Balance issue? Help!

[khryslerkid]

What valve train are you useing? Cam, lifters, rockers.

 

[coronet70]

What valve train are you useing? Cam, lifters, rockers.

I'll have to look into that. I don't remember. Everything's pretty stock, with a mild cam.

 

[moper]

It's my guess here, but if a cast crank had welding visible - it was more than likely internally balanced using the old weighted balancer and no torque convertor. If it was me I would pull the crank and give it to a shop to see what the imbalance is. You may have the parts to fix it, but in the wrong combination, or you might not have the right parts. You won't know until the crank tells you. So you can guess, or you can uncover the reality and address it. One thing is for sure - if the imbalance is making it shake starting at 2K, running it is a sure way to break it.

 

[bm02tj]

It may have been balanced to zero on flywheel end and not damper
You may have a lobe going on cam so low power at RPM

 

[coloradodave]

Coronet70: From your #5 post:
"The engine was rebuilt not long ago, but I don't believe anything was balanced....can't believe that nobody advised me to do that. Not the machine shop that turned the crank, or the shop that bore the cylinders. I did have a vibration before the engine was rebuilt."

Did you tell the machine shop that prepped the crank that the motor vibrated? Regardless, a quality shop will always recommend balancing all the rotating components. They did you a disservice by not advising you. They're supposed to be the professionals...

 

[coronet70]

It's my guess here, but if a cast crank had welding visible - it was more than likely internally balanced using the old weighted balancer and no torque convertor. If it was me I would pull the crank and give it to a shop to see what the imbalance is. You may have the parts to fix it, but in the wrong combination, or you might not have the right parts. You won't know until the crank tells you. So you can guess, or you can uncover the reality and address it. One thing is for sure - if the imbalance is making it shake starting at 2K, running it is a sure way to break it.

Yep, tired of guessing. The only thing that I can think of is to pull the oil pan and grind the weld that's on the crank. Would that be a good idea, or bad idea?

 

[khryslerkid]

I would take all of your components to a shop and have them balanced.

A guestion to the forum; Would a cast crank useing Sixpack rods, take a differently weighted TQ ?

 

[Mike67]

I would not grind on your crank!!!! Take it to a machine shop, with your components, flex plate, dampner to be balanced. Explain what's happening they may have some other suggestions.
You may, depending on your cylinders, be able to get away with a light hone, re-ring and new bearings depending on how many miles/maintenance upkeep ect. You can buy an electronic scale and blue print your pistons and rods to get them within a couple of grams of each other if you're comfortable doing it (assembling) yourself. If you do decide to do it yourself make sure each component references which cylinder and direction it came from. I always have a stamp kit to mark the caps & ends.
Your other option is buying a rebuilt shortblock.
Good luck.

 

[coloradodave]

Really bad idea... As Mike said, you need to have a competent machine shop check the balance of all your rotating components to either find the problem or eliminate balance as the problem. Anything else and you're just 'spitting in the wind'. I assume you did all of the ignition checks that could also be responsible?

 

[coronet70]

I figured it was a bad idea, just wanted to back that up! Getting it balanced isn't too expensive. It's just all the work that I've already done needs to be done again. Tends to break your spirit! Time to stop guessing and get it done.

 

[moper]

You cannot fix any imbalance on your own. And an additional issue is balancing cannot be done with the pistons on the rods. So it may be an exercise in redoing a lot... I wish you luck. This is one of the reasons I internally balance everything so they run nuetral balancers and convertors.

In regard to 6bbl rods and a cast crank - I do not believe that could be done without use of Mallory. That's more than likly why the engines that got those rods got a forged crank (heaviest counterweights) plus the bigger balancer. Those rods are really, really heavy.

 

[furyus]

Only thing I can think to add is if possible, i would have the converter sent to have the balance checked. I had a bad converter from ATI. They made me jump through hoops before they would take it back. Worked great with the replacement. And all my symptoms were the same as yours. If that isn't it, then I would pull the engine.

 

[PurpleBeeper]

The idea to check the motor mounts with brake torqueing is a good one. Also, you said you have a "weighted balancer".... but which one? The cast crank motor balancers are MUCH thicker than the big-rod (six pack) balancers. The big-rod balancers look like the neutral balancers in thickness.

From what I know, big-rod motors were built up until '73 and all had forged cranks. For sure you'd have to balance an engine if it had big rods on a cast crank.