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CP Piston cracked

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I have a 250 that lost compression last week, and when disassembled I found a cracked piston, a 14;1 CP.  Is this common in the 14:1 compression ratio CP pistons?  Gotta know what to go back with that will last a while.  The rest of the motor is built, Carillo rod, polished crank, Exceldine valves, ported head, etc.  Any thought on what piston to go back with?

Edited by scoot450R

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Can you post a picture of where it cracked? How'd the plug look? Post a pic of the plug too. CP have worked well for me, very well in mod motors. How may hours were on it? And how many hours on the cylinder?

Edited by Eddie8v

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We use the CP pistons and it is not common for them to crack.  I have seen it when there is detonation. CP pistons are quality pistons and I don't think you will see any more life from a comparable piston from another manufacturer.

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Running VP mixed with pump gas. What should I be running with the set up listed in the OP. Can't post a pic right now I'm at the track. Didn't really look at the plug either. What are the signs of detonation? Thanks for the help.

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What VP fuel? Who remapped your ECU, or are you running the stock ECU for now?

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CP is typically at the top of the food chain with regard to quality.  I'm sure its possible to get a bad one every now and then.

We had a 10 250 with a CP 14:1 long rod setup come through the shop because of a cracked piston. 

I'm pretty sure the guy was running it on 93 pump fuel though.

One of our 450's cracked a CP,  OEM,  and Vertex, all in succession, before I figured out it was pulling coolant through a porous head.

Run time on the 3 was less than 5 hours. I was scratching my head till I figured out the head problem. 

Luckily none of them shattered.

 

The common thread in each, was something else was causing the pistons to fail.

I wouldn't hesitate to replace the piston with the same CP or even a 14.5:1.

Edited by nesc103y

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Does the ground strap on the plug look melted or have specks of aluminum on it? Specs of aluminum on the porcelain? Depending on how lean the tune up is and how much timing is in it I would suspect detonation. I'd put another 14:1cp in there and run straight vp fuel

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If he's running lean and detonating on a mix of 50/50 pump gas with oxygenated VP fuel he'll be even leaner by running straight oxygenated VP fuel. Problem needs to be diagnosed before a cure can be given.

Does the ground strap on the plug look melted or have specks of aluminum on it? Specs of aluminum on the porcelain? Depending on how lean the tune up is and how much timing is in it I would suspect detonation. I'd put another 14:1cp in there and run straight vp fuel
Edited by Eddie8v

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Yep if it's oxygenated that'd be the case. Piston quality of the cp should be a non issue i think

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Running VP mixed with pump gas. What should I be running with the set up listed in the OP. Can't post a pic right now I'm at the track. Didn't really look at the plug either. What are the signs of detonation? Thanks for the help.

Your question might be best answered by whoever built your motor.  He should know exactly what you have and what the fuel requirements are as well as how the ECU is mapped.

 

From what you have described, you have some really good components and I would suspect whoever built it did not contemplate running any fuel that contained pump fuel.

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I am not sure about the map. It has a Power Commander 5 on it and I don't really know what that even does. It does have a long rod and the fuel is VP MR pro 5. I don't understand the post about the ground strap. What is that?

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VP Pro 5, is it even sold by VP anymore?  Pro 6 I thought replaced pro 5 a couple years ago.  We run the pro 6 straight in my son's race bikes using the Carrillo long rod and CP piston.  Maybe the fuel is really old, it doesn't last forever.

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I'm sure it's pro 5, I'm looking at the can. The guy we bought the bike from was a pro that had a ride this year with BTO but he shattered his wrist . He may have had the gas sitting around for a while. Like I said we mix the VP with straight 93 pump 50/50. I guess that's maybe not a goo d thing for this motor. What is everyone referring to as detonation and what does that have to do with the plug. Are we referring to eat detonation? Thanks for all the help guys.

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Since you are running the Carrillo long rod, I assume you will have to run the CP piston that goes with the rod.  The pin is smaller and located differently in the piston than pistons for the standard rod.  I am not aware of another piston that would work with the Carrillo long rod.

 

From what you have described, odds are your issue is related to your fuel.  The Power Commander is a DynoJet product and depending upon what you have it may have auto tuning capabilities.  We use Vortex and have never been able to get any other ECU or tuner to work as well as the Vortex.

 

If you don't know how old the pro5 is or how long ago the can was opened, I would not use it in a race motor.  I would also quit using any pump fuel in any mod 250F.  If you don't like to cost of pro6 VP has less expensive fuels that will work well with a mod 250F but not be legal for AMA pro racing.

 

Is there anything on the motor to indicate who built it? 

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Detonation= pre-ignition. Caused by too much timing, too lean of a mixture, poor quality fuel, etc. The mixture ignites before the ignition fires and it causes terrible harmonics etc that can break stuff...

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Yes, the motor was built by a company in Florida called Lovingood motor works. I guess I'll call them Monday and get the scoop on this motor.

I actually opened the can of pro5.

What would be the cheaper alternatives of VP that I could use?

Thanks

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If you opened the can from new it was likely ok enough not to be the cause of your failure, imo. Do your checking and report back.

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