Dear all,

I noticed that my right cylinder doesn't have nearly the same amount of compression as the left one.  Could anyone think of a possible reason other than a cracked piston, ring, etc.

Is there any hope in repairing the bike? Is it worth the cost?

To explain:

I had just finished cleaning my carburetors for the second time. I did it correctly this time--specialty tools, carb cleaner, everything--(I noticed that the needle jet of one of the carbs was almost completely clogged--I forgot to take it out last time--and cleaned it as well as made sure that every hole was clear) and the bike started with some effort (playing with the throttle, choke, you know how it is).

It still needed to run at about 3000-4000rpm. If I tried to lower it to regular idle rate it would stall.  I had made sure everything was up to specifications (float height etc. everything) and could not understand why the bike still wasn't working.  I then took off the spark plugs (both worked) and then noticed that the right cylinder was giving a much lower compression (close to none).

I'm don't think that it's broken since if I get the bike to start and ride it around the block a few times the right side heats up as well. 

Besides for the above problems; each time I turn off the bike it's hard to get it to start again. The season has started and I have no idea what to do next, is there anybody out there with any advice?

Thanks

p.s. I'm in the nyc area, if anybody's around

Maybe try a leak down test?  Might just need a rehone and rings to refresh the compression.  There are cylinder walls and pistons for sale right now in the for sale section from dgyver.  You could have a shop getting that all matched up and when its done just take off the old, put on the new with a gasket kit.

Quote from: jhon123 on May 23, 2009, 10:19:04 AM
I then took off the spark plugs (both worked) and then noticed that the right cylinder was giving a much lower compression (close to none).

By "notice" do you mean you actually inserted a compression gauge tool into the right spark plug hole and measured the compression?

I doubt it will be a cracked piston. Could be a valve. I don't know if adjusting the valve shims to the specification would fix a dramatic drop in compression.

Regardless of the cause, I see no harm in tearing into the bike, even if in the end you decide that it isn't worth the money to fix the problem.

I would suggest the following steps:
  1) Adjust or at least check valve clearance. It is quite simple and should take 30-90 minutes, depending on whether you already know how to do it.
  2) Add a teaspoon amount of engine oil straight into the right cylinder spark plug hole and remeasure the compression. If it goes up significantly, then the problem is worn piston rings.
  3) Take off the cylinder head and the cylinder block. It would be helpful to have Clymer manual to guide you through the steps. However, if you would rather not to buy a manual, considerign that you may be ditching the bike in the end, I can describe in more detail how to remove all that.
  4) Check if the head valves hold kerosene. Pour some into the ports and observe whether any kerosine sips into the combusture side of the head.
  5) Inspect the cylinders. Inspecing the cylinder wear requires a precision bore gauge tool.
http://cgi.ebay.com/2-6-BEST-CYLINDER-BORE-GAGE-DIAL-0005-GAGES-GAUGE_W0QQitemZ330331929894QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4ce9513d26&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50
It would be better if instead of buying the tool you could ask a mechanic to measure the cylinder-to-piston clearance for you for free. The clearance should be within 0.05-0.06 mm.
  6) Price out the cost of the fix and make a decision whether it is worth fixing the bike.

Jenya

Thanks a lot for the information.

I wanted to know if anybody would know the listed compression (pounds) needed for both cylinders, and also the amount that would necessitate a complete rebuild.

On that point would anybody know of a possible reason for a sudden loss of pressure in the right cylinder (It was fine before I stored it for the winter)?

Thank you.

A rule of thumb is 100 psi for an engine to run at all.  I believe 150 -160 is more like normal for a bike with a compression ratio like this, less is acceptable as long as both cylinders are within say 10% of each other.  Somebody correct me if I'm way off...

A leakdown test would be a good thing to do as well.

Quote from: jhon123 on May 23, 2009, 03:22:28 PM
Thanks a lot for the information.

I wanted to know if anybody would know the listed compression (pounds) needed for both cylinders, and also the amount that would necessitate a complete rebuild.

On that point would anybody know of a possible reason for a sudden loss of pressure in the right cylinder (It was fine before I stored it for the winter)?

Thank you.

The spec out of the service manual is:

Standard compression: 142-199 psi
Minimum: 114 psi
Maximum Difference between the two cylinders: 28 psi

If I were you, I'd start at the top and work down. First make 100% sure your valves are adjusted correctly. If you're sure that's true and compression is still bad, measure the compression on the bad cylinder, put a teaspoon of oil in through the spark plug hole and measure compression again. If you get an increase in compression with the oil in there, it is time for rings and honing at least. If there is no change, your head gasket is probably blown.

