How to Reseat / Lap Valves (Basic Valve Job)



In this video i’m explaining how to reseat or lap valves in a flathead or overhead valve engine. Also can be called a valve job, but this is not a complete valve job. I also used to much valve grinding compound, it does not require a whole lot. Usually when a engine needs this done is when a engine has low compression that is found to be leaking around the valves, or sometimes a engine will backfire do to the valves not closing completely/properly. Thanks for watching.

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42 thoughts on “How to Reseat / Lap Valves (Basic Valve Job)

  1. Newbie here. Working on a Tecumseh engine. Tore it down yesterday. Can I use a wirewheel to clean up the carbon deposits on the valve cover, head, and valves? Then lap?

  2. I have a 1999 yamaha wr400 and I took it to the shop and they told me the valves were not sealing and preventing it from starting. will this fix the issue? thanks! great video by the way!

  3. Doing some work on my MGB and I've been told that my valves need reseating. Would that be because of carbon deposit buildup in the engine? It's only 6 years since the engine was given a complete overhaul and bored out to 1950cc by a well respected company in the UK. So I'm surprised that it would be coked up already…?

  4. How long you grind/sand one valve, about?? Depens, how bad they are?? And, how do you know, when you need new valves?/ Too much play sideways? Can't you just replace valveguides, instead of valves?? Thanks, youtheman!!!=)

  5. Hey good video – It was informative and you did explain how to lap the valves.  If you wanted to make your presentation better you just need to practice before you film it.

  6. @ 9:00  The combustion chamber in that cylinder head looks a lot like mine.  All dinged up.  Did yours suck a throttle valve screw like mine did?
     Mine is a 17.5 horse B&S and actually ate both screws and almost ate the throttle valve plate (except I believe it was too big to fit thru the intake port).
    I only found part of one screw, imbedded in the head; must have spit the rest out the exhaust port, 'cause the exhaust valve has a nick in it.
    Which is why I'm watching your video.
    Thanks for the info.

  7. I am confused. Is it recommended to lap your valves, when both the valves and head are new. I though lapping your valves was done to match the valves with the valve seat of the head.

  8. very good and thank you for making this video! I had a 99 buick century 3.1 engine and it had 196, 000 miles on it and the 2 valves where bent, one was exhaust valve. What causes this, is it the timing not right and if so how would the timing get off? I now have a Honda accord 2012

  9. I imagine when you use the compound and it is taking material from the edges the valve would begin to drop closer to the pushrods. Wouldn't one want to adjust valve clearances AFTER doing the valve seats?

  10. Thanks! Very clear video, for anybody that needs to do the job themselves. I got a quick one for you. I did a (cold) compression test on a single 250cc 1969 Triumph, it is low at 60 psi, but it was also -10 degrees celsius. Now it doesn't start in cold weather. The motor was fully rebuilt about 8 years ago, has 280 milles on it. After being stored for 8 years with no start, I checked the basics, including carbs, oil change, gas lines, tanks, electrical and such. It started for me about 4 or 5 times, ran for 20 minutes each time. Would you say cold weather is affecting it, or should I do a valve job, then check compression again? I checked gaskets and It looks like these were never replace, they are thinner than paper, and cracking, it has all original parts and when I mean all it is really ALL original parts from 50 years ago. Just hope I don't have cracked piston rings or something bad.

  11. Great video. Thanks buddy.

    I was checking the valve clearance on my dirt bike and saw that the intake valves had zero clearance. Pulled the buckets and shims and saw the the valve rod/stem (where the shim sits) on one of the intake valves was mushroomed to the point where it was flush with the retainer clip. On that particular valve, the shim looked like whoever had last serviced the valves actually ground down the shim rather than installing a shim that was manufactured at the correct size. Using a micrometer, I was able to tell that the shim was slightly uneven, off by about .02mm on one side.

    Knowing that the "good" intake valve also had zero clearance but showed no damage to the valve stem, could the combination of zero clearance and an uneven shim be what caused the "bad" valve to get distorted? Or is there something else to consider? There was no damage to the bucket or cam.

  12. thanks for the video. how would you tell what the size of an older Briggs engine is ? it has a 1 inch shaft and an up draft carb on it . i cant find the model # in it . i am using it on a go kart. thanks 4 your time .

  13. On a flat head I do not have that tool you that squeezes the spring. I was hoping there was an easy way to do it. Other than fighting the thing. Yeah, the tool right.
    I have the lapping tool just like yours with the rubber sucktion cups. I am having a hell of time getting it to stay attached to the valve. All I am getting is a half turn or so. Apply any pressure to it and it freezes up. You said to use stater fluid to clean it. Seems like that would dry it out and make it rot. I have been using hot water and dish soap.

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