Question on sealing heads / cylinders, Advice needed on lapping cyls to head Options

[Joe Owensby]

I have done a search here, and have found some info, but not all I needed. Most say to just lap the cylinders to the heads. I have a 2056 kit from Raby, with all new parts. How precise should the interface of the head to the cylinder be? My new heads have small machining grooves on the area where the head will mate. Small, but can be felt with a fingernail. The cylinders also have small machining grooves fromt he lathe cutting. I have lapped the cylinder to the head on one cylinder. I have done this to the point of getting a uniform type of mating all around the surface. However, this is to the point that the small grooves are still there, ie it is not a completely flat polished surface. I am guessint the grooves are about 3 thousandths deep or so.

I was wondering if the grooves could actually help sealing, as I have seen a lot of gaskets, etc. that have circumferentially grooved or ribbed surfaces to allow a higher unit contact pressure around the full surface, and maybe allow for accomodating slight imperfections in geometry. I also saw on Jake's website where someone, I think Len Hoffman, said there was a taper machined into the cylinder mating surface, about 0.0015 or so. On this site, there was a mention by Jake to first lap the cylinder on a glass pane, and then lap the cylinder to the head.

Any clarification you can give to this will be greatly appreciated. Thanks, Joe O.

[orange914]

I have done a search here, and have found some info, but not all I needed. Most say to just lap the cylinders to the heads. I have a 2056 kit from Raby, with all new parts. How precise should the interface of the head to the cylinder be? My new heads have small machining grooves on the area where the head will mate. Small, but can be felt with a fingernail. The cylinders also have small machining grooves fromt he lathe cutting. I have lapped the cylinder to the head on one cylinder. I have done this to the point of getting a uniform type of mating all around the surface. However, this is to the point that the small grooves are still there, ie it is not a completely flat polished surface. I am guessint the grooves are about 3 thousandths deep or so.

I was wondering if the grooves could actually help sealing, as I have seen a lot of gaskets, etc. that have circumferentially grooved or ribbed surfaces to allow a higher unit contact pressure around the full surface, and maybe allow for accomodating slight imperfections in geometry. I also saw on Jake's website where someone, I think Len Hoffman, said there was a taper machined into the cylinder mating surface, about 0.0015 or so. On this site, there was a mention by Jake to first lap the cylinder on a glass pane, and then lap the cylinder to the head.

Any clarification you can give to this will be greatly appreciated. Thanks, Joe O.

good question, anybody? (IMG:style_emoticons/default/icon_bump.gif)

[davep]

It is Jake's kit, best to get the clarification from him. No one better.

[alpha434]

Do not lap on a glass pane. Glass is NOT flat. Machinists commonly do it and it is WRONG. The machining trade is victim of bad traditions and miscommunication just like the automotive trade.

[Twystd1]

Joe,
You really need to post this question up on Jakes forums.
Jakes Linky


I wonder if the barrels and head were already machined for a matching fit with spiral grooves on the mating surfaces. Len/Jake have done that on some applications if my memory serves me right.


Alpha... he is lapping the barrels to the head...... No flat surface needed in this case....

And thanks for the glass info... I never thought of that. I guess thats why I have this big old piece of green granite in my garage from an old machine shop.... The bugger is dead flat.

Cheers,
Clayton

[brer]

Joe,
You really need to post this question up on Jakes forums.
Jakes Linky


I wonder if the barrels and head were already machined for a matching fit with spiral grooves on the mating surfaces. Len/Jake have done that on some applications if my memory serves me right.


Alpha... he is lapping the barrels to the head...... No flat surface needed in this case....

And thanks for the glass info... I never thought of that. I guess thats why I have this big old piece of green granite in my garage from an old machine shop.... The bugger is dead flat.

Cheers,
Clayton

super flat honing stone.
worth its weight in .... granite?

(IMG:style_emoticons/default/slap.gif)

[Twystd1]

What he said..........

CCC

[Cap'n Krusty]

Lemme see. You take precision machined heads, done in a VERY precise fixture, a precisely machined case, and precision machined cylinders, and you HAND HOLD THEM while destroying the planarity of the mating surfaces? You do the math. If my heads were roughly machined, I'd sure go after the guy that I paid to do them, and I sure wouldn't introduce random angularity into the equation. I'm thinking I'm not the only one here that can't handhold a cylinder to the tolerances of a fixture in a mill. Of course, that's just my opinion, I could be wrong. But I'm not. The Cap'n

[alpha434]

Fixture in a mill? Depend on whether it's a 5 axis or not. Can it machine both the top AND bottom in one op? If so, then it may be perfectly square. If it wasn't done in one op- then you've already introduced random angularity.

And the lapping is for surface finish. . . A better surface to seal with, my dear.

[mike373]

Jake uses a paste made from ajax and a little water, as a fine cutting compound. Twist and apply pressure toward the head while holding the cylinder with both hands. There should be a darker colored ring in the cylinder head that is uniform all the way around when lapping is complete. Jake informed me that 4-5 minutes off lapping should do the trick, per cylinder.

[blitZ]

Jake uses a paste made from ajax and a little water, as a fine cutting compound. Twist and apply pressure toward the head while holding the cylinder with both hands. There should be a darker colored ring in the cylinder head that is uniform all the way around when lapping is complete. Jake informed me that 4-5 minutes off lapping should do the trick, per cylinder.

Thats' also how I did my heads/cylinders, except I used valve grinding compound. It's a simple process, I believe you are over thinking it a bit.

[Cap'n Krusty]

Fixture in a mill? Depend on whether it's a 5 axis or not. Can it machine both the top AND bottom in one op? If so, then it may be perfectly square. If it wasn't done in one op- then you've already introduced random angularity.

And the lapping is for surface finish. . . A better surface to seal with, my dear.

Using a good machine shop with proper (and well maintained) equipment for the job means you don't have to "improve" the surface. A good machinist KNOWS the correct texture for the surface in question (VERY important with modern head gaskets) and returns the heads to you ready to install. If yours doesn't do that, then you should look elsewhere for machine work.

BTW, the shops I use sets up air cooled cylinder heads in a fixture that allows them to cut the mating surface and the surface of the casting in one operation, as they should be done. Shops that don't do it right shouldn't take in that kind of work. The Cap'n

[brer]

I sell that tool.

Halfway down the page


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[Jake Raby]

We all have our different methods..

My method has worked well for me, it has held 20+ PSI of boost and up to 14.75:1 CR on some race engines and at the same time it has kept us from EVER having a returned engine due to a head leak.

One should machine the head to the best of their ability, and then follow up the process with the lapping to get a better match between the cylinder and the head. This can eliminate irregularities from the surface of the cylinder- not just the head surface.

Thats just my way of doing it and I have based it upon my experience- just llike the Cap'n bases his.