Hole in top of left piston

[Bansheexpx]

Hey guys, I took my banshee out to the dunes the other day and was runnin WOT when my shee lost power. Pretty much knew it was a hole in the piston from the way it felt, but am not sure what caused it. I have used our search function and it mentions detonation, pre-ignition, lean mixture, etc. My left piston has a hole in the top, with no other damage on the skirts or cylinder walls. Since there was no det sounds, I'm leaning toward pre-ignition. Could my timing be slightly to far advanced (stock cut plate)? My shee has a coolhead, timing plate mod, fmf sst pipes, vitos power pistons, run with 40:1 mix using prem gas and HC1, compression 140, jetting at 330 main, 27.5 pilot, A/S at 1.5 turns out. Please if you have any ideas, I originally thought it was a crankseal leak causing a lean condition, but after reading my piston doesn't look like those, just a hole in the top.

[Bansheexpx]

Also, if I change to wisecos, will I need to buy different domes due to increased compression over the vito powers?

[midlifecrisis]

That sounds to me like an air leak, have you done a leak down test? If no damage was done to the domes, dont change them, but check the seal on the head if its a 2 pc.

[sleeper06]

x2 on air leak one thing everyone forgets when they blow shit up is too pressure test it before you tear into it,now your guessing at what it was and it could have been narrowed down

[252wheelieking]

x2 on air leak one thing everyone forgets when they blow shit up is too pressure test it before you tear into it,now your guessing at what it was and it could have been narrowed down

 

Im having a similar problem with my banshee....where can I buy a leak down tester before I blow mines up.

[TIM LUTZ]

Post a picture of the piston. Where the hole is can tell a lot. Is the piston dished at all?

What plugs are you running? Could the plug on that side have come loose? Mt guess would be an intake air leak on that side, loose plug or too hot heat range on that plug.

[Spidy]

Im having a similar problem with my banshee....where can I buy a leak down tester before I blow mines up.

 

 

If you build one yourself, it's a lot cheaper! Here is a link on how to do it.

Leak Down Tester

 

Good luck!

Edited December 8, 2010 by Spidy

[thrill-billy85]

Im having a similar problem with my banshee....where can I buy a leak down tester before I blow mines up.

 

i make and sell leak down testers for $40 shipped. PM me.

[Bansheexpx]

So I was under the impression if it was an air leak, that would cause a lean condition and my pistons would have siezed or at a minimum had heavy wear marks on the side of the pistons and walls. I was also under the impression that if it had a hole in the top of the piston it was either det or pre-ign. Can someone explain further? Thanks for all of your quick replies!

 

Jon

[hercalmighty]

An air leak can cause a hole in the piston.

This was from cracked air boots

 

 

 

[Bansheexpx]

Here are a couple pictures of my piston while its still in the bike..I looked through the exhaust and intake with a flashlight and so far the piston skirt and cyclinder walls look great, just the hole in the piston.

 

What can you guys tell me? The hole is on the exhaust port side.

 

Heres what my coolhead looked like also.

[Bansheexpx]

K guys, here are some more pics of the problem..let me know what you think, I should be getting new pistons and top end kit today or tomorrow.