73 340 RR Back to life

[MoparJimT]

He did use all my parts except he supplied the flex plate which is the one I installed, it was a used factory unit. The TQ was new and empty as far a I know, it was supplied by the trans shop the rebuilt my trans. Thx

I appreciate you and Builderguy providing your thoughts I will keep digging.

Sorry TQ was supposed to be TC for torque converter

 

[HawkRod]

So thinking about this, there are three possibilities:

1. He didn't do the balancing right, although he had the right TC and HB on it.
   The most likely scenario in this case is somebody built the bobweights using the wrong numbers that don't reflect your actual piston/rod weights. Balancing a reciprocating assembly has a little bit of Voodoo in it, but it is an iterative process where you slowly work your way down to a balance on each side of the crank to less than 4-6 grams for a street engine. It sounds like you have quite an imbalance by the way you describe it.
   If this the balancing was done wrong then the engine must come out and be torn apart and rebalanced.
2. He did the balancing right, but with a different set of parts than what you have on it. Internal balance is possible, but not likely as I believe this motor would need Mallory metal to do that (the reason I know this is I tried to make mine an internal balance and it would have been too hard).
   Another possibility is he did the balance with the correct HB on the engine, but no or a neutral TC on the engine.
   If any parts were different when balancing, then you need to find the right combo used. Regular or external weighted HB and/or regular or weighted TC or flex plate.
3. The balancing was done correctly using the correct HB and TC, but something changed since it was done.
   The only scenario I can think of here is that your HB slipped because it is old and the rubber ring failed. I have heard of this happening but I have never seen it myself. I would think the HB would show some evidence of this.

I would move through this list in reverse, since addressing #1 is obviously quite invasive. It sounds like you are dealing with a quality shop, so hopefully working with them should yield a solution to your issue.

Not sure if any of this helps - I'm just brainstorming here...

Good luck!

 

[mpgmike]

It may also be power steering pump or something else. Try removing the accessory belts and see if you still have it.

 

[HawkRod]

It may also be power steering pump or something else. Try removing the accessory belts and see if you still have it.

Excellent - I forgot about that and fully agree. Easy to try too!

 

[MoparJimT]

Thanks hsorman, I appreciate the different scenarios. I am actually preparing for the worst case in having to take the engine back out but will definitely try the easier stuff first.

Thanks to mpgmike as well, Great idea and will do that first. I did remove the belts when I heard the rubbing noise but all pulleys spun freely and true. The noise was the inspection plate rubbing the flex plate so I put it all back together and ordered a new inspection plate.

 

[MoparJimT]

So I ran through the gears at idle to make the TQ was purged of any air, I removed the drive belts and ran the motor. Both produced no change.
Pulled the motor and took the crank, HB, flex plate and TQ back to the machine shop. They tried to re-balance using Bob weight from the original weight card. Heres what did not seem correct, when spinning the crank with everything mounted the TQ wobbled, thet tells me and we confirmed the flex plate was bent. We ordered a replacement. Also the readings on the front of the crank stayed steady at 11.6 grams the back fluctuated by 20 gram up and down when tested multiple times. Having researched a bunch of research, I found a note in a mopar balance article the said only balance the crank, HB and flex plate not to include th TQ, others say include the TQ with a stator lock (which they were using) and another that said cut a used 340TQ in half and remove the guts and balance with it.
So what is the correct process. Any thoughts?
Flex plate arrives tomorrow and they are going to see if the wobble goes away, then we will take it from there.

Thx

 

[HawkRod]

So I ran through the gears at idle to make the TQ was purged of any air, I removed the drive belts and ran the motor. Both produced no change.
Pulled the motor and took the crank, HB, flex plate and TQ back to the machine shop. They tried to re-balance using Bob weight from the original weight card. Heres what did not seem correct, when spinning the crank with everything mounted the TQ wobbled, thet tells me and we confirmed the flex plate was bent. We ordered a replacement. Also the readings on the front of the crank stayed steady at 11.6 grams the back fluctuated by 20 gram up and down when tested multiple times. Having researched a bunch of research, I found a note in a mopar balance article the said only balance the crank, HB and flex plate not to include th TQ, others say include the TQ with a stator lock (which they were using) and another that said cut a used 340TQ in half and remove the guts and balance with it.
So what is the correct process. Any thoughts?
Flex plate arrives tomorrow and they are going to see if the wobble goes away, then we will take it from there.

Thx

So I have the exact same situation with an externally balanced 340 and automatic. I did not want to balance the engine with a torque converter - too difficult. What I did was get the below flexplate, and I will use a neutrally balanced torque converter (simply knock the weight off the existing torque converter or buy a new one). I feel there are too many variables with trying to balance the engine with the torque converter. I would humbly suggest you do the same.

Since you dug back into the engine, I would recheck things. Are all the pistons and rods the same weight (within a gram or two)? Rods are a pain, you must have the total weight the same, but also the big end weight the same. Do you know the weight of your rings, pins, and bearings? Bottom line is be sure your bobweight is accurate. It is 100% of the rotating mass and 50% of the reciprocating mass. Leave nothing to chance at this point, IMHO.

By the way, my father-in-law (and me too now) balances street engines to 4 grams or less on each side. That's the target I would be asking for.

I just recently finished balancing my 340 stroker. Here is what I ended up with:

You can see I was about 3.2 grams off on one side and 1.3 on the other. Not worth chasing this further on a street engine.

I hope some of this helps - thanks for keeping us posted.

