Hey guys

I picked up a busted bottom end up on the weekend from nxrsr20. Thanks Rob

I have since pulled the engine apart to check the condition. It had a major blow up since it was running with no coolant for a period of time. (Unsure of what actually happened)
Now that I have it apart I can see the skirt of one piston broke off and went through the bottom end.
My main questions for you tech guys are

1. looking at the photos I have attached. Does it look as though the crank case has small cracks or are they casting marks? (I'm assuming this is where the skirt got jammed through when it was spinning)
2. Does the centre web of the crank cases have a service limit. It looks as though the piston skirt has rubbed on one side of the web. however the surface of the crank looks to be in good condition.
3. Where the cylinders attach to the crank case the surface has pitted in a couple of locations. (where the coolant passages meet) Can the crank cases be machined (decked)? and the difference in height made up with a thicker base gasket?
4. Overall is it able to be rebuilt. the outer crank bearings are pretty noisy but the centre bearing feels good. Obviously the crank will need all new bearings and seals as there is metal particles everywhere.

Anyway any help will be greatly appreciated.
Thanks alot
Scott

more pics attached
Thanks

Hi Scott
Now the VERY last thing I want to do is to pretend that I am an expert, but expertise more often than not comes from experience....!
So with that in mind here is my sixpence worth based on 'my' experiences.

The crank cases on the MC21's motors (I have 2) are pretty frightening to look at first for time. They appear to have loads of little 'hair-line' cracks all over in the crank area. Yours doesn't look any different to mine.
It has to be a pretty big BANG to do any serous case damage...i.e..rod letting go and seeking the outside world. In a battle between alloy and steel, steel is usually the winner!
Carefully clean the 'outside' of the crankcase and check for any damage there. I feel sure that you will be okay but check VERY carefully using an eyeglass if possible.

The crank, in my paranoid opinion, is a different kettle of fish though. Have it rebuilt with new bearings and seals. Don't take a chance if you intend to keep the motor.

As I said these are just my opinions based on my own experience which is based on several years of two stroke engine building..... BUT not much with NSR's. I'm learning all the time though.

Mike
_________________
I don't mind dying...I just don't want to be there when it happens!

Hey Mike thanks for the reply.
Yeah I was thinking those marks are just the casting marks. There are definitely some scraping marks from where the skirt got chewed up but I don't think it would ultimately hurt the engine once its all cleaned up. Ill make sure I clean everything up and check the cases inside and out. I will be getting the crank rebuilt for sure.
Any ideas on getting the Cases Decked to clean up the pitting?
I'm assuming there are different thickness base gaskets available to adjust the squish.

Thanks again.
Scott

If the pitting is minor then a sheet of 10-15mm glass with some fine abrasive paper would be my first thought but I am sure that there will be other more experienced (better) answers.

Mike
_________________
I don't mind dying...I just don't want to be there when it happens!