Compression test?
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Road Master
Joined: Sep 2008
Posts: 1,231
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From: FLORIDA
Compression test?
1st of all don't flame me too bad! I am not very mechanically inclined but willing to try.
OK, so I am reading the manual on how to perform a compression test on a 2006 Heritage and it mentions a throttle plate. Specifically it states "with the throttle plate in the wide open position crank engine continuously 5 to 7 compression strokes"
Is that just holding the throttle wide open? I can't find a throttle plate in the manual? Sorry if this seems stupid to u but I would like some help here
Also can u do the test without opening up the throttle? I guess what I mean is what difference does it make
UPDATE 10/4/11 at 18:45
1st want to thank everyone for the advice.
Did the test got 150psi on the front and 148psi on the back cylinder. I did not leave the battery hooked to a charger however and the battery is 6yrs old.
Think those numbers are OK for the yr and engine size?
OK, so I am reading the manual on how to perform a compression test on a 2006 Heritage and it mentions a throttle plate. Specifically it states "with the throttle plate in the wide open position crank engine continuously 5 to 7 compression strokes"
Is that just holding the throttle wide open? I can't find a throttle plate in the manual? Sorry if this seems stupid to u but I would like some help here
Also can u do the test without opening up the throttle? I guess what I mean is what difference does it make
UPDATE 10/4/11 at 18:45
1st want to thank everyone for the advice.
Did the test got 150psi on the front and 148psi on the back cylinder. I did not leave the battery hooked to a charger however and the battery is 6yrs old.
Think those numbers are OK for the yr and engine size?
Last edited by scasey; Oct 4, 2011 at 05:47 PM.
Tourer
Joined: Jul 2007
Posts: 497
Likes: 8
From: New Egypt, NJ
And yes, all that means is hold the throttle wide open. The difference is that with the throttle closed the engine won't get as much air and the result will be low compression readings (becasue less air will be compressed by the engine). Battery charger to make sure the starter has enough kick to keep the engine turning at a consistent speed.
Cruiser
Joined: Jul 2011
Posts: 210
Likes: 1
From: Pacific Northwest
Also, if you get a low reading on either cylinder, you can do a 'wet' compression test (normal compression test is a 'dry test'). A wet test is simply adding a little bit of oil to the cylinders through the spark plug holes and doing the compression test again.
A significant increase in compression with a wet test vs dry test indicates worn rings. If compression is still low with a wet test (with no increase), it indicates valve seat(s) or head gasket being the culprit.
A significant increase in compression with a wet test vs dry test indicates worn rings. If compression is still low with a wet test (with no increase), it indicates valve seat(s) or head gasket being the culprit.
HDF Community Team
Joined: Jun 2006
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From: san antonio
Then it's time for a leak down test.
Seasoned HDF Member
Joined: Mar 2007
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From: TOAK western branch
Ok. I did a compression test at 90,000 and I had 195 on the front and 193 on the rear. I know its good but what is perfect and what is a concern. I know you are allowed a 10% variance but would 210 psi be better. Im just asking for some trivial knowledge. At what point do I think about top end work or an excuse to go bigger.
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Cruiser
Joined: Jul 2011
Posts: 210
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From: Pacific Northwest
Do a wet test and see if it goes up any. That will tell you the condition of the rings. If the rings are still good you should get little or no variance between wet and dry compression tests.
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Thread Starter
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Road Master
Joined: Sep 2008
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From: FLORIDA
Ok. I did a compression test at 90,000 and I had 195 on the front and 193 on the rear. I know its good but what is perfect and what is a concern. I know you are allowed a 10% variance but would 210 psi be better. Im just asking for some trivial knowledge. At what point do I think about top end work or an excuse to go bigger.
Seasoned HDF Member
Joined: Mar 2007
Posts: 66,948
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From: TOAK western branch
Did cams lifters pushrods and tensioner at 90,000. Stock top end. Almost all freeway miles.