Balancing of stroker kits and vibrations

-
zhandfull

zhandfull

Well-Known Member
Joined
Mar 8, 2006
Messages
2,987
Reaction score
102
Location
Rancho Cucamonga
The 360/408 in my Dart has always had a minor but irritating vibration or harmonic that has just bugged the **** out of me. I didn't build the engine so I'm not sure if it was internally balanced or not when assembled. Anyways I pulled it out a year ago and installed a Mopar magnum 360/390HP crate engine with the correct flex plate and the issue seems to be gone.

The stroker kit is an Eagle Street and Strip Rotating Assemblies 20502030. Anybody know what the bob weight is suppose to be on these cranks as delivered? I pulled the piston, rod, rings, and bearing and weighed them as an assembly. They weigh in at 1294 grams on my fairly nice digital postal scale carbon and all.

Crank has some drilled holes in the counter balance so maybe it was balanced. But other strokers I have put together with forged cranks needed mallory metal. This crank is cast and doesn't have any of that.

Anyways I'm going to have it check, just thinking out loud here mostly. Any thoughts from the techs.
 
So far as I know you'd have to go right to the builder. Balance is pistons, rods, and crank. All you have to do to destroy balance, if it was ever right is to change one of em. Then add the balancer and flex plate to the mix..............................

Either that or simply HAVE it "re" balanced.
 
Little research and I see that my weighing of the piston and rod assemblies doesn't mean anything regarding bob weight.

I did notice the front of the crank where the balance mounts is galled up a bit. Wonder if that could be a cause or a result of my issue. I'm pretty sure everything was new when assembled. Probably less than 10'000 miles on it.
 
If it was a eagle balance job it may be a "bit" off...

Each item needs to be weighed and the rod weight needs to be split between reciprocating and rotating.

Most of the time those bobs end up in the 1700-1800 range IIRC.
 
If the crank is showing any signs of movement in the dampener then it had harmoins present, and enough that the dampener couldn't do it's job. I'd call the marks a symptom - not the problem. I would never trust a supplier's claim of "balanced". There are too many different opinions of what "in balance" really is.
 
Not much help because of the variatrions. Scat kit w icon forged and I beams My bob weight is 1748 and crank has 2 pucks added to it.
 
crackedback said:
If it was a eagle balance job it may be a "bit" off...

Each item needs to be weighed and the rod weight needs to be split between reciprocating and rotating.

Most of the time those bobs end up in the 1700-1800 range IIRC.
Click to expand...

I'm not sure who or even if the assembly was balanced. Says right on the Jegs website for this kit. That it is not balanced. Supposedly a reputably builder in the Lancaster area built it. Hard for me to imagine anybody building a performance motor without addressing that. Although out of all the receipts that came with the car I don't remember any for balancing.

moper said:
If the crank is showing any signs of movement in the dampener then it had harmoins present, and enough that the dampener couldn't do it's job. I'd call the marks a symptom - not the problem. I would never trust a supplier's claim of "balanced". There are too many different opinions of what "in balance" really is.
Click to expand...

I'm kind of thinking the same thing. Everything was new when assembled I have most of the receipts. I think the vibrations I was feeling caused the damage to the crank where the balancer mounts. The balancer was still tight and I used a puller to remove. But some pretty bad looking metal on the crank in the front 50% of balancer mounting area.

Guess the question now is the crank savable or usable? Here is a picture, the bottom groove is suppose to be there but you can see the galling above towards the top.

I should of probably stopped running the engine earlier. I keep thinking it was everything but the engine. It wasn't a terrible vibration just the type that it would drive the driver nuts feeling it through the steering wheel on long drives. I even changed out the solid motor mounts to rubber.
 

Attachments

  • 1972 Dart 093.jpg
    38.5 KB · Views: 333
What does the inside of the balancer look like?
That crank looks like the balancer was beat on and tightened with a hammer insted of honed to fit.
Balance job? Dont take anything to that machine shop.
 
sireland67 said:
What does the inside of the balancer look like?
That crank looks like the balancer was beat on and tightened with a hammer insted of honed to fit.
Balance job? Dont take anything to that machine shop.
Click to expand...

No signs of hammer abuse. I no expert but tend to agree with moper above in that the balancer was unable to handle the excess harmonics. Must likely do to a lack of a quality balance job and or possibly no balance at all.

This is the result of ignoring the symptoms. But of course I am open to other opinions as well and will ultimately be fixing the engine. I would say the crank came out the worst of coarse but the inside of the balance has some of the same damage that may be able to be honed out.
 

Attachments

  • 1972 Dart.jpg
    71.4 KB · Views: 320
I'm missing the later years of 360's, but the crank doesn't look right?

