Quote:
Originally Posted by coconup
Side note about piston rings break in. I didn't know this was a thing and I hope I didn't screw it up already with all the cranking and misfires ��*♂️. Is there a recommended break in oil I should use? Right now the engine is filled with the oil I usually run it with ( https://www.autodoc.de/elf/12744089), which is a semi-synthetic 10w-40. |
I doubt that you are facing any long term trouble with ring break-in. There is a school of thought that says conventional rather than synthetic or semi-syn oil is preferable during the break-in period since it is slightly less slick and (according to this theory) helps rings seat more easily. But there are other folks who dismiss that idea as a fable and say to just run whatever oil in the engine you plan to run long-term. And the latter view IMHO is supported by the recommendations of engine manufacturers themselves for new cars, who almost universally specify synthetics nowadays (at least in any kind of turbo diesel or turbo gas engine) but don't suggest anything about running conventional oils for the first few thousand KM.
As both you and ngoma said earlier, the fact that the compression readings were pretty consistent across all cylinders is a very positive sign, and it's likely you can expect those numbers to rise as the engine runs more, seats the rings, goes through several heat cycles and gets rid of any fuel washdown from starting attempts, and you test with a fully charged battery.
If it were me personally I would not even bother testing again until after you have put some miles on the engine. Right now you have already seen results that argue against there being any serious problems, and your readings could be skewed again by the fact that the engine has been hard to start and running poorly. It could be a sort of circular information loop that doesn't actually tell you that much about the underlying soundness of the engine.
A possibly relevant story: ngoma and I working together on a project many years ago fought a massive battle with a D24T that refused to even start. We could not figure out why, after verifying good timing, injection system health, glow plugs, etc. Finally as a last resort, speculating that maybe we had washed all the oil out of the cylinders with extended starting attempts and the rings just couldn't seal anymore, we removed the injectors and filled the cylinders with motor oil (or maybe it was ATF?), rolled it over by hand a few times to wash the oil around in the cylinders, then spun it on the starter for a while to blow the oil back out and prevent hydraulic lock. Reinstalled the injectors and bled the fuel system, and bam, the engine started and ran perfectly on the first try, to my memory. I think it started and ran well ever after too. So it was a lesson in how much the effectiveness of the ring seal against the cylinder bore can be (temporarily!) compromised even in an otherwise strong engine by loss of the lube oil film that provides an important part of the sealing effect.
Look forward to hearing what you find out, this is an interesting and strange issue but it has to be related to the quality of ignition. Normally I would say it sounds just like retarded timing but since you have ruled that out, it does sound like "delayed" ignition despite correct static injection timing, due to poor performing injectors (spray pattern or incorrect opening pressure or delayed actual injection due to air bubbles in fuel) (or low engine compression), could well be the cause.
FWIW, the seat of my pants tells me that a good series of next steps would be to verify that the injectors are working well as you're doing, and resolve any inlet side fuel system air leaks as was advised. But then, assuming you know timing and everything else are correct, try to minimize the amount of time the engine spends running for short moments on the engine stand, and instead install it back into the vehicle, get it filled with coolant, and try to give it a chance to run for extended length of time with a load on it and really get good and warmed up, get the oil hot, etc. That may be what it needs to get all the material washed out of the engine from the internal work that was done and get the rings sealing right.
