80 gs 550e. probably a bad transmission. help me diagnose/replace it!

[Guest]

Hey guys,

I just got a 1980 GS 550 E

It seems like it runs really well, it just has one major issue.

When I'm in second gear and accelerate quickly (except for when going downhill), the bike lurches forward repeatedly... It feels as if there's missing teeth or something on the second gear, but I'm hoping it's something more simple.

It shifts in and out of all gears (including second) excellently. It's just that when I'm IN second gear, it feels like its rapidly engaging and disengaging power.

I've heard that grinding and clacking noises are to be expected if the transmission is bad, but this bike is silent, even when its lurching. It just delivers the power in very jerky way. and only in second gear. every other gear feels great.

I've actually bought a replacement transmission off ebay. It looks like this:





I'm guessing i have to replace the transmission. Can anyone help me find a thread or a guide on how to do this?

I'm a relatively inexperienced mechanic... so I can use all the help I can get. But I'm determined to fix this myself.

What tips and tricks can you recommend? What tools will I need? Will I have to split the case? Should I buy an engine stand?

Thanks guys.


Here's a pic of my bike. I'm excited to get her running well. Thanks everyone.

[almarconi]

First thing you will need is a factory service manual. The engine will need to be removed from the bike and completely taken apart to get to the transmission. Depending on the engine, you may be able to remove the bottom half of the case to get to the transmission while leaving the crank and top end attached to the top half of the case. Check the service manual but more than likely you will need to split the cases to get your transmission removed. Inspect all the parts carefully. The problem with used transmissions is that you can not really see the parts of the gears that wear (the slots where the dogs engage) without removing the gears from the shafts. Not that hard but it can get expensive real quick if some of the gears are bad. OEM gears are pretty much your only choice for replacement parts.The service manual will have specifications for measuring the shift forks and all the other parts.

How many miles on the bike? While you are in there you may need to replace rings, valve stems, gaskets, etc. While you have it torn down its a good idea to measure everything. This will add to the cost of your rebuild. As far as tools you will need basic hand tools and some specialized engine tools like a ring compressor, a good torque wrench, clutch basket holding tool, etc. Air tools are great if you have them. Some people use a stand to support the engine but a bench will also work. Not a project for the faint of heart. You also need to make sure everything is kept clean and organized if you want a successful build.

Your problem may be related to your clutch. Has the bike been sitting for a while? Many times the clutch plates get stuck together and will not engage/disengage. I would take the clutch apart and check everything for wear. Make sure the cable is properly lubed and adjusted. Measure the clutch springs, I'd replace them if they are original. Replace the oil with a good quality 15w-40 diesel oil.

[egetron]

The bike has 37,000 miles on it.

I would LOVE for this to be a clutch problem... but that doesn't make sense to me (granted I don't know much about how this stuff works)

Wouldn't a clutch problem exist throughout all gears? And wouldn't a clutch problem make shifting in and out of gears difficult? To reiterate, the bike shifts wonderfully into and out of all gears and delivers power smoothly in all gears except 2nd.

The problem with used transmissions is that you can not really see the parts of the gears that wear (the slots where the dogs engage) without removing the gears from the shafts. Not that hard but it can get expensive real quick if some of the gears are bad. OEM gears are pretty much your only choice for replacement parts.The service manual will have specifications for measuring the shift forks and all the other parts.

So you're saying that I shouldn't use the transmission I got off Ebay? In the Clymer manual I have, it recommends AGAINST replacing individual gears. The manual says that it requires special Press-Fit tools and expertise to do it properly.... which is why I thought I could just replace the whole thing.

I can't really tell, but this transmission I got off ebay appears to be really clean. I was told it came off of a low-mileage bike.

My hope is that once I get the engine apart, I'll find a transmission with some worn gears, and I can simply replace the whole thing with this one I've purchased.




Some Tool-related questions:

What kind of air-tools and what size air compressor would you recommend?
What tools do I need for measuring? Micrometer? Digital Caliper? Are those actually the same thing?


Thanks for your advice!

[almarconi]

So you're saying that I shouldn't use the transmission I got off Ebay? In the Clymer manual I have, it recommends AGAINST replacing individual gears. The manual says that it requires special Press-Fit tools and expertise to do it properly.... which is why I thought I could just replace the whole thing.

I did not say that, what I said is that you need to inspect the gears very carefully. I purchased a used transmission from ebay for my RF900. It looked perfect until I really started looking at the wear points. I ended up replacing 3 of the gears because they slots where the dogs engage were worn. I could not see this from an ebay picture and could only see it once I removed all the gears from the shafts. I would not recommend any service manual other than a factory suzuki manual. Let me give you one piece of advice, replacing the transmission is not trivial or cheap in terms of money or time. You do not want to install a suspect part only to have it fail and then have to tear the engine apart again. My motto when it comes to engine rebuilding is if in doubt, throw it out.

I don't know anything about the history of your bike. It's possible the PO revved it up to 10k rpm, put it in second gear and rode wheelies for miles. You might have broken teeth on second gear or a bent shift fork. It could be many things causing your problem. Remove the oil pan and see if there is any metal in the bottom of the pan.

What kind of air-tools and what size air compressor would you recommend?
What tools do I need for measuring? Micrometer? Digital Caliper? Are those actually the same thing?

