low compression, new piston only? - Aprilia Forum: Aprilia Motorcycle Forums
Aprilia RS Forum: RS50, RS125, RS250 Discussion of the Aprilia RS50, RS125 and RS250 motorcycles.

 
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post #1 of 2 (permalink) Old 07-25-2015, 06:34 PM Thread Starter
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Default low compression, new piston only?

my af1 125 is reading about 110PSI on a compression test. So i figure its time for a new piston.

My question is, do i just order the same size piston as is in there or do i order one that is one step bigger?

Also , in the dirtbike scene there is an endless discussion on whether or not to hone a nicasil cylinder when changing pistons.

Some say you need to ballhone it, others say that nicasil is so hard that honing wont do any good and the piston rings dont settle like the way they do in steel cilinders.

What are your opinions about this?

Lastly , has anyone got any experience with using ROTAX MAX pistons in a rs125 instead of wiseco or wossner or the likes? this being single ring pistons, how long would they last in a rs125?

regards,

Sander
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post #2 of 2 (permalink) Old 10-01-2015, 02:34 AM
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Firstly, 110 PSI isn't that bad for a ROTAX engine. I had a similar problem and fixed it by initially cleaning the cylinder walls and then retrofitting it with the pièces détachées moto - a new piston of the same size and new rings. It would be better if you could first dismantle the top-end and inspect the cylinder. A bit of cleaning around the cylinder walls can help to determine whether the cylinder is serviceable or not.
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