Hi all.

As some of you might know. I have a spare GX cylinder head in my store that was skimmed to the max by the previous owner.
It is now sitting at 73.0mm thickness.
It will need a light deck if I want to use it somewhere in the future to remove scratches. It will then probably be 72.8mm.
I am planning then to use a oversize headgasket that will be 0.5mm thicker than a standard head gasket to bring it back into factory specs with thickness.
(Will then be 73.3mm)

My concern is about the cylinder's comp.
Due to head warpage that occurred, the head was skimmed by the previous owner. With skimming as we all know more metal will be removed from certain parts of the cylinder head to bring it flat with other parts of the cylinder.
This then causes some of the combustion chambers to be slightly smaller that other combustion chambers. An example would be if the head is warped in a bow figure.
More metal will be removed from the back and front combustion chambers with the skim process to make it flat again.
So the front and back chambers will be smaller than the middle two.
Will this have a big effect and can it be corrected? Will a cylinder head place be able to cc the chambers and equal them?

I am just curious about this. With the thicker head gasket it will be usable again when needed but the chambers will be uneven in cc.

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big effect? nah, i woodlnt of thought so, depends on how much the head was warped.


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if you take the head to a good maching shop and told them your situtaion they should be able to correct the chamber size by taking some meat out of one of the chambers or something.

perhaps they might make a head gasket that is thicker in the parts that were skimmed more to make it sit flat again??

i dunno, im far from an expert

all the chambers will be more or less the an equal size? how much did it warp? can't imagine the size changing much.

I did take it in to a cylinder head shop.
The guy phoned me back 2 days after that and informed me of the following:

The head is skimmed to max factory specs of 73.0mm
The head is flat at the bottom where it sits on the engine block but the top where the tappet cover is screwed on, it is still warped.
Not in a bow like I explained at the first post but it is warped from the left front of the cylinder head to the right back of the cylinder head.
That is maybe why it was skimmed by the previous owner.To get it flat again.
Obviously it cannot be straighted on the cylinder head's top.
My concern is just with the chamber's cc.
Is it not affected in that they will be of different cc causing different comp ratios accross the cylinders?
Hope you guys understand what I mean.

Nah, it won't matter much.

If you were racing, you'd want to get that last 1/2 HP out of the enginee. If one cc is slighter smaller, you have to time the spark for the cylinder that is the highest compression. Unless the head is ported and combustion chambers matched it really doesn't matter. From the factory there are always differences ... see the Tech Section article "A-type Cylinder Heads" for information on how you can easily measure the CCs. Then let us know the difference between the highest and lowest.

You don't usually need to skim/mill the head flat because there are scratches on it. Most scratches don't cause problems.

ddgonzal

Thanks for the info. I think I will check the cc's of the chambers when I get some time.
I was just worried that when the time comes and I need to use the cylinder head that it will ping or something and I will not know why.

And also out of curiosity.

Hi all

I had a chance this weekend to measure the cc of the combustion chambers on my spare GX cylinder head.
Remember the head has been skimmed to 73.0mm due to warpage at previous owner.
Starting at the front and then going to the back of the cylinder they are:

1. 26,2 cc
2. 28,4 cc
3. 28,4 cc
4. 28,0 cc

What do you guys reccomend and think about it?
Will the differences be bad?
What place can I go to to make the chambers equal again.
Also, what compression will this cc's give on a GX engine. Will it be ok with pump fuel or will it cause detonation.
Sorry for all the questions.

As far as the fuel goes , if you are still running a factory GX engine then you'll be ok on regular fuel.Unless you have higher comp. pistons , then it starts getting interesting. Some good machine shops can make a "COPPER" head gasket at the thickness you need for the difference machined off the head, but you may need to supply a stock head gasket for them to go by.And the good thing about that is you can use the copper head gasket over & over again.

That's an 8% difference between cylinder #1 and #2. I would think that'll make a difference, you might have to retard the ignition to keep #1 from detonating, but then numbers 2-4 won't be working at full capacity. So I would take a grinder and remove a little bit of aluminum from #1, to make the CCs even.

The difference (without figuring in the width of gasket thickness) is 10.3:1 compared to 11.2:1. A pretty big difference.

What do you guys recommend? Just use a moto-dremel tool, where should the material be taken from? Or should this be taken to a professional shop?

Can anyone give answers?
Where to remove material and also what shop can maybe do this for me if it is not recomended to do it myself.