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? about 440 crank in low deck

Posted By: mac56

? about 440 crank in low deck - 02/08/10 11:17 PM

Hello
Everything I read seems to recommend cutting the counter weights for better fitment. What is the difference between an RB compared to a B in respect to the crank? I understand it being easier to balance but most advertisements say it is for fit. Can someone explain this to me?
Thanks
Posted By: moper

Re: ? about 440 crank in low deck - 02/08/10 11:32 PM

The diameter of the counterweights is different. the exact number I don't recall... But it ends up being close to .200" off it. I have also used them with no clearance issues. So "your results may vary"...lol Personally I won't use a factory crank anymore when there are cheap alternatives for a better peice that drops in. To have a factory one magged, stroke corrected, indexed, and ground/polished is $400. A 440Source B wedge main/counterweight crank is $600 or so for a new part that is much stronger.
Posted By: AndyF

Re: ? about 440 crank in low deck - 02/09/10 12:41 AM

The crankcase on a B engine is a little tighter so the RB crank hits. Typically a forged RB crank is too heavy for a 451 or 470 motor anyway so if you have to remove weight, and you have to gain clearance why not do both at the same time?

There are legit reasons for boring out the mains in a B block to the larger RB size so that is another way to solve one issue. That doesn't solve the clearance issue or the weight issue but it does allow you to use better main bearings and to use a stronger crank. Of course the block is a little weaker and it costs some money to bore the main line.
Posted By: mac56

Re: ? about 440 crank in low deck - 02/09/10 12:47 AM

Thanks Andy. That is where I was going with this. I did not realize there was a difference in the block other than deck height.
Posted By: 440Jim

Re: ? about 440 crank in low deck - 02/09/10 01:33 AM

A typical RB forged steel crank has counterweight diameters around 7.50-7.55"

This attachment shows what I measured on one 400 block on the inner cylinders (4,6 or 3,5). I have seen the front and rear counterweights clear at 7.5" dia.

You can also grind the block, or put really oversize bevels on the counterweights to clear the block.

Attached picture 5792109-blockweb3dim.jpg
Posted By: mac56

Re: ? about 440 crank in low deck - 02/09/10 01:42 AM

Thanks for the picture Jim. As they say worth 1000 words.
Posted By: CRE2004

Re: ? about 440 crank in low deck - 02/09/10 03:39 AM

Here's what it looks like after you run the CNC through it to remove that annoying area and radius it....

Attached picture 5792399-BBlockClearance.jpg
Posted By: StealthWedge67

Re: ? about 440 crank in low deck - 02/09/10 05:22 AM

commonly accepted counterweight diameter is 7-1/4". I had my machinist use this dimension, and it balanced out very easily from there.
Posted By: Thumperdart

Re: ? about 440 crank in low deck - 02/09/10 06:21 AM

I`m running a 413 crank w/the counter weights cut down and w/6.385 chevy rod and JE pistons, my bob weight is around 2230 grams,spins to 7000+ with ease and has been doing so for 10 years in two different combos. I don`t buy the strength bs(or lack there of)w/a stock crank as guys are runnin 8`s w/turbos using em. Don`t remember exactly how much was removed but it balanced out very nicely and was cheap.
Posted By: mac56

Re: ? about 440 crank in low deck - 02/09/10 10:47 AM

Quote:

Here's what it looks like after you run the CNC through it to remove that annoying area and radius it....


Nice work, but then you have a reputation for nice work. Was this done so the counter weight didn't have to be cut or were there other facts?
Posted By: moper

Re: ? about 440 crank in low deck - 02/09/10 12:43 PM

I had a stock RB crank that dropped in with a minor amount of clearancing where Jim noted in the picture. This is why I say some do fit...
Posted By: StealthWedge67

Re: ? about 440 crank in low deck - 02/09/10 03:05 PM

but even if it fits, what sort of swiss cheese does it look like after balancing it?? The counterweights are not only too large, they're too heavy for the 451 / 470 combo. Cutting them down helps both issues, probobly also helps reduce windage. Just seems like the right way to do it.??
Posted By: supercomp

Re: ? about 440 crank in low deck - 02/09/10 03:36 PM

Quote:

but even if it fits, what sort of swiss cheese does it look like after balancing it?? The counterweights are not only too large, they're too heavy for the 451 / 470 combo. Cutting them down helps both issues, probobly also helps reduce windage. Just seems like the right way to do it.??



Posted By: moper

Re: ? about 440 crank in low deck - 02/09/10 04:31 PM

I used H-beams and J&Es with the one that dropped it. The rods were not light but the crank still had a few 1" holes in it. Not that I consider that a big deal. But it did make for a bit of work when balancing it.
Posted By: mac56

Re: ? about 440 crank in low deck - 02/09/10 10:31 PM

So then there is no trick to cutting the counter weights is there? Just put in a big a$$ lathe.
Posted By: Thumperdart

Re: ? about 440 crank in low deck - 02/09/10 11:07 PM

Pretty much............
Posted By: mac56

Re: ? about 440 crank in low deck - 02/09/10 11:19 PM

Thanks Thumper
Posted By: AndyF

Re: ? about 440 crank in low deck - 02/09/10 11:34 PM

Quote:

So then there is no trick to cutting the counter weights is there? Just put in a big a$$ lathe.



