NH2112
07-06-2008, 18:58
I recently spent a couple months going through one of our "pushbacks" from front to back, sending the 6.2l out for a rebuild & to have main web cracks repaired, making a new wiring harness to replace the bird's nest, etc. Got the engine back ($3400 spent rebuilding a 6.2l when I tried to convince the boss to just put a 4BT3.9 in instead), got everything wired up and working, broke in the engine according to rebuilder's instructions....and I have a fuel knock. A bad fuel knock.
*Found the knock in #3, swapped injectors between 1 & 3, and the knock followed the injector.
*Got new injector from diesel shop, put it in #1, and there's still a knock that goes away when injector line is loosened.
*Pulled glow plug and found half the tip was missing (brand new 60G.)
*Checked compression on #1, got 410psi so there's no crack in the piston crown and the valves aren't bent from the glow plug tip going through them.
*Tried fitting my borescope through glow plug hole to see if the tip was in the cylinder but it's too big.
*Boss had me check compression on all 8, range was from 400 to 420psi.
My next step when I get the time is to pull the head off and see if there's anything obvious that would account for the knock. The injector is brand new so I'm ruling that out for now - it started knocking immediately upon installation, all I had to do was put the tranny in gear with the park brake on and the load on the engine caused it to knock. Idling in neutral there was no knocking. Could the glow plug tip have embedded itself in the piston crown? Would I hear a sound from the tip striking the head? Would this raise the compression ratio enough to ignite the fuel too early? If so, if I retarded the timing a few degrees should the knock go away or quiet down? I need to find out relatively quickly before we put too many hours on the engine (boss said to just run it for now) just in case it's something the rebuilder screwed up. As of yesterday it had about 12 hours on the rebuild.
Any ideas here? Thanks in advance! I still wish I'd been given the go-ahead to source a 4BT3.9 w/SAE #3 bellhousing. As much as I like the 6.2l I don't really think it's a good choice for a 30,000lb vehicle pushing airliners around. We have to get it rebuilt every 2 or 3 years, and I think the Cummins won't have that problem.
*Found the knock in #3, swapped injectors between 1 & 3, and the knock followed the injector.
*Got new injector from diesel shop, put it in #1, and there's still a knock that goes away when injector line is loosened.
*Pulled glow plug and found half the tip was missing (brand new 60G.)
*Checked compression on #1, got 410psi so there's no crack in the piston crown and the valves aren't bent from the glow plug tip going through them.
*Tried fitting my borescope through glow plug hole to see if the tip was in the cylinder but it's too big.
*Boss had me check compression on all 8, range was from 400 to 420psi.
My next step when I get the time is to pull the head off and see if there's anything obvious that would account for the knock. The injector is brand new so I'm ruling that out for now - it started knocking immediately upon installation, all I had to do was put the tranny in gear with the park brake on and the load on the engine caused it to knock. Idling in neutral there was no knocking. Could the glow plug tip have embedded itself in the piston crown? Would I hear a sound from the tip striking the head? Would this raise the compression ratio enough to ignite the fuel too early? If so, if I retarded the timing a few degrees should the knock go away or quiet down? I need to find out relatively quickly before we put too many hours on the engine (boss said to just run it for now) just in case it's something the rebuilder screwed up. As of yesterday it had about 12 hours on the rebuild.
Any ideas here? Thanks in advance! I still wish I'd been given the go-ahead to source a 4BT3.9 w/SAE #3 bellhousing. As much as I like the 6.2l I don't really think it's a good choice for a 30,000lb vehicle pushing airliners around. We have to get it rebuilt every 2 or 3 years, and I think the Cummins won't have that problem.