Dave951

As the title states, Can a cylinder head that has been o-ringed for 100mm be used on a larger diameter bore block (say 104mm)?

I know the Cometic MLS gaskets do not recommend an o-ring so can a machine shop remove the o-ring and redeck the head for the new application?

Some options discussed here:

1) Leave O-Ring in place, Surface head
2) Remove O-Ring, Leave groove
3) Remove O-Ring, Surface to remove groove
4) Remove O-Ring, Fill groove with high temperature epoxy.

michaelmount123

Just leave the o-ring in place and have the head surfaced. It will then be flat and suitable for larger bore and a Cometic gasket.

Humboldtgrin

Then get a thicker head gasket or an adjustable cam gear to correct the timing after removing that much material.

Dave951

Took it over the local machine shop today. I always feel slightly out of my element over there as I'm not very knowledgeable about machining and what is/isn't possible. As a side note its always reassuring when you plop down a part on the counter and the machinist remarks the make and model of the car before you even say anything.

I asked about leaving the o-ring in place while achieving a level surface. Short answer is no don't do that.

He estimated removal of material is 20 thousands of an inch to get a flat surface that will be beyond the o-ring groove. As Humbold stated above a thicker HG to accommodate the material loss is needed.

David Floyd

I run a head that was o- ringed for a stock bore used it many years with the ring in place and removed the ring last time I had the head surfaced groove still in place, cometic gasket with 106 mm bore, no problems either way

Dave951

Interesting David, that's good "from the field" testing.

Next time I talk with the machinist I'll have to ask him more about simply removing the ring leaving some groove behind. Perhaps he can shed some additional light on possible pros/cons (if there are any).

JacRyann

Note that Cometic gasket doesn't require full contact across thickness of cylinder top. It's only moulded compression ring that touches and this increases pressure at that ring for sealing. Measure diameter of O-ring groove and diameter of compression-ring on MLS headgasket. If they don't line up, just use the head as is.

Dave951

There is clearly either a bunch of misinformation out there or there are a lot of different options. So far we have:

1) Leave O-Ring in place, Surface head
2) Remove O-Ring, Leave groove
3) Remove O-Ring, Surface to remove groove

That seems to cover just about every option except use the head as a boat anchor.

I found this old thread where Chris White states that "Heads that have been O ringed for a 100m bore will not (usually) work with a 104mm bore set up. I have run into this several times (much to the disappointment of the guys with tweaked 100mm heads!). " Thread

Dave951

Went with option #3. Remove O-Ring, surface to remove groove.

In the process of measuring the volume of head and pistons to get an accurate idea of head gasket thickness needed to maintain desired static compression ratio.

rlm328

My head and block were o-ringed. I used a high temp epoxy filler to fill in the grooves without any problems. I am running a Cometic gasket.

Dave951

Looks like we have a forth option, I definitely had not thought of this one.

Dave951

Finished measuring up the volumes. I wrote a blog post on the procedure I used to go about it (Since the blogger editor is easier to use). Here.

Someone check my measurements, math..etc there. I didn't do a write up for the cylinder head volume since I forgot to take pictures.

Also I measured the cylinder head pad thickness as per 15-16a in the WSM. 22.83mm which is beyond the 23.6mm wear limit so some compensation is in order. That is ~ .05" from the factory new 24.1mm spec.

The final numbers were:

33.4cc piston dish volume
48.5cc cylinder head volume

Summit Comp Ratio Calc

Other values I used were:
104mm bore
78.9mm stroke
-.15mm deck clearance
4cyl

Going with a .051" gasket gives a static comp ratio 8.38:1.

To get 8:1 I'd need to run a .07" HG.

Update 6/28: Spoke to a wizard that lives by the misty lake. Serious wisdom and knowledge was bestowed upon me. I'm going to write a blog post about it as there is way too much misinformation floating around.