Sorry about my other thread, I messed up. How can it be deleted? Anyway, worked on my son's CU engine today to sort out the low compression on cylinder 1. The lifters were out of adjustment and after doing them as per spec, the compression is now 150 psi instead of the 100 it was. so all cylinders are 150 to 155 so that's good. But, when doing the no. 2 lifter adjustments we found that they were both very slack and huge up and down movement, so I reset the adjustment , 2 turns in, and retested the compression, but 0 psi. I slackened off the adjusters back to very slack and compression is now back to 150, so what is going on? Do we need new lifters?
Last time the engine ran were any of the lifters nosy - not pumped up with oil? Possibly set without being pumped up?
Yes, the no.2 was very noisy and tappety before we started the work on them today. Screwing in the adjusters was hard work unlike n0. 1 which was easy and soft to adjust. And as I said, adjusting the n0. 2 lifters with 2 turns gave 0 psi compression.
How about running it until it quiets down, so lifters pumped up. Cool overnight and then set again. I have this engine and it worked for me. I did not record any compressions though
Another thing of note is the screw in adjusters on no.2 are different than the n0.1 as there is very little thread protruding so can only just get the locknuts on, that can't be right surely. The van was driven to a few events recently and covered 300 miles and no less tappety.
You over adjusted them. If they are drained down you can still adjust them but it's not so obvious when you get to zero gap because instead of being supported by oil, the ball bearing is supported bt a weakish spring inside the lifter. Do it again more carefully.
After adjusting hydraulic tappets, you won't get full compression until they have self adjusted. After adjusting, I crank over the engine with the starter without the plugs in to get them to start self adjusting without the usual popping and banging.
Before starting on the no. 2 adjustment, both rockers were very loose but compression was good at 150. I had to screw the adjusters down by hand a long way until just touching and a hint of tap. I then did 2 turns in and found them more solid feel than the no. 1. We don't understand why very slack adjustment and pulling rocker arm well back and forth gives good compression but 2 turns adjustment gives 0 compression. Maybe 2 turns was too much, to get compression back, I unscrewed the adjusters back to just touching and the 150 compression came back.
Good question. It does seem odd both no. 2 lifters are like that and the tappety never goes away. At least we have got 4 good compressions now so some progress towards fixing this ailing and poor performing van.
Fundamentally if the rockers have slack the valves spend a long time closed fully over each cycle. In that state, the adjusters can expand... Hydraulic lifters are designed to self adjust pumping up with oil driven in by oil pressure and then sealing off as pressure comes on them from the rocker end to open the valve. So they should gradually expand to meet the screws when running. If you over tighten the screws you are starting to hold the valves open all the time by pushing with the adjuster and any possible expansion with oil pressure causes the adjuster to hold the valve open even more. Listen to what people are saying. They do fail, they can take a while to expand. If one had air in it for instance, the air bubble might stop it pumping up until vibration shakes it out as the pressure comes on it from the cam.
Thank you for the clear explanation, Ok so explains the 0 compression after my over adjustment. I have taken up the slack as it were by hand but not given them the extra turns, so should be safe like that? even if by some miracle they pump up? Is it worth replacing both lifters?
Temporarily, take it for a good run to get the tappets purged of air, then let the engine cool down and then re adjust. If there is not enough preload the tappet piston smacks the circlip.
So .... what does the manual say ?? Might be a better place to check rather than guesswork... Sent from my SM-G960F using Tapatalk
The reason you lost compression is because you screwed the adjusters in so far that the hydraulic part of them was doing nothing - you bottomed the pushrods out on the follower body THEN you added 2 turns so the valves could not shut - no compression. No offense but you need to try to understand what you're doing (same with the carbs) rather than hoping that blindly following some instructions will sort it all out.
Point taken, we are all learning aren't we and doing our best to keep our vans running. We have the manuals and this excellent forum and a bit of youtube and as my son said today, there are very few garages and mechanics out there who genuinely know our vans and that situation will get worse in time so we have to diy or go modern. We certainly want to understand how stuff works, that's why we come on here to get help from folks like you @Zed who are much more experienced than we are. The no 1. compression was down and resetting the lifters has got it back to 150 so we are pleased with that. Hopefully we can leave this one for now and focus on the idle issue.
