Discussion
First, see if its rings or valves.
Get some thick gloopy engine oil, say the 20W50 that Halfords sell with a big label on saying "not for use in post 1980 cars" and a squirty oil can.
Put a couple of squirts down each plug hole in turn and do a compression test. If the reading increases from the "before" reading then youve got knackered piston rings and it is unfortunatley engine out. If there is no change it could well be valves that are knackered in which case its 'only' a case of whipping off the cylinder heads.
The theory being the oil forms a temporary seal around worn rings and helps boost the compression ratio temporarily.
Regards
Iain
Get some thick gloopy engine oil, say the 20W50 that Halfords sell with a big label on saying "not for use in post 1980 cars" and a squirty oil can.
Put a couple of squirts down each plug hole in turn and do a compression test. If the reading increases from the "before" reading then youve got knackered piston rings and it is unfortunatley engine out. If there is no change it could well be valves that are knackered in which case its 'only' a case of whipping off the cylinder heads.
The theory being the oil forms a temporary seal around worn rings and helps boost the compression ratio temporarily.
Regards
Iain
uglymug said:
HI Iain,
Thanks for the tip. Is this done with engine hot or cold?........TA
either should do the trick..
Also check the valves on that cylinder are opening and closing .. if valves are bent then could both be stuck open.. but my money is on the rings.. and a scored bore
Like the Rev says either should do, my money is on engine cold, cos a) It will keep the oil nice and thinck and gloopy hopefully forming a better seal giving better results and b) so you don't start burning yourself on hot manifolds etc (I've the scars to prove thats not a good idea)
Regards
Iain
Regards
Iain
My money is on the valves and/or camshaft. The latter can get so worn that the valves don't move, so you get no compression reading.
I've had broken piston rings before and they would have to be completely disintegrated to give no reading. Also you would see other symptoms such as massive oil leaks due to the blow-by.
So - if the reading comes back with oil, it's the rings, else it's the valves. Don't use too much oil or you could hydraulic lock the piston, just one teaspoon.
I've had broken piston rings before and they would have to be completely disintegrated to give no reading. Also you would see other symptoms such as massive oil leaks due to the blow-by.
So - if the reading comes back with oil, it's the rings, else it's the valves. Don't use too much oil or you could hydraulic lock the piston, just one teaspoon.
adam quantrill said:
My money is on the valves and/or camshaft. The latter can get so worn that the valves don't move, so you get no compression reading.
I've had broken piston rings before and they would have to be completely disintegrated to give no reading. Also you would see other symptoms such as massive oil leaks due to the blow-by.
So - if the reading comes back with oil, it's the rings, else it's the valves. Don't use too much oil or you could hydraulic lock the piston, just one teaspoon.
You should see my Lotus engine. One and two pistons have lost large chunks out of the sidewall on the thrust side; no. 1 has broken rings, no. 2 doesn't! Yet no compression on either cylinder.
You never really know until it's all in bits...
A leakage test will prove without doubt whether it's rings or valves.
There is a proper bit of kit that can be used but I imagine it would be possible to diy something.
Basically it is a compressed air pipe that has a spark plug thread on the end. Doing each cylinder in turn move the car back or forwards in gear until the relevant piston is tdc (I think - I'm mechanically challenged but would both valves be closed at this point ?)(can tdc be gauged with a screwdriver down the plug hole ? I have only ever done this with a Lotus 2.2 16v engine and that could), crack 100 psi in and see where the air goes.
If out the crankcase breather then rings, if out the exhaust or plenum/air filter then one or both of the valves depending which. No-where (i.e. holds pressure for a minute) and there's not much wrong.
There will always be a degree of leakage and the proper bit of kit puts a determined volume of air in and gives a percentage leakage reading but with no compression at all then all the air is going somewhere so it should be easy to determine the problem.
There is a proper bit of kit that can be used but I imagine it would be possible to diy something.
Basically it is a compressed air pipe that has a spark plug thread on the end. Doing each cylinder in turn move the car back or forwards in gear until the relevant piston is tdc (I think - I'm mechanically challenged but would both valves be closed at this point ?)(can tdc be gauged with a screwdriver down the plug hole ? I have only ever done this with a Lotus 2.2 16v engine and that could), crack 100 psi in and see where the air goes.
If out the crankcase breather then rings, if out the exhaust or plenum/air filter then one or both of the valves depending which. No-where (i.e. holds pressure for a minute) and there's not much wrong.
There will always be a degree of leakage and the proper bit of kit puts a determined volume of air in and gives a percentage leakage reading but with no compression at all then all the air is going somewhere so it should be easy to determine the problem.
Gassing Station | Wedges | Top of Page | What's New | My Stuff