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GS550 Bored 740cc Officially Done!

  • Thread starter Thread starter Guest
  • Start date Start date
Hey brveagle, How about an update on the 740 operating experience? Ray
 
Gammaboy said:
Stupid question - why would you do this (ie GS550/650 big bored to 740cc) vs using a GS750 motor?
Click to expand...

And the 550 is much much lighter, shorter, quicker and more nimble than the 750.

Ray, you can ride mine all you want.
 
Ok Tom, Once the weather returns to a more suitable (for me) temperature of at least 75
f, I'll take you up on that. Did you bore yours out or is it still 673cc? I'm thinking the 740cc version might be a bit of a terror? Ray
 
No, I just bought another 550, very nice original one. I think it will get the 673 treatment, plus nice suspension and brakes, and then my original cafe clone will get the kicksass 740 or whatever it is engine.

The problem for me is, I am always short of round tuits
 
Right, got it. makes perfect sense :)

Are the GS550/650 a pressed together crank?
 
Sorry for the delayed response guys, don't log into here too much.

I ended up "detuning" my gs550/740cc bike. It was just running too hot. I was even running an oil cooler and full synthetic.
It's back to a 673 for more reliable performance.

To answer some questions, I did not really know how to build a motor when i did this. It was a HUGE learning experience to me. The gs750 2 valve pistons share the same wrist pin as the 550's (80-82). However, they were hitting the head. I then had a block spacer milled in the amount of 4 mm. It was "just a guess" after much "measuring". at this time i did not know much about squish and how to measure for it. I ordered it through cometic. Great company.
This sunk the pistons in the cylinder, which is not ideal, but the bike ran great. (other than being really hot, ALL THE TIME).

It if had more free time, i would really love to experiment with smoothing out a 650 head to remove the high spots of the combustion chamber in the head. I would imagine by doing this, you would have a "high compression" motor that would not require a block spacer.

Summary: Still love and ride my gs. Just have it as the 650 top end.
 
Thanks for the update, brveagle. I have been wondering about the heat issue, so that input is definitely appreciated. I was also dying to know how you got the 750 pistons to 'fit', thanks for clearing that up.
 
I looked at my 750 pistons and 650 cylinders today, looks like the sleeve would only be about .030 inches thick after boring for the 750 pistons. Is that what you had?
 
Look into using 750 sleeves. And see if the block will let you put the larger sleeves in.
G
 
Hey Brveagle,

I am looking at doing a project very similar to this. I have a Gs550t currently, and I am trying to decide if I should just go with 650 cylinder or be adventurous and try to go with the 740 build like you did. I know you had troubles with to much heat and everything, but I was hoping to get a few more details on the size of the oil cooler and how you hooked up the oil cooler. Also, did you just bore the 650 sleeves or did you remove the 650 sleeves and put 750 sleeves in the the 650 cylinder. When I found your thread I thought it was a really cool idea, and I figured if you had any other pointers you could shoot them my way. I would really like to see this project though.
 
Hey, Ace. Did you notice the dates on this thread? :-k

It started 8 1/2 years ago.

Might have been better to send him a PM (assuming he is still active on the board)
or send him an e-mail (assuming he has one in his profile).

.
 
Last edited:
Oh man...... ha ha ha I guess that just shows how much of a newbie I am. I read the whole thread, but I guess I just saw that the last few posts were put up early last year, and was just hoping to get some more info. I have the tendency to overlook things. Thanks Steve. I guess you havent heard of anyone else trying this project have you?
 
No, and I don't really remember seeing this one on its first time around. :oops:

Several have done the 673 conversion, this is the first time I have heard of taking it to 740.

.
 
Ok. I have been looking to do something to my old bike and I know alot of people have done the 673 conversion, but I was wanting to take it to the next step. I have not done an engine rebuild before, so I might just start with the 673. It would be a fun learning experience by the look of it.
 
I dont know. somebody said to re sleeve the 650 cylinders with 750 sleeves. Sounds like alot of work to me, and I think it would cost alot of money
 
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