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General Category >> Rubber Side Down! >> Valve Lapping
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Message started by NMSavage on 01/16/18 at 08:47:52

Title: Valve Lapping
Post by NMSavage on 01/16/18 at 08:47:52

Quick question for those that have gone before.

I'm installing the Weisco 94 piston and the Phase 3 cam. Do you old hands recommend lapping the valves while it's torn down? 3100 miles on the clock...or is this an after inspection issue?

Thanks,

*

Title: Re: Valve Lapping
Post by Dave on 01/16/18 at 09:35:47

Lapping valves is normally only done after seats are ground to confirm everything is seated. (You can't grind the valves on Japanese bikes).

I wouldn't think a bike with only 3,100 miles needs a bunch of cleanup, unless it was running really rich or burning oil.

If you are equipped to remove the valves and clean the head of carbon....that is something that I do before putting and engine back together again. I use Walnut shells in a pressure blaster to clean things up, as it is not abrasive if you happen to miss one and it comes loose later on.

Title: Re: Valve Lapping
Post by Gary_in_NJ on 01/16/18 at 10:22:07

Is it too late to perform a leak down test (is it all apart)?

Title: Re: Valve Lapping
Post by NMSavage on 01/16/18 at 11:47:09

Dave,

Thanks. I vote with you that it probably doesn't need the full monte. It was running pretty dead on for lean/rich...nice tan plug, no backfire, no roll off rpm changes. Only excess oil consumption is what I spill, other than that, no oil burning or leaking. Planned on cleaning up the combustion chamber and both ports. Just checking with the brain trust on what you experienced men recommend.

Gary_in_NJ
Head is still on the engine...I can sure reinstall the spark plug. It's been awhile since I've done a leak down test. A quick reminder would be welcomed. Thanks.

*

Title: Re: Valve Lapping
Post by Gary_in_NJ on 01/16/18 at 12:19:07

Steps:

1. Hold piston at TDC
2. Hold carb at WOT (or remove carb)
3. Thread the leak-down tester (differential compression) adapter into the sparkplug hole.
4. Charge the cylinder with a reference pressure (I use 80 psi)
5. Make sure that the cylinder is able to hold 90% (72psi) of the reference pressure.
6. Check for leaks
a) air escaping the exhaust is a problem with the exhaust valves
b) air escaping at the carb is a problem with intake valves
c) air escaping from the crankcase breather is a problem with the rings
d) rapid air escaping from the breather is a hole in the piston

Title: Re: Valve Lapping
Post by NMSavage on 01/16/18 at 12:33:55

Thanks Gary_in_NJ. Pretty much the same as my old gray matter remembered...better detail though. Much appreciated. Hope I can muster up a tester from auto parts store loan program.

Title: Re: Valve Lapping
Post by verslagen1 on 01/16/18 at 13:27:28

e) rapid air escaping from behind is a fart.

Title: Re: Valve Lapping
Post by NMSavage on 01/17/18 at 14:02:47

Is that kin to a backfire or a different sort of belch of power?

Title: Re: Valve Lapping
Post by verslagen1 on 01/17/18 at 14:29:23

A couple of ghost peppers will do that to you. :o