Vintage Dirt Bike Q & A

I am ready to reassemble motor on my 79 cr250 I ordered Wiseco top end there are 2 rings available cd & cdm for chrome bore this cylinder had 70mm piston in it but there was head damage from motor failure at some point before I got bike. My question is what rings to use as the cylinder walls are good so it must have been replated or replaced ? I read not to use the cdm rings on nikasil cylinder how do I determine whether this is a chrome or nikasil cylinder

Home remedy - you can tell an iron liner from a chrome bore with a magnet. Take a small magnet and slide it carefully along the bore. If it sticks, it's iron. Or you can take it to your local shop and they can tell you what it is.

_________________
osu_cowboy

the cylinder has not been sleeved will a magnet stick to either chrome or nikasil ?

no.

_________________
80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

I believe the Wiseco's come standard with a chrome ring that is not to be used with the chrome bore; you need the other ring for the orginal chrome bore.

The bikes came stock with chrome bores. It would have to have been replated if it was nikasiled. It's highly probable that any worn cylinder that hasn't had a steel sleeve put in is chrome. If the piston that came out is an oem one as well, that would make it even more probable it's the stock chrome bore.

My understanding is that if you have them nikasiled, it doesn't matter which of the ring types you use. The replating services allow you to use aftermarket or NOS oem kits, they just want to know which because the tolerances are different. I think the rub for your case, then, is that whether it's chrome or nikasiled, you can use the ring designated for the chrome bore.

If you know that it has been replated, then you will know it's not a chrome bore. Nikasiling is better and I don't think anyone does replates in chrome. Certainly it wouldn't be customary.

I don't know how to tell the difference because I've never seen a worn original chrome bore side by side with a worn nikasiled bore. The NOS chrome bores that I've seen look more silver than the nikasils I've seen. You might shoot Millienium Techologies, one of the better replating services, an email and see if they have any input.