850 barrels DO in fact fit in the 750 cases.....

[Nessism]

Did you do the oil in the cylinders trick after your first compression test? I'm guessing not or you would have mentioned as much. At any rate, the oil helps determine if the rings or the valves are at fault.

As a side note, based on your seemingly prolific rotation of GS bikes, those decent 750 parts are likely to see reuse again (with new rings of course).

 

[tkent02]

Did you do the oil in the cylinders trick after your first compression test? I'm guessing not or you would have mentioned as much. At any rate, the oil helps determine if the rings or the valves are at fault.

Yes, I did. Numbers came up just a tiny bit, only 1-3 PSI per cylinder indicating valves are at fault.

As a side note, based on your seemingly prolific rotation of GS bikes, those decent 750 parts are likely to see reuse again (with new rings of course).

Yes, and I have been wanting to try the 850 conversion anyway, so no worries. I guess if it works well I will be looking for 850 pistons from now on.
It's just puzzling. I tried the compression on one cylinder of the 1000 just now, then again with the exhaust completely blocked, it went down only about three PSI. That might explain the low power but not the low comp readings.

Oh, well.

 

[Big-Jim]

The cylinders that come with the later CV carb 850s are different, the sleeves are too fat to fit.
The later head goes on the earlier cylinders just fine, identical except for the intakes. Still deciding which carb/head setup I want to use. Would prefer the CV style but my CV head will take more work and money to get in good shape. Can't find anyone local who works on these heads, might just take the best head, lap it a while and call it good for now.

This is the set up that I am running on my gs 750/840. I use an ported 850 head with 34mm flat slides. better mid range and top end punch but the CVs are alot smoother too
Jim

 

[tkent02]

This is the set up that I am running on my gs 750/840. I use an ported 850 head with 34mm flat slides. better mid range and top end punch but the CVs are alot smoother too
Jim

I have also a later 850 head with CVs, not ported at all.
I would rather use this due to the better compensation at different elevations with CVs.
I live at 5,500 ft, my recreational riding is all up higher than that, up to 14,000ft, around town stuff is all at 5200-5500.
SO, do you think the CVs are a good idea in this case?
Are they more powerful than VMs or is your power due to other mods?
I would have thought not from my experience with 750s, my old 1978 750 was faster than the '80 and the same as the '83 I had last year.
I think my CV head needs more work than the VM head, but I can do it if it's worthwhile.
And, does your engine vibrate much more than it did as a 750? Did you do anything to alter the weight of the 850 pistons?
Thanks,
Tom

 

[SqDancerLynn1]

Their was mention in a previous post about the need to reuse the 750's cam gears & to eliminate the idler gear that the 850 uses. Unless you split the casas and change the timing chain

 

[tkent02]

Their was mention in a previous post about the need to reuse the 750's cam gears & to eliminate the idler gear that the 850 uses. Unless you split the casas and change the timing chain

750 and early 850 heads are identical, same part numbers on all the bits and pieces except the cams themselves, idler gears are the same, tensioner parts, sprockets are all the same. The 850 uses 1000 cams for a broader powerband...
I might try both cams to see which I prefer.