1978 GS750 Head, 4:1 exhaust, spoked wheel, some background & advice

[martin_montreal]

1978 GS 750 (e) I think; (CDN). 2 v / cyl - 8 valve engine (has kick start).

UPDATE 10 june 2022
Questions related to pics

1. which head gasket to use? The one on the left is UPDATE NOT missing 1 round green washer - THE ONE IN THE PACKAGE DOES BOTH SIDES...IT WAS SPLIT AND SLIGHTLY BENT AT THE FRONT MIDDLE SO I PUT ANAEROBIC GASKET MAKER BETWEEN THE SECTIONS AND SOME WEIGHT ON IT TO REPAIR; right might best be saved for a set of Yoshimura oversized racing pistons when new unbroken timing chain and more bottom top end work is done in future
2. is the top of the block clean enough for gasket and head installation? CLEANING AS BEST I CAN EVERWHERE...
3. UPDATED, I TESTED the new used rebuilt head I bought by letting alcohol sit on the ends of the valves, with spark plugs installed to confirm no leakage. Will install with the shims from the head I pulled I guess then swap them around after installation. Any tricks here? I doubt it. It seems like a crap shoot to me lol.
4. rectangular o-ring gasket under head: should I oil it or put anaerobic or some other type of non rubber eating treatment on it?
5. head gasket installation - I never put any stuff on head gaskets but I see guys doing so in youtube videos... Input here? I WILL PUT SOME WHERE I REPAIRED THE HEAD GASKET
6. Timing chain Tensioner piece - how to install:
GUIDE, CAM CHAIN NO.1 B,C&EC,N&EN item Forum depicted in this parts diagram - I had to remove it to pull the head - well it sort of just came off...
7. Half moons: are in the new head should I leave them or remove, clean and use Black or Grey RTV on them or thinner Anarobic...
8. Am using a new valve cover gasket. Really don't want ANY leaks... so
9. Any other input besides, torquing retorquing etc. Will remeasure timing chain... etc. Thx!


Last year:
Plug was blowing out of number 3 cylinder. Number 3 compression was low like 60 v. like, I need to find my notes but ~120-140 in the others. .
Heli-coiled it but crooked; removed it; Big Serted it using a ring on a Ford Triton tool.
Not sure If I f*cked up and touched a valve during the job; I think it sealed per all the testing I could do.
Adjusted valves: all shims needed swapping.
After the job, the bike ran rough; idled poorly but it would go from 3 to 4 cylinders and rev fine in the higher rpms.
4:1 exhaust had leakages at block so assumed that was part of it; sync'd carbs statically then.

This year:
Sync'd carbs with gauges;
Checked compression in number 3 - ZERO "0"... even after pouring a little motor oil in there
Pulled valve cover.
Tolerance of number 3 in spec. (Number 2 exhaust valve was tight for some reason but irrelevant at this point).
I had broken 1 of the number 3 exhaust bolts when removing the exhaust; some fins are broken on the heads; a few of the bolt inserts for the exhaust will need helicoils SO

Now:
Pulling head ...
Rather than repair, considering buying a (obviously, hopefully good) used head.

What are my options. What years what models. What is recommended? Was advised any 8v gs750 head or 79 850...
Carbs seem okay. Was always a bit rich with pods and 4:1 but mostly reved up and down adequately. I don't have a big budget, just want to make it run okay and saleable in case I opt out. It's my second bike and I might replace it with another similar and then take my time getting this done... Ideas input welcome. Thank you!

[mattd1205]

you’ll likely need a 1977 or 1978 GS750 head. The 1979 GS750/850 heads were slightly different in that they had an extra 10mm bolt that is located directly in front of the cam chain tunnel. This bolt ran through the cylinder and threaded into the head. That being said, the previous owner of my 78 GS750 bolted a 1979 GS750/850 head to 1977-78 style cylinders with no ill effect other than the typical oil weeping that happens in that area. Since you’re in there anyway, You could also bump up your displacement to 850cc by getting a set of 850 cylinders. Some say it’s a drop in upgrade and some say you need to slightly modify the cases with a dremel. I plan on doing this to my GS750 provided I get the time to do so.

[martin_montreal]

you’ll likely need a 1977 or 1978 GS750 head. The 1979 GS750/850 heads were slightly different in that they had an extra 10mm bolt that is located directly in front of the cam chain tunnel. This bolt ran through the cylinder and threaded into the head. That being said, the previous owner of my 78 GS750 bolted a 1979 GS750/850 head to 1977-78 style cylinders with no ill effect other than the typical oil weeping that happens in that area. Since you’re in there anyway, You could also bump up your displacement to 850cc by getting a set of 850 cylinders. Some say it’s a drop in upgrade and some say you need to slightly modify the cases with a dremel. I plan on doing this to my GS750 provided I get the time to do so.

Hi,
Thanks for the information. I did not see a notification for the comment. Need to reconfigure this site for that so apologies on my tardy response back. When trying to make a leakdown tester out of my compression tester end of day yesterday, I broke the latter so having pressurized with air and sensing the valve on at least cylinder number 3 was hissing, I just pulled the head. The Clymers did not talk about that 10mm bolt so I was surprised when I realized that it was holding the head from budging. Suffice to say my bike has them! I may get my hands on a 79 scrap bike that apparently had a 'rebuilt engine'. I took a bunch of pictures and posted them here. Need to determine next steps...

Need to keep the budget low. I went to see a bike on the weekend. The advert said 82 GS750 low miles. It was an original owner 22,000 kms never dropped GS850 shaft driven bike. I didn't like the position it was low and felt the front was a bit mushy but the bike was mint asking $1250 CDN. Didn't buy it but still wondering... lol I put progressive shocks and springs in mine and was wondering best plan. In the interim need to fix this either way.

[mattd1205]

You have the early style head according to your pictures. This is the extra bolt hole for the late style head that I was referring to.

[martin_montreal]

You have the early style head according to your pictures. This is the extra bolt hole for the late style head that I was referring to.

- Got it. Thank you for posting! If that were all I found could I use it or bad idea? Concurrently trying to find the correct, good quality head gasket and the rectangular o- ring might be not only difficult but confusing as I suppose they would differ as a result of that bolt.

[mattd1205]

- Got it. Thank you for posting! If that were all I found could I use it or bad idea? Concurrently trying to find the correct, good quality head gasket and the rectangular o- ring might be not only difficult but confusing as I suppose they would differ as a result of that bolt.

Mine is mismatched (early cylinder and late cylinder head) and it works fine. It leaks oil from that area but I don’t think I can blame the mismatch for that. Head gaskets are going to be an issue as suzuki discontinued the head gaskets for the GS series earlier in the pandemic. Really sucks because the recent manufacture ones were multilayered steel as opposed to the original material head gaskets that weren’t oil tight for very long. You might be able to find an OEM MLS gasket or maybe try one of those crusinimage ones on eBay. Those appear to be MLS as well. I’ve never tried one but I’ll probably try them out when my engine gets tired. The MLS gaskets don’t need the cam chain oring so there’s that.

[kochic]

been running a MLS gasket on my gs1000-1100 hybrid for few years now, no oil weeping. You just need to be sure to have a clean and flat mating surface.
Marc