Maistrelli
Well-Known Member
Can a 273 crank be used in a 5.2 Magnum engine? Magnum damper on 273 crank?
273 crankshaft, 5.2 Magnum
- Thread starter Maistrelli
- Start date
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nm9stheham
Well-Known Member
Balance has to be considered. I can't quite figure out if the crank balance is the same. Magnum 5.2L piston+pin+ring weights are very close to LA 318, but the Magnum rods may not be the same. I just don't have the rod data.
What year of 273 crank?
What year of 273 crank?
pishta
I know I'm right....
magnum rods have a different width little end, narrower. So thats potentially less weight right there. Also lack of fuel pump eccentric on magnum crank.
The fuel pump eccentric is on the camshaft, not the crankshaft.
Maistrelli
Well-Known Member
1965
It should bolt in and go. All 318s were neutral balanced that I know of.
pishta
I know I'm right....
Doh! Of course I knew that....WTH?
Plymouth 65
I'll be in the shop
The 1965 273 crankshaft has the small torque converter pilot diameter. Just so you're aware! 65'
nm9stheham
Well-Known Member
Yes, that's a fit problem for the trannie. The OP would have to have the crank pilot hole turned out.
I worked out the bobweights with the data I have. 273 and 5.2L are pretty close but it still may be off enough to be 10-20 grams off of balance..... or some of my data is a bit off.
I think RRR is correct on both being neutral balanced for the dampers and TC/flex-plate/flywheel.
pishta
I know I'm right....
I think 10-20g is within factory spec. Ive heard motors being much more out off the line.
If I was to mis match components I would have the machine shop properly balance the rotating assembly.
What we need to know is why the OP wants to put a 273 crank in a Magnum.
probably wanting a forged steel crank instead of cast
nm9stheham
Well-Known Member
Well, the tolerance around a number may be that much, but what I am coming from is that the nominal numbers are that much off.
BUT, the good news is that I just weighed some 2 BBL 273 rods & pistons and pins, and with the new data, the bobweight number is < 10 grams off from my 5.2L Magnum data. So this looks pretty decent for being balanced.
Racing? No way. Going in the pickup to go out and cut firewood? A-OK
I'm curious about that too.
One thing you have to remember is how the rods are balanced. Not just total weight but end to end.
nm9stheham
Well-Known Member
Absolutely.... I don't work out bobweight info unless I have big and small end weight data too. I've gotten to where I just give my bobweight number and crank to the machinist.
Why is that pertinent? Might simply be what he has.......OR as has been said maybe he wants a steel crank. The why really doesn't change anything.
Oh just curious. Sometimes people have crazy ideas. It's more like why would you need to?
Maybe he was gonna wear the rods as a necklace? LOL
Maistrelli
Well-Known Member
Using an A833, crankshaft has pilot bearing.
Maistrelli
Well-Known Member
Because I have a good one and 5.2M crank needs ground.
It might work but there will be other things that won't be right. Why take the risk. Just turn and polish the Magnum crank.
Maistrelli
Well-Known Member
I plan to have it balanced, new O.S. pistons, flywheel, clutch, PP and damper.
Maistrelli
Well-Known Member
What's the average cost of -.020 rod & main journals? Anyone have crank ground lately? What others things won't be right?
nm9stheham
Well-Known Member
Balancing is going to cost 2-3 times grinding a crank. If you are not racing, then changing pistons to oversize does not necessitate a re-balance. So haw hard are you going to be running this engine?
Just be aware: Since both the 273 and 5.2 are 'internal balance' engines, there is no need to balance the crank with the external parts. Each of those external parts are individually balanced.
$125-$150 as a guess on the regrind.
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