GS550 Head Swap Questions

[leecatd8209]

Missed a shift last night that led to a pretty good over rev. Managed to spit and sputter home, and now today she won't run. 0 compression on cyls 2&3, and pretty low on 1. My bore scope showed definite exhaust valve contact across all 4:



I picked up a loaded head, NOS head gasket, and a cam chain tensioner gasket because mine is leaking. Anything else I should pick up? Tips, tricks, mods, advice for while I'm in there?

[Guest]

Plan on replacing the base gasket while you're in there.

[leecatd8209]

Plan on replacing the base gasket while you're in there.

I really didn't want to take the jugs off. Is that necessary? If I have to go that far I'm gonna end up doing way more down time than I can afford at the moment.

[cowboyup3371]

You will disturb the base gasket when you pull the head no matter how careful you are so yes, it is very necessary unless you are willing to have some good leaks

[leecatd8209]

Then I might as well do pistons and rings while I'm in there...

[cowboyup3371]

Your pistons should still be in good shape but rings wouldn't be a bad idea

[Steve]

That picture shows a pretty good impact on the piston. I'm not so sure that I would run them in <my> bike.

And yes, if you don't replace the base gasket now, you will do it in another two weeks, along with all the other gaskets (again).

.

[cowboyup3371]

Thanks Steve, you have a better eye than I do as I didn't really think there was anything there.

[leecatd8209]

Alright, so my parts ordered list has expanded to include a base gasket and O-rings, piston rings, and everything to rebuild the tensioner while it's off. I'm gonna hold off on pistons, hopefully I can polish down the high spots to avoid any heat risers, but if they're too bad I'll try to find a set.

Thanks for the help!

[Steve]

It's not the high spots and heat risers I would worry about.

The impact might have induced a stress fracture that will develop with elevated temperature.

For some reason, the cracks never seem to weld themselves together when the temperature goes up.

.

[Nessism]

The pistons will be okay. Just inspect them for cracks when you pull them out.

Be sure to remove the valves from your new head and inspect everything. Lap valves as necessary and replace the valve stem seals. Viton seals are best, aftermarket, but most aftermarket gaskets are crap. Best to stay OEM for those.

[leecatd8209]

It's not the high spots and heat risers I would worry about.

The impact might have induced a stress fracture that will develop with elevated temperature.

For some reason, the cracks never seem to weld themselves together when the temperature goes up.

.

That's what dye-pen is for.

[leecatd8209]

The pistons will be okay. Just inspect them for cracks when you pull them out.

Be sure to remove the valves from your new head and inspect everything. Lap valves as necessary and replace the valve stem seals. Viton seals are best, aftermarket, but most aftermarket gaskets are crap. Best to stay OEM for those.

I didn't consider valve seals, now would for sure be a good time. Thanks for the reminder!

[hannibal]

Why do you need to replace the head? I guess the piston to valve contact destroyed the valves guides and head?

[leecatd8209]

Why do you need to replace the head? I guess the piston to valve contact destroyed the valves guides and head?

Mine has some questionable crack repairs in it, and it was much cheaper to buy a serviceable head than just valves, plus it came with spare covers, cams, buckets, shims, etc. I'll use whatever's in the best shape from both.

Everything looks very good in the spare, and if it specs out I'll just be able to replace it as a loaded assembly to save some time and aggravation.