Internal/external balancing

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Near as I can tell, it's around 04/01/72 when they changed over from forged to cast cranks. If you're going to swap in a forged crank in place of a cast crank, I'd rebalance the engine, get a '72-up 318 harmonic balancer (so you don't have to modify your crank pulley), remove the weights on your torque converter (or get a 318 flywheel if your car has a manual trans), and reuse your existing timing cover and water pump.
Way ahead of you. Crank is at the machinist now and has been balanced with the new pistons and rods. Flywheel is a 4 speed unit for a 318 forged crank. I want to pick up an aftermarket fluid-type damper with the correct timing marks for the cast crank timing cover...which is why all the questions in the first place.
 
It should be no problem to get a fluid damper for a '70-up small block. It's probably a bit tougher to find the earlier one. Either way, you can put a paint mark on the damper where TDC should be. I recommend verifying TDC with any damper regardless of brand or condition. You can always remark, or, put on some timing tape if it's off a bit.
 
Way ahead of you. Crank is at the machinist now and has been balanced with the new pistons and rods. Flywheel is a 4 speed unit for a 318 forged crank. I want to pick up an aftermarket fluid-type damper with the correct timing marks for the cast crank timing cover...which is why all the questions in the first place.


Yeah...I’d hold off on the FD type of damper unless you bought a real Fluidamper with the recessed face. If you have a standard FD or chicom knockoff you’ll have to space the pulleys and brackets out .750 inches. It’s a royal PITA unless you have access to a lathe to make nice, square spacers or I guess you can fudge it and use washers.

Just remember that the water pump pulley has to be spaced out .750 from the water pump itself to start, and then everything but the damper pulley has to move out that much and then you have to get all that crap lined up.

March Performance does make a serpentine pulley set that you can buy and then use all your stock brackets and such and then it will all bolt up, but it ain’t really cheap. May be a better option. I know I’m switching my junk over to that deal because it’s cleaner. And the water pump is overdriven 14% or something like that which is where it should be.
 
Yeah...I’d hold off on the FD type of damper unless you bought a real Fluidamper with the recessed face. If you have a standard FD or chicom knockoff you’ll have to space the pulleys and brackets out .750 inches. It’s a royal PITA unless you have access to a lathe to make nice, square spacers or I guess you can fudge it and use washers.

Just remember that the water pump pulley has to be spaced out .750 from the water pump itself to start, and then everything but the damper pulley has to move out that much and then you have to get all that crap lined up.

March Performance does make a serpentine pulley set that you can buy and then use all your stock brackets and such and then it will all bolt up, but it ain’t really cheap. May be a better option. I know I’m switching my junk over to that deal because it’s cleaner. And the water pump is overdriven 14% or something like that which is where it should be.

I didn't know any of this. They never tell you that crap in the ads, so thanks for mentioning it. I don't know that there's anything wrong with the original damper other than it's 50 years old.
 
Most aftermarket balancers are neutral balance with bolt-on weights for the external balance motors. So pretty much any aftermarket balancer will work if it has the bolt-on weights (just take them off).

That said, Fluidampr offers a neutral balance for '71+ with the 'later model' timing cover.

In the question section on that page, Fluidampr states this listing does NOT require spacers/spacing of the damper. Should be bolt-on and go.
 
Most aftermarket balancers are neutral balance with bolt-on weights for the external balance motors. So pretty much any aftermarket balancer will work if it has the bolt-on weights (just take them off).

That said, Fluidampr offers a neutral balance for '71+ with the 'later model' timing cover.

In the question section on that page, Fluidampr states this listing does NOT require spacers/spacing of the damper. Should be bolt-on and go.


It is NOT bolt on and go unless it has the recessed face. And you don’t have to space the damper, you have to space the water pump pulley and everything else that runs off the pulleys.
 
It is NOT bolt on and go unless it has the recessed face. And you don’t have to space the damper, you have to space the water pump pulley and everything else that runs off the pulleys.

