1980 GS750L - To rebuild or not rebuild?

[Guest]

Afternoon, all.

I picked up this pile about 6 months ago and have been waiting for it to warm up a little before getting serious on bringing it back to life. I purchased the mc on a cold, dreary night and with poor lighting so I didn't have a lot of time to go over it with a fine tooth comb. Previous owner indicated that mc sat outside for about six months (there was a mouse nest in airbox) which gave me some pause but with a title and for $200 I figured why fuss. Fast forward to a few weeks ago, I reached out to a local mechanic to have him check compression and check the valves. Mechanic had me come over and informed me that engine was seized. I then loaded it back up on my trailer and hauled it back home where is now sits with valve cover off. Did a little research on un-seizing a stuck engine and gave it a shot. Engine is now un-seized. I drained oil and there was water/oil mix. Previous owner installed some kind of oil cooler doohicky on it. Thoughts on this? Leave, remove, other?

While this would be my first foray this deep into an engine, I am thinking that the best course of action to really get a sense of what is needed is to take it down to the cylinders to determine if this patient is worth reviving or if I make peace with my idea of turning this into a lightly modded cafe racer and move on. I know, it would be much easier to go to local mc dealership and just buy something new but I like these old mc's and would prefer that this not end up in a heap somewhere. Oh, and I'll learn something along the way hopefully (maybe it will not confirm what my wife thinks I am with respect to these projects of mine). Pros on it: clean carbs, nice exhaust, title, possible diamond in the rough; Cons: a lot. If I decide to move forward, any tips/ideas on things to consider/keep in mind other than technical manuals as I embark?

Here is a picture of (not sure what to call it/her) it.

[Uncamitzi]

wow... It actually looks pretty good. If I had the time that's exactly what I would do... oh wait.. ... That's almost exactly what I have done.. Kidding aside. I'm surprised how much a shadetree mechanic can do on these bikes.. and I've learned a TON of things here on the Forum with some great guys that always seem to have the answers. I bought a 1980 850GL without knowing ANYTHING about motorcycles 4 years ago. I've pretty much rebuilt the thing with help from here. Everything from right rubber to put on the ground to the rubber in the handle bar grips is covered SOMEWHERE here with links to BassCliffs (http://members.dslextreme.com/users/bikecliff/) site and other places (some good info on youtube too) Given the time...I'd do it all again... So... spend some time and some bucks to do it...... my vote... Just don't expect a lot of increased value to your final result.. the bikes price is what the bikes price is.... Have fun!!

[Z32650S]

Guami, welcome and by all means... go ahead and jump in. You have made the best $200 investment in a great experience. There are plenty of really knowledgeable members on GSR to help you along the way. No promises on how cheap it will be in the end, but that Basscliff site has upgrade tips and shop manuals to save you both time and money. Dig in!

[tkent02]

I wouldn't tear it down, not yet. Get it running, do the maintenance like valve adjustments and such, ride it a bit. Chances are the compression will be OK after a thousand miles or so to scrape the rust off the cylinders, the rings will probably seal, everything may be fine. I have revived several dead GSes that were seized, most of them do OK after a while. Some don't, some are smokers, some leak like a sieve. Of course it depends on how solidly it was rusted up, and how badly the engine was worn before it was left out in the rain, but most do pretty good. That model 750 is the only engine in the GS line that isn't considered bulletproof, it's possible it had a problem that led to it being parked all those years ago.

If it does need to be rebuilt, you will at least know if the transmission, crank bearings, and all of the other things are good so you don't spend the time and effort to do a top end on a turd. And the first ride on the rebuilt engine you will know it runs correctly, carburetion is right, timing is good, everything as it should be. That way you can run the Hell out of it right away to seat the rings.

Third reason, get it running good enough to ride, enjoy riding it while you start looking for a nice tight used GS1100E engine to drop in that puppy. Cheaper than rebuilding that 750, and a Hell of a lot better engine.

[Latrans]

Ooh! I'd buy that for $200! Good job on freeing up the engine. You mentioned getting water out of the crank case. Here's a trick I learned from a friend of mine: Run some transmission fluid in place of engine oil. Just for a little bit, enough to push it through all the passages and bearings. Transmission fluid has a bunch of additives that will help clean out deposits and absorb residual water.

[guami007]

Thank you for the encouragement gents. Looking to slowly move on this. Hoping to spend as much time on it as possible but with 6-8 months of really cold winter here in upper mid-west, I have to take advantage of the one nice day (summer) that will be coming our way at some point before winter sets back in.

tkent02 - your sig scares me

I have begun to remove external bits/pieces on this mc. Removed complete exhaust, other bits/pieces, and this oil cooler which I mentioned in first post. Any idea why anyone would put one of these on an 'L'? Carbs have been rejetted by the way so me thinks some previous owner 'tinkered' with this thing. I can post clearer pics if needed. Valve cover is next...

[loud et]

As tKent said.....stop disassembly and get it running.
You are going to to through months of work and fixing to get it all nice and how you want it......then get it running and find out the thing has a bad crankshaft bearing or that the transmission has a bad gear or a bent clutch fork shaft......
Do the basic carbs overhaul, adjust the valves and sync the carbs.
Just ride it for a few hundred miles to make sure it shifts good and the engine is solid. Even of it leaks oil and drips all over the place at least you can verify you have a solid drivetrain.
I wouldn't put a lot of effort into paint and polish and upgrades or worry one bit about appearance until you know you have a bike worth riding.

