Leak down test small diesel Volvo MD7A

[pembquist]

I have a Volvo MD7A in the boat and a MD6B for spare parts. Want to do a leak down test on the 7A but started with 6B to get things sorted out without the extra complication of doing it on the boat the first time. My gauge is home made with an orifice made by filling a nipple with epoxy and drilling it out with a #60 drill bit. I loosened the rocker arm shaft so that the valves were all closed. At 48 PSI I get about 2-3 PSI drop on the front cylinder and at 45 PSI I get a 30 PSI drop on the back cylinder. The test is done with a cold engine and the leakage seems to be coming out of the crankcase but I need a better way to isolate where the air is coming out. I'm guessing the back cylinder has a stuck or broken ring so next thing is to take the head off and take a look.

My questions are:
When it comes to testing the MD7A should I do the test with the engine warmed up?

It seems like I read that between 5 and 20 percent leakage is considered great to OK. The problem is it depends on the leak down tester what your results are going to be and I have another Harbor Fright leak down tester which has a much larger orifice and would make the percentages look a lot better. Do any of you know what a good percentage and orifice combination would be for these small Volvos or similar 13HP diesels?

I noticed that the rocker arms are not centered on the valves or the pushrods and cannot be given the location of the part of the head that the rocker arm shaft passes through (I don't know what you call this, the bearing surface the shaft rotates in.) Does this seems normal? Again this is the parts engine, maybe it has the wrong rocker arms on it, too wide where they mount on the shaft or something

[skipperpete]

Don’t overthink the leakage test, use more than 50 psi, I prefer 100 psi, no restriction. The percentage is just for customer reports, the important thing is to determine where and how many points the leakage is coming from and how bad the leaks are….. exhaust valves AND piston rings are the most common combo. I’m not even much into using a dummy injector to admit the air, if I’m in a hurry I use a hand held tube with a rubber cone ( from an old petrol engine compression tester) that goes into the injector hole, I can easily hold it against 100psi (but if the MD7 has copper injector sleeves don’t do this, 100psi could pop the seal on the sleeve)
I normally avoid trying to hold the piston at TDCcompression because it’s risky and time consuming, much prefer the BTDC with the rocker gear off completely on small engines or with the adjusters backed off and reset as the test continues on big engines. I use a small copper hammer to tap on the valve stems, it’s surprising how many inlet valve leaks vanish when this is done…. Almost never on exhaust valves though.
Listen carefully for the leaks, the main one will always be the rings, less hissing is good, more is not…. You can feel the volume from the oil filler on the rocker cover with the palm of your hand or a sheet of paper.
The next most common is exhaust valves, normally heard as bubbling in the aqua-lock. Zero is the preferred leakage.
Intake valves are heard leaking into the air cleaner or intake, turbos make this a little harder. Again , zero is good.
Bubbles in the coolant top tank means a blown head gasket (or maybe a cracked head or block) zero preferred.
And finally the very confusing leak between cylinders caused by the head gasket being blown at the narrowest point, the indicator is air coming out of the adjacent cylinder but may also be heard at the exhaust or intake unless the rocker gear is off completely and the valves are all closed. I don’t enjoy working on hot engines in the tropics so I do minor stuff like this without warming up the engine ….unless the valve clearances require a hot set.