Hi, Im finishing a mild '72 cast crank 340 build and want to break it in on a runstand. Whats the cheapest solution for starter connection? My cars auto so I dont really want to buy a $300 ext balance flywheel for one start up. Ive heard of cutting open and using 1/2 of a torque converter which sounds good except what about the external balance part? Seems like an off balance mess. Thank you
340 External Balance Run Stand
- Thread starter mostrood
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It sounds like you need a flywheel.
Thats what Im afraid of...
Starter mounts are available on ebay for like 30 bucks. As for the flywheel or converter, you just gotta do what you gotta do.
Well, wtf are you gonna use for the CAR? A converter or a flywheel, right? There ain't no free fairy dust that's gonna do it.
I've seen videos on YouTube with a converter mounted. Myself I had a flywheel and a friend loaned me his bellhousing.
Oh theres no free fairy dust..? Wow thanks
You find some, you let me know. You can call Precision of New Hampton and they'll sell you half a converter.
Thanks ya I guess Im just confused on the cutting the torque converter open and using the ring gear side vs the entire torque converter. I read in For A Bodies Only to cut in in half, just confused on the external balance part.
Then use a B&M flex plate that's external balanced. Then all you need is a neutral converter.
I'm not sure about cutting in half. Like Rusty said get external balanced flex plate?
My question would be if you just did the engine why is it still externally balanced?
Scody21
Just send it
Sounds like you should save some money and brake it in on a dyno. The worst thing is not having load on a motor durning brake in which is what a run stand does…
Scody21
Just send it
Your close to @Newbomb Turk he loves running his dyno…
Later year 340s are an externally balanced engine.
Newbomb Turk
Well-Known Member
True that.
Not sure exactly where the OP is in Idaho but I can make it to the panhandle in 3 hours or less if the wife isn't riding with me.
Then its four hours.
That's not what he's asking. Trust me, he knows that. He was wanting to know since you built it, why did you leave it externally balanced?
I would think if you were cutting a balanced torque converter, it many not be balanced when you are done?
I just rebuilt the engine I have. Why does it matter?
Newbomb Turk
Well-Known Member
Cost is the number one reason. I don't like external balance. If it's a stock build then you can leave it.
Even at that, if you are converting an external balance crank to internal balance the cost is prohibitive.
Including ALL the other costs involved in a new build, I'd consider the cost to internal balance one an added bonus.
Alrighty then. Happy trails!
Newbomb Turk
Well-Known Member
It doesn't matter. What you have is fine. I wouldn't have converted your crank to internal balance either. It is very cost ineffective for what you are doing.
If you did want to do that (keeping in mind external balancing is not my favorite thing) you'd need to get a new damper. You can buy a cheap one or an expensive one. Either way it adds to the cost.
Then you have to put slugs of Mallory into the crank to get enough mass in the counter weights on the crank.
If you don't know the reason why your crank is externally balanced is because the cast crank you are using doesn't have enough mass in the counterweights to offset the weight of the piston and rods.
So what is done is extra weight is added to both ends of the crank (or sometimes just one end in certain cases) and that external mass on the ends of the crank add enough mass to get the crank balanced.
That Mallory metal (that's the brand name...it's actually pieces of tungsten) is expensive. That adds to the cost of balancing.
Then you have to install the mallory. Which means you have to take all the bob weights off the crank, take it out of the balancer, put the crank in a fixture so its end is up and you have to drill and ream the hole for the mallory in the face of the counterweight.
Then you press the mallory in and TIG weld it. All labor intensive. And that means $$$$$$$.
Then the crank has to go back on the balancer, all the bobweights installed and you spin the crank again.
If you did your math you should be able to make a couple of corrections and you should be done.
All that adds up to killer costs. It just isn't worth it in a case like yours.
And, I didn't add in the fact that the cost of the reamers for different diameters of mallory.
I don't remember the last customer crank I had to use mallory but I remember mine.
I was running aluminum rods so I would have to drill a bunch of holes in the counterweights to get the crank light enough. That's kind of the opposite issue of external balance.
So I tired of all that drilling and decided I would clean that up by reducing the diameter of the counterweights in the lathe. That would take a bunch of weight off and then balancing would go much quicker.
I decided that if a little off is good, a lot off is KING. I'd just add mallory to make up the difference if I took more off than I needed.
The principle is the smaller the counterweight, the less rotating mass. AT 8500 rpm I wanted light. So I turned the counterweights down until I just touched the rod throws.
I had to add three pieces of mallory in each end. By the time I was done I was into just materials about 200 bucks. At that time a balance job with a clutch was 325 dollars. Now add another 200 for mallory.
If I was charging a customer it would have added another 200 plus another 175 just to install the mallory. At least.
And that was over 20 years ago.
You're fine with what you have.
Newbomb Turk
Well-Known Member
For something that stock? Maybe I need to go back and read the OP.I didn't think this was ever going to see the track.
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