Machine 360 crank to fit in a 340 main block

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Rocket

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Just curious if anyone has any information on the cons of milling a 360 main forged crank for installation in a 340 main block. Does the removal of the material weaken the crank? Would the crank need to be hardened after the machining?

Just wondering as I am building a 360 stroker and wonder if in the future if I want to increase power and move to a 340 main race block if my forged crank would be reusable.

Thanks
 
It's certainly been done before and I don't see why not. And yes the journal surface should be retreated as the surface hardness is only about .001-.0015
deep IIRC.
 
I think you remember correctly. The hardness depth is very shallow. It can be retreated, not a problem.

When the crank is cut down, the machinest will ask you some questions. What bearings is one of them. Take time with the machinest on this topic and walk through it slowly so you get to understanding it all well.

The 360 in a 340 block is the first stroker to the small block done in the early 70's. With the 3.58 stroke and a .030 340, you'll end up with a 372 cid engine. NICE!
(378 @ .060 over)
 
fishy68 said:
360's never used a forged crank. Only 360 forged crank you can buy is aftermarket.
Click to expand...

You are correct sir.

Undercutting the 360 crank this much is no big deal.Guys do it to stock cranks all the time. Usually its forged,but the 360 crank is plenty beefy. It also should shed more weight in the rebalancing process.So what you will have is a big small block with a fairly light weight rotating mass,therefore quick revving.It will like to breath due to the big bore of the 340,so it's gonna luv serious heads!

Kind of the small block version of the 451/470.
 
Thanks for confirming what I thought. The crank I am planning to get is a forged unit. Never hurts to have options down the road.
 
Rocket said:
Thanks for confirming what I thought. The crank I am planning to get is a forged unit. Never hurts to have options down the road.
Click to expand...

You might look at removing the material from the block and have it align bored, rather than from the crank. It's another option to consider.
-Brad
 
Doesn't somebody make a forged crank with a 360 stroke and 340 mains? I thought Callies or someone did.
 
Brad54 said:
You might look at removing the material from the block and have it align bored, rather than from the crank. It's another option to consider.
-Brad
Click to expand...

I'd rather take it off the crank. The 360 mains are huge. Taking them down to 340 size still leaves plenty of material and cuts down on some rotating mass.
 
mopar used to sell a 3.58 stroke 340 main crank...

pretty sure eagle and scat will have them
 
Buying the correct 4340 forged crank, direct from the manufacturer would be the safest and cost effective way to go, My .02.

It'll be costly to get those journals machine that much, if it's done correctly.
Considering they would need to be turned oversize, then hardened and then ground/polish to finish size. Then all the radii...

There are other options.
 
340butterduster said:
Buying the correct 4340 forged crank, direct from the manufacturer would be the safest and cost effective way to go, My .02.

I agree with 340 butterduster. Cutting the crank that far is going to move the oil holes away from the center of the journals too.
Click to expand...
 
Buy the 360 main forged, and plan to have the mains of the race block align bored to 360 size later... Or simply build a complete 2nd engine later...
 
I did that very thing to my 340 with a factory 360 crank with internal balance, and it runs quite well. But the mallory weight needed makes it expensive to do.
 
Just my .02 take it for what it is. At the price of crankshafts now it would be better if you just bought a new crank. I had a SB mopar crank cut down for a SB chevy jod journal. It cost me 380 bucks plus shipping a heavy chunk of iron, just to have the rods cut, widened, and nitrated. If you look at that the price a new Eagle crank is less than $750. I understand that the rotating assy is an odd stroke it just dosn't make sense to me to spend $600 to have a crank cut down and rehardened even if it needs to be reballanced. Sell the used crank and use the money to buy a new one.
 
Thanks for all the input. I did not expect the machining costs to be that high to remachine and harden the crank.

Here is another option. What are your opinions? I have seen spacer kits available for using a 340 main crank in a 360. I believe callies and Mancini carry them for around $300 bucks. Any experience with these? I do not know anyone who has used these personally.
 
