Top end advice 79 CR 250

The bottom end of my 79 CR 250 project is all back together with a new rod..now to the top end.. the piston that I took out had 69.68 stamped on it which should be the 1st over?..the bore after cleaning it up is at 69.69 with no apparent taper and one remaining troublesome light scratch...so from what I understand I have two choices...bore it to the size of an available piston or if possible have the cylinder nicasil plated. Powerseal in PA will bore and plate it to what ever size needed....Any pros/cons or experience with plating on a vintage bike you would like to share?

Now to piston choice...looking for opinions and availability of pistons...wiseco does seem to be more available...wossner next, mahle not..
Wiseco or Wossner?....and with either or both what is the recommended clearance...I see debates on manufacturers clearance recommendations for the big bores but not as much for the 250s....

As usual your advice is greatly appreciated...

thanks
bob

Either one will probably have you set for a long time, but I am sure you could also find a new liner somewhere.

check phil at husqvarnaparts, contact him as he has lots of stuff off the web page

I was told that Nikasil is not suitable on steel or iron liners. I had asked about having my 390WR cylinder plated as it is loose on a 3rd over piston.

just got a wossner 69.95mm piston...will have the jug bored to fit the piston...

Nikasil works fine over iron. For a while 360 pistons were not available, Forest Stahl's solution was to use the STD 390 piston (2.0mm over 360 STD) and Nikasil the liner.

That's good to know. I am about to assemble the lower end of the 390WR. I would love to have the liner Nikasil coated and finish honed to fit a 3rd over Wossner. Who do you know that can do the plating and honing?

Try contacting Powerseal. I sent my cylinder to them for just a bore. They did a good job and quick turnaround. I didn’t have my cylinder plated, but it is one of their services.

Anyone who does Nikasil on modern cylinders should be able to do it on an iron liner but the two I have used are Lancourt (who pioneered Nikasil on iron liners) and Millennium. Lancourt does all of the warranty plating for Yamaha, but I have heard people having bad service from them. Millennium is also where Eric Gore works through, so they have a lot of experience with vintage cylinders.

I never used Millennium Technologies directly... had plating work done through Eric Gorr (on aluminum cylinder) and what came back was first class.

He mentions plating cast iron sleeves on his website. http://www.eric-gorr.com/index.php/services/vintage-mx/services/vintage-mx

Powerseal does plate cast cylinders.....they were not sure if they could take it back to the stock bore with Nicksil so instead of spending the extra $ for the plating i'm just having them bore it to 70mm/fit the piston

A few dumb questions...I got the jug back from Powerseal and am ready to put everything back together...the manual has a limit for ring gap but nothing for the initial spec..i know Wiseco recommends .005 per inch of bore but the piston is a single ring Wossner..would it be the same since they are both forged?..base gasket, is is recommend to be dry or a light coat of grease? Now for the real dumb question which way does the head go back on..is the "bulge" on the mating surface to the right, left or doesn't it matter?
thanks
bob

Do you know that a castiron cylinder when it’s glazed is harder than chrome or nikasil? There’s a reason why all disc brake discs are castiron. The only reason nikasil is done because of the heat transfer with the LQ cooling. I’m not sure how much it improves a air cooled engine.

I believe the rule of thumb on the ring gap is .004” per inch. A forged piston has nothing to do with ring gap.

As far as a base gasket install dry. Make sure you lap the head into the cylinder before you wash it for assembly. Don’t forget about doing a leak down test on a newly assembled engine. Make sure you torque the head bolts and retorque after running.

Head position if the sparkplug is in the middle it doesn’t matter. If the sparkplug is offset it leans towards the right side.

Your statement about disk brakes is a bit misguided on a bike forum where they are all stainless steel

so thats the reason disc brakes are all cast iron? because when it glazes its harder than nikasil? you know we have usually post jokes in the "kellys ongoing goofy thread" or even general discussion..

theres quite a few reasons for nikasil or like coatings..do you have the punchline for that one?

Hey Bob, going to the York swapmeet? Just keep the finned side up. Unless the fins taper. And BB Hahahahaha

Yes I understand the bik discs are stainless. We tested newly developed disc brakes on a dynamometer. One disc brake mechanical caliper was stopping 9,000 lbs of force. Two calipers was 18,000 lbs of force. We changed from a steel disc to a castiron disc and the stopping power increased. The material on the pads and the increased stopping power of the castiron disc were the higher ratings. All through the testing the castiron disc showed no wear at all.

The liquid cooled cylinder allows better cooling through the nikasil over a castiron sleeve. The castiron sleeve is a barrier that tends to hold the heat in more. Two different metals. I hope I said it right.

Who is WE? What is a "Dynomometer"? an instrument that measures the power output of an engine,? Has to do with brake rotors how? What does this have to do with Squids post? Hahahahah

Squid, good thing you went the simple original route. I wish you many happy hours building and riding your husky.

As for nikasil rebuilds, its a bag of ravenous rats on its own. Very sound reason why Porsche and BMW stopped using it in production 20yrs ago.
If you want to play with it go to the Porsche fundis, a class, applicatio and cost way beyond a/c vintage bikes.

If it's any use I always replace the head with the bulge to the left. Don't know why, probably because the first Husky I had was assembled that way.
Nikasil has it's place (if you have the money). All my bikes (apart from the new CCM I am building) still have their original cast iron liners. The original 1973 CCM is still going strong !