GS550 shifting issues 1977 & 1978

[Chuck78]

I've had some shifting issues on two gs550 engines the past few years that I have not torn into yet, but am looking for some more advice and expertise, as we plan to do a road trip on one or the other in a month.
I rode my wife's 77 gs550 last night for 45 miles or so, and the "occasionally gets stuck in first gear" issue now seems to also happen in second to a lesser extent, and the shifting is hard regardless (especially in 1st&2nd) slow and sluggish I'd say, lots of foot pressure usually required, and it slams into gear once it starts to go. The other 550 engine shifted slightly better, but would get stuck in neutral and wouldnt go into first on occasion. Once I tear the bottom ends of these 2 GS750 engines down on my bench to build up one nice one, I should gain more familiarity with how the shifting mechanisms work, and maybe have more insight on the cause of the 550's problems. Where should I be looking for wear and tear? I plan to do the 550-673 swap on the 77 550 engine with the "gets stuck in neutral" issue, but I bet the same parts that cause that problem are worn in the 78 "stuck in first" engine.

Could these problems be caused by bent or worn shift forks? Bent shaft somewhere? I have read that the sides of the gears have notches or steps in them that have to do with shifting, and that they get worn over time.

What parts am I most likely to need to single out to find the cause of the problems?

[Chuck78]

I am wondering if the 750&550 shift forks are the same... Or if the 650 (5 speed) has any compatible parts with the 550, as there is a 650G in the junkyard here that I was contemplating buying the head/pistons/cylinders off of anyway.

[tkent02]

Get the head, pistons and cylinders, nothing from a five speed will fit. Get the 650's exhaust if it's one you would want to use. Get the carburetors and boots if you want to go with the CVs. A 450's six speed looks similar to the 550, but when you get in and actually compare things it's not even close either.

If you do need 550 engine or transmission parts I may open one up to get some parts, haven't decided yet, but I don't need four complete ones sitting here.

[Chuck78]

fortunately, I got the cylinders, pistons, and head off of another 650G that the junkyard had last year. I may get the same parts off of this one just to have as spares. I also got a $35 4 into 1 header that fits the 650 head perfectly, and looks like a slightly downscaled version of my MAC GS750 4 into 1. I held it up next to the 550, and it seemed to fit perfect. Score!

it is possible to access the entire gearbox without pulling the head, right? Just pull the engine from the frame and split the cases, and work on with the engine laying on it's side?

I am surely going to need some 550 gearbox parts, it is just a matter of when will I have the time to tear into it. It has been running like this for over a year, and I don't see any catastrophic failure in the near future, but who knows if it could get worn so much that it just doesn't want to shift at all ever. I might just start to gather all the parts to rebuild the original (on the shelf) '77 550 with the 650 top end, and just address the 77 engine that gets stuck in neutral. right now, I'm trying to build a 920cc GS750 engine, as the engine in my bike developed some major oil leaks, and I deemed it no longer rideable.

[tkent02]

it is possible to access the entire gearbox without pulling the head, right? Just pull the engine from the frame and split the cases, and work on with the engine laying on it's side?

Probbly easier with it upside down, back of the top case sitting on a box or something, but yes. But you may as well do the 650 top end at the same time

[Chuck78]

Seems as if the 1-2 shift fork is bent from slamming into second gear, drag race style, and the shift drum has some wear on it in that area as well. I just got a major score in an 1,800 mile 81 GS550L complete transmission and shift linkages on ebay for around $90 shipped! AWESOME!
Pulling the engine to remove the lower case half to swap this in has now necessitated my expediting the GS550-673cc project, so while the engine is out, I might as well pull the head and grind out the case to accept the 650 sleeves. That leaves some carb work to fiddle with right before two big trips, hope I can get both of our new engines built and tuned in time!

[Sci85]

Chuck, I can hopefully save you some time. First, read up on all the posts for the conversion. There's a few little things that can kill making good time if you are on a deadline. Decide up front which cam you want to use as well as if you are going to re-time them. Cam sprockets matter as well. Also, Don't forget the timing plate from the 650 and check the bolt clearance against the cover. I believe early models may require grinding down the bolt. As far as jetting, so far stock 650 jetting seems to have proven the best unless the head has been reworked. I recommend you start there before modifying the jetting. And yeah, the shifting has never been smooth on the two 550 engines I have run. Could just be a poor design. I've learned to be very intentional in the lower gears when shifting.

Good luck and keep us informed on the progress.

