Low compression d902?

[hyakkimaru16]

I've got a d902 with 700 hours that I'm having trouble starting. Over the couple of years I've used this mower it would occasionally lose prime and I would have to bleed air at the injectors for several hours to get it to start back up. It was always really difficult to get started but once it was running it would run great for 6 months or whatever the case, and then it would just randomly lose prime. I replaced the low pressure fuel pump, fuel hoses, tanks have been drained and cleaned and lines all blown out. Good fuel pressure, I just rebuilt the injection pump and new injectors. I have bled all the air out of the system and when I crack the injection lines at the injector all I get is rhythmic squirts of fuel. I don't see any air bubbles like I normally would when I was bleeding.

However at this junction I cannot get the engine to respond at all. It's just spinning over and it will occasionally speed up a little bit and then slow back down. I decided to take the oil cap off to check for a compression loss which is something I should have checked a long time ago but here we are. There is definitely some pressure coming out of the oil cap while cranking.

I'm hoping for some opinions, I will post a link to a YouTube video below. My question is does this visually look like enough compression loss to make this engine not start? When it shut off on me this last time it was running perfect and then it acted like it ran out of fuel. It has done this to me numerous times over the years and I decided I should put a new injection pump and new injectors in to try eliminate this problem. Especially after I found out the previous owners had accidentally gotten some water in the fuel. In the process of rebuilding the injection pump I found rust. Same thing with the injectors. I opted for new injectors and a full overhaul on the injection pump.

 

[deep diver]

@hyakkimaru16 the pressure coming from the oil fill cap when cranking can mean the rings are worrn, but engines usually fade slowly. They’ll still try to start or run badly before they completely quit from low compression

 

[hyakkimaru16]

I've spent some more time on this unit and still cannot get it to run. While cranking there is a little bit of white smoke coming out the exhaust. I have installed a new injection pump and new injectors and I have bled the fuel system as per service manual and beyond and have gotten no response. When I crack the injector lines all 3 have great pressure squirting out and no air bubbles. What should I do? Should I test compression next? I tried putting oil in cylinders and nothing changed. Tested glow plugs and power to them all tested good. When the mower shut off it just sounded like it was running out of fuel and rpm dropped until it stalled. I've never had an issue bleeding these Kubota before, they are super simple. What am I doing wrong?

 

[hyakkimaru16]

@hyakkimaru16 the pressure coming from the oil fill cap when cranking can mean the rings are worrn, but engines usually fade slowly. They’ll still try to start or run badly before they completely quit from low compression

I figured as much. I don't know what is preventing it from starting.

 

[hyakkimaru16]

I did a injector pop test and all three injectors of the new injectors fired perfect and the fresh injection pump had no problem doing so. I fixed my compression tester and tested all three cylinders. No wonder it won't start. The highest compression one of the cylinders had was 190 PSI. I am going to pull the head and inspect valves. I spun the engine over with the valve cover off and everything appears to be functioning as it should so I think it's time to pull the head. Might be time for a fresh rebuild too.