Crank identification - 3.4 DOHC - Is it better?

[1988GTU]

Could also be a wiped cam bearing.

[davida1_hiwaay_net]

The gen III system is a priority main system. There is a galley between the crank and cam that feeds the cam above and crank below.

I doubt your failure is from lack of lubrication. The gen I and II were still good even though the gen III is better. The left hand lifter bank was larger and offset to allow full oil flow regardless of lifter position. The cam bearing bores had grooves around the back side of the bearing insert that allowed oil flow around the back of the bearing and down to the crank. Provided nothing was blocking flow to a component the system works great. It is virtually identical to a Chevy 4.3L V6. If the old Buick V6's (pre 3800) can survive turbo power then the 660 is going to be just fine. You may have also had a main bearing alignment issue or a cap that walked. Any detonation or severe pinging?

Thanks for the info! I do beleive there is a root cause, not that the engine is "weak design." I've boosted 2 of these (one iron and one aluminum head) as well as 3 Buick 3.8's; one of which has over 450 HP. The only other failure I've had was a block plugged in the oil gallery with chips of a failed plastic timing gear. The PO changed the broken gear but did not clean the crap out of the engine. That was a Buick 3.0.

On this car, I had the laptop connected to it, doing tuning runs. The most detonation I've seen was 5 degrees retard during early runs before the tune was dialed in. It had about 7 PSI boost at that time. There was no detonation at WOT during the runs immediately before the faillure. I had been pushing the boost up (project goal is 13 PSI) and making WOT pulls on the interstate. I went over the datalog and there was no detonation, 10.9 to 11.5 AFR, and the boost was right on target. The car went from 35 to 90 MPH in 11 seconds, though. So something was working right...

The only symptom was a SLIGHT power loss and burning oil smell during one pull. I stopped and checked and everything looked in order. Then after that, I attempted one more pull, but got the burning oil smell again before it was even at 3500 RPM, so I throttled it back. As I exited the highway to investigate the second time, the oil pressure was lower than normal and I could hear what sounded like an exhaust leak, but it was bottom end noise.

After that it was a very slow gentle 30 minute drive home during which the oil pressure kept deteriorating and stabilized at 25 PSI at 1500 RPM.

I never shut the engine down after the failure, and once I got home and parked it, the engine has not been started since.

I've got most of the things disconnected and hope to get the engine out today.

[geoffinbc]

The gen III system is a priority main system. There is a galley between the crank and cam that feeds the cam above and crank below.

I doubt your failure is from lack of lubrication. The gen I and II were still good even though the gen III is better. The left hand lifter bank was larger and offset to allow full oil flow regardless of lifter position. The cam bearing bores had grooves around the back side of the bearing insert that allowed oil flow around the back of the bearing and down to the crank. Provided nothing was blocking flow to a component the system works great. It is virtually identical to a Chevy 4.3L V6. If the old Buick V6's (pre 3800) can survive turbo power then the 660 is going to be just fine. You may have also had a main bearing alignment issue or a cap that walked. Any detonation or severe pinging?

[davida1_hiwaay_net]

It's the same.

3.1, 3.4DOHC, 3100, 3400 and 3.4 iron head all use the 981 crank.


I'd start with a Gen 3 block if you are having oiling issues.

Thanks for the inight. I will probably look for a Gen III block if this one is damaged. What is the difference in the oiling system? I've always ported out the oil passages in the block and bearing inserts on my builds. Never had one which I built this way to fail. Don't know if this treatment would bring the original block up to Gen III lubrication level.

I'm going to search and see if there are any articles on the Gen III lube system.

My reason for asking is, it will take me days to get another block (due to driving distance to the nearest junkyard where I can get one without paying $800 for an entire engine). If this one can be modified it would save me time, plus this is a friend's car and he wants original engine if possible.

[Superdave]

It's the same.

3.1, 3.4DOHC, 3100, 3400 and 3.4 iron head all use the 981 crank.


I'd start with a Gen 3 block if you are having oiling issues.

[davida1_hiwaay_net]

Hi, some of you guys have probably seen the other thread I am posting in. To make a long story shorter, I have built a turbo 2.8 engine, and there was some failure of the main bearings and/ or crank. I don't have the engine out yet so can't say exactly what happened. It was running awesome, but just started knocking and losing oil pressure so I babied it home and will pull the engine soon.

I've read that the 3.4 DOHC engines have a better crank than the standard 3.1 engine. I can get this crank from Advance Auto (Part Number 10570). Is there a way to know if this was really a DOHC crank and not a standard LH0 crank? They list some casting numbers in the description: Casting 981; 924; X153

I plan to make it a 3.1 during the rebuild but want to get the strongest crank I can. Also going to get rid of the super-heavy stock pistons and go with something better since they have to change anyway for the stroke difference.

Thanks in advance for any insight. I built a boosted 3.1 with a standard LH0 crank and it has held up well. But if the 3.4 crank is stronger, I want to get this one.

Sincerely,
David