Just performed a cylinder leak-down test on a WR400 with piston at TDC and enough input pressure (circa 5 bar) to the measurement device ( a general leak-down tester for all kind of engines)
- Engine was cold; as i am worried to damage the aluminium cylinder head when removing a spark plug from a hot engine.
1) Set the leakage meter to "set" (right gauge) by opening the input valve
2) Connected the leakage meter to the engine
3) Read-out the leakage % (see blue line in the picture) - 37%
Results are shown in this picture. According this device this is a moderate level of leakage (37 %).
However, all info I have seen -about this on the internet- tell me that circa 20% is the max...(?)
- My theory about this is, that the allowed % leakage is fully dependent on the orifice that is used in the tool. So, to mention a allowed leakage rate without specifying the orifice and input pressures etc, doesn't mean much. This orifice may not be standardized, so one type of measurement tool may given 20% and the other 80%. The gauge measures a pressure drop! The smaller the orifice of the tool, the larger the drop (the leakage % ). Furthermore, higher input pressures lead to turbulence and is similar to having a smaller orifice and a larger drop (leakage %).
By the way, the picture does not show the tool I used, but looks very similar..[talking about the colors and numbers and text on the gauge].
* What do you think?
--> Is this piston/rings/cylinder at the end of life? (engine from 2001, unknown miles, starts after 5 kicks usually, has reasonable power did not loose any power - at least I think its ok..., cannot compare with what it was 10 years ago as own it for 2 years now)
--> Would the reading be much better with a warm engine?
--> Do I have to believe the tool its judgement (scale says: leakage is at Yellow level / moderate leakage) or The general 20% (according most info on the internet this 20% is the max leakage allowable -?-)
--> Do Dirt Bikes have more leakage over the cylinder due to the high bore / stroke ratio?
PS I did not check were the leakage sound came from, I may do that later. I guess that leakage from a valve is much worse than leakage over the piston (being cold).
Edited by Arjan van Druten, November 26, 2015 - 03:56 AM.