Need input on broken crank and balancer!

[Daniel Jost]

So several months ago i had an engine failure with my car, i was in Cordova, IL at the drag strip and lost the engine at aprox. 32-3400RPM. The failure consisted of breaking the crank between cylinders 1 and 2 right in the center of the rod journal.. Also when i dis-assembled the engine i found that the crank balancer had cracked along the key way right in the grove on a 90* corner on the stress riser point from one end of the key way to the other.

Now here is my question i have, why did this happen? this is the second balancer i had fail the last one cracked idling from a stop light and moved so much it cut the crank sensor off killing the engine. I replaced it and had the same thing happen again 15,000 miles later!! this time it was at full load and aprox. 24PSI!!

Specs: 24PSI, 21* timing advance on Cam2 110 Oct Race Fuel, no knock
Arp studs, stock balancer (85' 3.8turbo), stock bottom end, H&R Parts N' Stuff Polly motor mounts

I would like to get this resolved why this happened, is it a stock balancer issue that i dont know about, was there something wrong with the crank? Anything else? i would like to know there is no need to fail another engine becuase i dont have my stuff in order!!

Thanks in advance, Dan

 

[charlief1]

Was the rotating assembly balanced or did you just put the parts on?

 

[bison]

The only time the balancer cracks is when it runs while loose. So chances are this is the second loose balancer you have had on your engine. Ive seen many loose ones over the years. At least half had cracks from being run that way for a while. The crank is usually worn on the end where the balancer sits and would need to be plated and re-ground to fix it or replaced since the replacement balancer would wobble if just bolted on. Most half inch drive impacts arent enough to torque the bolt enough unless the pressure is really high. The crank failure may not be from the same problem but it could be if the balancer was wobbling. Not normal to break a crank that close to the front of the engine and especially at your power level.

 

[dr_frankenstein]

The only time the balancer cracks is when it runs while loose. So chances are this is the second loose balancer you have had on your engine. Ive seen many loose ones over the years. At least half had cracks from being run that way for a while. The crank is usually worn on the end where the balancer sits and would need to be plated and re-ground to fix it or replaced since the replacement balancer would wobble if just bolted on. Most half inch drive impacts arent enough to torque the bolt enough unless the pressure is really high. The crank failure may not be from the same problem but it could be if the balancer was wobbling. Not normal to break a crank that close to the front of the engine and especially at your power level.

What is the tolerance of the balancer before it becomes too loose? and is it possible that using the standard installation tool causes this? would warming it up and pressing it on be a better alternative? too many questions! LOL I have had this problem as well in the past.

A.j.

 

[Steve V]

Balancer should just slide right one. No heat needed ever,unless you are try to melt the factory loctite.

 

[Daniel Jost]

no i did not have the assembly balanced, also the bolt did come loose the first time causing that, the crank "looked" fine there wasnt really any damage. when i put the used one on i got it was TQ to spec, does it need to be tighter yet? maybe my issue was not using loc-tite

 

[dr_frankenstein]

Balancer should just slide right one. No heat needed ever,unless you are try to melt the factory loctite.

Hmm....... mine was tight...... like a regular press on....... I think you found my problem.

A.j.

 

[Alky V6]

Crank hubs, dampers should not just have a slip fit. They must have an interference fit. A damper without an interference fit will not work properly and will cause damage. A proper press fit for a damper with the diameter of the Buick crank snout would have an interference of .0008" to .0011".

 

[dr_frankenstein]

Crank hubs, dampers should not just have a slip fit. They must have an interference fit. A damper without an interference fit will not work properly and will cause damage. A proper press fit for a damper with the diameter of the Buick crank snout would have an interference of .0008" to .0011".

Thank you Don, thats what I suspected was the case..... So whats your recommended installation procedure?

A.j.

