Hole In Piston...

nparks · Post by **nparks** » Sun Jul 20, 2008 6:41 pm

Anyone ever see this before?

Is this due to a cheaply made bore kit, lack of oil, or what?

This happened at full throttle at about 60mph.

tru72 · Post by **tru72** » Sun Jul 20, 2008 7:40 pm

lean.....
looks like a 49mm nickle seal bore.. if it is , those are pretty hard to destroy! haha
i just had one at my shop, but upon further inspection it looked liked it heat seized, then had a major cold seize. Looked like his gasket got sucked in by the boost port and created a lean situation at high speed.. You might want to pull that bore out to and inspect your block. this customers one has 1 hole on each side right by the rear stud holes . My guess is that there is a air pocket under the head studs, which created a weak spot especially if its sealed really good. Air expands and then cracks it open. but im not to sure....
by the looks of that piston, you might want to check the back of the bottom gasket too.. I can see some missing pieces on the piston..
Are you premixing? this customer was using his injector.. i told him many times before to put about 3 or 4 caps of oil into his gas for safety. but i know he didnt, that thing was pretty dry..
aloha
D

evilone · Post by **evilone** » Sun Jul 20, 2008 8:55 pm

Have you checked your compression? LOL! It may be low.

nparks · Post by **nparks** » Sun Jul 20, 2008 8:57 pm

evilone wrote:Have you checked your compression? LOL! It may be low.

haha yeah just a little bit

nparks · Post by **nparks** » Sun Jul 20, 2008 8:58 pm

Worst part is, I think that all of that metal is in the crank and even though I removed the piston the crank won't rotate freely it gets caught up on something.

Kenny_McCormic · Post by **Kenny_McCormic** » Sun Jul 20, 2008 9:21 pm

leaned out and melted.

justinnielsen01 · Post by **justinnielsen01** » Sun Jul 20, 2008 11:30 pm

http://cgi.ebay.com/ebaymotors/POLINI-7 ... 0244122251

tru72 · Post by **tru72** » Sun Jul 20, 2008 11:38 pm

yep now you have to split it and clean it out.. the lazy man way is to pour oil in it and let it drain out. Aluminum floats and wil run out, but if i was you, do it correctly and slip the cases.Nothing is worse that having a small piece of aluminum hiding in the seals. when you ride it the vacuum sucks it right out and score your bore!
aloha
D

nparks · Post by **nparks** » Sun Jul 20, 2008 11:45 pm

tru72 wrote:yep now you have to split it and clean it out.. the lazy man way is to pour oil in it and let it drain out. Aluminum floats and wil run out, but if i was you, do it correctly and slip the cases.Nothing is worse that having a small piece of aluminum hiding in the seals. when you ride it the vacuum sucks it right out and score your bore!
aloha
D

Yeah I plan on splitting the case tomorrow and cleaning it. Any suggestions? Carb cleaner and an air compressor should get all of the shards out right?

Kenny_McCormic · Post by **Kenny_McCormic** » Mon Jul 21, 2008 12:58 am

Power washer.

tru72 · Post by **tru72** » Mon Jul 21, 2008 2:53 am

yeah thats fine..
make sure you check behind the seals, they have a spring type clip that can be taken out if careful.

keithw · Post by **keithw** » Mon Jul 21, 2008 9:14 am

Back in the old days this was pretty common in the dirt bike world. A friend of mine would TIG weld the hole to repair the piston. Worked well and made him a few bucks. For maximum power you want to be as lean as you can get without this happening. The problem is that with a small change in temperature, altitude, humidity or even riding style you go from just right to too lean. Anyone who was serious about riding kept a spair piston and cylinder and was good at swapping them.

Concidering the trouble I'm having finding the pistons I want, I'm going to stay just a bit on the rich side and play it safe.

keithw