750 to 850

[Steve]

And you can pick what cams you like - 850 are a bit 'softer' than the 750 - they'll both fit.

Plus Which cams would be best for this swap.

Id have to double check this info. I know that at SOME POINT they re-timed the 850 cams for more bottom end, but I dont know WHEN (what model/year) they did this for sure.

They did this for the 1980 model year.

Cafe is right about the different cam timing, not sure how much difference it makes in the real world though.

I would have to ride two bikes back-to-back, but it should have better low-end response with the advanced intake timing.
Since most of our riding is in the lower half of the rpm range, it would probably make more sense.

The 79' 850's cams were the same grind as the 79' GS1000. I believe that the timing was changed on later 850's by advancing the inlet opening.

Yep. I don't have the exact numbers here, but the intake timing was advanced 10 degrees for opening and closing.

.

[tkent02]

You have to use the 750 cam sprockets, do away with the 850 idler sprocket

No, '79 850 and all two valve 750s used exactly the same heads, idler sprocket, everything but the cams themselves.
Changes started in '80.

[Stormstyles]

So is the bore and stroke the same Then? I would think they were different!

[Steve]

I do not have numbers in front of me, but based on the responses above, I would say that the bore is definitely bigger (hence the need to change the pistons to match the 850 cylinders), but the stroke would be the same (because you are still using the same crank).

.

[tucker]

So would the increased compression (10:25) help out? I have an 850, to swap to my 750, just wondering about the compression and the cooling.
tucker

[49er]

So would the increased compression (10:25) help out? I have an 850, to swap to my 750, just wondering about the compression and the cooling.
tucker

If you use the stock 850 jugs and pistons, the compression will be 8.8-1.
To get 10.25-1 you need a Wiseco Kit for the 750. Those pistons will be the same dia as the stock 850's but with the higher comp domes.
You won't have any over heating issues with that CR, unless you leave the engine idling in heavy summer traffic for long periods.

[Stormstyles]

So where would be the best place to acquire a big bore kit for the 750 then?