Leak down testing is done with a spec gauge (leakdown tester). It is
measuring the pressure loss by percent.
The advantage of the leak down test against a comp. test is that You can see
the actual loss, and hear where it is going to (exhaust, carb, cylinderhead,
radiator - in the worst case). If You do a compression test, You get a
number, which is only good if You can compare it to an older reading (on the
same gauge, with the same cranking speed, same temperature etc). Normaly
speaking the comp test is best to tell You differences between the
cylinders/stages. If You have more than 2PSI difference between the
cylinders on an engine, usualy indiates a problem.
Leak down testing is somewhat "constant", and gives You an independent
number to work with. Though this method also has its own problems. The
normal pressure loss is always greater on big engines then on smalls (more
sealing area, more loss, aslo depending on bore/stroke ratio etc). I used to
meter mini engines (848-1275ccm). A completely healthy 850 would show around
5%, while a 1275 in good nick would be 7-8%. The worst engine which actauly
was running showed 45+ loss. But that was an extreme case. Normaly good used
engines are between 10-20%.
Gergo
2011/6/26 <healeyguy at aol.com>
> What's a leakdown test?
>
> Basically pressurize a cylinder with the valves closed and see how long it
> takes for the pressure to drop. Somewhat simplified explanation.
> Aloha
> Perry
>
>
>
>
>
>
> -----Original Message-----
> From: Greg Mandas <gmandas at yahoo.com>
> To: Oudesluys <coudesluijs at chello.nl>
> Cc: healeys at autox.team.net <healeys at autox.team.net>
> Sent: Sun, Jun 26, 2011 8:30 am
> Subject: Re: [Healeys] 100M Compression -- leakdown
>
>
> Whenever I discuss compression with my mechanic, he says I really need to
> do
> a
> leakdown". He says it's more informative.
> Uh... What's a leakdown test?
> Greg
> 5BJ8
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