Early 18V head question

G'day mates! I'm vicariously in New Zealand rite now 'cos my sis is visiting there showering me with pics - AWESOME country!

I'm planning the 900 mile Dillard voyage; wanna do a head job (early '72, 93K mi.) This motor runs like a lil bear, starts instantly, pulls good to about 4500, gave me 31 MPG highway, but has never been apart and needs valve guides etc.(deceleration smoke), so the question is:

With this 8:1 compression would there be short or long term bad if I have the head shaved a bit, say .005"? Of course its gonna get the full machine shop spa treatment and 3-angle job, and new valvetrain gear - I'll do water pump, front seal, and timing chain and assoc. bits same time (and radiator service).

I was thinking maybe a shave would compromise sealing of the 93000 yr. old rings (LOL), but I also know higher comp. makes better throttle response and fuel mileage. Any cautions here?

Also wondering if there's an absolutey BEST quality head gasket set and timing set? Thanks!

I would use a copper head gasket.

Marco,

Modest milling of the head will not make a big difference in compression ratio, will certainly not raise it to the 8.8:1 ratio of the high compression engines from earlier years, and will not make a difference in the butt dyno. Shave it if it's not flat, but don't expect a difference in power.

The only head gasket to consider is the Fel-Pro/Payen head gasket, which we use in street engines as well as race engines. There's nothing else out there that anyone would recommend. As for timing chain setups, do note that the simplex (single row) setup advances cam timing about four degrees, which pushes the engine's power rpm range down slightly, while the duplex (double) timing chain setup retards cam timing about the same amount, which moves the power band up in rpms slightly. So if you like the power band about where it is now, I suggest replacing the timing set with like kind.

Dick

Marco:

Payen head gasket set.

County or find a NOS set of timing chain and gears. Yours very likely has the single row chain. Make a switch to the double row/better wear.

An .05 shave won't do much for you. .020/.030 will give you a bit more compression. Make sure that your head hasn't already been shaved in a past life as you can break through into the water passages if it has already been done.

Slightly OT, but why would the single row and double row timing chains change the cam timing. Surely the relative positions of the key slot and the timing marks aren't deliberately changed from the original ? Just struggling to understand. I would have just fitted these without thinking I would change anything.

Ken,

Cam timing change was an emissions control move for the North American market. The small change to the orientation of the sprockets resulted in a slight reduction in exhaust emissions based on the federal drive cycle test new cars had to go through, both then and now...

Dick

Thanks Dick. It all makes sense now. My 72 GT is a retirement present to myself, and while I have a reasonable knowledge of car mechanics, I am still finding out many interesting details abut MG's. This forum has been a great help.

A minimum resurface of a cylinder head would be part of normal deal when refreshing or rebuilding a head, and as metioned this would not effect compression ratio very much. I do however suggest one does not drasticly increase compression ratio thru head resurfacing with OEM 8.0 to 1 piston in seasoned high mileage engine, even if it all work well for you, if you ever go to rebuild the engine, now you destined to use 8.0 to 1 pistons again.