Last time I had a vvibration, it was a 340 with a 360 converter......
I went to Firestone for balancing, twice, the car never left town for the
next 20 years, got a buddy to put in the 4 speed and he found it. maybe
I'll go back to Firestone now,
 
crackedback said:
If it was a eagle balance job it may be a "bit" off...

Each item needs to be weighed and the rod weight needs to be split between reciprocating and rotating.

Most of the time those bobs end up in the 1700-1800 range IIRC.
Click to expand...

Agreed... No one has a out of the box,balance build. Trust no one.
 
I checked the converter, flex plate, and balancer way before pulling the engine. They all seem to be a neutral balance. The crank bought new has a 2050 gram bob weight. After digging into this a bit deeper my crank seems to be balanced with holes drilled and material removed from the counter weights. Seems to indicate to me some sort of balancing job took place. Assuming a bob weight of 1700-1800 as mentioned above. It would make sense to remove weight rather than add to the counter balances on the crank. Maybe it just wasn't done right.

I'm going to call my crank guy in the morning and see if it's fixable. If it is then it will be getting rebalanced.

Cranks are a little pricey around $400 for cast and $1,000 for forged. Add another couple hundred for each if you go through M.P.
 

Attachments

  • 1972 Dart 094.jpg
    53.7 KB · Views: 294
  • 1972 Dart 095.jpg
    56.9 KB · Views: 307
Don't discount that it could be a converter / front pump/ bushing issue. I would guess that transmission misalignment at the bell could be a factor
 
I would not run that crank. You can see the damage, and the harmonic dampener recieves the vibes through the press fit on the crank. If that get's loose or the surface area is decresed, so is the effectiveness. Not to mention there may be damage to the internal structure of the crank where it was ok for what you were doing, but may be an issue down the road. Harminocs are bad. They stress the block, crank, all the parts, the flexplate & convertor - loosen faseneters, etc. And the worst part is you don't have to feel them for them to be present. So for the reasons I mention I'd get rid of it. Skip the Eagle cast cranks BTW.
 
I built my own 408, forge eagle crank, scat I beam rods, srp pistons, balanced by a reputable speed/machine shop. Weighing pistons are easy. After that you need a little more expensive tooling. They balance rods one end at a time. Bob weight is determined by the weight of pistons and rods on each journal. Factory 360 bob weight is about 2150 and is why it's externally balanced. Cast cranks are to light and must have Mallory metal added unless the bob weight can be lightened. Stroker pistons make it easier for internal balance because bob weight is much lighter. After market rods are usually lighter too. Your problem is probably in improper balanced crank or bad harmonic balancer. The crank can probably be repaired. No expert but I did a lot of home work when I built my motor. I didn't have the money to build it the first, sure didn't want to build it twice. Engine bearings always tell the story. Hope this helps, Russ
 
I agree with Moper, I got my crank from Indy for $620. Sometimes you just have to pay to play.
 
moper said:
I would not run that crank. You can see the damage, and the harmonic dampener recieves the vibes through the press fit on the crank. If that get's loose or the surface area is decresed, so is the effectiveness. Not to mention there may be damage to the internal structure of the crank where it was ok for what you were doing, but may be an issue down the road. Harminocs are bad. They stress the block, crank, all the parts, the flexplate & convertor - loosen faseneters, etc. And the worst part is you don't have to feel them for them to be present. So for the reasons I mention I'd get rid of it. Skip the Eagle cast cranks BTW.
Click to expand...

I was running this through my head last night as well. Was ready to start fresh and then it occurred to me that I have two other stroker 340's with forged cranks that I could spend less money on and finish. So this morning I continued to remove clean and tag parts. Hit the pistons with the soda blaster to knock off the carbon. Hit the crank snout and the balancer with some emery cloth.

I reassessed the mounting area and figured less than 15% of the mounting surface is actually not to my liking. I'm going to set the crank in the block with the balance mounted. If the run out of the balancer doesn't look bad. I'm going to roll the dice and put this thing back together for the cost of balancing and a gasket kit. Honestly in my head I think the odds are pretty good in my favor of it running and lasting a long life. Moper I'm definitely not disagreeing with your advice and total respect it and appreciate it as well. Sometimes I just think a lot of us get to caught up in everything has to be perfect attitude and we end up not getting anything done. It's a bit of a gamble but it's the also the difference of probably $400 to put it back together and probably at least $2,500 to 3,000 to start with a new rotating assembly. I'll take the chance of throwing away $400 and if it grenades it least there won't be any compromised parts on the used market. :D
 

Attachments

  • 1972 Dart 097.jpg
    58.5 KB · Views: 235
  • 1972 Dart 098.jpg
    63.9 KB · Views: 244
Ultimately it's your money so I've got no skin in the game...lol.
On the locks - use a very sharp pick - I like dental picks. They come right out.
 
You must log in or register to reply here.
-

Back
Top