 

[Just a Six??]

no i did not have the assembly balanced, also the bolt did come loose the first time causing that, the crank "looked" fine there wasnt really any damage. when i put the used one on i got it was TQ to spec, does it need to be tighter yet? maybe my issue was not using loc-tite

Always balance them & use the Locktite! I also find mine will push on with a little coaxing but on removal I always need a puller to get them off. Thats on 5 stock cranks & always the same way.

 

[Alky V6]

Thank you Don, thats what I suspected was the case..... So whats your recommended installation procedure?

A.j.

First check to make sure you have the proper interference. I then put a very thin coating of antiseize in the ID of the damper. Use a damper installing tool to press the damper into position. Tighten the crank bolt to spec. I use a dab of red loctite and 200 ft/lbs torque. I hold the crank during the torque procedure with a flywheel turning tool or two.

 

[ijames]

Don, the stock hub on the stock crank is not an interference fit and slides on and off without an installation/removal tool. The BHJ aftermarket dampener does go on with an interference fit like a Chevy and you have to use a tool to put it on and get it off. If someone has a copy of the factory service manual I'm sure it covers this, but I can't get to my copy right now.

 

[Lee Thompson]

?????

Crank hubs, dampers should not just have a slip fit. They must have an interference fit. A damper without an interference fit will not work properly and will cause damage. A proper press fit for a damper with the diameter of the Buick crank snout would have an interference of .0008" to .0011".

I have disassembled more than 1- 109 eng. with the stock hub. I have NEVER had to use a puller. They ARE a slip fit and run forever that way. Now I know BHJ are an interference fit but the guy with the original ? did not mention that he had anything other than a stock hub.

 

[bison]

Crank hubs, dampers should not just have a slip fit. They must have an interference fit. A damper without an interference fit will not work properly and will cause damage. A proper press fit for a damper with the diameter of the Buick crank snout would have an interference of .0008" to .0011".

The stock balancer (not to be confused with a damper) is not a press fit. Its a slip fit. .001 interference is typical for a damper. Any more will gall the crank and damper.

 

[bison]

Hmm....... mine was tight...... like a regular press on....... I think you found my problem.

A.j.

If you have a CAT crank the keyway may not be cut deep enough in the crank. This would be a problem if you tried to run a stock style balancer on it since the pressure from the interference could crack the balancer. Most aftermarket cranks are larger OD where the balancer/damper goes on.

 

[Daniel Jost]

it was a stock used balancer.. what do you mean balance it, how am i doing this? am i balancing the whole assembly?

 

[bison]

no i did not have the assembly balanced, also the bolt did come loose the first time causing that, the crank "looked" fine there wasnt really any damage. when i put the used one on i got it was TQ to spec, does it need to be tighter yet? maybe my issue was not using loc-tite

Explain how you torqued it to spec please.

 

[bison]

First check to make sure you have the proper interference. I then put a very thin coating of antiseize in the ID of the damper. Use a damper installing tool to press the damper into position. Tighten the crank bolt to spec. I use a dab of red loctite and 200 ft/lbs torque. I hold the crank during the torque procedure with a flywheel turning tool or two.

200 is not enough on the stock balancer. If i recall properly its 280 with 30 weight on the threads. 200 may come loose on a stock style balnacer and crack and fail

 

[bison]

What is the tolerance of the balancer before it becomes too loose? and is it possible that using the standard installation tool causes this? would warming it up and pressing it on be a better alternative? too many questions! LOL I have had this problem as well in the past.

A.j.

The installation tool i use is my hand. There are no other tools need to slide it on if its the stock crank and balancer. There is no need to heat it up. If you had a fluidamper you could ruin it by heating it

 

[bison]

it was a stock used balancer.. what do you mean balance it, how am i doing this? am i balancing the whole assembly?

Yeah the whole assembly would be balnaced with the balancer on it since its counterweighted. This is not likely why you had a failure though. Ive swapped out cracked or wobbling balancers on at least 5 engines without re-balancing and never heard of any odd behavior or failures.