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How far down the rabbit hole will I go... `78 GS750

  • Thread starter Thread starter bottobot
  • Start date Start date
B

bottobot

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Here`s the backstory on this bike. I gave it to a freind as a wedding present almost a couple years ago. I bought it for a $1000 bucks. It ran ****ty then and runs ****ty now. Well he bought himself a new Triumph Bonneville and gave the bike to his semi-estranged father. Now they got something in common and were able to bridge a few years of never talking with motorcycle riding. Nice warm fuzzy story. In the meantime I had left the country for a year and had returned with no real bike to ride. Friends Dad had gotten himself a new bike, and now have no need for beater. Its been sitting and no one else in the family wants it so they give it back to me :D

Now its in my workshop getting a workover.


Now I am not really sure what I am going to do to this poor beast as I have a number of other projects in the queue, but this bike has really grown on me. So first thing I do is hit the net and find you all here at GS Resources. What a great bunch of helpful people you are. The welcome kit and a few others say ``Dip your carbs and do a rebuild!``

Tutorials are read and I commence. A completed carb rebuild which can be found here.

Now I am going to attack my gasket set and replace my head gasket.

I am pretty good about posting photos and such so stay posted as I go to work on this puppy.

If any of you are in the Vancouver, BC area and would like to drop by my shop and say hello please do! Just send me a message with your number and I`ll give you directions.
 
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There are almost as many GSR members on Vancouver as there are in the East-central US.
A few may be dropping by. ;)

Eric
 
Well I got deep into the cylinders today. Found a few things to indicate where the oil was getting in. There is a rubber square-ring that seals the cam chain area from the head and it was definitely pooched. So that would explain some of it. There were also tears in some of the o-rings that go around the bottom of the cylinders themselves that were torn, though they might have torn during cylinder removal. It was pretty clear that wear the top half of the cylinder meets the base there was oil weeping all the way around pretty much. I am pretty confident it was a gasket issue and not worn rings that were causing the fouling. I'm out of my budget for this bike for parts and such so even if worn rings are the issue, I'll just have to put up with it till I can order some in a few weeks. Give it another couple weeks to get em and then we are looking at a month before I could do em anyway. Might as well see if it goes in the meantime and get my other projects happening.

If I do need new piston rings then I'll go whole hog and repaint the whole engine, get the valves re-seated, do the shims, then bore out and size-up the pistons.

For now here are some progress pics. I like to put things in ziploc bags and label em. If I am disciplined it makes for a much easier putting back together process.


I give everything a nice place to rest while I bang on other things.


I love looking at a bike with its guts hanging out. I wonder if its worthwhile to try cleaning the pistons? They have some buildup from the oil burning.


Tommorrow I'll start putting these fresh gaskets on :D
 
Did you get valve guide seals too? I would run a light hone through the cylinders before reassembly if it was me. You might have a tough time finding o/s rings and pistons for some older bikes.
 
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gearhead13 said:
Did you get valve guide seals too? I would run a light hone through the cylinders before reassembly if it was me. You might have a tough time finding o/s rings and pistons for some older bikes.
Click to expand...

Yeah I got the seals. I don't have a honer so I won't be putting a hone on even though I would like to.
 
Watching Steve tonight clean the pistons on his 650, doing it isn't that hard. Take some carb cleaner and a wire brush and go at it. Should clean up fairly quickly (his did and look about the same as those) and you can then inspect them for any damage.
 
The pistons in the photo look good. Very little or no dark coloring on the piston skirt which means the rings were sealing nicely.

Better say six Hail Mary's when you assemble the engine. Aftermarket gaskets are a real gamble and we don't want you getting an oil leak.:p
 
Nessism said:
The pistons in the photo look good. Very little or no dark coloring on the piston skirt which means the rings were sealing nicely.

Better say six Hail Mary's when you assemble the engine. Aftermarket gaskets are a real gamble and we don't want you getting an oil leak.:p
Click to expand...

Well today I start putting things back together so I am definitely be saying my prayers. I'll be saying a few more things if these gaskets don't hold up...
 
Got the gasket off the top of the valve section. Some has stuck on and I am loathe to take it off with any kind of tool lest I nick the surface. Think I could use some 400 grit?




