Leak down numbers?

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Model T Ford Forum: Forum 2016: Leak down numbers?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Laughary on Saturday, July 02, 2016 - 01:02 am:

I have a leak down tool and I'm trying to remember the difference tween that and a compression tester.

My engine blows no smoke but I'm starting to suspect cylinder number two weaker than the rest because the cylinder sleeve temperatures are always a bit lower than the others.

Does anybody know what kind of numbers I should expect to see? I think I'm supposed to move each cylinder to TDC and add air pressure.

Haven't used it in awhile and will try swapping coils around first in case that one is just firing a weak spark. I'm also chasing wires in case there is a short. Now that I have eliminated clatter of the lower pulley I hear an occassional miss.


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnCodman on Saturday, July 02, 2016 - 08:35 am:

The cylinder must be at TDC on the compression stroke to test leakdown. Bear in mind that the piston under air pressure will want to move to BDC so you will have to find a way to hold the crank motionless. Since the engine can turn in either direction, holding the crank won't work unless you can position the piston just a degree or two BTDC.
Typically a leakdown test result is expressed as a percentage. The higher the better. By this I mean that the greater the pressure that the cylinder holds, the better the test results.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Saturday, July 02, 2016 - 09:10 am:

A compression test should show if there's a difference plus it's a simpler operation. I like to do T's cold because of their relatively low compression. Do a dry then a wet test and it'll go a long way in telling you the engines condition. A leak down test might show a cyl. lower than the rest but won't tell you if it's valves or rings unless it's blowing out the intake or exhaust manifolds.


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