Quote from: Big Rich on November 20, 2017, 08:47:57 PM
If carbon is building up around the valve seats, your exhaust valves would be slightly open all the time. So yes, your compression would be lower than it should be.

Exactly, and also it's likely there's more carbon build-up on one side of the valve than the other which can lead to bending the valves enough that they won't seal against the valve seat even if you clean the carbon off.

Likewise, the carbon on the valve is not only an uneven surface compared with the valve seat, but it's abrasive. So it'll cause uneven wear in the valve seat along with peening so the valve seat will wear to the degree that it won't seal even if you cleaned the carbon.

Suffice to say carbon on the valves is a not so great thing.

Quote from: Big Rich on November 20, 2017, 08:47:57 PM
If carbon is building up around the valve seats, your exhaust valves would be slightly open all the time. So yes, your compression would be lower than it should be.

But think about it. In a normal motor so much carbon flies through everything, you dont get a coating more than a few atoms thick @ any given time on anything. More interestingly exhaust valves have less carbon than intake due to the faster flow speeds and higher temps. So a building carbon situation is a problem by itself, the lower compression and looser valves are just another symptom.
Cool.
buddha.

I have seen a lot of exhaust valves that "lost their seat," a term that means they no longer seal. Almost always it is an exhaust valve, and when it is taken out, there is no metal color left--only carbon. If left untreated, the valve will "burn," that is lose metal and will be totally ruined. I It is not supposed to be done, but I have lapped in valves and had them work for a long time--the purists will disagree, but lapping does work although I recommend new exhaust valves especially. The Buddha is right about the intake valves--I've seen carbon really thick on them. A couple of suggestions--run valve clearances a little loose, especially on the exhausts, and run the mixture a little rich.

Got the cheapie tester in today and it's not looking good, will take it to the bike shop for a confirmation.

Pressure was 110 and 120 :¬(

This is very annoying because the bike runs well and it doesn't feel like it's losing power. This could just be bad readings so I guess I'll have to wait for Friday for a confirmation.

Assuming that this is a carbon build up and bearing in mind the bike is running well what would be the best solution here.

If it's running fine then just ride it. Eventually it will stop running fine and you will need a top end rebuild. Then you can evaluate the valves, but replacing them is cheap insurance compared with the cost of the rebuild. Rings, valves, valve seats, gaskets.

+1. Keep running it for now - at least til the end of your riding season.

Plan on (and budget for) a top end rebuild. The service manual gives really good details about what needs done, and what needs replaced.

You could (and I don't necessarily recommend it) try and clean the carbon out yourself. Just like how people run Seafoam in their gas because their carbs need cleaned....there are tricks to cleaning carbon build up. I haven't done it,  but I know there's plenty of tricks for it around the internet.

+2 on the ride it - my 50K miler was using so much oil for the last 15K of its life with me, I sold the bugger for 675 - after paying 800 for it 10yrs and 42k miles ago. Anyway, worn out these bikes are worth about as much as they are nice and fresh.
Cool.
Buddha.

Quote from: The Buddha on November 22, 2017, 06:46:44 AM
Anyway, worn out these bikes are worth about as much as they are nice and fresh.

BTW, this is a good point but also a two-edged sword. And the reason why this is true is because the typical GS500 buyer is a beginner and can't tell the difference between worn out and nice and fresh. Or putting it differently, there's a floor on running-motorcycle value, around here it's the $1500-2K range for a bike you can put on the road and use right now. Everything from ratted out UJMs with rust and dents and missing parts to Buell Blasts with faded plastics to my well-sorted GS500 are in the same range.

If you find a GS500 for $2K it might be worn out, it might be nice and fresh. It's hard to know. Unless you do that compression test before buying, it's going to be hard to know this stuff about a bike you buy used. I have seen GS500s that are only 10 years old with under 3K miles on them that won't run, while my 25+ year old bike with 21,xxx miles on it runs like new.

However, a bike you know inside and out and you know you just finished a top end rebuild is probably worth more to you than a used bike with unknown heritage.

Just putting that out there lest you are tempted to sell this bike and start over. You've done a lot of work to find the issues with this one. You'd have to do similar work to find issues with any used motorcycle of this age. They all likely require similar amounts of investment to get them to "nice and fresh". This one rings and valves, another one a starter and clutch, another one has an undiagnosed bad rod bearing, another one generally needs new everything like tires, brake pads, caliper rebuilds, fork rebuild, etc. which all adds up to the same price as a top end rebuild, another one needs you to undo a lot of the previous owner's attempts at making it a cafe racer, etc. The rare gem out there doesn't need anything but you might spend years trying to find it.

mr72 is right about a bunch of things. First, unless you really know what you are doing, a used bike is a pig in a poke (does anyone use that expression anymore?). However, if you sort out your own bike, you know what is going on with it. Second, many of us find great satisfaction in fixing problems and making things better; the GS500 is a good engine to work on. Also, do ride it until it starts running badly before you worry about a top-end job. Remember, if you are not going to ride it for a while, you'll need to do something about making sure the carbs stay clean. Others can talk to you about winterizing. I ride at least a little every week or so, so I don't have the winterizing problem.

