Hello, everyone.

Short intro: My name is Mauricio, I'm 38 and live in San Jose, California. I'm very mechanically inclined and I will do everything that is needed to fix this bike, short of boring cylinders.
The bike is a 2002 that I recently bought as a project bike. It actually looks better than what I would consider a project bike.

Bike doesn't start. It cranks, but that's all. I started by doing a compression test. Standard stuff... both spark plugs out and grounded, full throttle, a few cranks per cylinder. Done while cold. Right cylinder read 130. Left one read 90...
I then did the oil test. I poured a spoonful of oil in the left cylinder and re-did the compression test. This time the gage went up to 150 psi, but not in a steady way. Rather it would go up and down very rapidly (as in building compression with each stroke and then releasing it on the exhaust one, I guess? - which is a bit weird to me, since the other cylinder gave me a steady reading).
Anyway, according to what I've read here and in other Internet places, this significant increase in compression should mean that the loss is happening on the lower end (piston, rings...), so I went on and opened up the cylinders.
The cylinders look in very, very good condition. Shiny, no score marks, no burrs. A couple of vertical stains (I'll take a pic tonight and post it), but look and feel superficial (as a matter of fact, you can't really feel them).
The pistons, after cleaning them, look almost new! The left piston has a few small vertical marks in one side on the top, right above the first ring.
The rings measure well within specs, as do the cylinder.
So, what gives? How is this thing not having compression?
One theory I have is that the rings might have been assembled in-line, not staggered, but I'm not sure.
Also, the carburetor is not assembled correctly: It was missing one choke, one of the jets was completely lose, even a carburetor valve spring was missing. I don't see how this could affect the compression, but I'm not sure.
Another thing, seeing as the cylinder and pistons seemed ok, I checked the camshafts. The exhaust is also well within Clymer's specs, but the intake camshaft is short. I'm talking about cam height. The piece itself looks to be no older or newer than the exhaust's one, which brings me to another doubt that I have... The Clymer manual.
The one I bought is supposed to cover models from 98 or something to 2002. However, the carburetor diagram it has is not the one shown in microfiche places for the 02 model. The carb I have, although missing parts, matches the ones I see for the 02 models at the wiki site and at ronayers.com. This has me doubting some of the specs on the Clymer book, particularly the cam height.

Questions:
1. Has anyone run into spec discrepancies between the Clymer book and actual data?
2. Has anyone measured a new intake camshaft and if so, can you share the cam height?
3. Could the carb affect the compression reading?
4. How else could that cylinder be missing compression?
5. I'm thinking of reassembling it and testing it again. Good idea? Bad idea? What do you suggest I do next?

Thank you anyone that takes the time and gives me suggestions. I can't wait to ride.
(pics of the piston to follow)

http://s1221.photobucket.com/albums/dd466/vasama0/Maos%20GS500/

sorry... new and embarrased to say I don't know how to post pics...
edited... never mind, I just learned... here's the pics:

... anybody...?

Thinking of changing rings anyway...

Id hone the cylinders and stick on new rings just for peace of mind...

Why not do it while its apart? You'll kick yourself later if you didn't, and then you need to

the scratches at the top shouldn't be there but don't seem to be a problem... grab some good new rings and gap them correctly, take it to a machine shop and ask them to check that the bores are true, maybe get them to hone them if you don't have the tool, a good cross hatch helps to break in new rings. remember to check the gap with the rings in the cylinder bore, while the head is off this is a perfect time for a good valve job, 3 angle them and put new seats in, If you are going to do any port work make sure the intakes have slight texture and the exhaust is nearly polished. texture on the intake keeps the fuel from condensing on the walls. have the machine shop knock the lip off the cylinder if there is one (can cause weird squish areas).

fully rebuild the carbs to stock or near stock spec depending on what mods your going to do, this is also a good time to regrind the cam if you want something a hair more aggressive but since most people don't do much crazy stuff to the GS finding the right grind might not be easy.

also remember never reuse gaskets on the engine, you don't want some crazy small thing ruining your whole day and having to rip it all down again just to rebuild it, gaskets can also cause a low comp condition and wont be helped by oil...

my favorite brand of rings is total seal, but I don't know if they have rings for GS's or not they probably have ones that will work.

