear cyclinder also had 130 psi compression with a 30 percent leakdown and a little more air comming out the carb and a little air out the timing plug." Final readings are 90 PSI or higher with less than 10% variance between cylinders ('97-98 EVO Softail), than compression is normal. Assuming you did the leakdown test at TDCC with the engine at operating temperature, I would say you have leaking intake valves or pushrods adjusted incorrectly and worn rings. Did you try putting 1/2 oz of oil in cylinder and retesting?
Road Master
Joined: Sep 2006
Posts: 837
Likes: 1
From: NORVA / Pittsboro, IN
I've got a 95 Electraglide Evo with 71,000 miles. .....The bottom ends will run forever if you treat it right(CHANGE OIL REGULAR) Anyway, I'd run it till you have a reason to go in.Except for the lifters, early Evo's had a problem at about 50,000 mile, brgs would come out of rollers, if you don't catch it in time you can loose the whole engine.
https://www.hdforums.com/forum/membe...m-failure.html
I thought the earlier EVO's had the better (Torrington), then the change to the INA.
2nd Gear
Joined: Dec 2008
Posts: 6
Likes: 0
Dude 30 % leakage is toasty! I don't know anybody thinks 30% is a good leak test. If you hear air from the carb, you need a valve job. I've seen motor with lowish compression like your 130, but I've leak tested shovels that have only 15 %, and they were making like 40 horsepower! 20% is my limit, 21% and it's coming apart! Also if I hear leaking in the intake or the exhuast it's coming apart. It might run ok, but the top end is toasted!
Advanced
Joined: Sep 2008
Posts: 67
Likes: 0
From: wisconsin
If you have 130psi and a 30% leak down and it runs fine and doesn't use oil that is abnormal, run it, the motor is not going too just come apart over night. I do agree with blackjack66 it probably does need to be freshened up, but if the funds aren't available to do so then run it. I would do the leak down again and see if the numbers are the same, if they are then think about rebuilding it.
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
It seems as though everyone here is assuming that the compression test and leakdown were done properly. First lets assertain that is a fact. Was the motor at operating temperature when you did this?? Did you have the throttle wide open when you did the compression test?? If not then the numbers will be off.
I too like to see less than 20% on motors with rings that have gaps, and less than 5% with the gapless rings. Anything more than that and we reccomend that the bike be torn down over the winter and freshened up. This will give you more HP and torque along with some better mileage. You say that you can hear air coming out of the carb, this is a sign of intake vales leaking. While they wont get worse as fast as an exhaust leaking, they will get worse as time goes by, so freshening these up would be a plus. Hope this helps.
I too like to see less than 20% on motors with rings that have gaps, and less than 5% with the gapless rings. Anything more than that and we reccomend that the bike be torn down over the winter and freshened up. This will give you more HP and torque along with some better mileage. You say that you can hear air coming out of the carb, this is a sign of intake vales leaking. While they wont get worse as fast as an exhaust leaking, they will get worse as time goes by, so freshening these up would be a plus. Hope this helps.
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
http://www.bigboyzcycles.com/TwinCamComp.htm
Hope this helps.
Elite HDF Member
Joined: Jun 2007
Posts: 4,867
Likes: 268
From: People's Republic of Boulder Colorado
OK, I'll ask a question that shows my ignorance! Is a leakdown test the same as a differential pressure test that's done on airplane piston engines where you feed a specified amount of pressure into the cylinder and note the pressure difference on either side of a calibrated orifice? I did this type of test on my '94 FXDL and got 78/80 on the front and 79/80 on the rear. On an airplane engine that's considered excellent. I did a regular compression test too and got 125 PSI on both. My engine is bone-stock. Any advice/info much appreciated!
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Road Warrior
Joined: Sep 2005
Posts: 1,569
Likes: 12
From: Arizona
125 psi on both, when cold, is great. all i have ever used a leak down test for is to find where im loosing compression. if you had, say 125 on one cylinder and 90 on anothe,r then by forcing air into the chamber, the one with 90, would let you know where your loosing it. if you could hear it out the exhaust pipe then your loosing compression past your exhaust valve, out the carb then ist the intake valve, from the crankase then rings. if both cylinders are pretty equal and you do a leakdown test then the amount of time to loose pressure lets you know how much the parts are worn. ever engine is going to leak down, after all the rings have gaps in them. but with your reading id say your perfect. gapless rings are for race engines. you could use them on a harley but your vales and guides better be in new shape because the rings arent going to leat any pressure by so it will find a spot and all of it will go there. id rather have a little pressure go past everything equaly then to force it all through the intake. just my opinion, we all have those, well opinions and butts and they both stink.