These are all fixable problems, and you should even be able to do it with the engine in the frame, so don't give up hope yet. At very worst, you'll have to overbore the cylinder a bit and get a new piston, but that can be done and isn't too terribly expensive...

and you end up wiht a slightly larger engine to boot   

Thanks a lot guys.

I'll go through the things you recommended and post if I run into other problems, or if I need to know where I can acquire specific parts.

Alright, here's the sad update.

While riding the bike around the block (since the right cylinder didn't work the gas wouldn't burn, the mixture would get rich, it would rev high, and would die if under the 4000rpm range. I adjusted the carbs a million times, but they couldn't compensate for a bad cylinder), I heard a loud clang, and the bike abruptly turned off.

The bike no longer cranks at all.

As far as I can tell the right cylinder blew out.  I don't want to take the engine apart since I would have no idea what to do if I did so, nor do I have the tools.

So now I'm down to two options.  The First is to get rid of the bike, work, and hope that my next bike doesn't cause me nearly as much trouble.

The second option is to find a new engine somewhere and hope that it isn't too expensive.

I have a 2000 gs-500, with new Pirelli Sport Demons (300 miles) on them.   

If anybody lives in the nyc area and wants to buy let me know, If anybody has any other ideas that can help, I would appreciate that as well.

Thanks.

Quote from: jhon123 on May 25, 2009, 04:26:05 PM
As far as I can tell the right cylinder blew out.  I don't want to take the engine apart since I would have no idea what to do if I did so, nor do I have the tools.

If you are unwilling to work on the bike, then I think you are better off getting rid off it, either as a whole or part it out and sell pieces on eBay.

You've pushed your luck by riding the bike on one cylinder while knowing that the right cylinder is dead. Who knows what that clang sound was. Maybe a bent valve. I don't know if GS heads are interfering.

Jenya

I found a motor for my gs when the scum bags at Suzuki wouldn't cover the spun bearing at 6k miles though sites like these. Just put in the part you want and you'll have a dozen offers the next day. I paid 550 for a motor with 1100 miles on it and got it in 5 days. If it grenades again I'll do the same thing. It's easy and cheaper than another bike.

http://www.uautoparts.com/used-engines/
http://www.necycle.com/
http://www.fullthrottlecycles.com/

I just took apart the engine.

You would not believe the damage I found.

The right piston was completely destroyed.

I'll try to post pics as soon as I can.

Well there's your problem:

Pictures don't show for me. Shows only broken image squares.

He's trying to link to a picture in his google email.  You need to upload them to a hosting site like picasa or imageshack then use the link provided in the upload surrounded by the IMG tag.

Good call; I'll try again.

Looks like the piston had hit the valve. Is the valve bent in the head?

The valve was completely destroyed (it's in about 7 pieces). The entire cylinder is chipped while the spark plug is stuck in by a piece of metal.  The are metal shaving all around the upper engine.  The bottom engine is ok though but it would probably be cheaper for me just to buy a new engine as I would have to rehone , buy new pistons, rebuild kit, and cover case (pieces of valve are lodged everywhere including where the sparkplug used to be)

It seems that all of the problems I've been posting since over a year ago have been because of this cylinder (messing around with the carbs  could only help so much, the engine was reving high because it was running on one cylinder, it constantly flooded since the right cylinder wasn't burning the gas and would then flood).

The engine definitely has been taken apart before (there is latex everywhere), too bad the guy I bought it from didn't tell me (I doubt he put it together correctly), but I guess at least now I know what to look for.

I'll try to post pictures of the valve when I get the chance.

Well. if you recall, when you posted your post, the first thing I recommended you do is to adjust the valve clearance. Perhaps, you would have avoided all this complications, have you done that. So best thing now is to learn the lesson and make sure you perform proper maintance on the bike in the future.

I have spare engine parts: cylinders, head, pistons, etc. Was going to use them to rebuild another engine during the winter, but I guess I could sell them too, if you decide to fix the engine.

sucks its blown, but glad to see you weren't afraid to tear into it.  Make an inventory of everything that needs replaced and start pricing things.  Spare engine parts can be sourced for rather cheap on here, especially to a fellow member willing to do the legwork to fix their own problems.  I commend you for doing the work, to bad it was to late.

Nick