need to help for ST2

[moses]

Hello friends. First of all, I would like to announce that due to my poor English, I am forced to use Google Translate, so please accept my apologies in advance. Let me get to the point. I have a Lister ST2 engine coupled to a centrifugal water pump. Last summer, the engine suddenly stopped working and locked up.
After the repairman inspected the cylinders and cylinder head, he went to work turning them, new pistons were installed, and the engine was started. The engine worked for a while at 1500 rpm, but when I increase the engine speed, it stops again after a few minutes of operation. The only thing that is missing is that after stopping, when I turn the crankshaft, it turns but gets stuck somewhere, meaning it locks up. After a few hours of turning it again, it is unlocked. After that major repair, the oil ring broke once and was replaced.
How do you interpret this? Unfortunately, due to the engine being in a specific condition, it is difficult to move the engine and there is no skilled mechanic available to find and fix the problem. And I want to do it myself.
So I would be happy to benefit from your opinions and experiences on this matter.

[AdeV]

Hmm, that's pretty weird.

My immediate thought is it's over-fuelling on one cylinder leading to a hydraulic lock when there's too much diesel in there; but honestly that seems like a stretch - and you'd be able to discount it by opening the decompression levers, at which point the engine should turn all the way around.

As it's happening at higher speeds (and, presumably, load?), it could be temperature related. When you say it "gets stuck somewhere", do you mean like a hard-stop? e.g. turn the engine by hand in it's normal direction - does it stick like it hit something, or does it get stuck like it walked into wet asphalt, sort of soggy but persistent? Once it's stuck, can you rotate it backwards, or is it now stuck in both directions?

If it's a sort of "sticky" stuck, my gut feel would be it's got too hot, the pistons/rings have expanded, and it's sticking with one piston up at top or bottom dead centre where it's most likely to have the least wear in the barrel. Given that it frees up again later, this is my best idea. Another possibility would be a bad bearing, although AIUI if a bearing seizes, it rarely works again without an overhaul.

If it's a hard stop that you can reverse away from, then something physical is interfering. I can't imagine what - if it were a stuck valve you'd know about it already, because it'd be bent all to hell having been hit by the piston - if that's even possible with an ST engine.

Personally, I'd buy an infra red temperature gauge (one of those you point at something to get a temperature): Run the engine at 1500 for a while to get it up to temperature - record the temperature of both cylinder heads (just below the valve covers). Now run it up to working speed & watch the temperatures. If they start rising significantly; you're headed for a seize, so shut it down. But at least you'd have confirmed it's getting hot: Next challenge is to find out why...

[moses]

Hello and thank you for your help and advice.
 Stuck, not locked. That is, I turn the handle but it gets stuck somewhere and doesn't move. Of course it goes backwards. I also feel like it's a physical collision. And of course it's caused by temperature. Another thing is that when it turns off, a lot of black smoke comes out. My guess is that the fuel settings are messed up. Also, it burns about 10 liters of diesel every 4 hours under load. Of course, I don't know if this is a standard amount or a lot!

[AdeV]

Hello and thank you for your help and advice.
 Stuck, not locked. That is, I turn the handle but it gets stuck somewhere and doesn't move. Of course it goes backwards. I also feel like it's a physical collision. And of course it's caused by temperature. Another thing is that when it turns off, a lot of black smoke comes out. My guess is that the fuel settings are messed up. Also, it burns about 10 liters of diesel every 4 hours under load. Of course, I don't know if this is a standard amount or a lot!

Black smoke is suggestive of over-fuelling - you would typically get black smoke when increasing throttle under load. But it's also burning - unburnt (or partially burnt) is light grey smoke (and often lots of it). I think you're going to need to whip the heads off immediately after it's failed to determine the cause. It kind of sounds like it might be hydro-locked, i.e. enough raw diesel has built up in one of the cylinder heads to prevent the piston from completing a stroke - except if you operated the decompression lever, that should let it roll all the way over.

With respect to the fuel consumption - I don't know... but if you can tell me roughly what RPM you run it at under load (assume when it's working OK!), then it should be possible to calculate an efficiency, which should tell us if it's in the ballpark or not.

If you're pretty sure it's overheating, then the things to look at are the fan on the flywheel (make sure it's not clogged up with stuff), and also the fins on the cylinders (also need to be clean and clear). Although if it's any consolation, I have a lawnmower engine which overheats for no apparent reason... and despite cleaning it thoroughly, it still refuses to behave.

[moses]

Hello again.
I am confused about a few things. 1- In order to fill the valve clearance, I need to find the top dead center of the engine. Is this possible using a thin rod that sits on the piston through the injector hole and moving the piston accurately? Because I was unable to find the mark on the flywheel.
2- Adjusting the compression lever also requires top dead center, which I guess is caused by the engine locking up at a certain point due to its incorrect adjustment. 3- In the manual for calibrating fuel pumps, there is a mark (A)(B in picture) that is defined by a certain amount. While in my engine, this size is not correct and is even negative (5 mm). When the comb reaches the far right, the fuel is cut off. 4- I do not know how to work, arrange, and adjust the part shown with the letter A in the photo.