Don Terrill’s Speed-Talk

Pete1 wrote: ↑Tue Oct 08, 2019 9:35 pm Get the lighter pins. The rest can be easily taken out of the pistons.You will need a mill for that.
If you can hit the old weight within 5 grams, (10 on bob weight) it will run with no problem.

Knight rider wrote: ↑Tue Oct 08, 2019 6:42 pm No sending them back I've already had .070" machined off the top as I said the H rods that I have don't suit any OTS piston for a 393 stroker Cleveland so I'm using 408 pistons mqchined to suit

I thought the Bob weight was at 50% so it's one pistons weight not two but I'm not sure

Knight rider wrote: ↑Tue Oct 08, 2019 4:27 pm Hi this is my first post in here, I'm after some advise as on whether I can run with a piston and pin combo what is some 73g heavier without rebalancing the engine.
The engine is. 393 clevo street car that sees the drags sometimes with a max rpm of 6800.

I have spoken to the guy that did the balancing before as he has all the weights and measurements. He said the Bob weight would be 5% different and to get it back would need to add Malloy to the crank. Now I only pulled the engine to do some porting head work and put new rings in at the same time but the stroker kit I used was a procomp one which don't use Cleveland pistons so valve reliefs aren't right so decided to change the pistons as well while I was at it, sounds easy well the rods are H rods but procomp used 6.1250 rods with std Cleveland journals sides so I ended up using 408 pistons and had them machine to the correct comp height.

I really don't want to pull the crank and have it balanced again at a cost of 500-600 bucks. All the pistons are within a 1 or 2g of each other. The only other thing I could do is run lighter pins but that would only save 20g

Now the easy answer is balance it but I'm not sure it will make any difference

Love the site by the way and feel free to tell me I'm being dumb wouldn't be the first time

Pete1 wrote: ↑Tue Oct 08, 2019 10:52 pm "5 + 5 = 10 grams. 50% of weight for reciprocating is 5 grams."

Roger on that. After 4 martoonies, thingz get off a bit.

For vintage circle track engines, we go for as light a bob weight as we can get. I have taken more than that off of forged pistons many times.
From just looking at the picture, I would say it was quite possible.

BillK wrote: ↑Tue Oct 08, 2019 9:27 pm

Knight rider wrote: ↑Tue Oct 08, 2019 9:10 pm

Looking at the crank there are some pretty big drilling in the CW the one at the rear is about 1"x4" deep and the web has also had a chunk cut off it and the front one has three holes about 3/4"x4" deep

Those are some deeeeeep holes ? Is the counterweight actually that big ? 1" x 4" is 400 grams That crank must have been designed for a pretty heavy bobweight to begin with. Your guy might be able to make a couple of slugs of steel and press them in to the existing holes and weld them. He might have to do it that way if there is not a good spot to add heavy metal. I have done a few like that over the years but dont really like it. Sometimes you dont have a choice. I have never had one come loose but that thought is always in the back of your mind.