Are the cranksafts out of a LA and Magnum 360 the same? the reason I'm asking as I was looking for a "reground" crank for my LA and several vendors show the same crank part number for 71 thru 2003. If so I have a good magnum crank I could use. Mainly concerned with balance as I know the external balance weights are different between the two.
? about 360 crankshaft.
- Thread starter mod5v
- Start date
-
nm9stheham
Well-Known Member
The Magnum pistons and pins are lighter than the LA. The rods are almost identical, and the cranks are supposedly the same. The lighter pistons+pins in the Magnum changes the balance and is the reason that the external weights are different.
nm9stheham
Well-Known Member
And check post 15 here on the big end rod width. Not sure if the Magnums just use wider rod side clearance or if the cranks have different journal widths. Easy enough to measure the journal widths on your cranks. I know the SCAT I-beams we used on an LA crank have a narrower big end than the stock LA rods, and the total side clearance goes way up, but they work fine.
Connecting Rod 'Weight'
Connecting Rod 'Weight'
Last edited:
mguner
How many is too many?
Seems like that could effect oil pressure as well as the amount of oil thrown at the rings....
Well here is the deal. 360 truck motor. bad bearing damaged crank. just want to clean everything and pop an different crank and bearings in there but don't want to take everything to a machine shop to have it rebalanced. people been doing it for years just not sure if the magnum and LA crank counter weights are the same.
FWI the rods on the magnum are narrower at the small end for the piston.
FWI the rods on the magnum are narrower at the small end for the piston.
Marcohotrod
Well-Known Member
contact the reground crankshaft vendors and ask them about the fact that the magnum piston is lighter, MAYBE they will shed some intelligent info. maybe the external counterweighting is the only difference. I mean the actual crank grinders, not the parts store
moper
Well-Known Member
I got a crank and bearings for my '76 LA 360 for $300. Rather than paying for a used crank to be re-balanced and still need bearings you might just order up a crank kit for it.
nm9stheham
Well-Known Member
Understood, and I had the same exact concern with the wide ride side clearances. But with those wide side clearances, our 340 runs 30 psi hot at 750 RPM idle in gear with 10W30 (using the HV oil pump), so it does not effect pressure that I can see. An no oil burning in 800 miles with just a good quality moly top ring set.
And if the OP is using the LA rods, then if they fit on the Magnum crank with decent side clearances, then it is not an issue.
nm9stheham
Well-Known Member
And Crankshaft Supply shows the same crank from 1971 to 2003, replacing the 2 common PN's of 360 cranks for all years. Not notes are there for any balance change. So it obviously is the same crank. And I have found 3 other references that show the same crank PN's for LA and Magnum. The OP might want to call a company like Crankshaft Supply and ask, as suggested. 612-521-2235
http://crankshaftsupply.com/crankcatalog.htm
They also show 2 rod PN's for LA vs Magnum which all makes sense.
Here is some bobweight data:
An Error Has Occurred!
FWIW, I am at the point after researching this that I would install it with confidence, with the same LA rods and pistons, etc., with the LA flexplate and damper.
http://crankshaftsupply.com/crankcatalog.htm
They also show 2 rod PN's for LA vs Magnum which all makes sense.
Here is some bobweight data:
An Error Has Occurred!
FWIW, I am at the point after researching this that I would install it with confidence, with the same LA rods and pistons, etc., with the LA flexplate and damper.
nm9stheham
Well-Known Member
Which makes sense. They are supposedly lighter at the small end only.
But I don't think the crank needs to be rebalanced..... the change in the extranal weights makes up for the bobweight change fo LA vs Magnum. I suspect it will not be balanced within 1 or 2 grams this way, but will be balanced to factory levels. 90% of the balance work change on these cranks takes place at the 2 large counterweights at each end anyway, which is where the external weights add in.
moper
Well-Known Member
Grinding was actually more than the crank kit when the cost of bearings gets added. And my crank grinder is one of my tech school instructors!
Ok thanks to everyone. I have a nice standard "magnum" crank I will use otherwise I can get a regrind with bearings from Orieleys for 200$ exchange. The crank that I am replacing has #1 main worn past where it could be ground so it would have to be welded up not where I want to go a this time.
Every crankshaft made if it is cast iron is "nodular" or "ductile" iron. The only other cast iron is grey iron. That's like a frying pan. They don't make crankshafts outta the same stuff fryin pans are made of.
Right. There were a FEW NASCAR versions of that engine and they even used the cast crank. 7500 plus RPM.
Infecteddog
Well-Known Member
It's just about a 318/340 stroker crank now.
Anyway, due to the external balance being different- I could see that the weights may be the same.
-