There are several tricks to cutting down the counterweights. First off you need to know what dimension to cut it to. Then you need the right fixture to bolt to the crank flange so the lathe can hold the crank. It also works better if you have the right tool to center the nose of the crank. And the last trick is to have the correct type of cutting tool.
Posted By: Thumperdart

Re: ? about 440 crank in low deck - 02/09/10 11:51 PM

Let me re-phrese that(4 u Andy)it`s no problem for the machine shops that I deal with. How`s that?
Posted By: 440Jim

Re: ? about 440 crank in low deck - 02/10/10 12:38 AM

Quote:

Here's what it looks like after you run the CNC through it to remove that annoying area and radius it....

That is nice looking.
Posted By: CRE2004

Re: ? about 440 crank in low deck - 02/10/10 12:58 AM

Quote:

Quote:

Here's what it looks like after you run the CNC through it to remove that annoying area and radius it....


Nice work, but then you have a reputation for nice work. Was this done so the counter weight didn't have to be cut or were there other facts?



I've always wanted to do it, so I did I've spent the time going from the lathe to mock up and still having fitment issues so I thought I'd eliminate the real problem. Now I don't have to put a half inch wide chamfer on a crank to keep it from hitting that spot nor do I have to whack the OD unless I want to do a "no holes" balance job. I've also turned the cranks down on some 4.375 combos and had to add a piece of heavy metal which I wouldn't have had to do if I had cut the block rather than the crank. Now If it's a combo that needs clearance at BDC, I only have to turn the crank(or cam cut the counterweight) enough to clear at BDC.
Posted By: CRE2004

Re: ? about 440 crank in low deck - 02/10/10 12:59 AM

Quote:

Quote:

Here's what it looks like after you run the CNC through it to remove that annoying area and radius it....

That is nice looking.



Thank you.
Posted By: mac56

Re: ? about 440 crank in low deck - 02/10/10 10:38 AM

Thanks for the pics and info guys. Very helpful.
Posted By: Oyvind Mopar

Re: ? about 440 crank in low deck - 02/10/10 10:01 PM

There is at least one advantage in keeping the stock crank diameter; it puts the mass out to where it does the best job of balancing against the crankpin forces. To benefit from this advantage you need to cut the corners off the throws, which in total will make a lighter crank, than if it is just turned down. Look at recent Nascar cranks, they are made like this, they even put numbers of mallory metal in the slim counterweight, to save on mass in total. (But it makes no sense if you then bolt a heavy steel flywheel to the crank!) The question is if the machine shop will put the extra effort in the balancing, but it should be possible for a little extra fee to get the holes drilled out in the corners first for balancing the overweight crank. I am luck enough to have my own crank balancing machine!
Posted By: mac56

Re: ? about 440 crank in low deck - 02/11/10 12:08 AM

Quote:

There is at least one advantage in keeping the stock crank diameter; it puts the mass out to where it does the best job of balancing against the crankpin forces. To benefit from this advantage you need to cut the corners off the throws, which in total will make a lighter crank, than if it is just turned down. Look at recent Nascar cranks, they are made like this, they even put numbers of mallory metal in the slim counterweight, to save on mass in total. (But it makes no sense if you then bolt a heavy steel flywheel to the crank!) The question is if the machine shop will put the extra effort in the balancing, but it should be possible for a little extra fee to get the holes drilled out in the corners first for balancing the overweight crank. I am luck enough to have my own crank balancing machine!


Thanks for you opinion.
Posted By: polyspheric

Re: ? about 440 crank in low deck - 02/11/10 04:04 AM

one advantage in keeping the stock crank diameter

That's also the highest inertia for the amount of weight.
Posted By: dennismopar73

Re: ? about 440 crank in low deck - 02/12/10 05:01 AM

i've got 2 of these cranks
1 has been in race motor for over 9 years
running 9,80s 9,70s
the other has just been done
the shop did both the main turn down and
counter weights
cost 150$ for turn & $100 to turn radius
on counters
will not do any more
to easy to call 440 source send me 500 ci
stroke
Posted By: mac56

Re: ? about 440 crank in low deck - 02/12/10 11:31 AM

Believe me I know about debate on just ordering 500 stroker crank. I have been struggling with it for 2 months but I have all the parts necessary for a 470 build except the crank so, not only do I have the cut a factory crank or buy aftermarket dilemma. I also have should I leave these parts on the self for more inches. (that probably won't happen)
That brings us to the Canada factor. Some of the prices you guys talk about for having work done is like a dream here. Not sure why but machine work and getting new parts here comes at a substantial cost,
This post did answer the real question for me. I didn't realize there was a difference in the bottom of a B block compared to an RB block.(why counter weights interfere)
Sorry so long.
Posted By: ZIPPY

Re: ? about 440 crank in low deck - 02/12/10 10:18 PM

I bought my crank at a swap meet, www.lsmeng.com magged ground and polished it for a reasonable price with good quality, and I worked the counterweights myself with angle grinder, sandpaper rolls, etc. I have maybe 2 1/2 or 3 hours work into it but spent alot of that time just staring at it.

Thought process: factory counterweights are not even close to being round, stock 440 cranks hold up just fine at 7000 rpm even with boat anchor pistons, and I see no reason why the modified counterweights have to be perfectly round either to run the same rpm....especially with 8lbs less reciprocating weight than stock.

Not much material needs to be removed to make the counterweights 7.25" diameter (plus or minus 1/16", if modifying them by hand).

If you're doing a 1000hp deal ignore all this, throw away all your oem stuff and buy it all brand new. If you're doing a 550-600 deal, though, this will work great.
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