External or Internal Flywheel… need asst.

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madhatta360

madhatta360

1973 Duster 340 H-code TX9
FABO Gold Member
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Allentown, PA
Trying to determine if my 340 is internal or external based off the flywheel pics and crank photo attached. Car is 73’ but it’s not the #’s matching motor and prev owner said it has steel crank. Based on the numbers on flywheel I know it’s 130tooth and the holes indicated to me internally balanced. Just want to make sure prior to ordering a new one, Thanks in advance

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Does it have a factory balancer on it? The OE balancer literally has "USE WITH 340 CAST CRANK ONLY" cast into the front of it.
 
NoCar340 said:
Does it have a factory balancer on it? The OE balancer literally has "USE WITH 340 CAST CRANK ONLY" cast into the front of it.
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Didn’t check- pulled the trans today, flywheel is spent. I’ll look around the balancer/crank pulley tomorrow to see if I see it anywhere. Thx for letting me know
 
Why is the flywheel "spent"? As said, that is a neutral balanced flywheel which would seem to indicate a steel crank, but that's no guarantee. Can you get us a picture of the balancer? If it's also a neutral balancer, then chances are it's a steel crank. Did the engine run smoothly with no vibrations? The only real way to make the determination between steel or cast is to get the oil pan off.
 
RustyRatRod said:
Why is the flywheel "spent"? As said, that is a neutral balanced flywheel which would seem to indicate a steel crank, but that's no guarantee. Can you get us a picture of the balancer? If it's also a neutral balancer, then chances are it's a steel crank. Did the engine run smoothly with no vibrations? The only real way to make the determination between steel or cast is to get the oil pan off.
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Flywheel has bunch of heat fractures, probably hard to see in the photos. Engine ram smooth no problems, I’ll grab some pics of balancer tomorrow.
 
madhatta360 said:
Flywheel has bunch of heat fractures, probably hard to see in the photos. Engine ram smooth no problems, I’ll grab some pics of balancer tomorrow.
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Those will very, very likely machine out when the flywheel is refaced. It's pretty rare for the cracks to go very deep at all. Even if refacing doesn't remove them all, it will the great majority. I'd have it refaced and see what it looks like. If the engine did run smooth, then very likely it's a steel crank.
 
Resurface that flywheel and put it back in. You know the flywheel works and is proper for your engine.

No sense in causing new problems with a new flywheel that could end up being wrong.
 
Years ago the best deal I could find on a new flywheel was from 440 source.. 130 it's the same as the big block..
 
NO, that is not necessarily a neutral balanced flywheel. The clocking of those two holes at the 8 o'clock position in your picture could still indicate a 340 cast set up. Go to post #2, then proceed.
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RustyRatRod said:
Hell yeah! Somebody got the book out! lol
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Haha nice, appreciate all the input on the flywheel resurface options. I’m about to head back out to the garage to check the damper, I’ll report back.

This is the downside of buying **** that you didn’t build, never actually know what u got ha
 
madhatta360 said:
Haha nice, appreciate all the input on the flywheel resurface options. I’m about to head back out to the garage to check the damper, I’ll report back.

This is the downside of buying **** that you didn’t build, never actually know what u got ha
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That's true.....but even still, you're better off than having nothing. At least you have something to build on.
 
Max1196 said:
NO, that is not necessarily a neutral balanced flywheel. The clocking of those two holes at the 8 o'clock position in your picture could still indicate a 340 cast set up. Go to post #2, then proceed.
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That's exactly what I was thinking, hence my suggestion to check the damper. The flywheel counterbalancing on a cast-crank 340 is a hell of a lot less than it is on a 360, so it's less obvious. Fun fact: A 340 cast crank is "zero balance" when used in a 318.

@madhatta360: If it turns out to be an aftermarket damper, look for a counterweight bolted in from the rear (timing cover side), in the area of the pulley bolt holes. The counterweight should be stamped with its application.

It's probably worth mentioning (as it has been many times) don't sweat having a cast crank. You aren't going to hurt it unless you plan a 500 shot of nitrous at 7 grand on 35° of timing. Even then, the block will probably let go first.
 
welp, that's what happens when you are used to looking at the 360 balance set up. Could very well be external balance. Check the damper to verify.
 
now we got some juice haha…. Here we go!

damper says “use with 340 cast crank” but interestingly enough the engine stamping on drivers side starts with JM- that would mean 1971 correct?

so this is fun- ideas? not really pulling the pan just throwing that out there lol
 
About to pull valve cover for what’s it worth; I know they are J heads but that doesn’t say much regarding the block
 
J is 1973

With it being external, even more reason to minimize procedures and have it surfaced. You could do the single balance hole yourself with the one you have as a template. Pretty easy.
 
Yeah I’m just wandering now if they put a steel crank in because there are signs of bottom end being resealed so I know work has been done.

did the 10,000 day on stamp for JM 340 (can’t make out the letter) 4080 def later 1972
 
madhatta360 said:
Yeah I’m just wandering now if they put a steel crank in because there are signs of bottom end being resealed so I know work has been done.

did the 10,000 day on stamp for JM 340 (can’t make out the letter) 4080 def later 1972
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If they did use a steel crank and an external damper and flywheel they probably junked the crank.

That added external weight would be more than a steel crank needs and they’d have to take the weight out of the counterweights.

Unless of course they used Tungsten connecting rods. Or lead.
 
You KNOW the balance was good with the flywheel you have. The first thing I would do is gamble the cost of a proper (Blanchard ground) resurface, before I did anything else.
 
33IMP said:
You KNOW the balance was good with the flywheel you have. The first thing I would do is gamble the cost of a proper (Blanchard ground) resurface, before I did anything else.
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Yeah that’s where I’m at, plus way more cost effective
 
Bring it to our Machine shop in Danielsville to get cut.. Its looks to be a cast crank flywheel. If the engine was replaced with a steel crank it may be the wrong flywheel for the engine. You will have to make sure it is a steel or cast crank. Or you will have a balance issue. Did it vibrate? I have flywheels here.

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