GS550 Bored 740cc Officially Done!

[tkent02]

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?

[gmansyz]

Look into using 750 sleeves. And see if the block will let you put the larger sleeves in.
G

[Nerobro]

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

Ray, you can ride mine all you want.

200lbs, and an extra speed in the gearbox says a whole lot doesn't it? :-)

[Ace07]

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.

[Steve]

Hey, Ace. Did you notice the dates on this thread?

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).

.

[Ace07]

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?

[Steve]

No, and I don't really remember seeing this one on its first time around.

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

.

[Ace07]

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.

[mrbill5491]

740 ccs? Is there any material left on the cylinders?

[Ace07]

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

[gmansyz]

Hiya All.
There are a few things to consider here. First, Suzuki usually allows enough material for boring 3 mm over bore. 65mm would be the max bore for the 650 cylinder, leaving about .080" sleeve thickness. How much work is too much????? Or $$$'s?
Putting bigger sleeves in the 650 cylinder is $100- $200. Sleeves are extra. But, why not use the 750 sleeves and maybe the 850 pistons? Or turn the 850 sleeves down or get some after market sleeves? If you are committed to this adventure, why not spend the money?
As for the running hot and needing a cylinder spacer, it is, after all, an air-cooled engine. Did you check the actual compression ratio???? Also, did you match the pistons to the 650's "Twin Dome" combustion chamber? This is very important as the old 550's and 750's were open Hemi's.
Why it runs "Hot"? It is relative. Maybe the oil cooler is not plumbed in to cool all the oil or is just too small?
Now, how strong is the clutch?
Or, why not just swap in an Air/Oil GSXR 750 or 750 Katana engine? You get a six speed trans and a real 90+ horsepower.
Laters
G

[brveagle]

I used the gs650 cylinder and had it bored out. (650 sleeves) As i think i mentioned before i did swap it out back to the 673cc top end to gain reliability back. I truly guessed on spacer size after shimming attempts proved what the thickness should be to have the piston clear the head. And i ran a lockhart oil cooler plumbed in via the oil sending unit. I was young and wanted to "build a motor". I learned alot.

[Ace07]

Thanks for replying guys. I am willing to put in as much work as needed to make it the 750, but I would like to spend a maximum of 1500 dollars on this project. I am glad to hear that the 650 cylinders can be bored out to the 750. I don't want to go with the Kantana engine, because someone said that there would have to be alot of frame modification. I don't want to do any frame modifications, because I really like the way the bike looks now. Gmansyz, how would I go about making the pistons match the combustion chamber? Would I have to have custom pistons? I have done some calculations on what I need to do to keep the standard compression ratio of a 650, but I didn't think about changing the piston shape. I also had the idea of using a GS550e oil pan on the bike, because some of them already have built in oil cooler outlets and inlets. I would then use a small electric turbo oil pump to circulate the oil through the cooler, that way the motor oil pump would not have to do any extra work and there would be less oil pressure drop. I am just not sure if the Gs550e oil pan would fit on my Gs550t bottom end.

[gmansyz]

Hiya
Glad you learned a lot brveagle. I ask, why did you not use the 550 head? How is the oil cooler plumbed in? And the Lockhart cooler is just too small. Try the big GSXR unit.
Ace07, I have seen the GSXR engine wedged into a 550 frame. Or rather, a 1052 with a turbo. Actually, minimal mods are needed to do this.
Now, if you use the 550 head, you may not need to modify the 750 pistons. Or mod the head either. Check the combustion chamber volume and diameter and the dome volume and diameter of the 750 pistons as well. And confirm compression ratio before worrying about modding anything. I believe the 550 head does NOT have the "Twin Dome" chamber shape. Do not use anymore compression than 10.5:1. Also, both guys, try for some drop in cams as well. Otherwise you will have too much pressure. Which could lead to hard starting. Degree the cams as well. Think of some porting too. Helps more than you know, along with using GSXR ignition coils.
Sorry, have no clue as to the differences in oil pans. Though, I would stay away from electric pumps as there is no purpose to them. Let the stock oil pump and added cooler do the work. Cool the oil before it goes thru the engine.
Probably no need for custom pistons right now but you would need to check valve to piston clearances and it the reliefs are in the correct place as well.
I may consider building a bike like this as well. Perhaps a 650G? and use bigger sleeves and GS 850 pistons? As I may getting a 550L early next year, I would rather not spend so much time on a 550 base. Though I would rather go to the GSXR engine, I already have more than enough projects going on.
Laters
G

[Chuck78]

This was discussed on caferacer.net as well.

the only builds that I have known that run a 650 head and 750 pistons both ran hot, and one guy hogged out the combustion chamber on the 650 head to match the 750 piston, which defeats the purpose of using the 650 head.

Here is what I just posted on the old caferacers.net thread. The 550 is lighter by far than the gs750, but the frame is more flexi. Some extra spine bracing by the ignition coils and the three most critical "OSS frame bracing" points would make any 673cc or 741cc gs550 a very ultimate platform for building a serious corner burning twisties machine... 440lbs lightened up & stripped down, with 80hp or more, wow! Below us my theoretical proposal:

Wiseco used to make a 65mm Big bore kit for the GS650 (I know this because I bought a Wiseco 65mm bore gs650 head gasket on eBay a while back). That would be the ULTIMATE piston to use, as it was designed for the advanced closed chamber raised port head that Suzuki engineers had great success with.

My other thoughts that never ever occurred to me until reading this thread were to just bore stock 750 pistons into 650 cylinders and use a 1980-1982 gs550 head, as the tiny vm22 intake port and carb boot size would be a bit small for a beastly engine.

Wiseco bores the gs750 out +4mm from 65mm to 69mm, so even if it had thinner walls, the 650 62mm 673cc sleeve should be able to handle a 65mm piston, and Wiseco used to offer big bore kits in 65mm for the 650.

I am going to make a big assumption here that the Hemi combustion chambers on the 550 and the 750 are about the same, which may not be correct. I don't have any 550 engines in pieces right now, but will be tearing one down to swap a nice 650 top end on over the winter (will cc the chambers then). if the chambers were about the same, then putting the 750 piston onto a 550 head should work out just fine. actually if the 550 chambers were a bit smaller, that would work out well because you could shape the piston to drop compression to around 10 or 10.5:1, or lower the cr by cutting deeper valve recesses into it with a basic milling setup even on an XY vise drill press milling conversion, and achieve a high compression ratio than stock. then run the 550 camshafts on approximately 110 lobe centers. seriously that sounds really awesome. I'm actually tempted to try. Some Keihin CR 29 or CR31 carbs would make a really great setup, or add the base model hot street megacycle cam grind for the 550/650.

741cc's and would definitely give a gs650 a view of the 550's taillight if done right! The raised port/closed chamber 650 head/piston design would win in terms of efficiency though, better fuel consumption. The 741cc if it worked out with a higher compression ratio and ability to make deeper valve cuts in the pistons, would really really make the ultimate if 550 if you could run even just the base hot street megacycle cams.

if you are going to the trouble of resleeving, I highly doubt a 750 sleeve would fit in there, but if you could fit something in between the 650 and 750 sleeve, you could track down some GS425 pistons and make a 790cc gs550!!!! Wow... gs750 and gs400 pistons/chambers/valves are identical. GS425's are a +2mm gs400/750 piston. Finding a 63mm or 64mm bore sleeve would be the tough part. CB350/360 sleeves highly modified could do it as a previous poster mentioned.