compression problem

[SammoHung]

Today I discovered that my No 1 cylinder compression is down to 11 bar! (Below minimum and also way-different to the other 3 which are all blob-on the maximum of 13.5 bar. NOT HAPPY

The first thing I noticed on examination was that the No 1 plug showed good colour for combustion and no signs of oil or anything dodgy IMO.....the only clues that I have plucked is that my efficiency is down of late by around 15 - 20%. Also, the plug gasket was brown and crusty cooking compared with the other shiny plug gaskets from the other pots.

I don’t burn oil or coolant what so ever(and never have), so I'm thinking that either the plug isn’t sealing properly due to a build up of dirty crud around the plug seat....or maybe some crud has fell in a previous plug change..(PLEASE NO!)

Anyone got any hints for getting crud out altogether without dropping any into the combustion chamber?

Other suspicion is that despite setting valve clearances a couple of years ago...may be the locknuts on one or both of the cylinder 1 valve tappet(s) have come loose and the clearances have rattled lower (keeping the valves open for too long???)

Any thoughts would be welcomed…Cheers

 

[stonesie]

The first suspect for me is the valves, maby 1 has a burnt seat and is not sealing properly.

To check this repeat the compression test then put some oil down each plug hole (a teaspoon or 2 should do it) then do the compression test again, the oil makes a very good temporary seal on the rings and if it dosen't heavely affect the results it rules them out)

i think the compression tester uses a rubber 'O' ring so it will seal on a slightly rough surfice.


But from what you have said i would check the valve clearances first, if the clearance is too tight the valve will not close fully when the engine is warm and this will damage the valve and seat.

 

[SammoHung]

cheers for the feedback, I will run the test and check the clearences ASAP:

nice tip with the oil....

 

[bombz4]

reminds me of my car! first was an exhaust vavle shot! then the rings a few weeks later!!!! hope yours doesnt go as bad! (rings were nothing to do with the valve!) but it does sound like it could be your valve.

 

[Fordy]

is the engine running rough? if so just get a new engine or repair yours new rings, new valve stems, new big end bearings and small ends bearings

repairing will be more expensive than replacing if you have to change the big and small end bearings

 

[SammoHung]

Not rough as such...only a slightly uneven idle and lower efficiency than it was a year ago..... I will check clearances etc first before considering the major stuff ……I think

I will have to wait till the weekend though so that I can have some light!!!

Dark nights are crap