Heads: are '77 & '79 the same?

[Sidecar Bob]

The title just about sums it up. Are '77 & '79 heads the same?

My friend was going to bring his Helicoil set over to do a spark plug hole in my right head. Now the right head gasket has blown so the head has to come off anyways. Will the right head from my '77 parts engine fit or do we still need to helicoil the one from the '79 engine?

[ritalz]

I think you will need to swap the cam to make it match. Otherwise it should be a straight swap.

[Whiskerfish]

The castings should be the same. You will want to swap the cams and the cam holders to retain the same break-in of the bearing surfaces.

[robin1731]

The castings should be the same. You will want to swap the cams and the cam holders to retain the same break-in of the bearing surfaces.

I disagree on the cam holders. Those are machined with the head. Swapping them from head to head could cause the cam to bind. You should swap rocker arms though. And make sure they stay on the sam cam lobes. Those parts do take a wear pattern to each other.

[Sidecar Bob]

Are the valves the same size?

[robin1731]

Are the valves the same size?

Yes, valves are the same on all 1000 and 1100's. I believe the same on the 1200 also.

[RB]

The heads are the same the cams are not..well I am fairly sure..hotter on older bikes. Seems like swapping the whole cam assembly would work the best..but I've never done it.

[Missourimike]

If I remember right, the '75-'77 motors are timed using 5 degree BTDC. The later models are set at 10 degrees BTDC. It's the cams. If I were to swap cams, I'd check the ease of rotation by not having any tension on the lobes(valve springs loose) before setting clearances on the valves. Just to make sure nothing is binding. Consider the difference in milage racked up on the different cams? I would think that it would be hard to tell the diff in wear just by milage alone, as the type and frequency of the oil can be a big factor.

[Sidecar Bob]

I installed the '77 head over the weekend. I used the '79 camshaft and moved the '79 rockers and their holder to the '77 head as an assembly.The bearings felt good - no noticeable play but no binding either.

BTW: I adjusted the clearances on the workbench before installing the head. Much easier than trying to do it between the bike & the sidecar.

[MikeO]

77-75 cams are the same 78-79 cams are the same cam holders should stay with the head it comes with. they are line bored together. 75-79 service limit on exhaust lobe is 36.5 mm or 1.437in. service limit on intake lobe 75-77 is 36.8 mm or 1.448in. 78-79 is36.5 or 1.437in. heads should be torqued before installing the cams use moly 60 paste on head bolts and torque 42-45ft lb

[Sidecar Bob]

Based on previous replies in this thread, I decided to see if the '79 cam holder would work with the '77 head. A friend who knows more about engine repair than me (started working on VW engines in his Dad's dealership at a very young age) was here and he agreed that it feels right. I think this is a good example of Japanese precision manufacturing.

At any rate, I'm not going to take it back apart now.

Why would it matter if the cam are in before the head is torqued? I have previously replaced head gaskets without disturbing the camshafts, figuring that removing the camshaft and followers was just extra work.

[Whiskerfish]

SNIP I have previously replaced head gaskets without disturbing the camshafts, figuring that removing the camshaft and followers was just extra work.

Me too!!

[CYBORG]

i have replaced heads with the cams already installed, and not had any problems, as well. would like to know what the reasoning is to do the cam installation after the head is torqued

[MikeO]

no need to do this

[Sidecar Bob]

FWIW, I put the parts engine "together" last night. After I put the '77 cam, followers & cam holder on the '79 head I tried turning the cam and I felt no binding or other problems.

Like I said "Japanese precision manufacturing".