Blow by and compression test results

[FordnMassey]

Hi all,

I have a 1965 Massey 35 with a petrol (gas) engine with some blow by. Being in Australia, the engine is a Standard 87mm, which I believe is different to the Continental that North American 35's have. It's a low compression motor, being 6.0:1.

The tractor came to me very uncared for and has no service history. The hours on the engine are unknown as the tractor meter was dead. I replaced the meter and almost everything fuel and spark related and it ran reasonably well, thought did consume around 1L/1qt oil per 50 hours. I have put 150 hours on it.

The blow by started recently and was suddenly noticeable. It's quite significant, puffing out from under the oil filler cap, which on this motor is spring loaded in place. The blow by worsens greatly and is proportional to the load on the engine. High revs with no load do not cause the blow by to show. I've only done around 30 minutes of light running since it started and it appears to be remaining at the same level.

Compression tests when I received the tractor showed 92/97/105/100 psi across the 4 around 3 years and 150 engine hours ago. These are now testing as 85/82/90/90.

I'm thinking that the blow by is likely to be piston/cylinder related, or as middle aged guys in Australia say, "it shat it's rings". I can't think of any other way the blow by can arise.

Questions:

1). Any other potential explanation for this blow by?

2). Any thoughts on those compression results?

Thanks in advance for your help.

 

[nyone]

Do a cylinder breakdown test first.

 

[FordnMassey]

Hi,

I'm guessing you mean a leakdown test. I'm unfamiliar with leakdown tests. What benefits do they provide over a compression test?

FordnMassey

 

[Mike1955]

My “guess” would be in the head. Valve seats and valves. Compression rings would be the next place to look. Just my opinion

 

[nyone]

Yes leakdown test. It shows you where the problem is not just that there is a problem like a compression test.

 

[careyo63]

Hi,

I'm guessing you mean a leakdown test. I'm unfamiliar with leakdown tests. What benefits do they provide over a compression test?

FordnMassey

You leave the pressure tester Attached and watch how long it takes for the compression to lower. Doesn't lower or leak down is real good. Drops Quick is Real bad! The Ford that was sent to me after I bought it.

 

[dodge man]

Blown head gasket, a hole in a piston, a cracked ring land on a piston, bad valves and/or valve seats or just worn out rings, pistons and cylinders. If it really is blowby it’s usually worn rings, cylinders or pistons.

 

[FordnMassey]

Turned out that the crankcase ventilation pipe was completely blocked with a sludge of water contaminated oil. Cleared that and resolved the oil cap blowing off.

Might still be "passing gas" excessively, but not as severely as I thought.

Leakdown test was good advice as it would have spotted that it was not blow by to the degree required to pop the oil cover off.

Thanks for the inputs.