XJ650 Valve Lapping Question

Hey all...I acquired a mess of a bike. I have a 1982 XJ650. I currently ripped the engine apart as I had very low compression in cylinder 4 (60 psi). Long story short, I had to rehone the cylinders and I am lapping the valve seats.

Here is my question. Can I use like 220 grit sandpaper and clean the top of the valve so the lapping tool will actually stick? Flat part of the valve. I don't think this woukd do anything. I have scrubbed and cleaned top with wire brush, but still had pits.l which is why lap tool barely sticks.

Thoughts?

 

220 is a lot too rough. You'll be making fairly deep cuts.
Start by soaking the valves in a 50/50 mis of Automatic Transmission fluid and Acetone at least overnight to soften the carbon, then go back with a wire brush (by hand, not motor) and plastic scraper.

If you make four more posts you can link photos. A closeup of the valves would be appreciated to see what the pits look like.

 

All carbon is off of the valves. Cleaned them up with straight pinesol and a wire brush. I need to smooth out the pitting on the top. Would 400 grit work?

 

I’ve lapped valves with my electric drill.
Apply the paste to the seat and the valve.
Insert the valve into the head then tighten the drill onto the stem.
Give it about 20 seconds while pulling the valve into the head.
There are YouTube videos you can watch.

 

I was thinking of taking a random orbital and pressing valve lightly.

 

Ive watched multiple videos and have done this previously to my 1982 Honda CB900C. Never tried doing it upside down.

 

You go ahead and clean up the face of your valves with whatever you want, finish up with fine emery cloth or tape, they will be fine.
But please don't use a chuck on the stems - you are Aasking for trouble. Lapping needs a cyclic motion, and some "feel".

 

I figure it's not really an issue, because that side doesn't come in contact with anything but gas, air and fire. I mean I'm not gonna grind them down crazy, just make smooth.

Although I kinda like "simmy"'s idea about reverse lapping, but I dunno, just trying to gather people's thoughts. Thanks.

 

I will post pictures in a few minutes. Hang tight.

 

1 Intake and 1 Exhaust Valve

 

Here is one almost good enough for tool to stick.

I tried using simmy's method, but I can fit my drill into head. Had to use rubber fuel line and that didn't really stay on when pulling valve to grind down seat.

 

Get a new sucker, stick it on and lap them the old fasioned way. It has worked since time began.

 

I'm actually working with 2 new sets and still same issue. I xant be the only one to ever have this issue.

 

I have lapped valves just leaning on the valve face with my thumb, grab the stem with thumb and for finger of your other hand. Lapping compound should be 800 to 1000 grit; available at McMaster-Carr

 

I didnt even think to try using my hand to do that, interesting.

 

That's all carbon buildup.
+1 on the above advice, especailly if soaking won't get all the carbon to release.

 

Not so easy to do on an XJ. The valve stems are down in the valve bucket well just a bit.
Using a length of vinyl tubing over the stem to get a better grip is advised.

 

Plus one on the tubing...

 

I was working on a car engine when I did that; tubing sounds like a good extension for saving the fingers.

 

Thanks everybody for the suggestions!! I'm gonna try to get a smaller diameter piece of tubing and reverse lap everything. Sounds less of a pain in the butt.

 

I was JUST starting to type “get smaller tubing”, but you figured that one out

 

I used a hose and did a reverse lap with drill and did reverse and forward a few times! Worked fantastic. Thanks everybody.

 

I lost count of the number of valves I lapped in by hand, using those blasted suckers.
Last few sets I used the tube and drill method, but being careful to not over-do it.
None of them have given any trouble.