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850 conversion

  • Thread starter Thread starter silverbullet132
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silverbullet132

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Looking at a possible 850 conversion on my 78 gs750. Searched the forum and it looks like pre 1980 cylinder bank + pistons is the best option?

Aside from that, what gaskets should I use? 750 or 850?
 
silverbullet132 said:
Looking at a possible 850 conversion on my 78 gs750. Searched the forum and it looks like pre 1980 cylinder bank + pistons is the best option?

Aside from that, what gaskets should I use? 750 or 850?
Click to expand...
I don't see why pre 80 would be better, with the 80 up you get bigger CV carbs more air and fuel, means more power. I'm sure someone will say the contrary, but I'm going 80 850 on 77 750 using the cylinder, pistons, head, carbs and cams from the 850 and will be using the 850 gasket set.
 
As gsrick mentioned, the main reason to stay with the '79 cylinders and head is to be able to keep your VM carbs. If you don't mind switching your carbs, feel free to expand your search to newer models.

I think I remember something about the newer cylinder blocks needing some minor machine work to fit into the crankcase properly, but can not guarantee that.

.
 
Ah ok, maybe I will get lucky and find a deal then. Was hoping to not have to sell these VM carbs as I just got them.

If I pull this off the bike will have a 78 ported head w/ yosh cams :) should scream haha
 
From Eric

From Eric

I had to do nothing.
Apparently some of the GSR members said that they had to grind some of the lower crankcase bores or something like that.
Mine just fell on.
Emoji_1F609.png



Eric
 
Thanks guys. Also, will my GS750 header fit the 850? Even if i go 1980+?
 
Use the part nos. to figure out what pistons and jugs will work. You can use 850 pistons and jugs from 79-81. The jugs (P/N 11210-45100) are the same across these models.



When I did the swap, the jugs would not fully seat because of a bit of casting flange in crank case beneath Nos. 1 and 4. But I ground those down with a Dremel after stuffing a lot oily rags in there to catch any bits. Then I ran plenty of oil through the pan to make sure nothing slipped through -- e.g., drain the oil, fill, drain that oil, re-fill with the same oil, rinse/repeat, then drain again, and put fresh oil in the bike. Basically do a double oil change, since you recycle one batch of oil a couple times to flush out the pan.

Note that because the 1979 850 used the same head as the 1979 750, you can use the carbs, valves, etc. from a 78/79 750 on top of any 1979-1981 850 jugs/pistons.
 
MisterCinders said:
Use the part nos. to figure out what pistons and jugs will work. You can use 850 pistons and jugs from 79-81. The jugs (P/N 11210-45100) are the same across these models.



When I did the swap, the jugs would not fully seat because of a bit of casting flange in crank case beneath Nos. 1 and 4. But I ground those down with a Dremel after stuffing a lot oily rags in there to catch any bits. Then I ran plenty of oil through the pan to make sure nothing slipped through -- e.g., drain the oil, fill, drain that oil, re-fill with the same oil, rinse/repeat, then drain again, and put fresh oil in the bike. Basically do a double oil change, since you recycle one batch of oil a couple times to flush out the pan.

Note that because the 1979 850 used the same head as the 1979 750, you can use the carbs, valves, etc. from a 78/79 750 on top of any 1979-1981 850 jugs/pistons.
Click to expand...

Thanks a bunch :)

If this cyl head with yosh cams checks out I will probably end up doing this. Though, I just found an entire GS1100 for sale local for $750. Decisions decisions...
 
Cyl head is ported and has yosh cams just going to use that with 850 pistons. Previous owner told me he had a big bore 850cc yosh kit in it, 2 of the pistons remain. Hopefully no boring is needed for the cylinders.
 
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