Lap new 3.3 cylinders to machined heads?

[JFairman]

Is it a good idea to put some valve grinding compound on the sealing surface where a machined head and new cylinder come together and then rotate the head back and forth on the cylinder by hand?
Or is it better to install these in the motor the way they are?

The cylinders and pistons are new Mahle 97mm 3.3 turbo from a sealed box and the 1976 930 heads were machined some years ago.
Recently I had the small bevel around the combustion chambers that were originally on 95mm cylinders machined by xtreme heads so they would fit the 3.3 liter 97mm cylinders and pistons.

If it's good to hand lap the heads to the cylinders which of these compounds I have be best to use? Or is something else better?
The tube of permatex valve grinding compund is water based and old but it still squeezes out and the can is 150 grit grease based compound.

Here's pics of the grinding compounds I have and the sealing surface of a machined head and new cylinder.

Thanks in advance for opinions on installing them the way they are or should I hand lap the sealing surface to a uniform grey and wash them off first?

[HawgRyder]

The first problem in lapping the heads to the barrels is to keep the two pieces in correct alignment.
In other words...you must have the barrel (or head) in exactly the correct plane to make sure the grinding action is the same all around the circumference of the seal.
Personally...if i had the heads and barrels machined...i would leave them alone...because the pieces would be smooth and in the correct plane as they come from the machinist.
Bob

[Lapkritis]

If done properly it can only help. Don't move too much material or apply uneven pressures. However, it's all for not if the assembly isn't squeaky clean. I personally use a sealant that is designed to fill minor imperfections on this and all head joints but it's far too common and accessible to gain support from any of the folks that showcase their wares and services as alternatives.

[nocarrier]

Hey JFairman. I just finished my turbo build and I also used brand new Mahle cylinders and freshly machined heads.

I didn't see any reason to lap the heads to the cylinders. Two well machined surfaces will seal together just fine.

[ertech]

How about with newly machined head and use cylinders?
Shoud we lap?
Thanks

[HawgRyder]

The old cylinders will damage the nice flat surface that the machined heads now have.
A better idea would be to mount the cylinders in a lathe and take a very small cleanup cut on the top surface.
Bob

[AlfonsoR]

Unless you're very experienced and methodical, I would not lap. The silicon carbide cmpd in particular can be very aggressive if high pressure is applied. The lapping strategy would be light pressure and the same duration across all cylinders so that the same amount of material is removed from each.

Remember that the cam housing still has to mate to the heads and that too has a specification for flatness across the three cylinders.

The best would be to have the case machined so that all cylinders start out at the same height with relation to the crank centerline. Second, each cylinder should be machine finished to the same height. Third, each head is machined to give you a consistent height for the cam housing to fit within a certain spec of flatness across the three cylinders on each side.

[BURN-BROS]

The last time I checked, there was a slight taper machined into the cylinder sealing surface. The surface closest to the bore was slightly taller than the outside edge.

If this is true, then it would promote a high clamping pressure at the most critical area of sealing. If you lap it, then it would diminish this important feature.

I noticed the taper on 3.2 cylinders, I have not checked on other cylinders that ran CE rings.

[mamut]

They should have a slight taper when they don't use a gasket, regardless.

[Henry Schmidt]

Originally Posted by BURN-BROS

The last time I checked, there was a slight taper machined into the cylinder sealing surface. The surface closest to the bore was slightly taller than the outside edge.

If this is true, then it would promote a high clamping pressure at the most critical area of sealing. If you lap it, then it would diminish this important feature.

I noticed the taper on 3.2 cylinders, I have not checked on other cylinders that ran CE rings.

+1
We don't lap this joint for that very reason.