[tkent02]

tkent02 - your sig scares me

Not a fan of history? Nothing scary about it.

[guami007]

Thanks for the suggestions/advice gents.

Here is where things are at the moment with tkent02's and loud et's comments taken under advisement. I rotated the crankshaft to TDC as shown in pictures. Angle of picture makes it look a bit off but it is spot on. Question here. Isn't the #1 arrow on camshaft sprocket supposed to be level/parallel with edge of cylinder head?




Next up, are view of left and right side of camshafts as viewed if standing in front of the mc. Questions here. On left and right view of exhaust cam lobes, there are groove patterns in the middle of the lobes. I can feel that groove if I run my finger across the lobe.

1. Is this normal?
2. Is this due to design of rocker arm that these ride on?
3. Was the design different on 1982 GS750T? I have a set of camshafts from this year/model and these grooves are not present on those camshafts?




Lastly, odometer on this mc shows a little over 8k miles on it. Normally I would say yeah whatever for a 36 year old mc but looking at things like the condition of rubber on left and right footrests would lead me to believe that they were either replaced with new ones very recently or this mc just never saw a lot of action as footrest rubber is like new.

[guami007]

Evening, gents.

I have been busy and have not had a lot of time to spend on this project. I didn't receive any feedback on some of the questions in previous post. Figured either no one knew (unlikely) or I broke some cardinal rule of sorts for continuing to dig into this and going against some sage advice. I really do appreciate the advice but something was telling me that there was something more to this as turning the crank by hand felt a little to stiff.

Today, I had some time to continue digging and here is what I found and think was definitely the source of the problem.

After removing the head, I looked down into the oil chamber and saw this atrocity smashed/wedged into the crank sprocket - a small nut made out of soft alloy of some sort. I looked over sprocket very careful as well as inspected the cam chain quite closely and did not see damage of any kind. Nut itself is gouged pretty good but no chunks missing due to it being a soft alloy.




This got me to thinking that this could easily prevent engine from turning over via starter motor but not when turning it over with a long breaker bar. Given how everything looks inside, I am beginning to suspect that last owner to do any work on this probably gave up on it due to engine not turning over when hitting starter. All cylinders look quite smooth w/o much scoring except cylinder # 1 that has a 2 inch or so vertical score on it as seen in picture. Probably due piston ring from same being bent. Not sure what would cause that.

Cylinder and piston # 1:





Piston and cylinder # 2:




Piston and cylinder # 3:

[guami007]

See previous page for post # 1 on this.

Piston and cylinder # 4:





Valves:





I am going to measure away at this point and see where things are at tolerance wise. Anyone see any other red flags with this?

TIA.

[Spyder]

Those cam lobes are truly fried, and you should consider using the "spare" set you mentioned. (After CLOSE inspection of the mating rocker surface.) You may need to replace a couple rockers too... The 16 valve 750's had top end oiling issues. There is a mod to help with it, with some washers in the relief valve spring. There is also an alternative oil pump set, I think from an 1100(?)... Next I would get'er back together fill it up with chrysler trans fluid, and without the plugs in it crank it over for a bit to get it circulating through. leave it for a few hours, and do it again. Do that for a few cycles, day or so. Drain it, fill it with Rotella and run it. Should be fine. That oil cooler will help keep it cooler in the hot summer months. If you don't like it, or just don't think you need it (and you do) send it my way, I need one, lol... Good luck...

Edit: That nut on the crank sprocket was why the engine was "seized" ...

[guami007]

Thanks for the response.

As far as the specs on the cam lobes, they all come in between 34.38 and 34.40 which is well w/in spec. Rocker surfaces appear fine as well so now your comment that these cams are fried has me unsure. I'm no mechanic but isn't spec spec?

I removed everything off of the head and am getting ready to lap the valves. I don't see any pitting on the valve seats which is a good sign based on what I've read. I used a carbon remover called Berkebile 2+2 Instant Gum Cutter as well as a soft brass wheel attached to my Dremmel. This stuff is by far better than anything else I've ever used. It cuts through carbon on contact. However, if you value your lungs, reproductive system, etc., I would strongly suggest wearing a mask regardless if used in confine space or outside. This is some nasty stuff (in a good carbon cutting way). I was unable to find locally so had to purchase it online.

Here are some pictures of the combustion chambers as well as 'EX' valves before/after putting to a fine brass grinding wheel on bench grinder. Please, please do speak up if you see anything concerning.

Combustion chamber/4 and 3



Combustion chamber/ 2 and 1



Exhaust Valve before/after





As always, thanks for any feedback.

[DohcBikes]

Those valves are beat to death, the cam is trash, as well as the rockers that it touched, it probably needs bored out because of the deep scratches that ring surely left, there was a random nut in the engine...and you don't seem to be measuring anything in addition to not seeming to have a true grasp on engine theory

Give it up. You can buy a nice 750l for less than it will cost to build that engine correctly.

[DohcBikes]

What on earth makes you think the valves need lapped, they need thrown away and replaced and you better hope you didnt get that dremel anywhere near your valve seats but it sure looks like you did