lapping compound

[mack]

What grit is everyone using for the final lapping of the valves. 280, 320 or higher grit?

[DiverRay]

I just got the kit at the auto parts. It has two grits, and the tool for spinning the valves. I started with cleaning ALL the carbon off, then did the fine grit to see if there was any problem areas. Got lucky, and only had one exhaust that needed the heavy duty treatment.
One thing I DID do was take just a little bit off the end of the valve stem. I used a fine stone on the grinder, and did a small touch at a time, cooling it in water to keep the temp down. If you don't, you will run out of shim and will not be able to adjust the valves. If your shims for the valves are still on the large size, 290 to 310, you may not have to. The engine I worked on was at 240 BEFORE lapping. didn't leave much room....

[MPittma100]

Machine Shop

In an effort to guarantee ZERO subsequent head removals, I have elected to let the guy at the machine shop, who has all of the right tools, to grind/lap/adjust all valves and seats + clean the head nicely. JMHO

[TomB]

The difference between the two pastes is so small I wouldn't worry which you use. Try to leave the finish a satin one, if its shiny the valves won't bed in so well. A rough paste we use would be a 180, and when you've near finished the lapping of a seat the paste you're sliding round on that started out as 180 is more like a 320.

You can get shims down to 200, 40 thou is a hell of a lot of wear on valves and seats so not so much of a worry, and as said on here a few times, you could lose more off the stem top if needed

[crazy steve]

You can get shims down to 200, 40 thou is a hell of a lot of wear on valves and seats so not so much of a worry, and as said on here a few times, you could lose more off the stem top if needed

Total adjustment range is only .046" (320-200 shim size), from a 240 down to a 200 is only .015" so there's less there than you think....

And you also have to be very careful about 'dressing' the ends of the valves. Make sure the machinist is aware that minimum allowable stem length from the top of the retainer groove to the stem end is 4mm (.157"); less than that and the shims will be pressing against the buckets, not the end of the valve and valve retainer failure will be the result.

[mack]

i hear ya

Steve. i know I have limited tolerlance. more than you could ever know. This restore has become personal! I've completely disasembled this pig in hopes of correcting the PO issues but this one is fighting me tooth and nail. Nothing I've touched has been simple! I wanted to get it up and running this year but $$ may make that a non starter. I could do in a half ass'd manner but that's not my style. This is personnal now, the bike I feel is testing me to see if I'm worthy. What it doesn't know is, I'm it's last hope, cuz if it won't work for me, I'll set it on fire in a field and spare my felleow riders the heart ache. if it works for me, I'll pamper it till i die. But it better wise up soon cuz I have a big pit right now that it will fit right in. Now about the grit is 280 sufficient to stop the leaks, I've already had the seats ground?

[TomB]

Total adjustment range is only .046" (320-200 shim size), from a 240 down to a 200 is only .015" so there's less there than you think....

And you also have to be very careful about 'dressing' the ends of the valves. Make sure the machinist is aware that minimum allowable stem length from the top of the retainer groove to the stem end is 4mm (.157"); less than that and the shims will be pressing against the buckets, not the end of the valve and valve retainer failure will be the result.

Oh man DOH!! yep sorry got my thous and mms mixed up. But 15 thou is still a lot of lapping and a lot of valve seat recession.

And I hoped you'd come in about the valve stem tops. As long as theres enough protruding through after the collets are fitted so the bucket sits on the valve stem and not the spring.

[TopCatGr58]

Hey Mack,

Seems like you're still not getting the answer you're looking for regarding which grit level to use!

You said in your last post that had the valve seats ground, so I'm assuming NOT the valves. I just went and checked in my garage for what I used in 2000 on mine when I did my rebuild....on a 50K engine/head where I replaced the valve seals, and then just lapped mine.

It was Permatex Valve Grinding Compound # 80036 / 34A smaller sized tube, water based....but it states can be used for lapping as well. Also on the tube it doesn't state the grit levels, but in the PDF I found about it:

http://www.permatex.com/documents/TD...tive/80036.pdf

It actually has a RANGE of grit within it...120, 150, 180, 220 . Like was stated, as you work it performing the lapping, the grit feeling gets smoother with more repititions/rotations. I would then pick up the valve with the suction tool to separate it from the valve seat which allowed some fresh paste to get on the valve face, and then put it back down and did the lapping again. I then checked to see if I had at least a 1/8" or was it a 1/16" wide band on the face of the valve/seat to tell me that I had done enough. It's been great for the last 15 years with terrific compression especially with my little big bore kit!

Websites I've found state that the material it uses, Silicon Carbide is used for fairly hard metals, that it breaks down due to it's brittleness, but because it's still carbide, can leave fine scratches!?

HTH!? T.C.

[mack]

Lapping

Thanx TC. I believe the FSM calls for 1.2 mm band on the valve, centered from tip to shoulder. However the location of that strip determines a few things with regard to the condition of the seats. I was getting an inconsistent strip almost like the valves had run out in them. I checked them but they were fine. The location told me that the seats needed to be re-ground(LIGHTLY)
I then lapped with a multi grit (permatex) and have a nice consistent ring on the valves but it's still fairly rough. Enough that the varsol is passing through. I've ordered some 280 grit so that I can just smooth out the grind so the conact surfaces will be smooth enough to seal without removing any more material so I will have some room for future shim adjustment. Not sure if it will work as advertised, the seats had quite a bit of pitting in them so who knows. This is the last mechanical work left before my final assembly and I wouldn't be surprised to learn I've wasted my time with this head and will have to replace it.