cylinder head minimum height

[stroj]

Hello All!

I need to skim the cylinder head of my car. From some documentation I've found out that the permissible minimum head height 107 mm. Currently the head has 106,95 mm and I need to take 0,04 mm. The guy at the workshop says there is no problem going below the 107 mm, he told me they will cut the valve seats the same amount.

My question is, if there is no problem going bellow 107, why does this minimum height exists in the brand manuals?

 

[Tmoose]

Is this a diesel?

Do you know when and why it was already milled to 106.95 ?
Does that may some bearing on why you have it apart now?

One reason for restricting the amount to be milled from OHC engines' heads is that warpage on the bottom is a good match for distortion in the cam bearing bore "main line." Some shops routinely "straighten" curley OHC heads as a first step since it improves the cam bearing bore co-linearity and reduces the amount required to flatten.

 

[stroj]

It is a diesel. An Alfa Romeo 1.9 JTD 16V 2003. I bought the car less than 1 year ago, don't know if it had problems before.
I got a leakage from combustion gases into the cooling circuit, and decided to take the head out myself. There are some pictures in the next link:

http://s797.photobucket.com/user/stroj/library/AR 147 Head

The guy at the machine shop told me that, due to the machine pattern in the surface of the head, it never had been skimmed before. On the other hand, the present height doesn't suggest that.

Never thought about the distortion on the cam bearing bores.That could lead to some premature wear?

 

[RossABQ]

The limit may also be because it affects cam belt tension.

Is the deck of the block level? Are thicker head gaskets available to account for milled heads?

 

[RossABQ]

It also affects cam timing.

 

[tbuelna]

Machining an additional 0.04mm (0.0016") from the head surface and putting it just below the recommended factory tolerance won't make any difference. What matters more is making sure the machined head surface is parallel with the cam bores. A difference of .002" in deck height will not prevent you from properly adjusting the cam timing, or significantly alter CR, or cause an interference between the valves and piston crown.

 

[ZephTheChef]

I've taken .050" off on multiple high compression builds before. Cam timing becomes a factor when you're taking a bunch off but if you do the math, it's not as much as many people believe...it was like 2 degrees in my case, even with the extreme of milling .050" off. In effect, I've milled off 33 times what your machine shop is suggesting with no problems...and in every case, these engines were for cars making a LOT more than stock HP. I wouldn't even think twice about taking .0015" off...that would be like a couple rubs with a piece of sandpaper, lol.

 

[tbuelna]

Cam timing should never be a problem regardless of how much material you remove from a cylinder head deck. Any aftermarket OHC drive sprockets are adjustable for several degrees of timing. Which is far more than 0.10mm or 0.20mm of material removal from the cylinder head deck surface would produce in variation in timing of the cam drive.

 

[stroj]

Thanks to all the replies!

To RossABQ
It is using already the thicker gasket. I measured the protrusion of the pistons to confirm it was the correct one.

I decided to mill the head. I assembled everything and it is working fine. Already counting 1990 km

Some pictures of interest:
-> Milled head:

-> Gasket in place:

-> Flushed, cleaned and lubricated lifters with rockers in palce:

-> timing marks


->running test