In advance of dropping the engine this winter to fix an oil leak, I and @mcswiggs did a compression test on my camper today. The results are puzzling No 1 = 92 (wet 94) No 2 = 130 No 3 = 122 No 4= 148 Obviously something wrong with No 1 but possibly not rings but we were also puzzled by No 4 which is above the 'as new' reading for a type 4, 2ltr previously FI now twin Weber's. Ummmm any ideas?
Maybe the compression tester? Worth warming it up & doing another one to compare the readings. It could highlight if it’s valve or head sealing rather than rings.
A few CC's of petrol or oil in the cylinder will push the results high . Or what I did was knock the compression tester on something, the needle fell off for the first time in 35 years and I put it back on with an offset between measuring two cylinders.
Are you able to watch the needle? It's important that it builds pressure in a couple of twitches but your low one could be still building if it has a problem.
Thanks chaps. The wet result in () was with oil in No 1. As for No 4 we repeated the test a few times and then went back to No 1 and got the low reading again...so guessing the tester is OK. I was watching them all and they they all twitched slowly up
Yep - we did all the tests several times. After we got the high reading for No4 (148psi) we went back and checked No1 but still only got 90-92psi. I forgot to floor the throttle during the cranking (doh!) but don't think it would make a huge impact. The engine was nice and warm when we started. The engine is a bit of an unknown quantity. It's an American import that was FI now running Webber ICTs. It's had something of a rebuild as it's got AMC heads, not sure about the pistons and barrels and don't yet know whether it still has its hydraulic lifters or what state the cam is in. But even so, 148psi seems higher than capable from a humble 2-litre? (Bentley say 135psi is the new state measure.) I suppose if the lifters weren't pumped up on No1 and the valves not opening fully this would lead to a low reading.. (As well as a cracked head, dropped valve, bore/ring wear, hole the piston, loose head...) Next stop, leak-down test?
Thanks for all your help Dom (@mcswiggs )...even without your heavy right foot The leak down test kit is already on order.
Fillowing on an asymmetry theme : Or somebody line bored it very crookedly, number 1 is diagonally opposite number 4. The crank is too close to the cylinder heads one corner, to far the other... Or a spacer that ought to be under number 4 cylinder has been added to No1 instead.
Cranking compression is directly related to CR. e.g. I have way too high CR for my stock cam - 8.7:1 - and crank at 170psi. It's possible your engine has very slightly higher than stock CR and the lower readings have all lost some seal, particularly one of them. 145 psi is not so high, I've seen plenty 2l with 135-145 psi.
Well with C19 less than I wanted to. I bought the camper a year ago and have been on a few trips. I want to go farther but I don't thrash the engine. So far only a few trips of about 200 miles return with no issues. I choose to cruise at about 55mph but I have taken her up to 70 to test once only. Average mpg is 23ish. I'm going to do a leak test next week sometime and in the winter the engine is coming out to fix an oil leak (suspected flywheel end oil seal) which will give me the opportunity to check some of the possible causes mentioned by @mcswiggs above.
Partly to bed it in partly to get it hot, etc etc, pottering engines about does them no good, your numbers aren’t far off, I bet you gain some compression
pretty sure it will be if it's a late 2ltr FI but could be wrong. If it's been unused for a while the lifters can get gummed up. This can prevent the valve (s) from opening at the right time giving you a low comp reading. Ragging it with fresh oil often clears it up.