Rocket said:
Thanks for all the input. I did not expect the machining costs to be that high to remachine and harden the crank.

Here is another option. What are your opinions? I have seen spacer kits available for using a 340 main crank in a 360. I believe callies and Mancini carry them for around $300 bucks. Any experience with these? I do not know anyone who has used these personally.
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I have never used them before but Chevy guys have been puting 350 cranks into 400 using the spacers for years. Just keep in mind it's 300 bucks or so for the spacers and if you check the fine print, they must be fitted and align honed so add another $200 to $300 to the price. Roughly the same price as a new crank. :toothy10:
 
Seems to me it would be easyer and cheeper to just bore the 360 core motor .040 and you would have the same thing. Only downside to the 360 is it has very large main bearings, and you have to make sure your oiling system is up to par. Not hard to do at all.
 
I have a 360(3.58) Scat steel crank in my stroked 340 with P&P Xheads.When dynoed was making 440ftlbs@4300rpm and 452hp@5700rpm,this is with a 4 speed behind.It has some great street manners LOL.Good luck!

My new 408 with Eddy RPM heads is being built for 525-550hp,should be fun in the little 66 Dart.
 
Rocket, we did that to a friends '70 Duster a few years back. Had the stock 360 cast crank turned down to 340 specs . We didn't have it hardened or anything like that we just droped it in and went racing. This was a bracket racer. We ran that engine in that car for 6 or 7 years never a problem. Car went 10.20's-10.30's @ 128-129 range. Can't speak for others..but we didn't have any issues with ours and it cost less than $100. bucks to have it turned. Good luck with it.

Terry
 
70aarcuda said:
what pistons are you going to use?
Click to expand...

I used the TC 1930 Clevite Pistons, you need to have the Valve reliefs cut in them though any competent machinist can handle this process. The Compression distance is 1.678 so final deck height at 0 with the 3.58 crank will be 9.591 leaving the machinist to square deck it .009 or more if needed. You can clean it up for compression you want with the head gasket. Compression with these and valve reliefs at 5cc ends up right at 10.5:1 with 62 cc heads. I am using the INDY/RHS X heads no port work at all. Comp Cams XE284 Hydraulic Flat Tappet, Gear Drive, Mopar Performance Crank, Eagle SIR ESP 5140 Rods, Line Honed with main studs, Head Studs...Cometic Gaskets Should be put together in 2 weeks from today. I had all the parts laying around including the block. Need to keep busy in my mind. This one is just a hobby motor that I am possibly trading for a 69 Dart GT...

Here is a current link to these pistons. I used .030 over. These ones are .040 over.

http://cgi.ebay.com/ebaymotors/MOPA...r_Truck_Parts_Accessories?hash=item5636ac50d8
 
Mad Dart said:
I used the TC 1930 Clevite Pistons, you need to have the Valve reliefs cut in them though any competent machinist can handle this process. The Compression distance is 1.678 so final deck height at 0 with the 3.58 crank will be 9.591 leaving the machinist to square deck it .009 or more if needed. You can clean it up for compression you want with the head gasket. Compression with these and valve reliefs at 5cc ends up right at 10.5:1 with 62 cc heads. I am using the INDY/RHS X heads no port work at all. Comp Cams XE284 Hydraulic Flat Tappet, Gear Drive, Mopar Performance Crank, Eagle SIR ESP 5140 Rods, Line Honed with main studs, Head Studs...Cometic Gaskets Should be put together in 2 weeks from today. I had all the parts laying around including the block. Need to keep busy in my mind. This one is just a hobby motor that I am possibly trading for a 69 Dart GT...

Here is a current link to these pistons. I used .030 over. These ones are .040 over.

http://cgi.ebay.com/ebaymotors/MOPA...r_Truck_Parts_Accessories?hash=item5636ac50d8
Click to expand...
Is that on a 318??

70aarcuda said:
what pistons are you going to use?
Click to expand...
I would think stock 318 pistons would be fine... I don't plan on doing any bore work... but I need a block first to determine that ;) lol
 
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