Removing metal from Piston crowns.

TVRleigh · Post by **TVRleigh** » Thu May 22, 2008 10:58 am

How think are they and how much is it safe to remove.

Thanks
Leigh

Post by **katanaman** » Thu May 22, 2008 3:07 pm

Are you on about the crowns or the bowls? you are limited on the crowns by the amount left above the top ring. Take too much off here and your ring will break out the top of the piston. No idea what's safe to be honest but I don't think it would be very much. If this is to shave the pistons as per your other post to reduce compression then I would have to do the calcs but I don't think you would get much as its not that large an area so quite a lot would need removed. Your other problem would be you would screw up the balance so an engine balance would be needed.

TVRleigh · Post by **TVRleigh** » Thu May 22, 2008 3:10 pm

No this is metal to be remove from the inside to get all the pistons the same weight.

Post by **katanaman** » Thu May 22, 2008 4:07 pm

Ah sorry put 2 and 2 together and got 6 lol. All the pistons I have seen done have had the bottom of the small end lightly drilled, kinda like dimples. You should never really have to remove much to balance pistons.

TVRleigh · Post by **TVRleigh** » Thu May 22, 2008 4:30 pm

some of mine have had upto 2mm valley cut under the small end.

but seemed a bit excessive.

see pic

mgbv8 · Post by **mgbv8** » Thu May 22, 2008 6:43 pm

I wouldnt mess around with taking any metal from the crown area if you want good reliable power from TVR pistons. I assume you have cast pistons with valve cutouts?

The cutouts make them weak enough as I just found to my displeasure. They may be ok for NASP use, but they cant handle the cylinder pressures on gas.

No prob with taking some metal from the skirts as per pics though. You can even skim a bit from the inside as well.

Boosted LS1 · Post by **Boosted LS1** » Thu May 22, 2008 9:46 pm

Take some weight from the ends of the pins if you can. Also, I'd remove weight from the flat pad area under the pins and from the inside of the skirts. How much variation in weight have you got and what are you weighing them on? I use scales accurate to 1/10th gram, kitchen scales are no good.

TVRleigh · Post by **TVRleigh** » Fri May 23, 2008 10:37 am

Boosted LS1 wrote:Take some weight from the ends of the pins if you can. Also, I'd remove weight from the flat pad area under the pins and from the inside of the skirts. How much variation in weight have you got and what are you weighing them on? I use scales accurate to 1/10th gram, kitchen scales are no good.

The scales I have measure in 0.1g's accurate to 0.2g

I think there was 2g difference from lightest to heaviest.

But the work shown was done by the balance company. but look a bit extreme. as some was upto 2mm.

I don't have cut outs and will not be running NOS but by run a supercharger next year.