compression test procedure question
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Tourer
Joined: May 2009
Posts: 401
Likes: 19
From: Middleboro, MA USA
compression test procedure question
I am getting ready to do my base gaskets and install a cam. I wanted to do a compression test before I pull things apart but oops, I've already sent off my carb for some work. The manual says warm engine and open throttle to test compression. Am I wasting my time to try and test with a cold engine missing the carb? I'm guessing the carb is needed if only to plug the intake manifold?
I am also guessing you will have different pressure reading between a hot and a cold motor.
BTW, Autozone lets you borrow a compression tester with a $42 deposit. As long as you return the tool within a year you get you $42 back. Not a bad deal.
I am also guessing you will have different pressure reading between a hot and a cold motor.
BTW, Autozone lets you borrow a compression tester with a $42 deposit. As long as you return the tool within a year you get you $42 back. Not a bad deal.
Seasoned HDF Member
Joined: Dec 2010
Posts: 7,736
Likes: 1,524
From: Coromandel Peninsula New Zealand
You can do the compression test as it is now but the results will be a bit skewed....however, if one pot is stuffed it will show up on the test as the differences between the pots will still show with a cold motor.
My outboard motor shows lower comp when cold than when hot. I use it as an example because I just checked them hot and cold at the weekend.
My outboard motor shows lower comp when cold than when hot. I use it as an example because I just checked them hot and cold at the weekend.
Thread Starter
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Tourer
Joined: May 2009
Posts: 401
Likes: 19
From: Middleboro, MA USA
Thanks for the replies. I am going to do a leakdown too. I just need to grab the kit. I'll do the compression test just to see if both jugs are the same or similar. Would blocking off the open intake manifold do any good?
Seasoned HDF Member
Joined: Dec 2010
Posts: 7,736
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From: Coromandel Peninsula New Zealand
No, you do the test at wide open throttle, so leaving it open is good :-)
Ultimate HDF Member
Joined: Aug 2012
Posts: 6,470
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From: on the road
the difference from hot to cold is basically negated un scientifically if you shoot a little engine oil in the bore before the tests.that will mimic a hot run condition
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Road Master
Joined: Oct 2011
Posts: 957
Likes: 2
From: Carlsbad Springs Ontario
test
I am getting ready to do my base gaskets and install a cam. I wanted to do a compression test before I pull things apart but oops, I've already sent off my carb for some work. The manual says warm engine and open throttle to test compression. Am I wasting my time to try and test with a cold engine missing the carb? I'm guessing the carb is needed if only to plug the intake manifold?
I am also guessing you will have different pressure reading between a hot and a cold motor.
BTW, Autozone lets you borrow a compression tester with a $42 deposit. As long as you return the tool within a year you get you $42 back. Not a bad deal.
I am also guessing you will have different pressure reading between a hot and a cold motor.
BTW, Autozone lets you borrow a compression tester with a $42 deposit. As long as you return the tool within a year you get you $42 back. Not a bad deal.
is appropriate and correct.
You can purchase a good screw in compression gauge at any auto supply store for $ 30.00 - $50.00 then follow the instructions included.
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Road Master
Joined: Jun 2012
Posts: 1,088
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From: Mo
I just did this on my bike befor i tore it down....cold and hot and the added oil.It gained 10 psi when warm and absolutly nothing when i added the oil accept smoked like a freight train when i started it...LOL