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gs650 to gs750?

  • Thread starter Thread starter Peteyboy
  • Start date Start date
P

Peteyboy

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





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

 
I've now checked all the threads, with the exception of the spark-plug threads - I don't have the correct tap for that. All are the original size, and good, apart from the one exhaust bolt thread that I mentioned earlier. That has been drilled and tapped to M10 x 1.5.

I did think that one or two of the cam cap threads may have been helicoiled, but if they have, they have been done to the original size, and hold a tap well.

This is an earlier head than yours - 16 bolts to hold the cam cover.
 
Thanks for doing that Steve, appreciate it. So I guess as it is 16 hole it's not going to work. Unless I got a matching cam cover too? Would my cams etc fit if I changed the head and cam cover?
 
I believe the cams are the same, but I'm not 100% certain. Maybe a check of a fiche would tell? As far as I know, the reason for the extra bolt was to cut down oil leaks from the front of the engine, between nos 2 and 3 exhausts.
 
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