I am putting together an NSR 250 and I have a few questions about the exhaust valve.
- when I install the cast (iron??) exhaust valve into the exhaust port they recess as they should into the recesses in the top of the port. When I install the square shaft that opperates the valve(s), they seem to bind up some and one cylinder then doesn't recess beyond the timing edge of the exhaust port. Can I grind a portion of the valve away or is it coated/treated in some way that I will compromise it? I have been working with the cylinder/exhaust valve assemblies dry/no oil up to now. Perhaps it will get better when lubed? What lube is proper for the exhaust valve?
I should mention that the cylinders have recently been re-nic-a-silled.
Mark
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Probably carbon build up in there somewhere.
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it wouldn't be fun if it was easy!

I would not grind the valve, instead look for the reason why the valve shaft if binding and fix that. The actual problem could lead to additional problems with binding valves, that could lead to overloaded servo motor, leading to fried PGM's down the road.

Thank you for your response. The cylinders are just back from Millinium Ent for nicasil. Brand new shiny and I have bead blasted the RC valves (4) to clean the carbon off. I am suspicious that some of the nicasil plating has changed the clearence within the RC valve recessed area in the top of the exhaust port... I can't feel any bumps or irregularities (as you sometimes do after re-plating) in the recess area but, it clearly has some sort of problem. I agree that putting it together would jepordise the servo and pgmIII. I suppose I am going to have to come across a right-angle grinder with a sanding roll and create some clearece in the RC valve recessed area...

do the valves sit cleanly in the recessed areas without the shaft in place? get a dental mirror and bendy-light to inspect the areas to make sure there is no carbon down there before grinding away.

The valves do sit in the recessed area without the square shaft installed. The cylinders are Brand new shiny, just back from Millinium Ent for nicasil.
I have bead blasted the RC valves (4) to clean the carbon off. I'm suspicious that some of the nicasil plating has changed the clearence within the RC valve recessed area in the top of the exhaust port. There is absolutely no carbon, oil, or anything in or on these cylinders. I might be able to post a picture if it would help.
Mark

what about the shaft? Is it straight/clean/worn?

The square shaft is clean and straight. The shaft rotates nicely without the RC valves in place. In fact, I have assembled this combination of shafts, RC valves and cylinders in every combination possible. Left valve only, right valve only. First in cly. A, then cyl. B. The problem follows the cylinder. I have a friend who is a porting genious with the proper tools. He has the expertice to create a little clearence within the RC valve cavity. I am going to give that a try. I will report back on the outcome.
Also, I was planning on using a synthetic oil on the RC shaft for final assembly (Amzoil) because of the heat. Does this make sense to you?
Mark

oil wont do much for you. Your better off with a high temp grease like Molybdenum disulfide grease. I use that on my RS250 valve shaft needle bearings with no issues.

cgallant wrote:oil wont do much for you. Your better off with a high temp grease like Molybdenum disulfide grease. I use that on my RS250 valve shaft needle bearings with no issues.

Go with Charles's recommendation here and use moly grease. That's how I put together all my RC valves.

Grinding in the recess (not the valve) will be ok IF that is the problem. See where it's binding by using a marker pen on the valve and rotating it within the recess, you should then see the witness marks where it needs a tickle.

Thank you both for the tip on molly-lube. That makes sense.
I will not grind on the valves. The valves fit and opperated properly prior to tbeinghe cylinders being sent in for nicasil plating. These were not sent through an "exchange" program where they send out new cylinders and you send in your cores as they don't have anything like this on the shelf. These were sent in, plated and returned for assembly. Numbers match what weas sent in. Now the valves don't feel right. I am left to assume that we lost some clearence in the recess area due to nicasil. I should know later today...
Thank you again for the good info and I will report back.
Mark

Ok, got it working freely. Found a little nicasil (I'm going to call it) "overspray" in the exhaaust valve cavity of both cyls. Broke several bits grinding it out of there but now it moves freely, can't make it stick. By the way, there was no grinding on the timing edge of the exhaust port (although I was tempted, kind-of mellow port timing as manufactured...).
Pistons are on the rods and I hope to slide it together tomorrow night.

Thank you for your help!!
Mark

Ok, it's been a while but I got the bike/engine together. The problem was a thicher mill value in the new nic-a-sil which reduced the clearance between cylinder and valves. Once I corrected the clearance, everything moves freely!!
Thank you for your help.
Mark
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What's the latest?