Did a compression test on my TSR Donigton today after running issues since a full rebuild, and cylinder 4 has zero compression, 1,2,3 have between 12.5 - 13.5 Bar Done zero milage since rebuild... any ideas, piston ring, cracked block? Pulled the head off tonight in preperation to take the cyclinder out tomorrow... and the valves seem in an odd arrangement... In TDC 1 E and I both closed 3 & 4 both valves open 4 both valves slighty open surely these should be closed like 1? Any help appreciated... The other thing that makes me think it could be the rings is the smell of petrol in the oil! Thanks
The valve positions sound correct. This is due to the cam phasing. When cylinder 1 is at TDC on the compression stroke (both valves closed), cylinder 4 is on the crossover from the end of the exhaust stroke / beginning of the induction stroke. This is called the valve overlap period and both will be slightly open, the amount varying with how wild the cam profile is. If the head is off, you can now check for valve sealing issues on number 4 cylinder by rotating the cam so that both valves are fully shut, then pour some petrol or diesel down the ports on that cylinder and check to see if it leaks or flows past each of the valves. If so this will be the problem. It could be down to a tappet clearance being to tight if it is the shim / mechanical type, or the valves may have had a knock before assembly of head on engine, meaning a valve may be slightly bent and not sealing correctly. If it is a shim type head, check the valve clearance with feeler gauges.
^^^ Thanks it is a shim type head so could need a narrower shim i'll check this tomorrow, the shims do need final gapping but not had chance to get the engine warm!
Carried out the valve test and i have a good leak of fluid on the inlet valve... Would this be enough to cause zero compressio? Also poured fluid in the cylinder bore to check the rings and there fine.
Is there a decent valve clearance on the valve in question? If not, it could be held open slightly. If there is clearance it suggests a bent valve, possibly been knocked since the head was rebuilt and fitted.
All good now shim to thick in cyl 4 inlet have good compression on all 4 between 10.5 - 11.5 bar. danster - thanks again for all he help and suggestions really appreciated.
