Lapping

[GC89]

Have any of you used one of the do it yourself lapping or wetsanding kits for your cylinder head? Im getting ready to replace a blown head gasket but none of the local shops can achieve the RA value needed. Or have can even measure their RA. I have one guy who builds racing engines, and uses MLS head gaskets all the time. He is very confident he can get it smooth enough, but I want to look into lapping just incase Im not satified with the finished product.

 

[cjsupra90]

Honestly, hand lapping the deck or the head is not the greatest of ideas. Although some have sucessfully hand lapped decks and heads, there is a very good chance that you will create a wavy surface cause it is for-one, hard to apply even and constant pressure at all times and the other thing is that edges of the lap plate can bit and dig in as you slide it across the deck or head.

The proper way to hand lap a part is to have a lap plate that is bigger then the part to be lapped and part moved on the plate with its own weight doing the work.

A good machinist who is willing to take the time and is using proper tooling should be able to give you the finish needed. Ask him if he uses PCD tooling. If so then you should have no problems finish quality.

 

[3p141592654]

Lapping is the only sure way to get the RA below 1 micron (50 microinches). That may sound like overkill, but HKS does spec an RA of better than 1.27um for its MHG.

Get a plate that is at least 8 inches in diameter, and lap in a figure eight pattern, or connect the plate to a 50rpm motor, and you will not generate waves.

 

[starscream5000]

Diamond paste.

 

[GC89]

diamond paste with a regular lapping block?

 

[starscream5000]

No, diamond paste with a lapping plate like 3p141592654 was speaking of.

 

[IJ.]

After it's been machined flat.....

 

[starscream5000]

:werd:

Wouldn't help much with having high spots, now would it?

 

[flubyux2]

that depends... if your guy has a CBN machine, you wont need to lap it. he can get it REALLY close with a traditional milling machine and fly cutter if he uses a slow table speed and a high cutter speed with multiple passes w/o adjusting the depth. if the milling is done right, itll have a rainbow effect on the surface.

HEY CHRIS! sup....

again, look into whether or not its a CBN machine (Cubic boron nitride, incase you were wondering). it doesnt use a cutter, its a huge, flat, circular "grinding" disc. the heads are like $20k or something outlandish. its a VERY precise machine for high end machine work.

btw, does GC8 mean you own a Subaru? or is that just a coincidence?

 

[IJ.]

Lapping is the only sure way to get the RA below 1 micron (50 microinches). That may sound like overkill, but HKS does spec an RA of better than 1.27um for its MHG.

Get a plate that is at least 8 inches in diameter, and lap in a figure eight pattern, or connect the plate to a 50rpm motor, and you will not generate waves.

12"x12"

 

[suprarich]

that depends... if your guy has a CBN machine, you wont need to lap it. he can get it REALLY close with a traditional milling machine and fly cutter if he uses a slow table speed and a high cutter speed with multiple passes w/o adjusting the depth. if the milling is done right, itll have a rainbow effect on the surface.

HEY CHRIS! sup....

again, look into whether or not its a CBN machine (Cubic boron nitride, incase you were wondering). it doesnt use a cutter, its a huge, flat, circular "grinding" disc. the heads are like $20k or something outlandish. its a VERY precise machine for high end machine work.

btw, does GC8 mean you own a Subaru? or is that just a coincidence?

As slow as it will go, I beleive the best results will get you a Catapiller spec of 75 which is very close, but will not meet a RA spec for HKS. This is the same machine we use.

 

[3p141592654]

:werd:

Wouldn't help much with having high spots, now would it?

The optics guys figured out the secrets of lapping 50+ years ago, and routinely maintain surface finishes to a few hundred nanometers or better.

We have a number of projects here at my work where we maintain lapping tolerances to 0.5 micron across 4 and 6 inch semiconductor wafers.

High spots with periods less than half the shortest lapping plate dimension will be removed. That is why larger plates are preferred.

 

[starscream5000]

I was referring to waiting on the lapping the block before it's been machined flat...

A lapping plate would do no good on a warped block, would it? The lapping plate couldn't get it flat right? Unless you spent hundreds on man hours on the block with the plate...

 

[GC89]

Right now Im looking at options assuming my block isnt warped. Its got 24k on a NEW toyota block and has never overheated from what I know. Im trying to avoid tearing the bottom end down. I wanted to know what my options were to smooth it out while still assembled. Its not a problem getting to spec if the block need machined Im just hoping I dont have to go there. Definatly wouldnt lap before in that case starscream . So that being said where can I get an affordable lapping stone?

 

[starscream5000]

This beast is $363.00

http://lapmaster.thomasnet.com/item...-plates-1176/lap5-0007-003-0002-4085?&seo=110

 

[3p141592654]

I was referring to waiting on the lapping the block before it's been machined flat...

A lapping plate would do no good on a warped block, would it? The lapping plate couldn't get it flat right? Unless you spent hundreds on man hours on the block with the plate...

You are correct, unless the lapping plate was bigger than the entire block! Even then, you would need a mechanism to keep the plate normal to the cylinder bores. Machines that can do this sort of thing exist, but are not going to be available to anyone without the capital budget of a huge manufacturing facility.

 

[starscream5000]

Do you have any links or suggestions on a decently priced lapping plate? I'm having somewhat of a hard time on finding a reasonably affordable one myself. Most I've come across so far are round, cast iron lapping plates. I was looking for something more along the lines of a square or rectangular lapping plate...

Thanks!

 

[3p141592654]

This one is not too bad. It could be bigger though at 8 x 8". Price is $166.

http://www.mcmaster.com

search for 2352A1

If you're near NJ I know of someone who might be willing to rent you his lapping plate.

 

[starscream5000]

I'll probably just buy my own and that one's a lot more forgiving on the wallet for something I'll only use about four times maybe...

Thanks!

 

[starscream5000]

2352A12

That's the correct part number BTW. I believe the proper way to do it would be to make many, slow passes <80 RPMs on the grooved side until you reach a desired finish, then finish things up with the smooth side for the ultimate smoothness possible with the tools at hand, correct?