Crank identification - 3.4 DOHC - Is it better?

[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

[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]

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.

[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]

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.

[1988GTU]

Could also be a wiped cam bearing.

[davida1_hiwaay_net]

Could also be a wiped cam bearing.

Could be. That makes sense too - this car was a field car that hadn't run in many years. The cam could have rusted on a journal.

Once again - stupid me hindsight 20-20 I should have town the engine down fully when I had it out the first time.

[davida1_hiwaay_net]

"WHAT" noy "WHY"

Well, I was a good guesser by the sound of the engine. The center 2 mains are wiped. They show massive amounts of adhesive wear and heat damage. The front and rear mains; as well as the rod bearings are not wiped but have contamination damage form the other failure.


Did not spin in the block. That's a good thing.


Rod bearing is not destroyed. Only shows some contamination damage.


Will be replacing that crank.


Will definately be further investigating. There is a root cause somewhere. Later I will roll out the upper main inserts and inspect the oil holes. I have to take my time on the full teardown of this engine because it is a project build I had running perfectly. I want to put it back in the same condition as easily as possible. So don't know if I will have it stripped down tonight. Haven't yet seen the cam bearings....

Sincerely,
David

[davida1_hiwaay_net]

OK got the engine torn down today. Had issues with air compressor and had to fix it to proceed with the engine. It shredded a belt on the coldest day of the year so far!

I think I have found a contributing factor for the bearing failure. The machining and alignment of the oil ports to the bearing inserts oil holes is truly awful.

Once the cam bearings are out I will be interested to see how well the intersecting passageways up there are aligned.

Combustion chambers look good. No carbon.


Intake valves are clean:


The bearing oil hole alinment is far from acceptable.

They are most all a little out of alignment. Two of them are severely misaligned.












This is very sad and GM should take more pride in their assembly procedures. I'll be interested to see what the cam bearing bores look like. Since they have the intersecting oil ports for the mains, that area could also be part of the cause of this failure.

Does anyone have good experience with King Engine Bearings? I am considering their main bearings with the extended oil groove (there's about 1/4" of oil groove on the lower main insert).

I've read up on it here, and it looks like the engine needs to have about 70 PSI oil pressure at full revvs. When I added the turbo I was trying to prevent exactly what happened, so I changed the rod bearings and the oil pump. The new Melling oil pump produced exactly 50 PSI (just like it should for a stock engine). Is there a formula for making a spacer for the spring? I will search here but would also appreciate any firsthand experience! I don't want to make it too strong and blow the filter or twist the pump drive shaft in half.

So far I'm planning:
-Correct main bearing bore oil port alignment and width.
-Check / correct oil passage alignment at cam bearings
-Oil pump spring pressure
-Check main bore alignment (take to machine shop)
-Better main bearings
-Grind flash from casting to improve drainback to sump.
-3.1 crank and pistons / basic rebuild

Sincerely,
David

[davida1_hiwaay_net]

Well, now I found the cam is not in good shape. Considering using a 3100 / 3400 block / crank / cam-lifters instead of this one.

I'm aware of the compression ratio and need for correct pistons, using iron heads on a newer engine. Are there any other big "issues" with this swap?

Will the distributor gear from the 3x00 "dummy shaft" work on the distributor shaft from the 2.8? I expect the gear material is different between the iron flat-tappet cam and the roller cam.

Is there a difference in the balance weight of the harmonic balancer?

Anything else to watch out for?

I'm going to junkyard to investigate a few core engines today, probably.

Sincerely,
David

Ps - sorry to ask a lot of newbie questions. I don't have a huge experience base with these engines.

[1988GTU]

The distributor cap assemblies interchange. Are you going 3X00 now? I recommend 2000+ 3100/3400 if you do.

[davida1_hiwaay_net]

The distributor cap assemblies interchange. Are you going 3X00 now? I recommend 2000+ 3100/3400 if you do.

I'm considering it. The 2.8 is really a basket case. I found the beginnins of a spalling cam lobe and lifter.

The car must retain the iron heads and original manifold setup, with distributor igintion, but I would like the roller cam and better oiling of the 3x00. If I do this, will try to get a 3400.

[1988GTU]

I'm considering it. The 2.8 is really a basket case. I found the beginnins of a spalling cam lobe and lifter.

The car must retain the iron heads and original manifold setup, with distributor igintion, but I would like the roller cam and better oiling of the 3x00. If I do this, will try to get a 3400.

To do iron heads on the roller engine you would need to tap the heads for the roller rockers and make space for the rocker arm bodies to fit under the cover and lim. Ignition is least of your investment and concerns.

[davida1_hiwaay_net]

To do iron heads on the roller engine you would need to tap the heads for the roller rockers and make space for the rocker arm bodies to fit under the cover and lim. Ignition is least of your investment and concerns.

Well, I was planning to use the heads as-is with their existing rockers. Just using the roller cam/lifters. I'm most concerned with durability of the bottom end, thius wanting the newer oiling system. This isn't a high RPM build but it will see some heavy loads on the mains because of the boost. I don't think the non-roller rockers will be a problem at this RPM level.

The Buick engines used roller cam with non-roller rockers from 86 to 90 (IIRC) and those engines last forever.

I hope to look at a few core engines today to get a better idea of what is going to or not going to work.

Thanks,
David

[1988GTU]

You would need custom pushrods and modify the guide plates at the very least. You would need to use all the mpfi top end (heads up) on the sfi lower end (block)