Engine questions

[yamahafella03]

hey mates,
how hard is it to swap a 750 engine for a 1100 engine in a 1978 GS750?? And if that is deemed hard to do or requires major work than is there a performance kit of some sort like 850 kit for the stock 750 engine?? thanks

[TheCafeKid]

You can purchase a bore kit for the 8v 750 motors that will yeild 844ccs i believe. However, finding a 79 850 MOTOR and pulling the jugs and pistons out of it, which will drop right onto the 750 case, will yeild 843cc. Big difference...not. A bore kit will cost you 500ish bucks, plus machining time and all that. You can also use a later model 850 jugs and pistons, but it will require some grinding to the 750 case to get it to fit....

[yamahafella03]

so is there anything that you can do to mod the 78 750 without grinding and wat not. all i got is 4 k&n pod filters and a 4 to 1 mac exhaust

[TheCafeKid]

yeah, find a 79 850 motor (or at least the jugs and pistons) and drop them on the 750 block. They will bolt right up. OTHER years of 850 require a little bit of grinding.

Incidently, if you are planning on using those pods and that pipe, you WILL have to rejet, if you didnt know already.

BTW, whats wrong with the 750 to begin with? I can tell you its a damn sight more powerfull than a yammie.

[TheCafeKid]

Also, if you want more "punch" off the line, and dont mind losing a bit of top end, change your rear sprocket size. I used to have a 52 tooth rear sprocket (stock is 41) on MY 750, and that thing had enough grunt to rip your arms out of socket and surely light the tires up if you wanted.

[yamahafella03]

nothing is wrong i just want more top end and more off the line capability. the funny thing is, i dont even own a yammie anymore i just use yamahafella cause its easy to remember and its my email

[TheCafeKid]

K engine tuning in general is a balancing act. More top end capability and more off the line grunt is a trade off. You can have alot of one, or alot of the other. Cant have alot of both. However, i think stock the 750 is pretty well balanced in this. If you'd like more grunt, increase your sprocket size a lil bit in back. If you'd like more top end, decrease it a lil bit. If you want more OVERALL power, you'll need a bigger bike or a bore kit/850 top end. I think that if you were to find and try the 850 drop in, you'd be pleasently suprised by the bump in power.

[yamahafella03]

so justa 850 engine or bore it out?? wat year for engine? do they makea 520 kit or w/e its called for my bike?

[KiwiGS]

As I understand it you can use a 79 850s barrel and pistons, no grinding or rebore needed. The 1980 and 850s have a different head.
I did a 630/530 conversion becuase 530 sprokets and chains seemed easier to get. Z1 can sort you out for parts and info, but it is not that hard to work out.
630 chain is 3/4"(=6/8") pitch and 530 chain is 5/8" pitch. So the conversion in teeth is divide 630 sprocket teeth count by 5 and multiply by 6. eg 630 15 tooth front = (15/5)*6 = 18 so use 18 tooth 530. Dont forget about the chain also mate.
A 92 link rear chain becomes 110.4 links (rounded to 110).
Cheers

[TheCafeKid]

Well, if you want to have NOTHING to grind, you'll need to find a 1979 GS850 set of cylinder bores and pistons. Your head will bolt to those (they are actually the same part number, the one on the 79 850 and the one on your bike), and those will bolt to your block. Obviously, since you have the top end apart, might as well change the valve seals (not hard) and install new rings on your new to you pistons. I do believe TKent has done/is doing this exact mod to his 750, so he may have more info. Im still looking for the parts to do it to one of my 750 motors.

You CAN get a bore kit, but like I said, you're looking at spending some bucks. The bore kit will yeild exactly ONE more CC than doing the 79 850 conversion. So frankly its not worth it.

I am not entirely sure they make a 520 chain kit for your bike, but they DO make a 530 chain and sproket kit for your bike, I know this because i have installed one on my 77 750 cafe project. Easy as pie. Check www.Z1Enterprises.com for 530 conversion kits.

[dardoonk]

The Wiseco 844 kit will give you a 10.25:1 compression ratio, compared to the stock 8.8:1 ratio. Not sure how many HP that is worth, but it will cost you about $450 to get it.

[TheCafeKid]

Indeed. Nother good point Kurt, hadnt thought of the compression ratio. However, 450 bucks is JUST for the kit, not to mention having the head and cylinders milled. And if you are going to that extent, you can use some high lift cams and heavy duty valve springs (you'll likely need them for the higher comp ratio) More bucks. What it boils down to, IMO, is this: the 750 is what it is. Its a middleweight bike, and in my opinon, has all the power you really need for a 30ish year old bike. Using that 79 850 mod will increase it, and put a BIGGER smile on your face maybe, but my 750 does me fine with a stock motor. (now I HAVE done some things to make it HANDLE better, and straight line speed is fun, but being able to keep speed in corners without crapping your pants is MORE fun ) When i want more balls, I jump on the 1100G

[dardoonk]

Agree, what the heck does anyone need with an 77GS that 100hp or so?
Oh, wait a minute!! I already started doing that didn't I? :-D:-D

I opted against the 850 kit myself because I couldn't justify the expected return vs what costs to do it right. At the end of the day, I won't have much more invested in just building the 1085 motor. With luck, finding a few "new to me" performance parts for the 1000 motor (maybe even the wiseco pistons) will allow me to step up to some Web cams to boot!

[tkent02]

I do believe TKent has done/is doing this exact mod to his 750, so he may have more info. Im still looking for the parts to do it to one of my 750 motors.

Still waiting for the morons at RideNow to send the correct rings, going on three months now. Got tired of waiting, my spare GS1000 engine is in the 750 now, motor mounts are made, just need to get it all hooked up and running.

I might still do the 850/750 thing. Someday.

[dardoonk]

TKent, did you put the 1000 motor in a 77-79 frame? Any chance you have templates for the motor mounts, or are they pretty easy to make?