field bike

[lew]

ok i have just took the piston out of my rsx 100 field bike and it was so messed up it was running on 1 ring and had a crack on the top of the piston! So i am ordering a new piston kit how long will i have to drive slow till its run in cheers lewis

[mchaggis]

A few hundred miles, slowly increasing the rpm and engine load to do it (almost) properly on a small bike.
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[chris-red]

according to my rxs owners manual for a new engine,

0~300miles
avoid operation over 4,000 rpm and let it cool for 10 mins after ever hour of operation, very the speed, do not use full throtle.

300~600miles
avoid operation over 5,000 rpm, do not use full throtle.
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[stinkwheel]

Just replacing the piston and rings without a rebore?

I would hone the barrel then take it easy for 100 miles or so, maybe bump up the oil feed rate too (or just bung a little oil in the tank for the first couple of tanks) then ride as normal.

You shouldn't need to do a 'full' running in cycle because the bore is already be run in and cured. The honing should have done its job on the rings by 100 miles I would expect.

Might be an idea to replace the small end bearing while you are in there though, if the piston is that shot, the bearing could have taken a hammering and it is no extra effort to replace it.
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[lew]

ok cheers i am ordering the piston kit today so how can i tell what size piston to order,do i measure the old piston somehow?to check it hasn,t been rebored?

[stinkwheel]

Tricky. Sometimes the piston crown is marked with A, B, C or +0,7 or something. With the state your is in, it may be impossible to tell.

When you get your rings, you can slide one down into the bore absolutely square (using the piston is a good way) then measure the gap at the end of it with a feeler guage. There will be a tolerance for how big this gap can be in your workshop manual.

I know of no other way of doing it without either having the rings in your hand or using some very expensive measuring equipment. Maybe someone else has a dodge?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.