Oh dear -low pressure

[wyke]

Had an ongoing issue with a lumpy 1256 HC 1974 Low mileage engine. Done elctrics and can not get it to fire on num 2 even though a spark is there.

Pressure results earlier this year

1 140
2 120
3 160
4 160

All whaen engine hot

Now - with engine warm

1 80
2 00 !!!!!!!!
3 100
4 100

Bit of a bigger worry on num 2 now . Not sure what has happened - as car only standing. Only took it to exhaust centre and back to get them to cut through rsuted front pipe with torch. Thinking it could be head gasket or crack in head. Could it be rings ?
Any views / advice welcome.

[droopsnoot]

Is that a dry test or a wet test? You can use these two to differentiate between pistons / rings, and valves.

Someone correct me if I'm wrong, but I think the idea is to to a dry test and note the values, then pour a little engine oil into each cylinder in turn and note the values again. If the bad one has increased, that implies piston rings because the viscosity of the oil acts as a "helper" and seals them temporarily. Of course, if it's the piston itself then it won't help.

[droopsnoot]

If it's been standing, it could be a valve stuck open.

[pbottomley]

The wet and dry test is a sound test done it several times myself.... Funnly will be doing a test just like that on my SL90 in a weeks time Finger crossed..

[griffonmark]

0n psi is a bit on the low side. Even with no rings you would get some pressure reading. Must be a big hole like the piston has fallen out or a valve is well stuck open. The valve train buckets are real dodgy on these engines and I used to fix loads with pushrods stuck through buckets. They were virtually all low mileage engines suggesting that a lack of lubrication around the bucket bearing or on the pushrod top could be a problem. Never had the same customer come back though. So may have been due to badly adjusted valve clearances. Take the rocker cover off and turn the engine over to see what the valves are doing.

[wyke]

Not sure what a valve train bucket is.
Have had cover off earlier in year to watch springs and adjust clearances - not really anything wrong or to adjust.
Oil ( wet test) made no difference to reading on num2.

[griffonmark]

What I called the bucket was the lump of pressed steel between the pushrod and valve stem. You might call it a rocker?