August 1st, 2019, 03:24 PM | #1 |
ninjette.org newbie
Name: Rich
Location: California
Join Date: Jul 2019 Motorcycle(s): 07 250 ninja Posts: 4
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Valve lapping?
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.
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August 1st, 2019, 05:32 PM | #2 |
Guy Who Enjoys Riding
Name: Jim
Location: North Carolina
Join Date: Jul 2016 Motorcycle(s): Ninja 250 Posts: A lot.
MOTM - Oct '18, Aug '17, Aug '16
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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.
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August 1st, 2019, 05:49 PM | #3 |
ninjette.org certified postwhore
Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot.
MOTY - 2018, MOTM - Nov '17
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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. |
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August 1st, 2019, 05:58 PM | #4 |
ninjette.org newbie
Name: Rich
Location: California
Join Date: Jul 2019 Motorcycle(s): 07 250 ninja Posts: 4
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Thanks for the welcome. This a very informative site.
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August 1st, 2019, 06:11 PM | #5 |
ninjette.org newbie
Name: Rich
Location: California
Join Date: Jul 2019 Motorcycle(s): 07 250 ninja Posts: 4
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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.
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August 1st, 2019, 07:15 PM | #6 |
ninjette.org certified postwhore
Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot.
MOTY - 2018, MOTM - Nov '17
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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. |
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August 1st, 2019, 10:01 PM | #7 | |
ninjette.org newbie
Name: Rich
Location: California
Join Date: Jul 2019 Motorcycle(s): 07 250 ninja Posts: 4
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Quote:
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August 2nd, 2019, 11:47 AM | #8 |
ninjette.org certified postwhore
Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot.
MOTY - 2018, MOTM - Nov '17
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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. |
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