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392 built banshee problems please read

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OK everyone I have a 01 banshee it has  (topend) Athena 392 bigbore (68mm 13-degree pistons) (ported/polished) it has a Vito's hemi head 4 (22cc domes) it has vforce3 reeds it has the Trinity stage 4 single carb kit it has full fmf SST exhaust (bottom end) has hot rods crank has Ricky stator billet timing plate it has Barnett dirt digger Kevlar clutch with extra heavy duty spring it has billet water pump impeller and all new gaskets,bearins,seals in bottomend. Well well when I got it it had slow oil leak I bought a new bottom part of the block and took it to mechanic and he did it all for me when I sent it to me it only had the bigbore kit and it still had Athena cylinder head with (24cc domes) well he finished it I put the motor on the bike and I started it and it had no power what so ever like it had a blown head gasket or only running on one cylinder well I took the top end off and the skirts were busted off the piston on the intake side but there were no pieces in bottom end,exhaust,or air filter and no metal shavings either well that's when I did all the upgrading ordered new pistons and all the new mods well I got it running and during break in on the first start after the new mods I was going back and fourth down the road in first gear only going to quarter throttle then when It told me to start hitting half throttle I hit half throttle 1 time and when it hit the rpms of half throttle it popped really loud in top end and shut off completely and wouldn't start back up so I took the top end off and the pistons were busted the same way as the first ones but no scars or scratches in cylinders and the domes where perfect and there was no chunks or shavings anywhere in the entire motor not in the bottom end or topend.  What can be causing this to bust pistons like that please help comment what y'all think thank you for your time.!!

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When piston skirts break off, that usually indicates an overly loose bore...

 

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6 hours ago, NYMXer said:

When piston skirts break off, that usually indicates an overly loose bore...

 

I had the pistons fitted perfect in the cylinders

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49 minutes ago, Robert Shaffer said:

I had the pistons fitted perfect in the cylinders

what does that mean? how did you make sure they were "fitted perfectly"?

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On 6/13/2017 at 0:52 AM, 91kdx25088 said:

what does that mean? how did you make sure they were "fitted perfectly"?

I am wondering the same thing. Did he have the cylinder bored to new pistons? Did he at least use feeler gauges to verify the clearance? The more I think about this, the more I think the bore is too loose.

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16 minutes ago, NYMXer said:

I am wondering the same thing. Did he have the cylinder bored to new pistons? Did he at least use feeler gauges to verify the clearance? The more I think about this, the more I think the bore is too loose.

using a feeler gauge of any type is completely the wrong way to measure piston to cylinder. using feeler gauges is as good as looking at it.

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18 hours ago, 91kdx25088 said:

using a feeler gauge of any type is completely the wrong way to measure piston to cylinder. using feeler gauges is as good as looking at it.

Not everyone has access to a dial bore gauge and micrometers, or can do the simple subtraction between the two. I offered "feeler gauges" as a minimum, not preferred. They are better than just "looking" at the piston and cylinder to check fit and wear.

Like you, I was wondering exactly how he determined "fitted perfectly", it was an odd choice of words.

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There's a lot that can go wrong. If your blowing off skirts, that is chatter. So you need to figure out why.
Athena cylinders are junk to begin with. Just because you have a 68mm cylinder doesn't mean a 68mm piston will be fine.
Any good shop will have a few on hand and measure a few to match the cylinder. The guys that I have used always sent me back pistons marked L and R.
Are you using cast or forged piston?
You need the bore set up for the one you're going to run. They have different clearances.

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