calling all racers

how close do the pistons need to be in regards to weight?is a 1 gram diff too much,1/10th gram?? for a kz street motor ,1327cc.

usually they are matched pretty close when you buy them as a setB)

I was told too weigh the pistons rod caps and rod bolts together. 1 Gram is fine. Never add weight. shave off lettering rough edges too get the desired weight. I plan on doing just that as soon as my bottom end is done. And i buy a gram scale.

Scott

on the 900-1000 motors the rods and crank are pressed together so you cant balance them that way.normally as long as the pistons are pretty close the 2 up-2 down setup of these motors does a good job of cancelling things out.

i think 1 tenth is best. less vibration. weigh the pistons with the pins in them

I dont think the balance needs to be that close, we do try to get it as close as possible, but when you look at the function of the engine..... how much more oil was on piston assembly 1 than was on assembly 3 at that cycle after all oil does add wieght to the rotating assembly and it changes everytime it rotates,
get them close, but I think you will find them from the factory to be fine, dress any sharpe edges, check the ring gap, and make sure the bore is round and has a good cross hatch pattern.

On any motor I rebuild I make sure every piston assembly is as close as possible. It only takes a few minutes and gives me peice of mind. With the bike I weighed the pistons, rings and pins after fitting the rings to the cylinders. On the kids Acura last summer it was the rods, bearings, pins, and rings and pistons. Granted that was a spendy motor and he wanted to spend the extra time on it, but he gets to rev it to 9K without a worry. :S

thanks guys. my 1135cc wiesco's were out 4.5 grams . i had a vibration below 3000rpm. the mtc 1327cc's were out 1 gram. i took a page out of my last builders book. he had added a 2nd oil hole in the piston for the wrist pins. so i drilled a 2nd hole in each pistons wrist pin boss and through to the oposite side of the pin whole till i got the pistons all the same weight. less than 1 10th gram dif.

mark1122 wrote:

thanks guys. my 1135cc wiesco's were out 4.5 grams . i had a vibration below 3000rpm. the mtc 1327cc's were out 1 gram. i took a page out of my last builders book. he had added a 2nd oil hole in the piston for the wrist pins. so i drilled a 2nd hole in each pistons wrist pin boss and through to the oposite side of the pin whole till i got the pistons all the same weight. less than 1 10th gram dif.

niceB)
ill be trying to get the JE's going into my 12r that close...extending the revlimiter is going to be tough on it, so i want it as smooth/balanced as possible:woohoo: