Valve Guide broke and new pistons for GS400

[MarkoGS400]

Hi!

I'm repairing my '78 GS400 engine and right now I'm doing cylinder head and valves. Accidentaly one of my intake valve guides broke and now I have trouble to get the rest of it off. I took off the valve guide ring as it broke and tried to get the rest of the guide of with a hammer but it doesn't move to any direction. Should I heat it and then try to hammer again? Any good tricks?

And then I should also find a new intake valve guide. Is that a part that I should find at almost any shop?

Another problem is to find new pistons. I have heard that GS750 uses the same pistons as GS400. Is this true? And how about these other cylindeer head and engine parts. Can I use any GS750/550/450/425 parts?

Any good tips and tricks websites for repairing GS400 engine?

[DimitriT]

Heat it. Aluminum expands more than iron. But consider taking it to a machine
shop. Pressing in the new guide will be tougher than banging out the old one.
They sell a tool which fits into the guide for this job. I think I saw it on the
Z1 enterprises web site.

I would reference the parts fiche on www.bikebandit.com for checking compatibility.
If the part numbers match you are good.

[MarkoGS400]

Thanks DimitriT for the tips! I have to work down that broken valve guide
maybe tomorrow. I think that I still need to get that cylinder head to professional machine shop because it's in quite bad shape.

Any other tips about that engine would still be extremely valuable! [-o<

[bwringer]

First off, get a shop manual.

Therein you'll find useful tidbits of information including: to remove/replace the valve guides safely, the cylinder head must be heated to a certain temperature, ideally in an oil bath in a machine shop. Since the aluminum expands at a different rate than the valve guide, it'll loosen up a bit and you can press or the guides out.

In other words, don't just try to beat them in or out of there cold. Take it to a machine shop where they have the equipment to heat the cylinder head thoroughly and use a press.

Overall, if there are problems with the head or engine, you might be better off trying to find a lower-mileage engine in better shape, then rebuilding that. If pistons are NLA, you may have to re-use a set.