[Sci85]

Oh, and I used the bs32's from my 550 with the 650 spec'd jets. I tried a bunch of different combo's including the 650 dynojet kit (waste of money) and ended up basically with the stock 650 setup. I am running the twin K&N's and 4:1 pipe.

[tkent02]

K&Ns and a pipe and stock 650 jetting works? If that's true I'm set, have two sets of 650 carbs to choose from. Did you have to raise the jet needles or anything?

I'm getting closer now, would have had the engine together except I forgot to order two cylinder studs, which were twisted quite a bit.

On the 550 shifting, I think they are often messed up bcause of how you have to wind it out all the time, people just naturally want to speedshift it and abuse the crap out of it. I have had two GS550s that shifted as smooth as baby snot just like any other GS. The old beat up leaky '77 engine in my 550 now temporarily is a real smoothy, as was the original '78 engine that was in it.

[Chuck78]

I plan to use the 550 cams & cam sprockets. What is this with the 650 timing plate??? As in the piece behind the points ignition or electronic ignition pickups? I know about grinding the cases. What else is a big deal or unexpected?

[Sci85]

BTW, researching this in the past, folks say the 650 cams are better for mid-torque improvements while the 550 cam is more of a hot rod, higher revving cam. I think Don used the 650 cam and likes it. I went with the 550 cam and I like it fine as well but I do like to rev it up

[Sci85]

K&Ns and a pipe and stock 650 jetting works? If that's true I'm set, have two sets of 650 carbs to choose from. Did you have to raise the jet needles or anything?

No, bone stock worked fine IIRC. I will need to check my notes for sure. I am using the Twin K&N filters not individual PODS. I went this way because it's so much easier to get them in and out but the pods would probably flow better so I can't say if the jetting needs adjustment with the individuals. I did play with the pilot jet but I think I even ended up back at factory or one size richer on that. My carbs were non adjustable needles. I do have a slight bog on roll on from slight throttle openings but not bad enough to spend a bunch of time fixing. It would probably use a slight needle adjustment but you should be fine with bone stock 650 specs as a good starting point.

What is this with the 650 timing plate??? As in the piece behind the points ignition or electronic ignition pickups?

Correct. The timing is different on the 650 versus the 550 and you need the timing marks on the 650's plate.

What else is a big deal or unexpected?

Nothing is a big deal which is why this is such a good swap for the money. The engine will run much stronger afterwards. I re-timed my cams as the original Suzuki timing is really weird. It's more work but I think it's worth the extra effort. However, I can't really quantify any difference so the choice is yours there.

It's important to get the squish band measurement right. Myself and others ended up using a non-OEM base gasket to get the measurement right. You can look at my build thread to see what I ended up doing there and what the number should be. The 650 head uses the more efficient squish band design which the 550 doesn't use so take the time to get that right.

[Chuck78]

I am using the Twin K&N filters not individual PODS.


Correct. The timing is different on the 650 versus the 550 and you need the timing marks on the 650's plate.



It's important to get the squish band measurement right. Myself and others ended up using a non-OEM base gasket to get the measurement right.

what is the part number on the twin K&N filter is that you used? And these fit BS32's in the correct spacing?

I looked back at another thread, as I did not understand why the timing plate could possibly be different, as the crank ends are very similar, and you're not changing the crank anyway, so the 550's timing mark for tdc doesnt change. it looks to me like the centrifugal advancer unit dial in several degrees more timing advance on acceleration, so it is actually the centrifugal advancer, or mechanical advancer as they are called as the older models are referred to, the newer ones are fixed pickups with no advancer, and the advance is all electronic. The timing plates are the same part # on both models.

[Sci85]

Oh, one more gotcha i recall. You need a 650 header. The exhaust ports are bigger even though the valves are the same size. You can use the 550 header but it will require some modification to use. And you want to use GSXR exhaust gaskets, OEM PART NO. 14181-17E00. And here's Suzuki_Dons thread on it what he did.

http://www.thegsresources.com/_forum...d.php?t=154723

And my condensed build thread...
http://www.thegsresources.com/_forum...d.php?t=211982

[Sci85]

The squish needs to be between .035" and .040". I think i ended up at .038" using gasket material from the Auto parts store.

RC-2382 is the K&N part number. The spacing is correct yes.

And yeah chuck, if you compare the two plates side by side, you will see the differences. Interesting that the part nums are the same as the marks are clearly different. Mine is an '82 model and still used the mechanical advance. I haven't tried running it ever with the 550 advance unit. Wonder what change it would have. Hmm...