948 head specs

[niftyrodman]

With these older heads, and, of course we dont know their history,may I ask, where can you find the exact thickness of a standard head. I need to know this before I send a head to the machinist so I can ascertain, how much I can skim off it. A measurement from the highest point in the combustion chamber to the face would suffice. Thanks.

[don58van]

Hi Nifty

The standard thickness for all factory A-Series heads is 2.75". That is from the machined surfaces on the top to the machined surface on the block mating surface.

Don

[niftyrodman]

Thanks Don you have made my evening. Im having trouble with compression, I mean, the motor starts and runs sweet, but its down across all pots to what it should have been and all new fresh bored etc. Picks up & revs sharp as a tack. Valve timing is right. So after a bit of research found that the head on it is a 948 copy, so Ive a second head to reco and of course add inlet seals( thanks Phil) and new guides, and having your information, can check that out and compare combustion chambers, but when you spend the time on them its only natural to become fussy. Also too there is another variable and that is, does it have the right head gasket.

[philthehill]

The head gasket will have little if any bearing on the compression unless it is shot.
The average head gasket will add around 3cc to the combustion chamber.

If your compressions are low you need to investigate further - to me skimming the head to achieve a better compression is pointless as it will not get rid of the underlying problem(s).

[oliver90owner]

I mean, the motor starts and runs sweet, but its down across all pots to what it should have been and all new fresh bored etc.

Are you sure the compression tester is giving accurate results? How even are the compression results? What are the typical pressures found?

I would be more worried about that knock at start-up. If you are going to check as far as small ends, do the pistons pass the crank or are they removed from the top of the engine (needing the head off anyway)?

[niftyrodman]

No its not the gauge, mate. The trouble is, that the engine after assembling laid around for about 5 years without being fired up, and just maybe there is a bit of tension loss there, that's all I can put it down to if the head is exactly as it should be.