Cylinder leak-down test procedure (with percentage gauge) - Page 2

zonie77 · #16 (**permalink**) 01-16-07, 12:12 AM

A common problem with N*s is rings sticking in the piston grooves because the engines are often babied. There is a GM procedure of pouring solvent in the cyls, letting it set, cleaning them out, change the oil, then test (by driving). Possibly this engine is a candidate?

We don't hear of valve stem seals going on N*s but it is possible.

km7648 · #17 (**permalink**) 01-16-07, 02:32 AM

Thanks.

I was doing the valve seals due to a puff of smoke that I get on startup - a classic valve stem seal problem?

Doesn't a ring problem give you the puff on hard acceleration or no smoke but ongoing oil consumption?

clarkz71 · #18 (**permalink**) 01-16-07, 06:16 AM

Remove the oil cap & listen, if the rings are leaking you'll hear air from the crankcase.

zonie77 · #19 (**permalink**) 01-16-07, 02:27 PM

Quote:

Originally Posted by km7648

Thanks.

I was doing the valve seals due to a puff of smoke that I get on startup - a classic valve stem seal problem?

Doesn't a ring problem give you the puff on hard acceleration or no smoke but ongoing oil consumption?

Yes, I was suggesting the ring cleaning for the high leakdown. I should've clarified that.

myronf · #20 (**permalink**) 10-13-07, 06:34 PM

I bought the same gauge set as KM7648. Makes no sense to me. When the right gauge is zero'd there is only about 10# on the outlet side of the regulator. I thought you wanted much higher pressure. Also, when there is no pressure on the inlet the right gauge reads75%, just like KM's. Comments?

97Concours1 · #21 (**permalink**) 10-14-07, 11:38 AM

Quote:

Originally Posted by myronf

I bought the same gauge set as KM7648. Makes no sense to me. When the right gauge is zero'd there is only about 10# on the outlet side of the regulator. I thought you wanted much higher pressure. Also, when there is no pressure on the inlet the right gauge reads75%, just like KM's. Comments?

Your right "Cylinder Leakage" gauge has been damaged by too much pressure. It should read 100% with no inlet pressure. It is only about a 30 psi gauge. You must always turn the regulator out BEFORE connecting the inlet air hose. If the regulator is turned IN, the right gauge will peg due to too much pressure and will be damaged. If you try to use the tester now you will not get correct readings.

97Concours1 · #22 (**permalink**) 10-14-07, 12:11 PM

I've got the same tester from Harbor Freight. The instuctions are wrong. I think the problem everyone is having is they are trying to set the tester while it is connected to the cylinder adapter hose (as the instuction INCORRECTLY state). The tester needs to be disconnected from the cylinder adapter hose to set the pressure. There is a valve that blocks the outlet while it is disconnected. This allows you to set the "cylinder leakage" gauge to zero. THEN you connect it to the cylinder adapter hose and take the reading.

FYI: A trick for finding TDC of a cylinder (ON THE COMPRESSION STROKE and not the other one). Put a long tube on the cylinder adapter hose that comes in the kit. Screw it into the cylinder you are testing. Put the other end of the long hose in your mouth. Crank the motor over, BY HAND, until you get air coming out of the hose. Keep going until the air tapers off and then begins to vacuum. At that point, crank back and forth slightly to find the middle between a slight pressure and a slight vacuum. You're there. Works like a charm.

FYI2: My leakage numbers were: 1-43%, 2-55%, 3-35%, 4-40%, 5-40%, 6-30%, 7-40%, 8-40%.

**Ranger** · #23 (**permalink**) 10-14-07, 12:53 PM

Why not just drop a 1/4" dowel rod down the spark plug hole. It will rest on the top of the piston. Then you can watch it rise and when it stops your at TDC.

km7648 · #24 (**permalink**) 10-14-07, 01:53 PM

Here's a quick update for everyone to let you know how things turned out. I know I appreciate hearing the Happy Ending after all the advice.

By all accounts (leak down, compress etc.) the motor is fine. It's been running great in my sand rail since last year. The leak-down tester that I bought and asked about is "different" that the other gauges but worked fine.

It turned out the the PCV valve setup on this engine was unrestricted. When driving, it would suck too much oil vapor into the intake manifold where it would collect. At idle or after sitting, the warm intake would allow the oil to drip into the cyclinders where it would be burned (on startup or prolonged idle) causing the smoke.

There is one major problem with that gauge set: If you connect unregulated shop pressure to the gauges, it will damage the inlet gauge by spinning it beyond its maxiumum range.

97Concours1 · #25 (**permalink**) 10-15-07, 12:18 PM

Quote:

Originally Posted by Ranger

Why not just drop a 1/4" dowel rod down the spark plug hole. It will rest on the top of the piston. Then you can watch it rise and when it stops your at TDC.

That's not a bad way to do it either, but it's a 50:50 chance that you are between the compression/power strokes where you need to be. You could be between the exhaust/intake strokes where the valves are open slightly. With the hose you know for sure, and then you can go right to the leakage test because the adapter hose is already in place.

The dowel rod is also difficult with a non-hemi type engine where the plugs are at an angle. My first experience with using the leak gauge was on an Aerostar van. I was by myself trying to find TDC on the cylinders while turning the engine over from underneith at the harmonic balancer. It was impossible to stick something down the cylinder, turn the engine over at the same time, and feel for TDC. In the van you can't even see some of the plugs you are working on. The hose method worked great in that situation.