I did a compression test on my type 4 engine after a rebuilt head put on side of 3 and 4. It's a 1700 block with 1800 pistons, cylinders and heads. I'm getting 110/120/90/120, is that ok? I'm a bit worried about number 3's result there.
What were the figures before changing the head? If you squirt some oil down the bore (eg through the spark plug hole) and re-test #3 does the reading change? If it does, it could indicate that the piston rings are a bit worn. If not, perhaps there is a valve not closing fully or maybe the head isn't seating well on the barrel...? TBH, 90 isn't too much off the other 3...if the motor runs at least as well as before the head swap, I'd ignore it and re-run the compression test in a few thousand miles. My 1.6T1 has similar compression figures and runs fine....It will get a top-end rebuild at some point this year, but I don't think its the current top priority.
Numer 3 is slightly low , time to drop the engine , remove tinware , remove head and take a look ... Look at rebuilding the head , might as well change the barrels , pistons and rebuild the bottom end whilst i`m at it , hmmmm , scooby looks tempting .... OR Do what most people would do before the advent of fancy tools , throw the tester over @snotty `s fence , give the van an extra special pat and plod along and enjoy the summer in blissful ignorance For what it`s worth i had two weeks en France with the oil light flickering away at tickover and compression on every cylinder was nowhere near three figures . That was supposed to be the `last hurrah` for a faithful engine which had served me well for 20+ years - lasted another 2 years before i finally got around to it Yours`ll be fine .....
This is the engine that had a dropped valve seat and was backfiring through the exhaust when you started it isn’t it? Did you check that you had matching heads with the same size valves on both sides of the engine? Did you check the compression ratio when you fitted the replacement head? Did you fit head gaskets (on one or both sides)? Those compression numbers just look like a tired engine that’s getting close to needing a rebuild and the difference between 3 and 4 is bigger than I’d be happy with.
Yes. Still a backfire on idle but runs fine other than that. Yes matching heads and valves. No. No. I did the oil down the spark plug hole trick and it didn't change the reading from 90. I'm going to run it for a while and see how it gets on then reset valve clearances and check it again. Thanks for all the advice.
so your new head did you replace the valves or was it a new head ... oild would increase comp results if it was ring wear but not if your valve/s are not sealing
I recently re lapped in the valves on my T1 engine in my bus because they were causing low compression. I could feel the lack of resistance to turning and hear the hiss from the exhaust on about three cylinders. When I checked again .. the compression did not change much..but the compression tester is 32 years old and the thread has worn off the end and the air leaks .. needs re threading.. But on the road the difference was between easily holding 68mph on the flat on part throttle and struggling to that speed flat out before lapping the rather pitted valves I have bought a complete set of new valves to go in next time round .. with lapping.
Wasn't me who did them but definitely lapped in and sealed. I have another head here and new valves for it so I'll build that one up and probably swap them over if things don't improve. I can change the piston rings at the same time I suppose. I really don't fancy dropping the engine again !
New rings in old bores won’t bed in without being honed, but I suppose you know that. Fit 96mm B&P and make it into a 1911cc.
