Bobcat 853 with Isusu 4JBI engine knock

[AnOldFixerUpper]

Hello, Recently I have acquired a 853 machine that has a strange symptom. I am looking for suggestions to what might be the problem. When I first start the machine up (cold) the engine runs very smooth and quiet (normal sound) then I let it run up to temp, say 15 mins or so and the typical diesel clacking sound is quite a bit louder. (Loud clacking, cannot really determine where noise is coming from- pretty loud tho) When I first noticed this I was afraid to run the engine, thinking I had a bad rod or main bearing...I could not really determine if I had a bottom end knock or if it was created by fuel knock. I figured the first order of business was to fabricate a oil pressure gauge and hose with required fittings and install on side of engine block. Last night I ran the first set of oil pressure test and here are the readings >>> Engine cold 55 - 60 psi at idle... 60 psi a mid - high rpm.. sounds like the pressure bypass is working! Engine at normal temp 25 - 30 psi idle, and 55 psi mid - high rpm. With this data, I have pretty well ruled out the bottom end and bearing trouble. My next test will consist of measuring for overfueling (injectors / inj pump and timing) I am going to measure exhaust temp on manifold (each cyl) looking for cooler > richer fuel mixture problems. One other posibility, could the injector pump timing be off a bit? Has anyone seen this before? I am open to suggestions. Thank you, Jon

 

[Tazza]

It could be an injector too i guess. As it runs well when cold, it seems odd that it does it when warm. Even if it was a worn bearing i'd have suspected it would make noise hot or cold...
Good luck in your search!

 

[AnOldFixerUpper]

It could be an injector too i guess. As it runs well when cold, it seems odd that it does it when warm. Even if it was a worn bearing i'd have suspected it would make noise hot or cold...
Good luck in your search!

Hello Tazza, Yes, I was thinking the same thing.. I cannot distinguish a certain place the knock is eminating from. I have already loosened the injector flare nuts in an attempt to isolate to one cylinder with no luck. Going to to that again tonight and see where it leads me down the troubleshooters lane. Thank you!

 

[jerry]

Hello Tazza, Yes, I was thinking the same thing.. I cannot distinguish a certain place the knock is eminating from. I have already loosened the injector flare nuts in an attempt to isolate to one cylinder with no luck. Going to to that again tonight and see where it leads me down the troubleshooters lane. Thank you!

if you have a infrared temp gauge you may be able to see a difference in cylinders by the exhaust manifold temps

 

[AnOldFixerUpper]

A little update! Last night I removed the valve cover to check valve lash.. WOW really amazing how clean it was inside there. Figured by the looks of the outside of machine the inside would be just as dirty, not the case! Cyl 1 at TDC had over .025 clearance..(bet 2,3 & 4 are out of spec too. It is possible I might be onto the problem. Specs call for .016 .. solid lifter cam.. in this unit, this could make quite a bit of noise. Will post update FYI!