I know that was the case at one time, but it looks like they fixed that? Or at least that's what their reply on that page suggests (I trust their reply more than the picture summit uses).
But I haven't bought that exact sku, so can't say for certain, but the information provided says that's the balancer OP wants. If it's not right, should be easy to send back to summit and let them know Fluidampr is FOS.
 
I know that was the case at one time, but it looks like they fixed that? Or at least that's what their reply on that page suggests (I trust their reply more than the picture summit uses).
But I haven't bought that exact sku, so can't say for certain, but the information provided says that's the balancer OP wants. If it's not right, should be easy to send back to summit and let them know Fluidampr is FOS.


The only FD’s that don’t require a 3/4 inch offset is those with a recessed face. Without that recessed face the FD a is .750 thicker than an OE damper and that’s the issue.
 
The only FD’s that don’t require a 3/4 inch offset is those with a recessed face. Without that recessed face the FD a is .750 thicker than an OE damper and that’s the issue.

Then based on the answer to the spacer question on summit's page, I'd hope they ship one with the recess!
 
Thank you! So, I would buy an aftermarket damper marked as "fits 70-72 with forged crank"?
68-72 balancer, either pump fits one cover, nothing wrong with a cast crank unless you put a blower on it. Btw some covers have no timing marks cast in, used a bolted piece of metal. 318-340-360 all ‘fit’, timing marks only difference.
Come to think of it, 318 has the same balencer.
 
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And the fact that it's for a cast crank.....right?
Well, I have both original dampers; one for the cast crank and another for the forged one. But the '69 is 51 years old and the '72 is pushing it. Since the inner and outer rings have a strip of 50 year old rubber in between them, I'm hearing "Danger, Will Robinson!"
 
If the engine is going into a street car, not seeing 6K+ RPM's, and the rubber still looks good, I'd use it. In fact, I'm putting together a '66 engine right now for that kind of application and I'm not worried about it at all. Minor edge cracks are not big deal. You mainly don't want oil soaked rubber that's getting mushy. If it going to be raced, Fluid Dampr all the way.
 
If the engine is going into a street car, not seeing 6K+ RPM's, and the rubber still looks good, I'd use it. In fact, I'm putting together a '66 engine right now for that kind of application and I'm not worried about it at all. Minor edge cracks are not big deal. You mainly don't want oil soaked rubber that's getting mushy. If it going to be raced, Fluid Dampr all the way.
No gonna be raced unless maybe a run or two for E.T. but probably not even that. Still, I want to build the best motor I can. It will be a hydraulic cam so probably 6-6.5K max
 
If the balancer is in good shape and the engine is going to be balanced, I wouldn't worry about it. A fluid damper is a better part, but, you will have to be the one who decides if it's worth the extra cost.
 
Check out "Damper Doctor" and "Damper Dudes" they rebuild dampers.
 
BHJ Dynamics Inc has both the early and late dampers. This is the BHJ that makes the honing plates and some other neat stuff. Go to bhjproducts.com.
 
BHJ Dynamics Inc has both the early and late dampers. This is the BHJ that makes the honing plates and some other neat stuff. Go to bhjproducts.com.


I thought the BHJ dampers were thicker than OE dampers too. Really, any aftermarket damper should be thicker because you can’t make it bigger in diameter, but it throws off pulley alignment.
 
Could be. They look like stock thickness to me, but hard to say. Have to call them and find out.
 
I thought the BHJ dampers were thicker than OE dampers too. Really, any aftermarket damper should be thicker because you can’t make it bigger in diameter, but it throws off pulley alignment.
Why should they be made thicker? The BHJ I have is the same as stock, the fluid damper is thicker but center is stock thickness, the ATI is also the same as stock. Just looked at all 3
 
Why should they be made thicker? The BHJ I have is the same as stock, the fluid damper is thicker but center is stock thickness, the ATI is also the same as stock. Just looked at all 3


Then you have a FD with a recessed face.

