Swap Cylinder Head or get it machined

[MTHughes]

I have a 79 GS750 with 2 broken exhaust bolts stuck in the cylinder head. I have tried drilling them out with every drill bit I can get but nothing has even made a dent in them. I have an extra cylinder head I got when I bought the bike from the previous owner so I was planning on just swapping them out. I just took the camshafts and cylinder head off and now am not sure I want to swap them. The cams that were on the bike look in very good condition whereas the ones from the extra cylinder head have very minor surface rust on them cause they have been sitting around for a while. So now I don't know what to do. My options as I figure them are:

1. Go to a garage or machine shop to get the stuck bolts drilled out by them and reuse all the original parts.

2. Replace the head with the extra one and use the camshafts that came with that cylinder head, again minor surface rust but that should wear off after a little use, maybe, I think.

3. Replace the head but use the original camshafts that came off the bike since they look in better condition. (not sure if you can just interchanage them though)

What does anyone else think? All help is as always SUPER appreciated!!

Thanks
Mike H

[tkent02]

I have a 79 GS750 with 2 broken exhaust bolts stuck in the cylinder head. I have tried drilling them out with every drill bit I can get but nothing has even made a dent in them. I have an extra cylinder head I got when I bought the bike from the previous owner so I was planning on just swapping them out. I just took the camshafts and cylinder head off and now am not sure I want to swap them. The cams that were on the bike look in very good condition whereas the ones from the extra cylinder head have very minor surface rust on them cause they have been sitting around for a while. So now I don't know what to do. My options as I figure them are:

1. Go to a garage or machine shop to get the stuck bolts drilled out by them and reuse all the original parts.

2. Replace the head with the extra one and use the camshafts that came with that cylinder head, again minor surface rust but that should wear off after a little use, maybe, I think.

3. Replace the head but use the original camshafts that came off the bike since they look in better condition. (not sure if you can just interchanage them though)

What does anyone else think? All help is as always SUPER appreciated!!

Thanks
Mike H

All three are valid options, for #2 it is very easy to clean the rust off of mechanical parts by electrolysis:

Before:


After:

[new bob]

I just had my cylinder head to the machine shop for the same thing.It cost me $60.00 to get it drilled and tapped and it worked out great.I would go that route.

[tkent02]

I just had my cylinder head to the machine shop for the same thing.It cost me $60.00 to get it drilled and tapped and it worked out great.I would go that route.

How many broken studs for $60?
I have a few to do now too.

[new bob]

I had to get just one drilled and tapped.

[Nessism]

I'd take the valves out of both heads and check for valve/seat/guide wear. You can check the valves for wear with a micrometer on the stems plus inspect the valve faces for pitting or burning. The valve guides can be inspected by sticking a valve in the guide, holding the valve a little ways off the seat and then rocking the valve to see if it wobbles (which is bad). Use the best valves of the lot and the head with the best guides (least wobble). If that one turns out to need the broken screws extracted, so be it. Oh, and use the non rusty cams.