Thread: 7:1 to 8:1 cyl head rebuild planning

Hi Neil, looking at the cylinder head on the engine in the pic that would likely have been a 7:1 when it left the factory. Although at any point in its history it could have been shaved (and this increased the CR) and the only way to really tell is to measure the thickness of the head. The factory 8:1 heads have a raised section about an inch long on the centre edge of the head on the manifold side, and it will have an “8” stamped on it. You can certainly have “a little bit” taken off a 7:1 head but be aware of cracks (these old heads are a bit prone to this) before you start working on it, and also be aware of taking too much off, as it may mean the pushrods end up being too long.

There’s plenty on the internet about this, at any rate. I think the “expedition Land Rover” site has a good write up…

Cheers,

Matt

Originally Posted by brookvale

Hi guys. been a while since I was here in AULRO.
Recently acquired a 61/62 88" ex NZ Army IIA, Chassis 24114028 B. Engine 251179467F
Chassis and body totally toast but engine and gearbox could be salvageable.
Did sell some Army bits off it
The tyres! - genuine original Dunlop Triple Tractions 6.50 16s ... sadly cracked to bu**ery
Engine# suggests 7:1 compression.
One or more pistons defo seized. Will find out how bad tomorrow!

Cyl head not yet removed from engine but could it be planed down to suit 8:1 ?
read somewhere that some later heads could be, depending on marks/numbers on head.
Anyone know what marks I should be looking for?
Gonna be $$$ to rebuild but there's fewer and fewer engines on the market these days so think it'll be worth a rebuild.

PXL_20230127_231220569.jpgPXL_20230310_015638213.jpgPXL_20230307_215333809.jpgPXL_20230307_220756370.jpg

cheers
Neil

All 8:1 heads and later heads have this raised boss, and it should be stamped either 8 or 7. And if it left the factory as 7:1 it can be planed to 8:1. But earlier heads without the boss are likely to have insufficient metal to safely plane.

Thanks muchly guys. Somehow I missed the Expedition FAQ pages.. no raised boss on head and my head casting # is definitely in the 7:1 "cracks more easily" period
Never mind, doubt if I'll miss a few horses compared with a previous SIIA I had with 8:1 !
but will fully check over for flatness and signs of cracking.
Several snapped studs in manifold to get removed too.
cheers. Neil

Originally Posted by brookvale

Thanks muchly guys. Somehow I missed the Expedition FAQ pages.. no raised boss on head and my head casting # is definitely in the 7:1 "cracks more easily" period
Never mind, doubt if I'll miss a few horses compared with a previous SIIA I had with 8:1 !
but will fully check over for flatness and signs of cracking.
Several snapped studs in manifold to get removed too.
cheers. Neil

I bought a 2.25 motor to rebuild, a few years back, had around 20 cracks in the head, every had I found to replace it was cracked except one which had two cracks that had been stitched.

Interesting - I have yet to see one cracked, although I have to admit I tend to long term ownership rather than owning lots of them.