@ajensen, ok thanks for those thoughts. It only had 15k/kms on it when I got it seemed not hard ridden, been very reliable, had a leaky stator which I fixed and and I can't fault it.

Took it to the bike shop for a compression test but they'd lent it out, but they also reckoned these bikes are bulletproof and that if it's riding well which it is, that I should just keep riding it. They suggested I run a couple of tanks of 98 octane through it and go for a bit of a burn up the highway.

Got some of this stuff to run though the tank http://www.supercheapauto.com.au/Product/Liqui-Moly-Carburetor-Valve-Cleaner-300mL/156710

I've bought an endoscope for 30 bucks and I'll still that down the cylinder and have a looks, not sure if I'll be able to see the valves but I'll get an idea of how much carbon is in there though. I've thought about maybe giving it a bit of a misting of water into the carbs but after viewing a few you tube videos on that I don't think it's very effective. Seems to be running fine so I'll put the valve cleaner through and a few tanks of 98 octane and give it a few more higher load highway runs and see what it looks like with the endoscope. But it's prolly not as serious at the moment as I might have imagined.

An Italian tune up might be in order https://en.wikipedia.org/wiki/Italian_tuneup

Quote from: user11235813 on November 24, 2017, 03:05:44 AM
if it's riding well which it is, that I should just keep riding it.

Yes to this.

QuoteThey suggested I run a couple of tanks of 98 octane through it and go for a bit of a burn up the highway.

This, however, makes no sense at all.

Quote
Got some of this stuff to run though the tank http://www.supercheapauto.com.au/Product/Liqui-Moly-Carburetor-Valve-Cleaner-300mL/156710

With any luck it won't hurt anything. Most likely won't help either, but who knows. I have run B12 mixed with the gas a couple of times in my bike, not that it needed it, just as a method to clean up whatever nooks and crannies I couldn't get to manually. IDK about this specific stuff, but the chances it will clean anything off the valves is slim if not zero.

Thing is, the carbon that flakes off easily will flake off when you run the bike at normal temperature. That's not the problem. But there is a carbon buildup that gets on the valves (and other parts of the cc including the top of the piston) that won't come off with any solvent. The normal course of action is wire wheel on a bench grinder to get it off, or chuck the valve in a drill press and use emery cloth to remove it. Or replace the valve along with the seat.

Thinking about it another way, if there is some kind of carbon that a solvent could loosen enough to chip off, would you want to chip it off? If it were along the edge of a valve then it would worsen whatever valve-sealing problem you have. And if a chip of it falls off it may find itself between the ring and the cylinder wall and score the cylinders or worse.

The head is not that hard to remove. So if you REALLY think you have carbon buildup you can tell by pulling the head and taking a look. Only cost is a head gasket and your time. Then if you find there's carbon you can decide to clean it, but you'll need some other tools. And it's going to be hard to talk yourself into putting the head back without doing the valve seats and stem seals. Then looking at the pistons staring you in the face it'll be hard to not pull the jug and do rings and clean up the pistons, then you've finished a top end rebuild.

Assume there is carbon buildup or some other cause of low compression. Worst case is you leave it alone, ride it, an it gets worse. Very worst case of getting worse is it winds up bending the valves. Eventually this will cause the bike to not run when hot, you will know something is bad wrong, and you will then have no choice but to remedy it. So by waiting for full-on failure to commence, you may add the full cost of replacement valves to the when there is a slight chance you might save some of that cost by machining the old valves if you do it now, but you probably wouldn't do that anyway. So really the choice is down to this: while the bike is running OK, do you preemptively do a top end rebuild now, or wait until it absolutely needs it? If it was me, I'd wait until it needed it, as long as you are not relying on this as your daily transportation. If it's your daily transportation, then I'd just find a time when it's convenient to be without the bike for 1-4 weeks and then do the rebuild then, knowing it will eventually need it. One way or the other, plan and budget for a top end rebuild (or whatever, get rid of the bike etc.) and beware that the bike may go from "running fine" to "won't run when hot" any day now until you do the top end rebuild. Could be a week, could be a year. But when that day comes, you will be forced to pay the piper.

@ mr72,

OK thanks for that comprehensive summation, plus some free gallows humour as well. Imagine if I took this in to have the bike serviced instead of checking the valves myself, they'd have simply measured the clearance and seen it in tolerance and given the bike back. Then I'd be riding it unaware that anything was amiss. I do take it for a lot of short rides so that could be an explanation. Yeah I was wondering about the higher octane thing, maybe he was thinking that a premium petrol might have better additives, but I do use fresh and good quality 91 though anyway.

I will take some pictures with the endoscope when it arrives and then run a couple of tanks of valve cleaner though and see what it looks like then.