Lapping Compound

[Mike Cathey]

I finally ran out of the lapping compound a friend gave me to lap in pistons and sleeves. Does anyone know what grit is used? The stuff I had was a yellow powder you mixed with 10 wt. oil.

 

[dave roach]

Mike

It sounds like diamond dust compound.Did it come in a small tube.

Dave Roach

 

[Mike Cathey]

Nope in a little metal can with a pry off lid.

 

[Daniel Richard]

Bon Ami mixed with automatic transmission fluid.

 

[steve wood]

I finally ran out of the lapping compound a friend gave me to lap in pistons and sleeves. Does anyone know what grit is used? The stuff I had was a yellow powder you mixed with 10 wt. oil.

i have some. mcmaster carr sells it.page 2687,timesaving lapping powders,non imbedding for aluminum

 

[Mike Cathey]

Thanks Steve,

I got a 1 lb. can of the extra fine for soft metals which is 320 grit non-embedding for aluminum. The p/n is 4781A32. $30 w/shipping and a lifetime supply

 

[TOM DRIVER]

For what it's worth, I used Toothpaste & WD 40

Tom

PS. Is this method still being used???

 

[57fairlane500]

We used to use toothpaste, now I use 60-66% nitro and a lake.

 

[Ray Sametz]

For what it's worth, I used Toothpaste & WD 40

Tom

PS. Is this method still being used???

If your toothpaste is 20 years old maybe, todays stuff dose'nt have the abrasives in it.

 

[Jim Allen]

Be very careful when selecting any type of non-embedding lapping compound. No type of compound that contains emery, aluminum oxide, silicon-carbide, boron, diamond or a charging abrasive should ever be used. Timesaver (yellow label) non-emdebbing lapping powder comes in four different grades & I do not see the grade specified in the McMaster Catalogue. Timesaver (yellow lable) grades TIM #40, #60, #80 & #100 can all be used on babbit, brass, bronze & aluminum. SELECT CAREFULLY!!!

Jim Allen

 

[mark ham]

What do you recommend Jim?

 

[Jim Allen]

What do you recommend Jim?

There is no valid reason to use any type of lapping compound to break in, or seat, because of out of roundness, a piston to a liner. An airplane propeller of the right size can easily do this & in the case of an outboard, a left hand propeller can be used.

For example, a 10" X 7" APC left hand prop, cut down to 8", is what I use to break in the Nelson .45 long stroke. 1.5 to 2 gallons of 15% nitro, with 5 ozs of castor oil added to each gallon, will properly break in this engine & many others as well. Run the engine at wide open throttle (28,000 to 29,000 RPM) using 4 ounces of fuel at a time. A very small amount of water cooling will be necessary (.020" outlet). I do this with the engine mounted on the complete, modified, K&B lower unit. A reliable tach should be used to determine the engines maximum RPM & to prevent over leaning the engine. I suggest the use of the balanced prop driver & a balanced flywheel because of the very large intake port in the crankshaft. ALWAYS OBSERVE NECESSARY CAUTIONS WHEN USING ANY TYPE OF AIRPLANE PROPELLER THAT IS NOT 100% CARBON FIBER!!!

Jim Allen

 

[mark ham]

Thanks for the information.

 

[Johnny Brown]

Lapping sure helps a mill stay runing during break in without high rpm.Helps with cycling, restarts are easier.I would go with the finest grn.use a light oil Marvile M air tool oil any thing really,go to town.Johnny

 

[Terry Keeley]

Think I'll try this with my helical lap to take the last tenth or two off a new piston, I'm not quite as confident as Jim to be able to dust that off in the lathe. Used some fine aluminum oxide paste last time around, maybe that's why they didn't last too long.

A bath in the ultrasonic will follow to be sure it's all gone...

 

[Keith Halverson]

The 3M stuff that comes in there headlight lens polishing kits is pretty subtle as far as I can tell. Have used it before to lap in some expensive 1/8 scale motors. Washes away with Dawn soap and water. (what i used).