Thanks so much for the advise.

I'm thinking of honing it myself. I've read that it isn't a complicated process. Anyone disagree with that? If honing is an OK thing to do at home, are there any suggestions as to what type of honing tool to get (any particular grit?)

I'm getting the rings and gaskets and installing them this weekend. I'll post pics as I go through.

Thanks again!

I agree with honing the cylinders,new rings,get a quicky valve job with new seats and seals.The carbs shouldn't cause an issue with the compression check.I would have ran the idle screw in a bit to be sure that they are open enough to allow air into the cylinders.I have never had any issues with the Clymer manual being wrong and I have used it for close to four years now on everything on my bike.

theres ball hones and spring loaded tri hones, im a fan of the ball type myself... (insert ball joke here) either will do, tri hones are better but ball hones are easier to use but they are very bore specific, so make sure if you go with the ball type you get the right size... with either one you want to make consistent passes up and down the cylinder bore so that the hone leaves a cross hatched pattern in the bore, not honing is bad for the life of your engine and horrid for your compression! Also run on a break in schedule either as directed by suzuki or by the wiki.

Quote from: vasama on June 17, 2011, 08:57:54 AM
......................................... This has me doubting some of the specs on the Clymer book, particularly the cam height.

Questions:
1. Has anyone run into spec discrepancies between the Clymer book and actual data?
2. Has anyone measured a new intake camshaft and if so, can you share the cam height?
3. Could the carb affect the compression reading?
4. How else could that cylinder be missing compression?5. I'm thinking of reassembling it and testing it again. Good idea? Bad idea? What do you suggest I do next?

Thank you anyone that takes the time and gives me suggestions. I can't wait to ride.
(pics of the piston to follow)

Having had one myself my guess is a sticking bucket since I had one on my 02 GS and a number of others around here have had them too.  Your jumping compression reading on the one cyl might indicate this too.  Can you turn the buckets freely with your finger tip and have you removed them from the head?

I replaced the sticking bucket and broken valve, lapped the valves, and put it back together at 21k miles after the bucket stuck and broke an exhaust valve one freezing cold morning and it's run as good as new for more than 60k miles since then.  My oil consumption is normal for a GS with over 86K miles on it now.  Shouldn't need to be replacing rings and honing cylinders unless you have some really high milage on that bike.

I had a Clymers for my 97 GS and bought a new one for my 02 GS and found it was really no different, they don't seem to update much but the cover.

Quote from: gsJack on June 18, 2011, 07:51:25 AM

Quote from: vasama on June 17, 2011, 08:57:54 AM
......................................... This has me doubting some of the specs on the Clymer book, particularly the cam height.

Questions:
1. Has anyone run into spec discrepancies between the Clymer book and actual data?
2. Has anyone measured a new intake camshaft and if so, can you share the cam height?
3. Could the carb affect the compression reading?
4. How else could that cylinder be missing compression?5. I'm thinking of reassembling it and testing it again. Good idea? Bad idea? What do you suggest I do next?

Thank you anyone that takes the time and gives me suggestions. I can't wait to ride.
(pics of the piston to follow)

Having had one myself my guess is a sticking bucket since I had one on my 02 GS and a number of others around here have had them too.  Your jumping compression reading on the one cyl might indicate this too.  Can you turn the buckets freely with your finger tip and have you removed them from the head?

I replaced the sticking bucket and broken valve, lapped the valves, and put it back together at 21k miles after the bucket stuck and broke an exhaust valve one freezing cold morning and it's run as good as new for more than 60k miles since then.  My oil consumption is normal for a GS with over 86K miles on it now.  Shouldn't need to be replacing rings and honing cylinders unless you have some really high milage on that bike.