Impact wrench comes to mind, a compressor in the 30-80 gallon range.
Digital calipers, bore gauge, feeler gauge, outside micrometer are some of the measuring tools needed.

[egetron]

Thanks for responding almarconi... I appreciate the advice.

I'll check the oil pan. I'm expecting to find metal in there.

Assuming I do need to replace gears, how can I go about inspecting this transmission I've purchased to see if it's worthy of transplanting into my engine? Do you mean a visual inspection? Or should I go ahead and order some measuring tools right now?

[gs11ezrydr]

From what you explained the 2nd gear engagement dogs are rounded off.You can either replace the damaged set of gears or send them off and get them repaired (welded) and back cut.Either way if you are planning on keeping the bike I would highly recommend getting the gears indexed and back cut to insure the trans. problems are cured for good.Indexing the dogs makes sure that all of them are engaging equally,and back cutting them makes them under load hold themselfs together,more the load,tighter they hold.Plus when shifting as soon as the dogs make contact they will pull themselfs into each other.Smooth flawless shifting.Inspect the shift cam,slots.pins,etc. and the shift forks.Repl.any detent springs.Any signs of wear will need repl.also.This applies to all motorcycle transmissions.

[egetron]

hey, gs11ezrydr

thanks for responding... what does it mean to get gears indexed and back cut?

Ok I found backcutting here:

http://aperaceparts.com/transmissions.html

From what I'm reading, this is pretty expensive... and seems to more necessary for racing bikes... or is this something that's worth doing for street riding?

[barnbiketom]

Just my 2 cents here guys... , but you could have this bike on the road , correctly running in a DAY if you got another engine. parts bikes are out here with no title.. running and cheep.

that combined with saving HOURS AND HOURS of your time, and money for books, and tools and probably will never git 'er done anyway.
I've split many a cases and am NOT going to sugar coat this for you. it is not for the inexperienced or weak at heart.

get another engine then go riding.

[Pete's GS]

Nice bike. I used to have one. You have a bent shift fork from an abusive previous owner who was trying to do wheelies on an old bike or tried shifting without the clutch like Ricky Racer, which, again, is not something you can do on an old bike. I'd get another motor. That's cheaper than pulling your present motor, opening the cases, and repairing that shift fork. This is not a bike you should sink a lot of money into.

[eil]

It sounds like you're ready and willing to crack open that engine and go to town. That's good! I wish there were more people as eager as you get their hands dirty on something they've never done before.

However, most of the experts here are telling you to not to bother and they're probably not wrong. You're looking at hundreds of dollars in new parts (especially gaskets and seals) and then another few hundred for the tools you would need. Plus the added complication that since you haven't done this before, there's a fair chance of making a mistake that will require doing it all over again or worse, a mistake that destroys the engine. Your time and money may be better spent sourcing and installing a new engine. Nobody is saying you can't do this, but give serious consideration to the downsides.

If you do really want to fix your engine, you might try to source a good one, swap that in, and then work on the original in your spare time. You'll still spend a lot of money, but you won't be pressured into getting it done as a condition of being able to go riding whenever you want.

There are also community colleges and trade schools that do engine rebuilding classes. Again, these aren't cheap either, but it would be worth doing before you learn all of the wrong things to do the hard way.

[egetron]

I'll say this, the main reason I bought this bike was to learn how to work on bikes.

So I may be inexperienced, but I'm not faint of heart.

I am willing to drop another thousand into tools and parts. Right now I have a set of wrenches, a torque wrench, and most basic hand tools.
I'm looking on Craigslist now for a reasonably priced air compressor and impact wrench (do I really need to get a 30 gallon? Can I get something smaller? Also is there a more quiet option? I'm working in a shared backyard)

That being said, is it REALLY cheaper for me to buy a new engine? Looking on ebay, they seem to be at least 400 bucks with shipping to SoCal. Am I looking in the wrong place?

I started a similar thread on Dotheton, they were the ones that gave me the idea to replace the transmission myself instead of buying a new engine. They all seemed to think it was cheaper. But they also said that you guys would know best.

http://www.dotheton.com/forum/index.php?topic=46853.0

I already have another whole transmission, which upon visually inspection of dogs/gears... looks basically brand new. (no signs of wear, as far as i can tell)

Also, are there any members in Los Angeles that anyone is aware of that would help me with this? I can pay you for your time in money, beer, graphic design services (I'm better than your nephew), whatever.

Thanks for all the help guys.

[tom203]

Second gear takes most of the abuse from rocket sled pilots- I always tell folks to check second carefully if the bike at least runs, I hate transmission problems!

[Maddevill]

Don't want to simplify too much but have you looked at your sprockets? Could be chain jumping teeth.

[egetron]

thanks for the reply Maddevill, I'll go ahead and check that tonight.

If it was the sprocket, wouldn't that make itself apparent in every gear though?

also, probably a dumb/searchable question, but how do I check the sprocket? Do you mean the one on the rear wheel or the one in the engine? Or both?

[almarconi]

I already have another whole transmission, which upon visually inspection of dogs/gears... looks basically brand new. (no signs of wear, as far as i can tell)

How did you do that without removing the gears from the shafts?