Compression Testing

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VT

Compression Testing

#1

Post by VT » Wed Dec 07, 2005 3:06 am

What's the best way to compression test a Big Twin by yourself? What's the best tool? Do you leave one spark plug tightened in the motor, while you test the other cylinder with a (tapered) rubber tip compression gauge from Pep Boyz? Gotta be something better and more positive than that. How about a gauge where the needle freezes at the highest point of compression? Where can we find one?
I'd like to use a compression test to see how tight everything is with the rings. My cylinders have about 26K on them and are scuffed some at the rear of each. I'd like to test for pressure difference, do my on calculations, check out the (solid lifter) tappet bearings and run the motor another 10K, before I do any bottom end work. I have new heads.



kell
Posts: 404
Joined: Sat Jun 19, 2004 2:58 am

compression testing

#2

Post by kell » Wed Dec 07, 2005 3:32 am

My compression tester has a check valve that holds the reading, and it screws in to the spark plug hole. I probably got it from JC Whitney or someplace like that. Get a compression tester like it so you can screw it in to one head, leave the plug out of the other head and just kick the bike over a few times until the needle stops moving.
Don't use that pep boys compression tester you described, it would work on a car but useless on a two cylinder engine.

VT

#3

Post by VT » Wed Dec 07, 2005 3:29 pm


VPH-D

#4

Post by VPH-D » Wed Dec 07, 2005 5:31 pm

I also have a compression tester that screws in, and has a compression release. It came from Sears quite a while back.
VPH-D

VT

#5

Post by VT » Wed Dec 07, 2005 6:36 pm

Thanks. I'm cruising over to Roebucks....and check out what they got.
http://www.sears.com/sr/javasr/product. ... +Equipment

Looks maybe more simple than what JCW offers. Less connections to leak maybe. Cheaper. I can pick it up at the local Sears outlet. Call first of course.

SkyHogg
Posts: 25
Joined: Wed May 18, 2005 10:52 pm
Bikes: 64 Pan, 77 Sporty, 05 Electraglide
Location: N. Carolina

#6

Post by SkyHogg » Sun Dec 11, 2005 3:36 pm

Just to reinforce what Kell said: there is no good reason to leave the other plug in. All it's gonna do is make it harder for you to turn the engine over. The pressure in one cylinder doesn't affect the other (well ... possibly, if you have some serious blow-by on both cylinders, but your engine would probably be shot at that point). So get the screw-in type with a check-valve and stomp away. It may help to note how many kicks it took to reach max. pressure, and compare cylinders. But if doing that you have to compare apple to apples, and start each kick from about the same position in the crank rotation, about equal pressure on your stomp ... and etc. And by that time you are probably gettin' as anal as I get sometimes, and will then realize that doing it the normal way works just as well.

VT

#7

Post by VT » Sun Dec 11, 2005 4:26 pm

Will do. Thanks.

SkyHogg
Posts: 25
Joined: Wed May 18, 2005 10:52 pm
Bikes: 64 Pan, 77 Sporty, 05 Electraglide
Location: N. Carolina

#8

Post by SkyHogg » Sun Dec 11, 2005 5:02 pm

Before somebody calls me on it, even with a serious ring blow-by problem, a properly functioning crankcase ventilation sysem should prevent it from affecting the other cylinders. Once I start typing i sometimes don't know when to shut up. Like the time back in '87 when .............. zzzzzzzzzz

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