engine swap- GS550 to GS750 (maybe big bore)

[Anonymous]

FIRST-------86 GS550ES-----------

my question to all of you out here is what would you do if you had the choice of a gs 750- 2 valve motor, running condition-mileage unknown, or a GS750- 4 valve, in need of rebuilding. this is to go into The above listed bike. (According to the third person info) the 4-valver has a spun rod bearing, possibly mileage-unknown. also how much are big bore kits for the 4-vlv ? and how big can you go ? :twisted: Thanks fellas.

 

[Billy Ricks]

Krash,
Wiseco has an 816 kit for the '83 and up 4 valve motors, I think they run about $400. I might even be able to get you a set of Cosworth 12:1 prototype forged pistons. You would have to send them to Total Seal to have the top two grooves recut and a set of their Gapless rings. The pistons, machine work, and rings would probably run about the same as the big-bore kit. They are not big bore but they are killer pistons. You should probably go for an '83 or newer since it is more compact than earlier motors. I would be careful about a motor with spun bearings. If it ruined the crank it can't be turned. You might also consider an early GSX-R motor. They are even more compact and would probably fit your frame better. The '88-'90 motors were short stroke high revving motors.

 

[HiSPL]

Billy,
How many sets of those pistons do you have? And, do you have any in the 1100 variety?

 

[Billy Ricks]

Billy,
How many sets of those pistons do you have? And, do you have any in the 1100 variety?

I don't have any myself other than the set I have for my own bike. A friend of mine is the guy that has or had them. He only has 750 pistons.

 

[HiSPL]

what, did he buy a crate full of these things when cosworth figured out they weren't going to make them? I am going to keep a 750 engine that I have and may someday build it up and put it in some other (non-GS) chassis. these pistons sound really cool. do they rattle and shake like wiseco does?

 

[Billy Ricks]

Actually it's Britt Turkington, '93 AMA 750Supersport Champ, that has them. He cut his teeth on an '83 GS750 he would ride up to Texas World Speedway from here in the Valley then race prep it when he got there. A little later then hooked up with Kelly Roberts who was a distributor for Cosworth here in the States. He managed to compete with the first generation GSX-Rs on his '83. After that he rode for Valvoline Suzuki before going on to the Yoshimura team. These are actually prototype pistons that I don't believe were ever available for public consumption. They look like little jewels.

Haven't gotten around to installing mine yet. I am hoping to run across a 750 crank and rods so I can bump mine up to a full 750 instead of a 700. If I find a crank I'll send it to A.P.E. for lightening and balancing. Other than that I've had the top two grooves recut and Gapless rings done by Total Seal. I have my V&H cams already and Britt already did my head for me. All new valves and spring kit and a bit of mild porting. I'll ride it the way it is for the winter then if I haven't run across a crank and rods I'll go ahead with the pistons.

 

[HiSPL]

8O

Wow, that must've been one helluva GS! does he still have it?

 

[Billy Ricks]

Wow, that must've been one helluva GS! does he still have it?

No, in fact by the time I got to know Britt he had already gotten rid of it. It was a wild ride from everything he has told me about it. Kelly Roberts builds some monster motors. They were running hollowed out cams and all kinds of wicked stuff. He said he used to see his GS out it California when he would race out there. The guy that had it would ride it to Laguna to watch the races.

The first time I met Britt I was looking for carbs. I used to see bikes sitting outside the place where he and a friend of his kept and worked on their bikes. I had a feeling it was his shop from reading about him in Cycle News. I picked up bits and pieces for my bike from him and got my RS Flatslides from him while he was racing for Yosh. Most of the GSX-R stuff on my bike is race take-offs from bikes he raced. The rear tire I've got on my bike right now was actually run at Daytona. It's a Dunlop 364 that I've only put a handful of miles on. I switched back and forth between it and a Sportmax GP compound. The 364 is still soft with no sign of age related problems.

 

[Anonymous]

whats wrong with your 550 motor? i have a 86 550 parts bike with complete motor.

 

[Anonymous]

the motor is starting to feel tired (40k tough miles) :roll: and 2nd gear is getting pretty bad. I have a motor from an 83 with 3400 miles on it that has been sitting in a garage but I would rather try to get bigger engine performance without buying another bike, rather than rebuild this engine. besides I like the bike and I recently put on a gsxr front end.