Valve lapping?

[Richied46z]

I just received an 07 250r with 13k that was running poorly. Cleaned the carbs and reset them twice. Adjusted the valves twice also. Did a compression test 65 on left ,85 on the right. Did a leakdown test on it and the intakes were blowing air like crazy. The exhaust were whistling too. Nothing coming from the crankcase so the rings seem to be fine. Now that I have the head and valves out can I lap the valves into the seats? I'm a vintage motorcycle guy and lap valves all the time,but I'm not sure about these engines. Thanks for you help.

[Triple Jim]

Hi Rich, welcome to the board. I wouldn't lap them much, so if they were run while set so they don't close and have eroded enough for "blow air like crazy" I'd think a real valve job would be a better thing to do. I'd think it wouldn't be awfully expensive, but I haven't been through it for a Ninja 250.

[DannoXYZ]

Lappings increases the contact ring width. Which reduces pressure per unit area. Which reduces sealing.

You'll want to cut valve-seats with angles dictated in manual and aim for narrow end of range on intake and middle of range for exhaust on seat contact.

Exhaust valves are probably fried from overheating due to running with too low valve clearance. This doesn't give exhaust valves enough closed time to transfer heat away. They need to be replaced due to hard coating, can't be machined.

[Richied46z]

Thanks for the welcome. This a very informative site.

[Richied46z]

Thanks good advice. I wasn't sure if the valves were coated. I couldn't find any info on people lapping the valves. Everyone seems to replace them. PO parked the bike 5 years ago. He was moving and just didn't want to go to the trouble of selling a bike that wasn't running well. So now I'm trying to get it running again.

[DannoXYZ]

Greetings & Salutations Richard!

What you'll find is that due to plentiful supply from decades of production, a used good engine can be found for $150-250 on Craigslist or junkyards. Certainly cheaper than cost of professional valve job. Most likely valve seats will need to be replaced as well since they wear out faster than valves.

Not to discourage you or anything, it's certainly worthwhile learning experience tearing engine apart. In addition to lapping contact seat, you'll want to cut upper seat angle (smallest one closest to ports) in order to narrow contact ring width to restore clamping pressure. This also has effect of widening flow area and improving flow.

[Richied46z]

Originally Posted by DannoXYZ

Greetings & Salutations Richard!

What you'll find is that due to plentiful supply from decades of production, a used good engine can be found for $150-250 on Craigslist or junkyards. Certainly cheaper than cost of professional valve job. Most likely valve seats will need to be replaced as well since they wear out faster than valves.

Not to discourage you or anything, it's certainly worthwhile learning experience tearing engine apart. In addition to lapping contact seat, you'll want to cut upper seat angle (smallest one closest to ports) in order to narrow contact ring width to restore clamping pressure. This also has effect of widening flow area and improving flow.

Thanks. These little bikes seem to be fun and pretty easy to work on. With everyone's advice and help I'll get this little monster back on the road again.

[DannoXYZ]

If you're doing valve job, I recommend finding shop with newer Sunnen VGS machine that uses cutting bits rather than traditional stones. These are similar to wood-router bits and can cut all three seat angles in single pass.

Even better, since you're most likely replacing seats anyway, is to replace them with copper-beryllium seats for much, much better thermal conductivity to keep valves cool. Also cut them with fully-radiused (curved) profile, which flows way, way better than traditional 3-angle and better than 5- or 7-angle "performance" cuts. In this case, I've even cut down valve-guides to improve flow even more. You won't want to do that on street build.