'79 GS1000 top end rebuild

[Guest]

Good morning. I am a newish member and this is my first post. I am rebuilding the top end of my beloved GS and have hit a stone wall.

I wanted to know exactly what I would need to order before I placed any orders, so I went the route of disassembly, order, reassemble. I knew before I started to double check EVERYTHING, so I did. When it came time for a compression reading things got scary. C1: 75lbs C2: 70lbs C3: 70lbs C4: 75lbs.
At this point I was mystified. This bike ran like a champ last season (to Sturgis and back) with no issue. So after a bad compression test I poured a little oil into the jugs. I got great readings across all 4 cylinders. So I was prepared for a new set of rings. I took the top end apart and went to measure the cylinders and found my bore gauge was just a tad too big (3"-4") So I turned to the old repair manual and saw that if you can insert a .06mm feeler into the cylinder without the rings you need to break out your wallet. I was able to get a feeler gauge >.1mm into the jugs. Reading on I saw that you can/should insert the rings into the jugs and if you get a reading > .25in in between you need to renew rings. well I could not. I looked for any identifiers on the rings to see if they are oversized. Nothing. looked at the jugs for machine marks. Nothing. I have no idea where my compression went. I am going to finish this post and this cup of coffee and start on the head too see if i got any leaks there. But if I do not then where do I go next.

Thank you all for letting me waste some of your time and brain power.

[Crazy_Russian]

did you do the compression test with the engine cold or warm?

[Nessism]

also, was the throttle held open during the compression test?

BTW, those feeler gauge tests are inappropriate unless you stuck the gauge in from the piston skirt side. The piston to cylinder wall clearance is set in the vicinity of the piston pin. Break out your Suzuki Factory Service manual for the appropriate information. Don't trust aftermarket service manuals.

BTW2, hope you adjusted the valves before judging compression too. Failing to do so results in bad readings (and engine damage).

[Agemax]

hi and welcome, also did you hold the throttle wide open when testing the compression?
if not that will give you a low reading

[Adam_B]

The engine was cold, and throttle was wide open. I poured gas into the heads and looked for leaks it took about an hour to drain half of the fuel out. That makes me believe that the valve seat may not have been the problem.

Before I took the motor apart I checked valve clearance and I think I made a noob mistake. My smallest feeler is a .004 mm. I can only deduce that my valves may have been stuck slightly open and the true measurement is/was less than the .003 limit. I am still not totally convinced that it is valves, only because of the oil test. Could the oil test help seal the valves enough to bring the compression up to par?

[Crazy_Russian]

ive head a case where i was getting an engine for my audi, first test was kinda low, added oil, all of the cylinders tested within factory spec, installed that engine in my car, just to find out that left and right head gaskets were blown and i was spitting water out of the tail pipe like there is no tomorrow. that being said, adding oil can do odd things to your reading. you have to do the test right the first time. warm up the engine, open up throttle, and then test it

[BassCliff]

Greetings and Salutations!!

Hi Mr.

Make sure you get the decimal places correct when dealing with millimeters or inches. The valve clearance range is .03mm - .08mm. Now have a heaping helping of "mega-welcome".

If you are here you probably have a 30 year old motorcycle that needs about 20 years worth of maintenance. You'll find all kinds of helpful tips, procedures, manuals, diagrams, "how-to" guides, etc, in the links below. Let's get started.

Let me dump a TON of information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



Please Click Here For Your Mega-Welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

More links to helpful threads in the forum:
Help! Your Bike Won't Start
DON'T DO THESE THINGS
Help! Your Bike Won't Run Well
Oh God! Pods!


Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Adam_B]

Thank you BassCliff. I am going to guess that I measured correctly and transcribed incorrectly. I have read your site (probably more than twice ) and it is full of enough information to keep me from posting before, that is why I finally posted. I didn't want to look like a complete noob.
I could not test the engine warm because I couldn't get her running to test. Should that effect my compression 100psi?

[Big T]

It will run on 100psi

and 100psi cold is probably 130psi hot (or better)

[Adam_B]

I believe it would run on 100psi. But I was way under 100. And like I said , I had virtually no problems last year and now can't even start her without a large dose of ether.

[Big T]

Did you winterize your bike?

Your carbs are probably plugged up

[Adam_B]

Just gave there carbs a nice bath. Courtesy of Mr. BC's website.