compressiontest hissing sound crankcase
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Three Wheelin'
Joined: Jan 2003
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From: Netherlands
compressiontest hissing sound crankcase
After removing the engine for a number of jobs (thanks for summing up), the cilinderheads will go off tomorrow. Reason is of course a leaking cilinderheadgasket. The horror scenario is that when testing compression, there was a hissing sound coming from the crankcase when testing cil #4. This does mean that the cilinders are damaged thereby leaking air via cilinderwall scores???
Chronic Tool Dropper
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From: Bend, Oregon
If the test you were performing is a leakdown type test, the noise in the crankcase is most likely cylinder/piston damage. With the cylinder heads coming off anyway, you'll be able to visually verify cylinder scoring, broken rings or piston damage.
A leakdown test is normally performed on a warm engine, and involves introducing compressed air to each cylinder individually, after rotating the crankshaft to get the tested cylinder to top dead center on the compression stroke. The air is introduced through a precision orifice tube, and the amount of air flowing is determined by looking at pressure drop through that orifce tube.
If you did perform the test on a cold engine with dry cylinders, the results may or may not be definitive. Since you'll have the heads off anyway though, the point is moot-- Take a look and see if there's damage. It's quite possible to hear some leakage when the engine is cold and dry, yet have no problems at all when it's warm and the cylinder walls are lubricated.
keep us current on what you find, please.
A leakdown test is normally performed on a warm engine, and involves introducing compressed air to each cylinder individually, after rotating the crankshaft to get the tested cylinder to top dead center on the compression stroke. The air is introduced through a precision orifice tube, and the amount of air flowing is determined by looking at pressure drop through that orifce tube.
If you did perform the test on a cold engine with dry cylinders, the results may or may not be definitive. Since you'll have the heads off anyway though, the point is moot-- Take a look and see if there's damage. It's quite possible to hear some leakage when the engine is cold and dry, yet have no problems at all when it's warm and the cylinder walls are lubricated.
keep us current on what you find, please.
Thread Starter
Three Wheelin'
Joined: Jan 2003
Posts: 1,991
Likes: 87
From: Netherlands
The compressiontest was simply: putting compressed air in cilinder at TDC through sparkplug hole using locally manufactured tool from old sparkplug and some clever piping and valves from central heating stuff. Cilinder #4 did not hold any pressure. You could hear it escape through the crankcase vent hose. Later, with the oil pan off and cranking the engine, you could hear air coming from underneath when #4 was at compression.
With the heads off, cilinderwalls all looked the same. Smooth as a baby's bottom. No scoring whatsoever. Puzzels me how the air found its way to the crankcase area!
Even bigger puzzle: Timing markings of camshaft did not correspond with timing marking of crankshaftbalancer. They were off by approx 60 degrees! I kinda made my own TDC markingon the balancer to be able to make correct timing again when reinstalling but how can this be? I thought that pully and balancer would go on only one way. Timing markings should line up on camshafts and crankshaft balancer, right? See pictures enclosed.
Also I found a lot of white powder around the #4 sparkplug thread. Cracked head?
With the heads off, cilinderwalls all looked the same. Smooth as a baby's bottom. No scoring whatsoever. Puzzels me how the air found its way to the crankcase area!
Even bigger puzzle: Timing markings of camshaft did not correspond with timing marking of crankshaftbalancer. They were off by approx 60 degrees! I kinda made my own TDC markingon the balancer to be able to make correct timing again when reinstalling but how can this be? I thought that pully and balancer would go on only one way. Timing markings should line up on camshafts and crankshaft balancer, right? See pictures enclosed.
Also I found a lot of white powder around the #4 sparkplug thread. Cracked head?
Last edited by Ad0911; Sep 17, 2010 at 06:16 PM.
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Joined: Apr 2003
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From: Abbotsford B.C.
balancer is on backwards as already stated,
by what you have said of putting compressed air into the cylinders, this type of test is a leakdown test,
you will ALWAYS get blowby past the rings and entering into the crankcase, however the information needed is how much air is getting by?
you need to know how many PSI you were putting in and how much the cylinder was holding say if you put in 100PSI and the cylinder held 95PSI that is still within tolerance.
good luck with it.
by what you have said of putting compressed air into the cylinders, this type of test is a leakdown test,
you will ALWAYS get blowby past the rings and entering into the crankcase, however the information needed is how much air is getting by?
you need to know how many PSI you were putting in and how much the cylinder was holding say if you put in 100PSI and the cylinder held 95PSI that is still within tolerance.
good luck with it.
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Chronic Tool Dropper
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From: Bend, Oregon
The true test is to get the cylinder to TDC with the balancer on correctly. With it backwards like that, there's a good likelyhood that the hissing was air passing through an open valve. Cam timing is off relative to crankshaft position.
Since you will be reworking the heads, you'll know quickly if there was any valve damage from the cams out of time.
Since you will be reworking the heads, you'll know quickly if there was any valve damage from the cams out of time.
