Harmonic Balancer Slipped......

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threewood

threewood

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I thought my car was haunted. My timing would change randomly. Finally came to a head last night. Previous night I installed a collar on my distributor shaft to keep the gear from coming up. Timed it to 20* initial / 35* total, vacuum unhooked. Adjusted the carb and all was well. Yesterday I wanted to up the idle a bit, and double check the timing. WTF!!!!

Timing mark nowhere to be found. Idle was smooth and the drill holes in the balancer were steady as a rock, reved it up and ran the advanced light up past 50*, no tdc mark. Switched timing lights and same thing.

Found TDC this morning.... F$%#! Two red dots are cw and ccw marks from the piston stop. Red slash is TDC.

So, my question is...what harmonic balancer do you recommend for a street driven 1962 318 Poly that rarely sees over 5500rpm? I looked around and don't think I need a $400 job. What is a good one for forged crank, pass side timing tab? Looks to be 7" diameter with a rough measure.

Thanks!
 

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Almost 100% positive a stock 340 balancer will interchange. Maybe rumblefish will know for sure.
 
RustyRatRod said:
Almost 100% positive a stock 340 balancer will interchange. Maybe rumblefish will know for sure.
Click to expand...

Why not a 318? Would have to be the "older" pre whatever year 70? They changed tiing cover and water pump.

WhatEVER you put back on, make sure you re-check it with a piston stop.
 
67Dart273 said:
Why not a 318? Would have to be the "older" pre whatever year 70? They changed tiing cover and water pump.

WhatEVER you put back on, make sure you re-check it with a piston stop.
Click to expand...

Either or. The steel crank 340 would be the same. I just grabbed a number.

They are the same, btw. They are listed on the Summit site.
 
Great info, thanks! The issue with driver or pass side timing tabs is really a non issue as I can add my own TDC mark after using my piston stop. I think as long as I get one for an internally balanced 318 I should be good. Thinking of getting this one from Jegs...

JEGS Part Number: 555-51670

Harmonic Balancer
Chrysler 318 1967-91 (Forged or Cast Crank)
Chrysler 340 1968-71 (Forged Crank)
7-1/8"
Internal Balance

and I will probably send my old one to DamperDoctor as a backup. I didn't even know they could be rebuilt!
 
The question about which damper to use is not just fit and TDC mark location, but it also involves the specific engine crankshaft material and dimensions, and other rotating weights to a lesser degree. These will effect the crankshaft torsional vibrations that get set up, and in turn will effect the way the damper is designed; the rubber ring thickness as well as the dimensions of the outer ring are changed for different engines.

So unless you can compare them side by side and see for sure that the rubber and outer ring dimensions are identical, just fitting is not the same as being a correct interchange. A damper can fit and line up right but not have the right damping frequency for a given crankshaft. I felt good in putting a damper listed as a 318 cast crank damper on a later 273 cast crank since they are the same crank. But I would want to compare that to a real forged crank 340 damper before putting it on a forged 340 crank....

EDIT to add...I see the Summit listing that was posted.....so it is likely OK but I don't 100% trust distributor listings! Maybe buy it and compare them before shipping off the old one. Let us know what you find.

So, rebuilding a stock one is often the better option for an oddball damper, because you have the right metal parts to start with. It will work the same as new assuming that the rubber used is similar.
 
They are both neutral balance engines. So what's the difference? If the balancers interchange, it will work fine.
 
There is more to it than that. If the outer ring weights are different, then they will damp at different frequencies. A damper's 'natural' damping frequency is designed to match up to the main torsional vibration frequency of the crank. The ring weight and rubber are changed to get to that desired damper frequency. That is why there are so many differernt damper designs.

If you look at that particular part, there are large grooves cast into the front and back of the outer ring. Those are put there on purpose in this particular part to the get the ring weight lowered to specific weight within the constraints of the ring dimensions, so that the whole assembly ends up with a specific damping frequency.

The good part in this case is that there is the same weight-reducing groove cast into the front of the OP's outer damper ring, and so it may well be the same part. If someone could look up the actual Mopar PN's.....
 
nm9stheham said:
There is more to it than that. If the outer ring weights are different, then they will damp at different frequencies. A damper's 'natural' damping frequency is designed to match up to the main torsional vibration frequency of the crank. The ring weight and rubber are changed to get to that desired damper frequency. That is why there are so many differernt damper designs.

If you look at that particular part, there are large grooves cast into the front and back of the outer ring. Those are put there on purpose in this particular part to the get the ring weight lowered to specific weight within the constraints of the ring dimensions, so that the whole assembly ends up with a specific damping frequency.

The good part in this case is that there is the same weight-reducing groove cast into the front of the OP's outer damper ring, and so it may well be the same part. If someone could look up the actual Mopar PN's.....
Click to expand...

So, until I have the new balancer in hand to compare with the old one I won't know if it will work correctly? I've never replaced a balancer before so this is new territory for me.

Edit: Just sent Gary P an email asking what he recommends. He built the motor:)
 
Any 318 will work but if you can pick,choose 69 and earlier applications. If it's an option
 
Response from Gary...
Mark,
Merry Christmas!

The 555-51670 item you purchased from JEGS is correct and will work with your Poly. Yes, all LA stock or SFI balancers interchange with the Poly. -snip- all internally balanced/zero balance LA dampners interchange with your Poly. No need to send yours out for revulcanzining unless you want to.

Keep me posted.
Gary
 
some getting over technical here. 1947235=64-65 273. 2658458=66-69 273, 318, 340. any internal balanced unit will run fine, and as U know 1969 and earlier timing on pass. side, 1970 and later on driver side. also 1971 and earlier had 1 pulley bolt offset, 1972 and later and most aftermarket 6 bolts evenly spaced
 
fluid damper...get the one that has the inset bolt circle so there is no pulley alignment issue. Should cover most harmonics.....CAT made(?) an inexpensive one, even an SFI.
 
threewood said:
Response from Gary...
Mark,
Merry Christmas!

The 555-51670 item you purchased from JEGS is correct and will work with your Poly. Yes, all LA stock or SFI balancers interchange with the Poly. -snip- all internally balanced/zero balance LA dampners interchange with your Poly. No need to send yours out for revulcanzining unless you want to.

Keep me posted.
Gary
Click to expand...

Just like I said.

My God. I am gonna poke my eyes out with a dull stick.
 
Make sure that the new balancer has the same depth as the old one so the pulleys line up...
 
UPDATE: Received the new balancer before Christmas. Perfect match for the one I'm replacing. Height and diameter are the same. It is set up for drivers side timing tab, only a hash, no degree marks. Also set up for later, evenly spaced pulley bolts. Found TDC with my tdc tool, scratched it with an awl and put a fine cut with a hacksaw and filled with white paint. The black paint on the new balancer rubs off with solvent:(

Rented the OEM brand installer from Autozone and it went on tight. Glad I used it too! Finally got timing set today. I'm happy with it at 17* initial / 33* total. Vacuum is around 16hg. Runs great and I will probably send my old one off to get rebuilt.

Thank you all for your help!
 
Well done. You got lucky. I had a brand new one slip but move back into the timing cover, wipied the timing cover, the thrust bearing, and the crankshaft in under 300 miles. $200 balancer cost me $2500 and the owner of the car another $900.
 
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