Bottom End Inspection and Replacement/Repair - 86' GS750ES

[DarkDevil]

1986 GS750ES
~40,000KM

Was running fine up until fall 2005. Picked the bike up from my uncle for ~200. I put a new clutch and brake pads on it in 2004, new sprokets and chain in 2005, and new sparkplugs in 2006 (In an attempt to solve the problem that follows).

In fall of 2005 i noticed a drop in acceleration. The bike could still get up to speed, but not as fast as it used to. It sounded like the bike was choking when I accelerated, or like I was almost out of gas (again, only when accelerating). Then later in the fall, early December (thats right, motorcycle riding in newfoundland Decembers ) I was having trouble getting past neutral and getting into 2nd. It seemed intermittent and there also seemed to be some correlation to how warm the engine was and how cold the weather was. So I assumed it was a problem with driving in cold temperatures, so I garaged it for the winter. Then in spring of 2006 I took it out for a few rides before moving away for 4 months, and in those few rides, the problem slowly got worst (clutch adjustments failed, as they did before garaging it), and I eventually lost 2nd and 3rd gear. It started with it just popping out of them (2nd first, and a week or two later 3rd) but then I just couldn't even accelerate a bit. I could maintain speed in them for a bit, but not generate a higher speed.

I've asked around and all opinions (along with signs) point towards Bottom End replacement/repair. I can get a used bottom end for 350CDN and attempt the work myself, or I can cart the bike to a shop, get them to repair it for the value of the bike.

I'm posting to get some opinions from owners (you've never let me down before) on what I should do. I'm a quick study, so I don't think the job will be too hard, but I could be mistaken. Besides the clutch replacement, and mounting my tires, I've done all previous work myself. I was able to find a shop manual for the '83 GS750E which outlines the complete tear down of the bike, but I'm wondering how much of that I would have to do. I don't want to disassemble the top end anymore than I have to (Ideally not at all).

Once I get the bottom end off, will it be as easy as just putting the new one on? and are there any "special tools" mentioned in the manual that I'll actually need, or can I get by with your basic shed/garage variety of tools. Will it take a long time?

I've searched the forums and the old Q&A with "Bottom End Replacement" and nothing helpful came up.

Thanks for your help, I'll be checking back quite regularly.
(also, was thinking of taking some pictures once I'm inside the engine, to get some opinions on weather i should just replace single parts for new, or the whole box for used.)

[Suzuki mad]

If its the same gearbox as the 1100 the only special tool you will need is a press and a puller to get the 2nd gear off the shaft if you need to change it.

From you post it sounds like the selector forks are in trouble. These locate on two rods through the engine. When you split the crank cases one half of the gears stays in the top half the other in the lower half. Remove the lower cogs and then you have access to the selector forks. It would be advisable to replace the gearbox drive bearings and all the seals before rebuilding if you can afford to.

If the gearbox wasn't whining then you may not need to replace any gears as that can get very expensive to do.

With a manual an some mechanical knowledge this job shouldn't cost you to much, or the 350CDN as you have suggested for a second hand bottom end.

Suzuki mad.

[Nessism]

Break down your engine carefully paying attention to how things are assembled. Since this is your first complete rebuild you may even want to take some photos so you can get it back together properly.

You can pull the head and put it aside without disassembly but this is false economy in my opinion – at least replace the valve guide seals. My opinion is to inspect all the valves for wear while you are in there. When you pull the cylinder/pistons make sure to match the various parts together by scribing on the top of the pistons – same goes for the valves if you pull the head apart.

When you get the cases split you are going to want to inspect everything very carefully. Since you have two bottom ends you can go through both of them and piece together the best parts from both. The key to doing this type of work is to remain organized and keep everything clean when putting things back together. Wouldn’t be a bad idea to replace the cam chain while you are in there since it’s a wear item. Also, my opinion is to replace the rings as well after a good hone to break the glaze.

Hope this helps and good luck.

[DarkDevil]

Suzuki Mad,
I don't have access to a press. Is there anyway it's function could be improvised?
I guess I should start ordering all the seals and whatnot that i'd need to rebuild? I'm just afraid i'll get it all taken apart, put it all together, and then get stuck retiming it or something like that. Is this going to be an issue. I'd assume an engine disassembly would completely rid the engine of any timing settings.
And as far as it sounding like a selector fork, I've had a few people suggest that being the problem. So sounds like that'll be the first to check.

Nessism,
I was planning on taking pictures, both for my own reference, and also so that I could publish them for anyone else looking to do an engine rebuild (if i'm successful.)
I've adopted the egg carton method for sorting out small parts (putting small parts in egg cartons and labelling them overhead on the cover. But I guess since i'll be dealing with larger parts I'll have to use another method. Is there any sort of marker that I could label with?
As far "a good hone" I guess that would entail bringing it to a shop?

Keep the replies coming. They're great help.