They are made thicker because you generally can’t make them bigger in diameter. The OE damper is made for the OE application. That means OE materials, OE stroke, OE RPM, even OE cylinder pressures. All that is considered, and probably more that I’m forgetting.

That means when you go from an OE 1018 steel forged crank (that is twisted to get the 90* offset on the rod throws) to say...a 4340 non twist forging, even at the same stroke, you change the resonance frequency of just that part. That means the OE damper is no longer tuned for that. Now change the connecting rod material. Same thing. Change the bobweight...same thing (a I knew I was forgetting some other parameters). Every time you change any part in the system, you change the requirements of the damper.

An OE damper is tuned for all of the above, plus the elastomer type dampers ALL have a relatively small tuning window so they are tuned for an RPM where they spend the most time...which is steady cruise RPM. Transient RPM out of tune is much less destructive than steady state out of tune issues.

That means if you are using an elastomer damper and the manufacturer doesn’t ask you about your RPM, bobweight and such, you have no idea at what frequencies the damper will be in and out of tune.

To that end (this is covered in the Chrysler engine manuals so it’s not a speed seceret) as all those parameters change, the damper has to change. That means it generally needs to get heavier. Since you can’t make the diameter bigger, it has to get thicker.

If you want to see cheap assed engineering, look no further than the SBC. There were at least two diameter dampers. The low RPM, low performance engines got the smaller damper, while the higher performance engines got the bigger damper. Once you get the damper to the maximum diameter you can’t get it any heavier unless you make it thicker.

That’s why the FD is thicker. To get it heavy enough to dampen across a broad range of RPM it had to be thicker. I can’t say for sure, but I think the Innovators West damper is thicker than OE too.

Again, if you buy an off the shelf elastomer damper and you have change any or all of the above pieces, you can bet that damper is compromised before you take it out of the box.

Luckily, the cranks and stuff are over engineered so you don’t always see crank failures from improperly tuned dampers. But, almost all crank failures are damper related.
 
Then you have a FD with a recessed face.

They are made thicker because you generally can’t make them bigger in diameter. The OE damper is made for the OE application. That means OE materials, OE stroke, OE RPM, even OE cylinder pressures. All that is considered, and probably more that I’m forgetting.

That means when you go from an OE 1018 steel forged crank (that is twisted to get the 90* offset on the rod throws) to say...a 4340 non twist forging, even at the same stroke, you change the resonance frequency of just that part. That means the OE damper is no longer tuned for that. Now change the connecting rod material. Same thing. Change the bobweight...same thing (a I knew I was forgetting some other parameters). Every time you change any part in the system, you change the requirements of the damper.

An OE damper is tuned for all of the above, plus the elastomer type dampers ALL have a relatively small tuning window so they are tuned for an RPM where they spend the most time...which is steady cruise RPM. Transient RPM out of tune is much less destructive than steady state out of tune issues.

That means if you are using an elastomer damper and the manufacturer doesn’t ask you about your RPM, bobweight and such, you have no idea at what frequencies the damper will be in and out of tune.

To that end (this is covered in the Chrysler engine manuals so it’s not a speed seceret) as all those parameters change, the damper has to change. That means it generally needs to get heavier. Since you can’t make the diameter bigger, it has to get thicker.

If you want to see cheap assed engineering, look no further than the SBC. There were at least two diameter dampers. The low RPM, low performance engines got the smaller damper, while the higher performance engines got the bigger damper. Once you get the damper to the maximum diameter you can’t get it any heavier unless you make it thicker.

That’s why the FD is thicker. To get it heavy enough to dampen across a broad range of RPM it had to be thicker. I can’t say for sure, but I think the Innovators West damper is thicker than OE too.

Again, if you buy an off the shelf elastomer damper and you have change any or all of the above pieces, you can bet that damper is compromised before you take it out of the box.

Luckily, the cranks and stuff are over engineered so you don’t always see crank failures from improperly tuned dampers. But, almost all crank failures are damper related.
So then a heavier dampener is better than a lighter dampener? Or just in certain cases. Kim
 
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