TonyB Posted October 1, 2001 Share Posted October 1, 2001 My 1500cc Cosworth precrosflow is now installed and running, with 50lb oil pressure. The compression on cylinders 2,3,4 are all 145-155lbs but cyl 1 is about 125-135lbs (all measured with the throttle open and engine hot). Also, above about 2,500 rpm oil is getting "thrown" out of the crankcase breather. Am I just being paranoid or does all this indicate ring problems in cyl 1?? Regards Tony Bates 1963 Super Seven Cosworth 1500 - SB 1761 Link to comment Share on other sites More sharing options...
oilyhands Posted October 2, 2001 Share Posted October 2, 2001 Cylinder one is down a bit but not drastically, overall the figures look a little low, have you tried a 'wet' test to see if there is any difference? Oily Link to comment Share on other sites More sharing options...
TonyB Posted October 2, 2001 Author Share Posted October 2, 2001 Wet Test?? Do you mean putting some oil in and seeing if the pressure comes back up? I tried it once, didn't seem to make a significant difference but will try again. Regards Tony Link to comment Share on other sites More sharing options...
TonyB Posted October 3, 2001 Author Share Posted October 3, 2001 Anybody else got any ideas?? Regards Tony Link to comment Share on other sites More sharing options...
Roger King Posted October 3, 2001 Share Posted October 3, 2001 Firstly, the idea of putting oil in the cylinder is to see if it brings the compression figure up. If it does, it is likely that the piston rings are the culprit, because the oil helps them to seal better. If it doesn't, it is probably the valves that are leaking. Bear in mind that this is only a very crude test and I have in the past seen leaking valves improved by the oil! There are really only four possible sources of poor compression:- 1)piston rings 2)valves 3)head gasket 4)crack in head or block Compression testers are notoriously variable, to the extent that I wouldn't place too much reliance on the absolute figure. It helps to know your gauge here, so it might be worth trying it on a few other engines. The variation between cylinders is important however and yours is a little greater than ideal. Sometimes, with a newish engine, it is worth doing a few hundred miles and trying again; in some instances, rings and valves will have bedded in and give better figures. Failing this, I think that further investigation is worthwhile. Probably the best type of test would be a cylinder leakage test. With this, you feed compressed air into the cylinder and read the amount of leakage off on a gauge. It is often possible to listen to the exhaust pipe, carburettors and engine breathers to hear where the leakage is coming from. If you can rig an adaptor from an old spark plug, you can feed the compressed air in and not bother about the gauge - it will still be possible to do the listening test and pinpoint the problem. Note that the cylinder you are testing must be at TDC on the firing stroke. Link to comment Share on other sites More sharing options...
TonyB Posted October 4, 2001 Author Share Posted October 4, 2001 Thanks Roger I'll try the leakdown test at the weekend, a friend has one I can borrow. Should the engine be hot or cold for the test? The engine is "new" having been rebuilt in 1990 and it has sat in its crate since then, so hopefully things will improve in a few hundred miles! Is the oil getting thrown out of the crakcase breather something I should worry about or just fit a catch tank? Regards Tony Bates 1963 Super Seven Cosworth - SB 1761 Link to comment Share on other sites More sharing options...
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