CRF100 motor

[hiawassee1]

Well I have to take the blame for my sons motor running low on oil. Well it locked up while he was riding, and looking at having it rebuilt. Shop around here suggested both the top and bottom end. Also thinking about punching it out while I'm at it.
Also thought about trying to find a used motor, any ideas where I might be able to locate one? Or any good recommendations on where to have it rebuilt?

 

[1gr8bldr]

If the top end has held together, no broken parts having fallen down into the case, then buy a top end off ebay. Comes with the jug, piston, rigs, etc. And get it in the 125 they offer. Take the head off real easy so that if a ring is broken, that it does not fall into the case. As soon as you start raising it, slip a white rag under the jug, stuffing it in the holes and covering the case opening. Once off, inspect, see what damage was done. Check the rod axil play. Thats just moving it forward and back, not rotating, just seeing how loose it is. The CRF100 that I did 2 years ago had seized the piston pin on the piston and was not rotating. Those things are almost bomb proof so I don't expect much damage. You can feel the difference in that 125 head. Edit, $168 ebay

 

[1gr8bldr]

If the top end has held together, no broken parts having fallen down into the case, then buy a top end off ebay. Comes with the jug, piston, rigs, etc. Less than $200. And get it in the 125 they offer. Take the head off real easy so that if a ring is broken, that it does not fall into the case. As soon as you start raising it, slip a white rag under the jug, stuffing it in the holes and covering the case opening. Once off, inspect, see what damage was done. Check the rod axil play. Thats just moving it forward and back, not rotating, just seeing how loose it is. The CRF100 that I did 2 years ago had seized the piston pin on the piston and was not rotating. Those things are almost bomb proof so I don't expect much damage. You can feel the difference in that 125 head. It's real easy to do, as long as you don't have broken pieces missing..... meaning they are in the bottom end. Then, it may not be worth going after.

 

[rayjay]

Hopefully it's the later motor with the ball bearings on the camshaft. I used to refurb a LOT of XR80s and XR100s before 2003 and they had the cam riding directly on the alum of the cyl head. It was very common for the head to have to be replaced along with the cam, rockers, cam chain, both cam chain guides , both cam sprockets, etc.

In all the ones I refurbed plus all the parts machines I had I have never seen one that seized up. Mainly it was the cyl head issue above plus worn out rings, pistons and valves.