1978 Cr250 Help! Piston and rings

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12/13/2017 11:15 AM

Im recently in the middle of a rebuild on my 78 cr250 and was curious what piston and rings are recommended. The bore is still stock 70mm bore size and hasnt been sleeved but I was wanting to send the cylinder out to Millennium to get re plated. I know for the standard chrome bores in 78-80 they recommend to run CDM rings. I can only find a stock bore piston kit by wiseco that comes with the CDM rings. Would the CDM rings be ok to run in a plated cylinder after I get it back from Millennium? Or is there a better alternative? Are there standard rings I would be able to run since the bore has been plated. Im having trouble finding them if there is. If you guys have any info or suggestions it would be much appreciated.
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12/13/2017 1:47 PM

My understanding is that the ring restriction was limited to the original chrome plating, not the current nikasil plating (and that there is no issue with using original oem rings with nikasil). The plating companies often want you to provide the piston, or buy from them, so that they can tailor the bore (I believe issues with tolerances being different between cast and forged pistons). The gist is, I think, speak with your plating company about it to be sure what you get works with their product and service.

Would love others feedback on this as well; it's been about ten years since I vetted the issue on replating the 78-80 barrels

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Twitter: @ftemoto
Instagram: @mstusiak

12/13/2017 5:08 PM

When we did ours, we had it re-chromed as we wanted to stay original. I do recall a special set of rings for chrome cylinders only. I think Wiseco gives you an option.

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12/13/2017 5:10 PM
Edited Date/Time: 12/13/2017 5:10 PM

Is that not a photo of a 1979 CR250 and not a '78? As I recall the '79 offset exhaust port was the only year it was made. In '80 it had the split down tube and the exhaust went out straight and the '78 was a totally different machine.

Paw Paw

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12/13/2017 6:02 PM

Send the cylinder to Millenium and ask them to provide the proper piston and ring set for their work whether it be Wiseco or Wossner. And damn, those Wossner pistons sure look sweet.....just saying. Millenium has never failed to impress and I have had upwards of 20 cylinders done by them over the past 15 or so years.

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12/13/2017 6:04 PM

Paw Paw 271 wrote:

Is that not a photo of a 1979 CR250 and not a '78? As I recall the '79 offset exhaust port was the only year it was made. In '80 it had the split down tube and the exhaust went out straight and the '78 was a totally different machine.

Paw Paw

78 and 79 were nearly identical bikes. 1980 was the one year only center port, split down tube with the plastic fuel tank.

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12/14/2017 5:31 AM

newmann wrote:

Send the cylinder to Millenium and ask them to provide the proper piston and ring set for their work whether it be Wiseco or Wossner. And damn, those Wossner pistons sure look sweet.....just saying. Millenium has never failed to impress and I have had upwards of 20 cylinders done by them over the past 15 or so years.

+1 on Millenium. Just had my ‘02 CR cylinder done by them, couldn’t be happier. Fair price too. BTW, they pull the studs as part of the process, so if you are having trouble getting them out, have them do it.

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12/14/2017 5:33 AM

Hey Nathan, Newman knows what he's talking about. I'd order the piston through millenium.

Question for Newman, whether it be wiseco or wossner, do you normally drill lubrication holes for the exhaust bridge on your Elsinores?

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12/14/2017 7:27 AM

newmann wrote:

Send the cylinder to Millenium and ask them to provide the proper piston and ring set for their work whether it be Wiseco or Wossner. And damn, those Wossner pistons sure look sweet.....just saying. Millenium has never failed to impress and I have had upwards of 20 cylinders done by them over the past 15 or so years.

Thanks a lot Newman, that's what I'll end up doing. I really appreciate all the help

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12/14/2017 11:11 AM

Paw Paw 271 wrote:

Is that not a photo of a 1979 CR250 and not a '78? As I recall the '79 offset exhaust port was the only year it was made. In '80 it had the split down tube and the exhaust went out straight and the '78 was a totally different machine.

Paw Paw

newmann wrote:

78 and 79 were nearly identical bikes. 1980 was the one year only center port, split down tube with the plastic fuel tank.

Corrrect, Joe. Diff between 78 and 79 cylinders is the intake port (bridged on 79, humongus hole in the 78).

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Twitter: @ftemoto
Instagram: @mstusiak

12/14/2017 11:15 AM

SLOWTIME wrote:

Hey Nathan, Newman knows what he's talking about. I'd order the piston through millenium.

Question for Newman, whether it be wiseco or wossner, do you normally drill lubrication holes for the exhaust bridge on your Elsinores?

I understood this to be an issue with whether the piston is forged or cast. Here's the wiseco instructions for the 78-80 piston in the event anyone needs them.

http://www.ftemoto.com/othergalleries/VMX/Wiseco_Piston_Instr.pdf

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Twitter: @ftemoto
Instagram: @mstusiak

12/14/2017 12:36 PM

Wiseco offer the option of Chrome bore rings or Nikasil / Iron bore. You ask for them when ordering.

Wossner ONLY give you rings for Nikasil / Iron bore.

Wiseco include instructions for drilling the exhaust bridge lubrication holes (as posted above by FTE) Wossner don't include them.... which I always find weird!! As they need them drilled just the same as Wiseco! Forged pistons need to have them drilled. Cast pistons don't.

Stevie

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