Topic: Valve Lapping Problem

[nivlac]

I'm lapping the valves on my cb650. The small suction cup side of my tool is too large for the smaller valve. I cut the diameter down a bit and it doesn't seem to get a bite on the top of the valve. I did a leak down test on the #1 set of valves. I used gas and the fuel diminished after about 5 minutes whether by leakage or to vapor consumption I don't know. My question is where can I get a smaller suction cup tool and is gasoline to do the leak test with? How much is too much lapping?

[reddyvv]

In a pinch you can use a length of fuel tubing over the end of the valve so you can hold it in your hand and turn it back and forth. You don't need to apply much pressure on the valve, let the compound do it's job. Once you see a nice even ring all the way around the valve and seat after wiping off the compound you are fine. Don't overdo it. If you have a good ring without any blemishes or scratches no need to bother with any leakdown test.

[lucky]

I'm lapping the valves on my cb650. The small suction cup side of my tool is too large for the smaller valve. I cut the diameter down a bit and it doesn't seem to get a bite on the top of the valve. I did a leak down test on the #1 set of valves. I used gas and the fuel diminished after about 5 minutes whether by leakage or to vapor consumption I don't know. My question is where can I get a smaller suction cup tool and is gasoline to do the leak test with? How much is too much lapping?

Lawn mower shop.
To lap just spin valve back and forth in your hands a few times.
DO NOT USE A DRILL!!!!


OF course you cannot lap valves properly if you did not check side play of the valve in the guide.

[Bailgang]

Some auto part stores may have the valve lapping tool with the smaller suction cups as well at least that's where I found mine but checking out a lawn mower shop is a good idea as well.

[70CB750]

Piece of hose is all you really need.

[Black 750K8]

Piece of hose is all you really need.

+1 and with a good clean square cut on the end.

[01Thomas]

OK, I've used a drill in the past, usually on the slowest possible speed. Everyone says not to use a drill - but why not?

regards
Thomas

To lap just spin valve back and forth in your hands a few times.
DO NOT USE A DRILL!!!!

[reddyvv]

Because there's no upside to a better outcome with a drill and the downside is that you overdo it and in the worst case end up with a recessed valve seat.

[Cabilao]

Sears have lapping tools in different sizes on their website.