what lapping compound grit?

[halfafish]

I'm going to lap the valves in my new SpeedMaster BB heads, but it's been about 40 years since I last did this. What grit is recommended? I have some 500 grit on hand but have no idea that's too fine, too coarse, or right on (I am channeling Goldilocks here...).

 

[moparownr]

The regular coarse/fine compound that is easy to find, is 120/280...Its been about 20 years since I've done this too, but I have always had excellent results with those grits! Hope that helps....

 

[SGBARRACUDA]

Man you talk about a lost art. I still have my hand lapping tools and a fine and coarse grit compound cans. I'll bet it's been 40 years since I last used it.

 

[318willrun]

I like Permatex valve grinding compound. I fill up a lid from a gallon of milk and add about 2 drops of water.

 

[RustyRatRod]

What you have should be good. Those heads have a finished valve job. They should not require a coarse compound at all.

 

[j par]

I think the last time I did it I used a quarter-inch drill bit and a piece of vacuum line instead of the stupid suction cup thing...

 

[MOPAROFFICIAL]

Like RRR said, shouldnt need it.
BUT...I have had bad valve jobs, chartered, and caught them this way...
I... just use fine, and use machinists dye, only lap till you go through the dye and look for concentric/round with no hiccups/road stripes...if you see stripes instead of a circle...its chattered.

 

[pittsburghracer]

Yep machinists dye and fine compound. I buy mine from Napa or Advance Auto. I got my last dye from Goodson.

 

[440 Mike]

Start with the dye to see what kind of job they did. I like the permatex for older jobs, and always use the stick so that I can hear the progress.