1978 GS550 cylinder head help

[enriquev9]

I have a 1978 GS550E that I’m restoring (post to be created soon). When disassembling four exhaust bolts broke. I tried to drill them out and remove them with no success. In fact I broke a drill bit in one and an easy out in another. I took the head to a machine shop and they informed me they could remove the broken bolts but at $80 an hour and with possibly having to drill the factory holes larger.

i decided to get a used head off of eBay and just rebuild the head so I have a fresh cylinder head. Here are my questions:

can I use the old drivetrain components on the used head I purchased with proper machining? (used head had no valves)

if it’s not a good idea to recycle valves and springs etc, where can I purchase affordable new valves springs etc. (I’m finding it hard to locate parts other than partzilla and bike bandit)

do you recommend a vendor for the cylinder head work and possibly the cylinder boring and honing?

any assistance would be deeply appreciated.

[Grimly]

Yes, you can re-use your old components, assuming you measure them and make sure they're not knackered. Check in the manual for spring length, check for valve stem straightness, check the new head valve guides for wear and sloppy fit on the valve stems. Give the valves an initial lapping into the new head, inspect the result. You might need to have the seats touched with a cutter, but perhaps not.
The camshafts should (hopefully) fit the new cam caps within tolerance.
Make sure to use Viton valve stem seals.

[Nessism]

I agree with Grimly. Hope the new head came with the cam caps because those cannot be swapped between heads.

Personally, I'd have the valves touched up by a machine shop with a centerless grinder. Be sure to tip the stems also. Doing this will assure the valve sealing surface is clean and ready to go back into service. Also install viton valve stem seals.

[Rich82GS750TZ]

Pardon the interruption. Ed, can you elaborate on “tip the stems”? First I’ve read that phrase. I may be rebuilding a head in the future for the first time and I don’t want to miss these finer points. TIA

[Nessism]

Tipping the valve stems isn't important with a rocker arm valve actuation system, but with a head that uses buckets and shims it's important. The valve recedes into the head with wear and the clearance goes away. No big deal, install a thinner shim. If the valve and/or seat is cut it will accelerate the process and at some point the shims will get too thin to allow adjustment. But cutting the valve stem down a few thousands solves that problem.

[Rich82GS750TZ]

Got it. Thanks for that. No worries for me then with the screw type valve clearance adjusters of the 16V TSCC.

[Nessism]

Got it. Thanks for that. No worries for me then with the screw type valve clearance adjusters of the 16V TSCC.

You best check for valve guide wear on that head. The rocker arm puts a side load on the valve which can wear the stem more so than a shim and bucket engine. There is no free lunch!

[Rich82GS750TZ]

If I decide to rebuild the head I will install new valve seals and make sure I know how to properly inspect the valve stems for wear.

[enriquev9]

Looks like the head comes with cam caps. Thanks for the advise. I didn’t even think that would be an issue.

i figured I could reuse the valve train but any ideas on where to source parts like the valves, springs, guides etc. This is for a worse case scenario.

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