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Old 09-14-2011, 07:45 AM   #1
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Default Piston Scratched - Exhaust side

Hi,

When pistons have scratch marks on them, its usually on the exhaust side. Why is this so?

I just had a race last weekend, my nova flash PT siezed. I thought the rod broke. But when I took the engine apart, the whole exhaust side of the piston was badly scratched. Why?

Sam
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Old 09-14-2011, 08:43 AM   #2
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Pictures would greatly help.
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Old 09-14-2011, 09:02 AM   #3
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Quote:
Originally Posted by sammies View Post
Hi,

When pistons have scratch marks on them, its usually on the exhaust side. Why is this so?

I just had a race last weekend, my nova flash PT siezed. I thought the rod broke. But when I took the engine apart, the whole exhaust side of the piston was badly scratched. Why?

Sam
Normally its from the engine not being fully broken in or not giving the engine enough time to warm up. Also lack of oil in the fuel.
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Old 09-14-2011, 10:36 AM   #4
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It is the hottest side of the piston so the material will expand more at that side. In a simple way the piston will shape as an egg rounding and so the it will run a bit tighter at that side.

Indeed a good rinning-in proces and a good warming up or pre-heating will prevent scratches.
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Old 09-15-2011, 08:10 AM   #5
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Thank you to all for your inputs and comments. Another expensive lesson for me.

Engine had at least 10 liters thru it before this happened. Fuel used was O'donnel speed blend. Below are the pictures of the aftermath Any other insights or thoughts most welcome.



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Old 09-15-2011, 08:36 AM   #6
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Ah, a Novarossi. This problem was a hot issue 2 years ago with the Flash with the Microcasted piston (also seen with 35-plus models and even a JP P7L) ans some .12 models.
The Flash did get a follow up model called the Flash Special with a CNC piston.

That is why Novarossi has made some kind of transfer ports comming out just under the exhaust port, fresh fuel will splash against the piston cooling it down.
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Old 09-15-2011, 05:41 PM   #7
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Quote:
Originally Posted by Roelof View Post
Ah, a Novarossi. This problem was a hot issue 2 years ago with the Flash with the Microcasted piston (also seen with 35-plus models and even a JP P7L) ans some .12 models.
The Flash did get a follow up model called the Flash Special with a CNC piston.

That is why Novarossi has made some kind of transfer ports comming out just under the exhaust port, fresh fuel will splash against the piston cooling it down.
Hmmmmmm...so this problem should have been taken care of in my 2011 flash PT? engine warm up started 2 mins before final...plus 3 mins of warmup on track..engine would have been sufficiently up to temps by the start..problem occurred in the 4th lap..
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Old 09-16-2011, 12:42 AM   #8
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An engine maker here in Holland thinks a pinch (hot piston and cold sleeve during warming up) in combination with current race fuels with a low amount of oil could create a short time cold weld and due the rotation forces again tear it appart damaging the surface.

The PT should have a black coated piston or hasn't it? That coating should give a lower friction.....
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Old 09-16-2011, 01:47 AM   #9
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Quote:
Originally Posted by Roelof View Post
An engine maker here in Holland thinks a pinch (hot piston and cold sleeve during warming up) in combination with current race fuels with a low amount of oil could create a short time cold weld and due the rotation forces again tear it appart damaging the surface.

The PT should have a black coated piston or hasn't it? That coating should give a lower friction.....
Yes.. the piston HAD a black coating.. but that coating is almost completely gone on the exhaust side of the piston.

Well.. I will be extra careful and take special note of warm up process in the future. Just ordered a p/s/r set for the PT and will see how it goes.

Thanks Roelof for taking the time to share your insights. Appreciate it.

Happy racing.

Sam
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Old 09-16-2011, 03:01 AM   #10
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While it is damaged already you can give it a try to smoothen the piston with a fine waterproof sandpaper, be sure you do not touch the upper side of the piston arround the rings and give it a try. I have done this with 2 engines and they were able to run on.

And for the future it is wise to get an engine heater like the new RB, competition heat or other devices you can click on.
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Old 10-10-2011, 07:54 PM   #11
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had the same thing happen to my jp 6 months ago - spent a gallon breaking in the engine with maxy's and had no problem, but during a race in which a I ran out of fuel, I purchased Vp power master fuel and after approximately 5 tanks of running this fuel, the piston seized with those same marks on the exhaust side people suggested that it was the fuel
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Old 10-10-2011, 11:10 PM   #12
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Friend of mine always suggested to use fuel with caster oil instead of synthetic lubricant, the carbon formed on the piston surface minimizes this.
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Old 10-11-2011, 10:44 AM   #13
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The scratches come from the engine not being broken in all the way.
If you do not run at least a gallon threw the engine this can happen.
I had the scratch issue 6 years ago when the plus 35 first came out.
Started break in my engines longer and the problem went away.

I have not had that problem in the last 15 engines I've bought since.
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Old 10-11-2011, 11:00 AM   #14
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Castor definitely helps, especially with low castor fuels like the OD speed blend and 9% Byrons.
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Old 10-11-2011, 04:42 PM   #15
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Would a bad exhaust manifold gasket cause this too? Overheating due to leak?
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