O
OLDENUFF
Guest
I would guess that #6 is the egg shaped oring. You are using 850 gaskets right?
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M
MisterCinders
Guest
Yes, I am using gaskets for the 1979 GS 850.
M
MisterCinders
Guest
After a little grinding in the cases, the swap went silky smooth. 
Test ride this evening went well.
Gotta get some hard riding in to break in the rings. Not a hard task on that 850 chain drive.
Test ride this evening went well.
Gotta get some hard riding in to break in the rings. Not a hard task on that 850 chain drive.
7
7981GS
Guest
What and where did you have to grind? 
Any pictures?
Eric
Any pictures?
Eric
M
MisterCinders
Guest
What and where did you have to grind?
Any pictures?
Eric
No pics of the grinding, but the jugs would not seat by about 10mm because of some casting flange in the 1 and 4 openings in the bottom. There was very little metal to remove, so with some oily rags to catch the metal dust and little Dremel work on those ridges, I was able to dry fit the jugs. The ridges stick out about 1mm or so and catch on the sleeves, so it was not to bad trimming them back.
Another GSR member, Nerobro, came by to help.
On Saturday, I tore down the old 750 top end and stripped and dipped my carbs. I also had fit the new pistons and fresh rings. On Sunday, Nerobro arrived on his gleaming white unicorn to save me from the disaster in my garage.
Here is a close up of the pistons with one of the old ones for comparison
At that point, it was time to install the block.
First we got the 2 and 3 pistons in place.
Then the 1 and 4 pistons got on board.
Now that everyone was comfortable, it was time for the head.
Now time for cams and timing.
With the cam timing sewn up, I did a quick valve adjustment check. All were in spec, but the No. 3 exhaust valve was at the tighter end of spec. So I swapped in a thinner shim. Then we buttoned up the top.
After that, I rebuilt my carbs to sort out some jetting on the needle and main, and account for the new pull of the 850. So far, she is digging the new guts.
R
rwcfrank
Guest
How would you rate the power to before with the 750 jugs? I am waiting for my frame to come back from the powdercoaters so I can start assembly on my 750/850.....
M
MisterCinders
Guest
On paper, it should be about 15 HP. Only had a short rIde in town, so it's too soon to tell. Feels healthy though.
M
MisterCinders
Guest
Did some more test riding to break in those rings. This 750/850 tears up the road. The increased power and torque, the fresh top end and newly cleaned carbs (they were clean, but I stripped and dipped them while doing the new top end because . . . of course I did) are like a perfect storm of engine running.
Did a quick compression test and the results are around 122 psi cold, and dead even across all four cylinders.
Thus, I am chalking this one up in the "win" category.
There are some lingering jetting issues, as I adapt to the new displacement. The stock VM26 carb jetting for the 1978 GS750 and the 1979 GS850 is almost the same, so I made only minor adjustments to the needle and main. Those changes were needed with the old engine, since it was running slightly rich in the upper circuits.
I also continue to have a weird starting issue, but that's for another thread.
Did a quick compression test and the results are around 122 psi cold, and dead even across all four cylinders.
Thus, I am chalking this one up in the "win" category.
There are some lingering jetting issues, as I adapt to the new displacement. The stock VM26 carb jetting for the 1978 GS750 and the 1979 GS850 is almost the same, so I made only minor adjustments to the needle and main. Those changes were needed with the old engine, since it was running slightly rich in the upper circuits.
I also continue to have a weird starting issue, but that's for another thread.
M
MadCapsule
Guest
Mister C, if you need an extra set of hands with this project let me know.
Edit: Never mind. Didn't read through the whole thread.
Edit: Never mind. Didn't read through the whole thread.
M
MisterCinders
Guest
Heh. No problem, dude. We should ride bikes BTW.
R
rwcfrank
Guest
MrCinders, did you oil the tear shaped o rings between the bottom case and cylinder prior to assembly? Also, should I oil the cylinder o-rings on the cylinders before assembly?
M
MisterCinders
Guest
No, but it wouldn't hurt to do that. Oil or grease on those gaskets is good. I don't like any RTV or other goop though.
H
Hone101
Guest
What gaskets will I need to complete this?
R
rwcfrank
Guest
A base gasket (850) head gasket (850) arguably the 1100 gasket will work but I am not going to open that can of worms (I used one). The tear shaped o-rings for the base gasket and cylinder o-rings if you need them.
O
overboostin
Guest
Would this be possible with a 750 with VM carbs to an 850 with CV?
S
SocialAnomaly99
Guest
What about boring the 750 jugs out to 850? would that stress the sleeve out too much?
G
Guest
Guest
Yes this can and has been done. Read the OP story start at the beginning , he has done it step by step for you with the same pieces that you have.
I was going to direct you to this thread but see you have found it. Nice meeting you the other day.
S
shryke300
Guest
I'm sorry to revive this, but I am trying to do the 850 swap. Can I PM any of you to discuss this? I've found a lot of the old threads and looked at the micro fiches, but I'm getting a little confused. HELP?
