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Lapping valves on 4 stroke

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Old 03-18-2011, 08:41 PM
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42etus
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Default Lapping valves on 4 stroke

What do you use to lap the valves on your 4 strokes? Tooth paste, kitchen cleanser, automotive compound? Also, what is your technique. My engine in question is a YS 91FZ and the exhaust valve is leaking.
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Old 03-19-2011, 12:24 AM
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Default RE: Lapping valves on 4 stroke

Use chrome polishing paste or extra fine lapping paste. Be careful to cleaning the parts free for lappingpaste before assembly the engine parts.
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Old 03-19-2011, 02:42 AM
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Default RE: Lapping valves on 4 stroke

I have used automotive valve lapping compound with good success on OS engines. (the finishing grade)
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Old 03-19-2011, 03:59 AM
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Default RE: Lapping valves on 4 stroke

I've successfully used some chrome polishing paste mixed with cigarette ash on Enyas.

Regards,

Holm
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Old 03-20-2011, 02:27 AM
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Default RE: Lapping valves on 4 stroke

Most often I find they really just need well cleaned instead of lapped.
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Old 03-20-2011, 07:06 AM
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Default RE: Lapping valves on 4 stroke

If the engine has phospher bronze valve seat/guide , beware that the margin on the valve seat is 1/2-1 mm wide. Be prepared to use a good jewler's loupe to examine the seat to check for remaining low spots. Don't just go lapping awaywithout checking, just remove the low spots.
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Old 03-20-2011, 03:17 PM
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Default RE: Lapping valves on 4 stroke

Can the valve seats be cleaned/lapped with toohpaste ? Capt,n
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Old 03-20-2011, 06:23 PM
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Default RE: Lapping valves on 4 stroke

I have used auto rubbing compound. What I do is apply the paste and drop in the valve. Then I use a small piece of silicon fuel tubing and push it over the valve stem. holding the tubing between my fingers and slightly pulling on it, spin it back and forth. Don't over do it. It doesn't take much to reseat them. What ever you use to lap them, make sure you clean them real good afterwords before reassembly. Be sure to clean the valves and seats well before you lap them. Sometimes all that is preventing a good seat is a bit of carbon or crud.
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Old 03-20-2011, 06:41 PM
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Default RE: Lapping valves on 4 stroke

This post is about a Y-S 91 FZ

On newer Saito four strokes, the valve seat is chrome plated aluminum. Be very careful that you do not cut through the chrome. You just want to clean off the seat.

My experience with well used four strokes, there are other parts of the valve that show wear. Like the keeper grooves and the very top of the stem as well as the contact face of the rocker arm.
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Old 03-31-2011, 10:23 AM
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Default RE: Lapping valves on 4 stroke

Update:

I glued the valves to 3/8" dowels with thick CA and used Mother's Aluminum Polish. Mother's is a very mild abrasive. The dowels made it easy to rotate the valves on the seats. When I was finished, I cut the dowels off, leaving about 1/2" then soaked the valves in acetone for about 10 minutes. That softened the CA which was then easy to remove. The YS runs great now!
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Old 03-31-2011, 10:31 AM
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Default RE: Lapping valves on 4 stroke

Good job
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Old 03-31-2011, 11:21 AM
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Default RE: Lapping valves on 4 stroke

I don't think toothpaste will work anymore as a lapping compound. None of the brands of toothpaste I used on my teeth has any abrasive qualities to it anymore. But maybe some brands still have some abrasives in them.
the aluminum polish is a good idea. Nice job.

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Old 04-01-2011, 02:07 AM
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Default RE: Lapping valves on 4 stroke

Brasso or Silvo (brass or Silver polish), followed by a really good clean. Don,t get any on the valve guides though.

I've tried gripping the stem in my dremel, it worked for me, but I wouldn't recommend it.

Do you guys have pencils with a small rubber (eraser?) on the end of them? I CA that on to the valve and twist it between my palms, lift and rotate a few degrees, repeat.

I have to agree that a good clean is probably all that will be required though.

Dave H
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Old 04-01-2011, 05:15 AM
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Default RE: Lapping valves on 4 stroke


Quote:
ORIGINAL: ThumbSkull

Most often I find they really just need well cleaned instead of lapped.
IMO lapping is a waste of time. If they are warped or eroded, they are way past being repaired by lapping. It is only useful as a check to see if it is warped. Many automotive machinists do not lap ground valves and will not waste time lapping older valves, they have other and better ways to check if they are warped.
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