408 Balancing

Hello,

I have a 360 Stroker Crank. Mopar Part Number P5007258, KB416 pistons, H beam rods, 318 Harmonic Damper and a 318 LA Flex plate the finger type. (also have the 360 Magnum round balanced flex plate) What do I need to get this internally balanced? (my chev friend thinks it will have to be externally balanced, but he said he is not 100% sure, he thought if external always external)

Thanks
Bruce

That crankshaft almost always needs to be ext balanced or youd have enough $$$ added weight in it you could of bought a steel which almost is always internal. You probably got a great deal on the crank, they are great cranks but many if its gonna take $3-400 in balance metal just goto a steel.

That crank is made by scat and is a good crank, I recently was going to buy one at $300 shipped new but passed because no one I emailed, the sellers of the crank, chicago connection IIRC could not even tell me the bobweight of the crank.

The only way to get that close to internal weight with minimum would of been to use the scat light pro I beam rods and some very very light forged pistons. And then most get a bit of weight. But your passed that now.

When I do have a ext. balance 360 based stroker I got to take everything, including the balancer and flexplate (what converter are you running, a weighted balanced unit or a zero balance and what trans? as some of the B@M flex plates for the 727 wont work on a 904 because they are too big OD because they are drilled for several different diameter converters? And you vert balance also is a factor) I also take the harmonic balancer which for a street motor I use the mid grade that comes with the three different balance weights that bolt in and let the balance shop determine which is best and easy for them to use.

A fully forged kit is the cake walk of balancing as far as effort, simply zero balance everything and the cheapest to balance. (Just drill on the crank)What you are doing is the most complicated but still very doable. You just have 2x things or better things to get in proper order.

What H beam rods are you using? Alot of times the box will have a overall weight and a big and small end weight for a general reference.

You can easily determine what your bobweight will be at home with a few common things and although its always best to let the machine shop guy do it all, you still then have a sheet to compare to because some shops do make mistakes.

And also in your case, any good shop could balance your street stroker, they balance things all the time and most have good equipment and you using good pistons and rods that will be very close if not spot on that they will love because it will be a easy balance job for them, but if you decide to use a race shop thats your choice as well.

Probably not the easy answer you were looking for but in the end you will think to yourself, it wasnt that hard.

Thanks for the info, I have never had an engine balanced before, so this is a leaning process.


Ok, so what parts do I need to take to the balancing man, I have these parts


Mopar SB 318 340 360 7.25" Harmonic Balancer Damper small block Chrysler - Has a bolt in weight
B&M 10239 SFI Flexplate for Chrysler 71-92 Chrysler 360 w/TF904
A standard finger type flex plate
Plus pistons, rods, bearings, rings etc

and

I have the 360 Magnum flex plate with balance weights on it. But I don't have a 360 Magnum Harmonic Balancer.

My Torque converter has no weights on it, so what I want to know is do I get this mopar crank balanced to the old LA balance or the New Magnum balance if I can't internally balance? (which means I will need a 360 magnum harmonic balancer)

Thanks
Bruce

I am not a small block guy but is the crank LA or Magnum?

His crank is neither, its a 360 main crank with a 4 inch stroke, the crank knows no difference. It would fit in either a la or mag 360 block.

Your bobweight will neither be for a 360la or 360 magnum you bobweight will be what your combination of parts balance out to be.

Id take your guy this, leave your magnum parts at home.

Mopar SB 318 340 360 7.25" Harmonic Balancer Damper small block Chrysler - Has a bolt in weight
B&M 10239 SFI Flexplate for Chrysler 71-92 Chrysler 360 w/TF904. He might spin it with no flex plate just for kicks of hes not done one like your before and he should know you have a(non weighted vert).
Plus pistons, rods, bearings, rings etc

He only needs one full set of rings and one upper and one lower bearing shell, 2 pin locks.

Ask for a copy of the balance sheet for your records, some wont give it unless you ask, hell some wont even bother to tell you the bobweight if you dont ask.

Take a look at the attached balance sheet for when I build my current 360 small block.

I went the route of external balance but using the 360 specific B&M flexplate, no weights on the converter and additional balance weight on my Coyco dampner. The rod big & small ends were balanced to within 0.5g (heaviest to lightest), see below:

SMALL END BIG END OVERALL
226.20 513.60 740.00 Lightest
226.40 513.80 740.50 Heaviest

This is from a heavy piston/light rod 360 ext balance, middle ground of a 360 la/360 mag.

Never mind the side notes, I was just subbing numbers.

Most cookie cutter internal forged strokers have a 2150 target weight on the crank and end up slighty under (drilled).

This 318 ended up being just a bit lighter then a thin rod 69 oem 318 at oem 2147

This with lightened 318 rods and kb hypers ended up at 2098 internal.

You can figure alot at home with little effort and get a good general idea of where you will be and if you will need to take out or add metal.

Im doing a 318 now thats just a bit more then 1750 grams but ive got to put the crank in the lathe and cut some off the throws to make it workable.

Its all not that hard but im still amazed how much things can change if you move a little weight in a few key areas.