Do you leakdown at BDC or TDC
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Do you leakdown at BDC or TDC
Anyone go to the trouble to hold the piston at TDC instead of
letting air pressure push it down to BDC while performing leakdowns?
If you DO do it at TDC, are you holding the crank at the flywheel
by dropping the cover or is there a better way ?
[Modified by Slalom4me, 8:38 PM 7/12/2003]
letting air pressure push it down to BDC while performing leakdowns?
If you DO do it at TDC, are you holding the crank at the flywheel
by dropping the cover or is there a better way ?
[Modified by Slalom4me, 8:38 PM 7/12/2003]
Race Director
Joined: Aug 2002
Posts: 13,356
Likes: 0
From: tucson AZ
St. Jude Donor '04 & '05
Re: Do you leakdown at BDC or TDC (Slalom4me)
Thats one hell of a good question.......damn you got me......
someone help us!!!!!!!!!!!!!!!!!!!!!!!!!!!
tony
:smash: :smash: :smash: :smash: :smash:
someone help us!!!!!!!!!!!!!!!!!!!!!!!!!!!
tony
:smash: :smash: :smash: :smash: :smash:
Racer
Joined: Aug 2002
Posts: 253
Likes: 0
From: Strongsville Ohio
Re: Do you leakdown at BDC or TDC (Slalom4me)
Most leakdown tests are done at TDC. The cylinders wear in a taper due to the piston side thrust on the power stroke. Hence, the top of the cylinder will be larger than the bottom. You would be more likely to show more leakage at the top and thats where the power loss would be if the rings were sealing poorly. :crazy:
Drifting
Joined: Dec 2000
Posts: 1,851
Likes: 5
From: Liberal Kansas
Re: Do you leakdown at BDC or TDC (Slalom4me)
If you're at true TDC air pressure won't push the piston down. If your off TDC the crank will want to rotate.
Dan
[Modified by Dan Plett, 9:39 PM 7/12/2003]
Dan
[Modified by Dan Plett, 9:39 PM 7/12/2003]
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Re: Do you leakdown at BDC or TDC (Dan Plett)
If you're at true TDC air pressure won't push the piston down.
If you're off TDC the crank will want to rotate.
If you're off TDC the crank will want to rotate.
comes next.
Apparently, I did not have the piston at 'true' TDC the first time I
did a leakdown (it was a while ago) and you know what happened.
I immediately resolved that I'd never be surprised again and built
a fixture that holds the crank via the ring gear.
I've never given this approach a second thought until someone
questioned why I go to the extra effort. When I responded by asking
how he does it, the answer was 'at BDC, of course'. Well aware of
how cylinders wear in a taper, I pointed out the flaw in his method.
He's an older gent and someone whose opinons I generally respect
but I inherently knew that on this account, he had to be mistaken.
Funny how the obvious eludes our notice sometimes.
Excuse me now, I gotta go try a leakdown just to prove that the
fixture is not required.