Hawk

 

[MoparJimT]

Thanks for the help and info.
I think I will follow your lead and have them order the b&m flex plate and a new converter. I keep thinking about why my original flex plate was cracked so I am nervous about reinstalling my old torque converter even though it was refurbished. I will not be able to return to AZ until Aug so everything is on hold until i get there. I did talk to them about the pistons rings and rods and it sounded like they did everything you described but I will double check. He said he brings them within 1/2 gram. He also let me watch how he set up the bobweight so they were all 100% the same weight.

Thank you again for sharing your expertise, I wish I could bring my stuff to your shop.

 

[ckessel]

Using that plate from B&M allows you to get more easily sourced converters too since it won't need to be weighted.

 

[MoparJimT]

Using that plate from B&M allows you to get more easily sourced converters too since it won't need to be weighted.

Yes I am finding that out as well, I ordered the flex plate and will figure out the TC next. Probably stay with the stock stall but would not mind some input.

I am running the following
Racetech pistons, I had them made to my CC chamber volume so I am at 10.1 compression.
Clay Smith cam, it is a cam I had ground a while ago and the specs they gave me based on the model number stamped on the end (H268OB)
268/276 duration
216 @ 50 degrees
110 Lobe Center
450 lift

Old School Edelbrock
LD340, machined for a spreadbore so no adaptor, plenum is notched

Thermoquard 6321, has the 1.5 primary bore and it was tuned to my cam.

Will be running TTi 1 5/8 long tube headers with accurate exhaust HP Hemi mufflers 2.5 in, 2.25 out.

Heads are early 340 2.02 J heads.

Thanks Again to all the Great Members on this Forum!!!!

 

[Nxcoupe]

You can't balance a crank with a torque converter attached. I've balanced engines. The torque converter is designed to be held in the rear by the pump bushing, and inside the stator and other parts spline onto their respective shafts. Without all this, the internal parts will succumb to centrifugal force and offset the weight and throw off the balance. Same with the converter housing, it can't run true with that little sheetmetal flexplate holding it, it too, will spin out of concentric. You have to use a weighted flexplate and balancer to balance an externally balanced Mopar. Just an fyi. We kept a special flexplate for balancing these engines and 440s too.

Next, you cannot remove the bolts from the flexplate/torque converter, and start the engine. The ring gear for the starter is on the converter, so the starter would spin the converter but not the engine.
Hope this helps.

 

[MoparJimT]

Thanks NXcoupe, you are 100% correct as I found out. I ended up taking the motor out and taking the rotating assembly back to the machine shop. What happened was as you described, the flex plate could not keep the TC steady. I decided to go with the b&m flex plate that hsorman recommended so we can complete the balance and replace the TC with a neutral one.

Thanks for you help I appreciate it!

 

[Nxcoupe]

Thanks NXcoupe, you are 100% correct as I found out. I ended up taking the motor out and taking the rotating assembly back to the machine shop. What happened was as you described, the flex plate could not keep the TC steady. I decided to go with the b&m flex plate that hsorman recommended so we can complete the balance and replace the TC with a neutral one.

Thanks for you help I appreciate it!

Welcome. Always glad to share what I know, and admit what I don't.

 

[HawkRod]

Welcome. Always glad to share what I know, and admit what I don't.

Agree! And together, with all of FBBO's collective knowledge, we make a pretty good team!

 

[MoparJimT]

Have not been able to post progress just not enough time.

I was able to resolve the engine vibration issue thanks to HawkRod, LLY, Builderguy and the rest for the FBBO members that helped me. Thanks guys!! Installed the B&M flex plate and knocked the weights off of the torque converter.
Engine is back in the car and running smooth. I then started putting the front clip on.

Started with the fenders

Worked my way forward

I think this is the most important part of the car. Meep Meep

Refurbished the grill and new halogen headlights.

Installed the rechromed bumper and reconditioned the bumper guards. Straightened and polished the headlight trim. They will need some more work when I get the car back to Colorado.

Back up on the lift to install the inner fender splash guards and touch up the under coating.

Hood on but really struggled to get the gaps right. I still never got it 100% but when I looked at the gaps before I took the car apart they are pretty close.

Started taping on the strips but quickly saw my door gaps were also off the rear of the doors were too low. Had to re-align them which took 3 hrs. That put me way behind so I only got 6 of the stripes on 5 to go. Putting the strips on was alot easier then I thought. They turned out really awesome for my first time. Just take your time tape them in place and measure side to side a million times and keep adjusting them. Started with the door so the front and rear quarters line up easier. Also used the installation kit that included the cleaner and gel so you can slide them for a correct fit before squeegee.

Heading back to AZ this weekend for 2 days, wont be able to go down after that for a while so I am hoping to get it done and ready to bring it home.
Wish me luck!!

 

[Basket case]

looks fantastic! Love that color. Wish my '73 had looked that good.

 

[Dan64]

That looks awesome!

 

[YY1]

That is a beautiful car!.

Can I ask about the grill...

is the center horizontal a molding?

 

[HawkRod]

I was able to resolve the engine vibration issue thanks to HawkRod, LLY, Builderguy and the rest for the FBBO members that helped me. Thanks guys!! Installed the B&M flex plate and knocked the weights off of the torque converter.
Engine is back in the car and running smooth.

So was the engine rebalanced with the new external flex plate or did the external flex plate alone solve the problem? (I assume the engine had to be rebalanced.)

Regardless, congrats on solving the issue and the car looks super!!!

 

[MoparJimT]

So was the engine rebalanced with the new external flex plate or did the external flex plate alone solve the problem? (I assume the engine had to be rebalanced.)

Regardless, congrats on solving the issue and the car looks super!!!

Had them re-balance with the new B&M flex plate.