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Old 08-03-2006, 01:57 AM   #1
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Default Question Regarding OS 12 TR Rebuild

Hi Guys,

I have a question for you guys out there who have rebuilt a OS 12 TR-R spec or have put the R spec Piston/Liner in the standard TR.

Basically, it appears that you can only buy the TR-R spec Piston?Liner now and this is a direct replacement for the original crankcase. Thats all fine and fits together well.

MY QUESTION IS.....

The TR-R spec piston has a cutout of the skirt on one side (or I guess you could call it an indent, should this cutout point towards the exhaust port or towards the carb side of the engine?

OS support told me it should point toward the exhaust side as the skirt indent is there to clear the backplate, but the piston clears the backplate either way you put it in.

One thing I noticed though is with the indented skirt facing the exhaust port, the exhaust port is open UNDER the piston at TDC at the same time that the intake is open in the crankshaft....is this all normal?

Any info would be much appreciated

Ta

Steve
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Old 08-03-2006, 08:12 AM   #2
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the indent side of the piston faces the carb
i have one of these r spec tr engines myself

they are small track killers!!
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Old 08-03-2006, 08:30 AM   #3
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mrgsr is correct. The indent is not made to clear the backplate, it is made to clear the crank shaft at bdc. It is a keeper of an engine for local club racing.
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Old 08-03-2006, 09:56 AM   #4
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The indent side of the piston faces the carb for good fuel/air flow to the front intake port at BDC.
If the indent is reversed facing exhaust then you might block the fuel/air going to front intake port at BDC.

Last edited by FREELANCE_RCer; 08-03-2006 at 10:26 AM.
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Old 08-03-2006, 06:24 PM   #5
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Thanks Guys,

It didn't make sense to me the other way....but you think OS Engines Tech support would have a bit of a clue don't you!!

Well, looks like it's coming out and being redone...again!

Thanks for the replies

Steve
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