gs650 to gs750?

[Guest]

Hi all,
Apologies for another new thread, thought my question would get lost in the other one.

I have just stripped the head and jugs off my 1985 gs650gt. I have done this because the casting of the threads for the exhaust bolt has snapped off, I'm struggling to find someone to fix it that I am confident in, and there aren't any 650 heads around that aren't knackered! Is there anything else that will fit that is easier to find? Maybe gs750 jugs and pistons, would this work?

Many thanks again.
Pete

[60ratrod]

the 650s and 750s are 2 different animals. you would have to do a lot of work to get 750 jugs, pistons, and head to fit. now if it was a 550, you could make the 650 stuff work, and if it was a 750 I think you can make the 1000/1100 stuff work. just keep looking for someone to repair that messed up thread boss or looking for another 650 head. or you could fix the threads yourself with a helicoil kit

[Peteyboy]

Excellent, I love this place, answers in an instant, thanks mate!

[tom203]

By removing the head, you've done the hard part! Now locate someone with an EDM machine- they will make short work of eroding the broken stud and then you can helicoil for a new thread or possibly retap for a bigger size thread.

[steveb922]

Petey, EDM (Electrical Discharge Machining) is often referred to as spark erosion over here. With the history of shipbuilding and engineering up your way, you should be able to find someone to do it. Or alternatively post a pic - it's not as difficult as you might think to insert a helicoil, as long as you have sufficient metal to work with.

[Peteyboy]

Thanks guys, but that is just the problem. There is not enough metal left to helicoil? I've just nipped out and taken these pictures.





Thanks
Pete

[steveb922]

Ouch! I'm not sure whether that could be built up, drilled and tapped. Someone here will be able to tell you. I have some (2, I believe) 650 heads in the workshop. I'm needing one for a 674 conversion, so I've already checked one, and know it's good. I'll see what the other is like.

I'll try to post photos later.

[Peteyboy]

I know! I didn't even noticed until I had nearly finished everything else. Buying someone else's project eh!
If you could let me know how it is, that would be brilliant, especially if you were able to sell it.

Thanks again for your help, it's appreciated!

[steveb922]

Okay, I found a spare 650 head. I've no idea what year it is from, so if anyone knows how to be certain it will fit a 1985 model, that would be useful.

First thing I checked was the head-to-barrel mating surface. Opinions, anyone?

[salty_monk]

Looks like it will be ok with a Skim to clean it up to me... He could use his own valve gear with new stem seals I would have thought.

[steveb922]

Some more info - two valve guides are missing. One exhaust bolt thread has been drilled and re-threaded, looks like 10mm. All other threads look good, but I'll check with a tap asap. It looks like a silver head that has been re-sprayed, and would need to be re-painted. I haven't noticed any dings or broken fins.

[Peteyboy]

Hi Steve, certainly sounds promising. Could I just use the existing valve guides from my head? If you could check all threads, that would be great! Might be able to get the old girl running sooner than I thought!

[duaneage]

Be aware the 1983 head has 17 bolts not 16. Make sure your valve cover is the same.

[steveb922]

Be aware the 1983 head has 17 bolts not 16. Make sure your valve cover is the same.

Useful info, thanks. I'll check that along with the threads, hopefully tomorrow evening.

[Peteyboy]

That's a great point about the 17 holes, mine does have 17 and it's difficult to get a head gasket for!