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Join Date: Jul 2006
Location: S. Florida
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Checking new piston and wristpin balance

Set up my old triple beam in my little kitchen today and I'm checking the weights of my new Mahle 3.3 turbo pistons and wristpins that were in the cylinders inside a sealed Mahle box when I bought the set 6 years ago. If there's any differences I'll shuffle around the wristpins to get them as close as possible and then get out the die grinder and make them all weigh the same down to 1/10 of a gram.

When you pull a new Mahle piston out of the cylinder it came in all the ring gaps are lined up in a row. I'll stagger them oil ring at 12 noon and the compression rings at 4 and 8 o clock when I install them back into the cylinders unless someone says there's a better position for them.
I numbered the pistons and cylinders so they'll go back together where they were inside the sealed box.

When I eventually get the rods out of the motor I'll balance all the rod caps to the same weight and then the rods all the same weight down to 1/10 of a gram with the caps installed.
I've done this before on old 4 and 6 cylinder SOHC BMW motors and they run and rev so smooth when you take the time to balance the reciprocating parts down to .1 gram.
I have ARP headstuds, 40mm aluminum injector blocks, and another set of turbo heads I ported matched the intake ports to 40mm last spring. I'll port match the flat intake manfold to 40mm when I remove it.

Meanwhile the car is still on the road and running great!


Old 02-13-2014, 10:55 AM
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I did the same exact thing when I built my motor.

I ended up not needing to do any grinding.

I Know you are semi local to me and If you'd like you are more than welcome to borrow my burret and stand if you want to cc your cylinder heads too.

Man your car looks amazing! I love those wheels and valance!
Old 02-13-2014, 11:24 AM
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Ohaus triple beam? Living in S Florida? Driving a gorgeous 930?

Is there something you're not telling us?



(just yanking your chain, Jim
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Old 02-13-2014, 12:54 PM
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Quote:
Originally Posted by WinRice View Post
Ohaus triple beam? Living in S Florida? Driving a gorgeous 930?

Is there something you're not telling us?



(just yanking your chain, Jim
S'funny...upon seeing the Ohaus triple beam scale, my first thought was: "Last time I saw one of those was when I was at college in Vermont, and we weren't weighing engine parts"

Carry on Jim...
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Old 02-13-2014, 01:01 PM
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And here I was thinking about weighing powder charges for my 300 Win. Mag...not drugs.

Hummm, I must be getting old.

Mark
Old 02-13-2014, 01:43 PM
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lol.. funny
Actually I bought the Ohaus scale back in '84 from a landlord/friend I rented a room from and when I worked as a dust buddy in the body shop at Gunnar Porsche Racing in the late eightee's it stayed in the engine assembly room for a while where it was used for weighing motor parts.
Kevin wanted to buy it from me but I didn't want to sell it and I've used it for weighing and balancing rods and pistons in my E21 chassis BMW 3.5 and BMW R90S motorcycle I bored out to 980CC among other things.

Anyway, the wristpins are all within .2 grams of each other and the pistons go from 479.4 to 483 grams with the rings on them so I guess I've got some grinding to do on the heavier ones. Not looking forward to that.

Old 02-13-2014, 01:57 PM
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