Head swap 81' GS850G

[Anonymous]

Alright guys, I need some help! I am replacing the origional head off of my 81 GS850G with one that I won on ebay (which happens to be off of a 79 GS1000). I was putting in on the engine when I noticed that it didn't have any mounts for the cam chain tensioner. Can I substitute the GS1000 for the old one? If not will any other heads work? Thanks for any advice!

[focus frenzy]

they use basicly the same tensioner and it is located in the back of the cylinder block.
the 750 and 850 wich is based from the 750 use a idler gear in the head that is not used for some reason on the 1000.
the 1000 head should not even fit on the 850.

[first timer]

i have heard you can put a 81 850 head on a 78/79 gs1000, with little mods to the head. you get a little higher compression and bigger valves? you just have to weld a couple holes maybe the idler gears?

anyone care to comment.

-ryan

[bwringer]

On an 850, the tensioner bolts up to the block, not the head:

Here's a photo of my 850:

http://www.bwringer.com/gs/images/camchaintens/cct_03_mountingbolt.jpg

Here are more photos and more info concerning the cam chain tensioner:

http://www.bwringer.com/gs/camchaintens.html

I was not aware that the 1000 head would work on an 850. Isn't the cam chain different? I'm not saying it can't be done, but maybe you're the first.

The engine and driveshaft from the 1000G and 1100G will drop into an 850G frame, and I believe that some 750 heads will interchange... anyone seen Nick lately?

Good luck, and let us know how your frankenbike works out!

[Anonymous]

Maybe I'm not explaining the problem correctly, I removed the valve cover off of the origional head and between the two cams there was a metal sprocket that was bolted down placing tension on the cam chain. That "tensioner" is held down with 4 bolts. On the head that I bought (79' GS1000) there is no holes to mount this peice between the cams- I can't find a 81 GS850 head to replace the origional so I need to know if the GS1000 head will work. Thanks!

[Anonymous]

Still confused about the orgional problem

Maybe I'm not explaining the problem correctly, I removed the valve cover off of the origional head and between the two cams there was a metal sprocket that was bolted down placing tension on the cam chain. That "tensioner" is held down with 4 bolts. On the head that I bought (79' GS1000) there is no holes to mount this peice between the cams- I can't find a 81 GS850 head to replace the origional so I need to know if the GS1000 head will work? Thanks!

[SqDancerLynn1]

Not sure if maybe you could drill and tap some holes to mount it? I think without it the cam chain will be too long

[brs127s]

That is actually the cam chain idler sprocket. You would have to shorten you cam chain to run without it, but that would throw the timing off.

[humhead]

The 81 850 head is very different from the 79 1000 head. First, the intake ports are different. Your 81 850 carbs won't fit. Second, the 1000 head has larger valves. Unless you're going racing, this isn't a good thing. Third, check the combustion chamber volume. I'm pretty sure the 1000 chamber is larger, which would lower compression. You already know about the top cam chain idler gear. you'd need to weld the head to accept mounts for the gear.
Yoshimura added the idler gear to the head of their 78 AMA superbike

Unlike the GS750, the GS1000 doesn't have a cam chain idler roller between the cams, so the Yoshimuras welded aluminum plates to the cylinder head, machined them flat and installed a stock GS750 idler roller in the GS1000 head. The change required use of a GS750 cam cover.

The 750 head uses the same idler gear as the 850. Lastly, the exhaust ports are larger, as are the headpipes. Your best bet is to find another 850 head, Or if you can afford it, a 1000g/1100g motor.
Terry

[Anonymous]

Thanks for all the help, I guess I going to be listing a very nice GS1000 head on ebay and keeping a look out for a GS850 head in good condition. If anyone comes across one that is in good shape please email me, Thanks!
Mrezba@hotmail.com

[Anonymous]

Problem solved

Thanks again, I a fellow GS'er found an GS850 head on ebay for me so problem solved!