850 upgrade to a "78" 750

[Canadian GS]

Looking for information on upgrading a 78 gs750 to an 850. I had seen information previously and lost track of it. I have the new pistons +pins,cylinders. What portion of the top end [ head, cams,valve cover,carbs] is reuseable?
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Life is the trip, not the arrival at the end!!

[humhead]

All of it. The 850 is a 750 with a 4mm bore job & shaft drive. You can use the 750 block & head or install an 850 block & head (minor grinding of the crankcase may be necessary to fit the 850 block.

Terry

[blackwolf]

I have an gs850 and thay are the same engine except the bore,the stroke is the same. the blocks are not different . imformation from clymer.

[humhead]

Information from my attempt to mate an 850 block to a 750 case. Minor grinding is required. Another member of this group had the same experience. Others report no clearance issues whatsoever. If you already have an 850 block, by all means try it! Don't be suprised if there are clearance issues I choose to trust my own experience over hearsay.

Terry

[SqDancerLynn1]

If you want to use your orig carbs use the 750 head. I think it will add some compression. You need to use the 750 cam gears with either head. The 850 chain idler is not used

[humhead]

The 79 750 & 850 used the exact same cylinder head. (Check any online fiche if you don't believe me) If you use stock 850 pistons, your 750 head & an 850 head gasket, you'll wind up with the stock 850 compression ratio. The cam gears are interchangeable, as is the cam idler gear assembly. The intake cams are the same. The 750 exhaust cam is ever so slightly different (a bit "hotter")


Terry

[nastyjones]

Terry, are you sure the cams are different? I am doing this mod on my 78-750 & the cams appear the same right down to the numbers on them. I am building up a strong street motor & have incorporated this mod myself.
Canadian gs, where are you located? I'm in SW Ontario.

Nasty

[christopher_2]

Can I bore out the 750 cylinder head and make it an 850, it seems like it from what I am reading here.

[nastyjones]

Well, actually you would bore out the cylinders not the head, but I think it would be cheaper to do what I did, find used parts from a 80+up 850. I used the cylinders, pistons, & cams as these parts were "mated" to each other as they wore. I picked all the parts up for, I think it was $125.00 Canadian.

Nasty

[humhead]

Nasty
According to the Suzuki parts numbers, The 750 Has a different exhaust cam.
The 850 & 1000 use the exact same cam part numbers, Intake & exhaust. We're talking a very small difference here. I'll check the 750 & 850 cams I have to se if mine have the same billet numbers.
Christopher2
You can bore the 750 BLOCK 4mm over & use the wiseco 850 kit, Use an 850 pistons & block and clearance your crankcase. You can use the 750 head or an 850 head. If you use an 80 or newer 850 head, you'll need the carbs as well. (They changed the head & carbs that year.)

Terry

[nastyjones]

Hey Terry,

Did you get a chance to check the 750 & 850 cams yet to see if the numbers are the same?

Paul

[humhead]

I've looked at 850, 1000 & 1100 cams so far. The 750 stuff is in storage. I've never seen cams with so little info on the billets! I can't find a sreial number or casting number on any of 'em!!! All I see is an intake & exhaust marking and a surface mark that looks like a dab of paint.
Unless I missed something (Quite possible) the only way to accurately verify the difference would be to degree the cams & see if the 750 opens sooner & closes later than an 850 exhaust cam. (Degreeing your cams is a good idea anyway...although doing it twice is a PITA)
The clymer manual for the 750 that I have doesn't have the detailed info on cam timing that the factory manual has. I'll try to dig up my haynes 750 manual & see if that has the cam timing numbers. I have the 1000 factory manual, so I can compare.
Sorry for the delay.

Terry

[humhead]

Update: Looked at the Haynes 750 manual & factory 1000 manual. The only difference I can find is .10mm bigger minimum height on the exhaust cam lobe.
Still haven't found any markings on the cams that differentiate 850/1000/1100 from 750.

Terry