Now the bottom side looks really scored, maybe a gasket was stuck on at some point and one of the PO's really went to town with a flat head or a chisel or something. I'm thinking of sanding it to make sure that the surface is good. It may be one of the reasons why it was weeping oil from this area. The paint is also in really bad shape. Pretty clear they didn't paint it properly. I'd also like to get at the valves so I can put new seals in but I don't have the right tool so thats gonna get skipped. :(

 
tkent02 said:
Watch out, they're all Canadians.
Click to expand...


Daam straight eH!



I wouldn't recommend sanding the gasket. A plastic scraper works. Some here Carefully use razor blades :|

Gasket remover works as well. Its just like paint stripper.

You could have the head planed. I'm estimating it would be $30-50.
 
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I am having some trouble putting the base cylinder on. I can't squeeze the rings together enough by hand to slide the cylinders down. I may have to go to crappy tire and see what they got that I can use. I need to find an oil filter anyways. Any suggestions would be real welcome.
 
You may want to check the diameter of those pistons and maybe the lift on the cams. Those look like Yoshimura pistons. Do they say POP Y on the side next to the wrist pin bore. The pistons look to have more dome than stock. If you have a stock head gasket it may not fit the bore. The cams look like they have some serious lift also. You just may have yourself a hotrod.
 
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bottobot said:
I am having some trouble putting the base cylinder on. I can't squeeze the rings together enough by hand to slide the cylinders down. I may have to go to crappy tire and see what they got that I can use. I need to find an oil filter anyways. Any suggestions would be real welcome.
Click to expand...

I know some people that used hose clamps on the pistons to get the cylinders on. They were very very carefull when doing it and didn't hurt anything but I'm not sure I'd do it.
 
I strongly advise you to remove the valves and replace the valve stem seals. Check Basscliff's website for a valve removal tutorial using a cheap C-clamp and piece of PVC pipe.
 
Nessism said:
I strongly advise you to remove the valves and replace the valve stem seals. Check Basscliff's website for a valve removal tutorial using a cheap C-clamp and piece of PVC pipe.
Click to expand...

I got the base cylinder on, which was super difficult but luckily a friend randomly stopped by and we were able to work in unison to sweet talk those pistons into the cylinder. So now I am definitively gonna look at that tutorial.
 
7981GS said:
Use a popcycle stick or a piece of plastic.

Eric
Click to expand...

I ended up using some plastic razor blades. Worked really well in conjuction with some gasket cleaner to get the rest of the gasket off. Then I was able to use them to get the rings on. The guy at Lordco was super helpful.


 
TeamDar said:
You may want to check the diameter of those pistons and maybe the lift on the cams. Those look like Yoshimura pistons. Do they say POP Y on the side next to the wrist pin bore. The pistons look to have more dome than stock. If you have a stock head gasket it may not fit the bore. The cams look like they have some serious lift also. You just may have yourself a hotrod.
Click to expand...

I didn't see this post. It could very well be that I have a hotrod. The pistons do say POPY on the side. Wierdly enough I did compare the gaskets to make sure they were the same thickness, and they are. Whats interesting is that the carbs have been re-jetted and there is an Dyna RPM Limiter on there. This bike has definitely been "raced out" a bit. After I clear out my build queue, you can see it in my forum sig, I am going to re-aproach this bike and re-do it properly. There is just so much wrong with it cosmetically that I don't have time for right now. I've more or less made the decision to put it back together and do a few more maintanence issues, like brake fluid flush and fork oil, and oil filter and strainer. Then call it a day and move on to the next. I need a couple more running bikes in my stable before I can spend the time on this one that it really deserves.

Here is another project that is active right now where a guy and his dad are restoring the same bike as me and doing a really killer job. Its making me super jealous and I want to do a lot of what they are doing to this bike too. Its hard to reconcile that I just don't have the time/money and tools to make it happen. Maybe in a few months. For now I will soldier on a get this bike running.

Your words of wisdom and encouragement have been very helpful to me everyone! I'm just an inexperienced backyarder trying to take it to the next level and it feels overwhelming sometimes.
 
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