• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

'77 GS750 hybrid question

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

Guest
ok, i gots a '77 GS750 that i'm thinkin of makin a hybrid out of with some 850 parts......question #1 is:

Will an '81 GS850 top end fit the 750? I'm thinking it will, but i want to make sure before i tear into the 750. I'm planning on running the pistons, cylinders and head from the 850 on the 750.

Question #2: Would using the 750 head on the 850 cylinders/pistons increase the compression? If so, i plan on having the 750 head ported and polished, just curious if it would make a bit more compression.

Anybody? Everybody?

TIA
 
I'm not the expert but I don't think it will work. Different crank stroke different piston pin height?? Bolt pattern may not be the same? I would compare the Cyl base gaskets for the 750 & 850 and the compression height of the pistons. The 850 is not a high compression engine, has mild cams. If you try it. Make sure to check piston to head clearence and valve to head clearence. You probably would be better off getting a big boar kit for the 750.
 
The 850 is not a high compression engine, has mild cams.
Click to expand...

Sigh.....................I love my 850, but sometimes wish it had more get-up-and-go.
 
750 Hybrid

750 Hybrid

The stroke on 750 and 850 engines is the same. The bore is 2mm larger.
I know others have switched to 850 cylinder blocks, but some machining is involved. I just checked the clearances using a '79 850 block and the top half of a '79 750 case. The bottom of the cylinder block hits the sides of the case. Looks like a little case boring is needed. An 850 block can be bored to approx. 870cc. Keeping the 750 head and cams will result in higher compression and better hi rpm performance. An 850 head from 1980 or newer will need the CV carbs that came on the bike. (This is a good thing, they work better.)

Another option is the wiseco piston kit. All you need to do is the 2mm overbore, no other change.
Either way, some machining expertise is needed. Hope this helps

Terry
 
Wiseco info

Wiseco info

wiseco's website is: http://www.wiseco.com If you click on "contact us" You'll see their office phone #. They should be happy to tell you who has them in your area. List price on the kit is ~ $440.00

Terry
 
thanx for all the info

thanx for all the info

appreciate it guys.....not sure if doing the converion is worth it now, being only 2mm....hmmmmm

thanx
 
would another 2mm seal the deal?

would another 2mm seal the deal?

It appears I was wrong in saying the 850's bore is only 2mm larger than the 750. Looks like it's more like 4mm. 65mm vs 69mm. Anyway try thinking of it as an extra 95cc's. <g>

Terry
 
Thanx Terry

Thanx Terry

that makes it worth doin :)

Now all i gotta do is find a good gasket set, new timing chain (may as well replace that while i am there) and whatever else i can think of.

Thanx again!
 
Re: Thanx Terry

Re: Thanx Terry

Wiseco's catalog lists an 840 cc big-bore piston for the 750 that measures 69 mm.
 
All the info I've been given says that the 850 block will fit straight on - no machining required!

Am I wrong on this? I hope not coz I've got an 850 block and pistons ready to drop onto my 750!
 
Why not bore it out.

Why not bore it out.

Why not put the 850 top end on but bore it out first. Having a 950 wiesco GS750 would be pretty nice. yes? Sounds like a good basis for a sleeper to me.

YOU WANNA PUT THAT CBR TI TLE WHERE YOUR MOUTH IS PUNK?
 
Bored 850

Bored 850

Wiseco doesn't list a big-bore kit for the 850. If they did, I'd buy one in a hot second for my GS850.

Vince
 
All the info I've been given says that the 850 block will fit straight on - no machining required!
Click to expand...
I have the top half of a 2 valve 750 case & a 79 850 block. I tried to fit the block on the case. The block was about 1/2" from seating properly on the case. I flipped the case over & noticed that the 850 cylinder sleeves were hitting the insides of the case. It looked like some minor grinding would solve the problem, but I'm going to get a professional opinion.

Terry
 
I think I'll just put my spare 80 gsx1100 engine in the 79 750E and forget the big bore kit. :-)

Earl
 
You must log in or register to reply here.
Back
Top