Skimming the heads on a 1977 GL1000

[Hedgepig]

Hello out there in Wingland
Does anyone know the maximum permissible amount that can be skimmed off a set of heads from a 1977 GL1000 Goldwing?
thanks

[scotterichmond]

The service manual says
.10 mm is the limit

[Hedgepig]

Thanks, Scotterichmond - I'll give them to my tame machinist with your info!

[Old Fogey]

Not strictly true. Maximum allowable warpage (still usable) is 0.10 mm / 0.004" . You would probably have to take the head down further than that to clean it up.
I know of heads that have had far more taken off, but I suggest a max of 0.40mm / 0.016". That should be enough without running into other problems.

[scotterichmond]

Not strictly true. Maximum allowable warpage (still usable) is 0.10 mm / 0.004" . You would probably have to take the head down further than that to clean it up.
I know of heads that have had far more taken off, but I suggest a max of 0.40mm / 0.016". That should be enough without running into other problems.

I sit corrected. Did not read close enough. so the head can be .004 in. warpage, and still be servicable without re-surfacing?

[Old Fogey]

Apparently so.
0.004" across the width of the head is not a lot; the thickness of a human hair.

I think the only thing that might cause a problem, if you had to skim it down a lot, would be the oil restrictor. The hole in the head may need to be deepened by the same amount.
I stress that I have never measured that; there may be enough clearance without further surgery.

[Hedgepig]

Hi, Old Fogey!
Thanks for the extra info - yes, I've finally made a start on my 'restoration' project! My tame machinist took a gnats off the heads and it has bought them up really well. The way things have worked out is that everything will be used off the old 200,000 mile Wing, except the engine and frame! Bit like the story of the broom you've owned for years; been a fantastic broom, lasted really well; it's only had 5 new heads and three handles............!

[Fred Camper]

Love to hear about wings that her used like that and not discarded at 14000 miles like so many.

[Hedgepig]

Love to hear about wings that her used like that and not discarded at 14000 miles like so many.

Yes, I agree! I have an identical K2 which I still ride most days to work and that one has just clocked 153,000 miles. It's had a touch of welding done on the frame over the years and survived a t-bone prang (new forks, radiator, mudguard, yoke) but it just keeps rumbling along. I think I'm wearing out quicker.....

[mikeinidahoidaho]

One thing to consider, skimming the head moves the cam center closer to the crank center, and will retard the valve timing a small amount. Later intake valve closing, from retarding the valve timing, will lower the cylinder pressure on the compression stroke and reduce botton end torque a small amount. Not really something to worry about, for most of us, you would probably never feel the difference unless a large amount was removed.

[Old Fogey]

Can't see how moving the cam closer to the crank retards the timing. With a toothed belt I would have thought the opposite to be true. But you'd have to take an awful lot off the head to even be able to notice any change at the timing marks, let alone in the performance. And surely the increase in compression ratio would more than make up for any timing loss if you are right.