I had a Clymers for my 97 GS and bought a new one for my 02 GS and found it was really no different, they don't seem to update much but the cover.

I forgot about your write up on that.What was the symptoms?One of my GS's is popping back through the left carb and I am suspecting something sticking on the intake valve.I have cleaned and tried two sets of carbs.I have also replaced everything in the fuel system and ignition system.I cleaned the tank and tank petcock also.

Get an internal-micrometer down the cylinders before you do anything, or better still get a shop to do it. If the bores have worn and are out of spec` or have become oval, new rings and honing is a waste of time and money.

ooo forgot about measuring, good catch sledge, you might be able to rent a dial bore gauge, I hate T gauges they are a lot harder to use...

O/P says the rings and bores are ok but I would be interested to know how the conclusion was arrived at.

Hello, everybody. Hope you all had a great father's day. I know I did!

Well, here's my update:
I took the cylinder to a machine shop. I luckily stumbled upon Yankee Ingenuity, a specialized motorcycle shop. Turns out they moved some years ago from Nevada from San Jose. I got to talk with the founder himself! Mr. Duncan measured my cylinders. They were both within spec! He cleaned both mating surfaces and honed the cylinders. After that, I went to the Suzuki dealership and ordered ring sets, as well as gaskets. On the meantime, I'll be measuring the camshafts for the gaps, and I'll be pouring some alcohol to see if it leaks through the valves. I will probably end up lapping the valves and replacing the seats and seals.
All in all, I'd say that everything looks very promising. I'll update more on the valves tomorrow.

It is possible that a bucket is somewhat off. It came off easily enough, but it doesn't want to go back as easy. I haven't tried removing the other buckets; will try tomorrow.

Thanks again to all for the invaluable input.

If you have traveled that far down the rabbit hole just rebuild the head... to do seats and valve lapping you have to remove them anyway so just throw some new springs and buckets in there... peace of mind is worth more than that will ever cost...  roughly 80 bux in parts from bikebandit for springs seals and retainers... and I would try to reuse any buckets that check out...

Quote from: crzydood17 on June 19, 2011, 09:27:31 PM
If you have traveled that far down the rabbit hole just rebuild the head... to do seats and valve lapping you have to remove them anyway so just throw some new springs and buckets in there... peace of mind is worth more than that will ever cost...  roughly 80 bux in parts from bikebandit for springs seals and retainers... and I would try to reuse any buckets that check out...

Agree 100%. I believe this will be what I'll do

Hello, all
Been short on time, but finally got parts (gaskets, rings, missing carb parts), and started putting it all back together last night.
Old rings were under service specs (left side really off, right side just under). Cylinders were in really good shape.
Regarding a valve job, I have a question: I did a leak test (see pic) using acetone. None of it leaked to either port. I'm thinking that this indicates that the compression loss was really due to piston rings, and that a valve job is not necessary at all at this point. Do you guys agree? Does anyone think that I should do a valve job just because I have the head open, even though the acetone didn't leak?
I cleaned all the carbon in the combustion chamber, and everything there looks really nice now.

I had some issues trying to reinstall one of the buckets. Too tight. I'll try tonight to swap places with the other buckets and see if it'll fit better in another valve. Would I be correct in thinking that this tight bucket shouldn't mean a broken valve because of the no-leak during the acetone test?



Thanks

Was able to fit the tappet (valve bucket) in another valve after heating it. It now even spins by hand!
I tested the valves again for leaks, but this time pouring acetone in the ports, not in the combustion chamber.
It seeped through both intake valves. No real leak, just seeping enough for me to notice the littlest bit of moisture around parts of the edges of the valves.
Now I'm unsure if this happened because of the penetrating nature of acetone. I'm wondering whether this seepage is enough evidence to justify lapping these valves. I just don't want to do something if it isn't needed (plus I really want to finish putting it all togeher to start the bike and move on to working on the carbs). I'm planning to redo this test with water. I'm suspecting that with water being denser than acetone, it might not seep like the acetone did.
Any opinons?