Piston Rings? Valves? Timing? All Three?

[Guest]

I've had a 1978 GS550 for a few months and I've been slowly diagnosing, adjusting, and replacing components to get it running well. It wasn't running when I bought it. It has just under 17,000mi on it, but had sat in a garage for a few years. Previous owner was taking steps to "cafe" it out, which I've mostly undone aside from the carb jetting/pod filters.

So far I've:
• Replaced spark plugs
• Adjusted point gap & ignition timing
• Checked and adjusted valve clearances
• Fully disassembled and cleaned carbs
• Replaced petcock, installed an inline fuel filter
• Replaced front brake brake master cylinder, brake lines, and pads
• Beaten my head against the wall

Right now it runs, and is rideable, but it appears that cylinder #3 is doing all the work. I initially determined this by idling it and disconnecting the plug wires. Disconnecting wires 1, 2, and 4 made almost no difference, but disconnecting 3 kills the bike. It should also be noted that one its heated up, a lot of blow-by gas comes out of the crankcase breather, which is currently just running to a uni filter.

I did a compression test, and these are my dry/wet numbers in psi. I forgot to hold the throttle open when I did the test, but can easily re-do it if you guys think it would make a significant difference.
C1: 60/180
C2: 64/130
C3: 160/off the chart
C4: 65/140

So, this would indicate piston rings. Right? however there's this weird symptom. Air blows OUT of the carbs on the cylinders with low compression, and a quick air hiss can be heard on every stroke. Here's a video so you can hear what I'm talking about https://www.icloud.com/photos/#0Yo1L...QLxdpikgqEMP3g

So, am I looking at Valves AND Piston rings, or is this possibly a cam timing issue? To make sure I wasn't crazy, I re-checked my valve clearances. I thought for sure the intakes were just too tight. I had not checked them using the meticulous "suzuki" method when I did the adjustment. Alas, they're within spec anyway. Intakes are a little on the tight side, all .04mm, with cylinder #3 at .06mm.

This is starting to look like something that an "italian tune up" isn't going to fix, but I want to make sure there isn't anything else I should be trying before I resolve to do a top end rebuild.

[fastbysuzuki]

Re-do the compression test with the engine hot and the throttle held wide open and report numbers before you do anything else.
warm the bike up to normal operating temp then do the test do not add any oil into the cylinder for this test.
Dry/wet ? Just how wet?
You say air is blowing out of the cylinders are you sure your valve clearances are correct?
Are you following the manual correctly?

[Gorminrider]

While you're waiting for a better answer than I can give you, why not go back and do the compression test properly?

I'd say "cam timing" isn't likely if the thing runs at all but it's usually easy to check TDC from the marks on the flywheel versus the cams

[Isoparmesan]

I rechecked the valve clearances last night, and did so using the method described in the Suzuki manual where you check the exhaust of 1 and 2, rotate 180, check the intake of 1 and 2, etc.

Intake clearances were:
C1: .04mm
C2: .04mm
C3: .06mm
C4: .04mm.

The bottom of the range listed in the manual is .03mm, so the clearances for 1, 2 and 4 are on the tight side but still with in spec. Should I readjust them to the middle of the range? I'm not sure if it's a coincidence that C3 is the only one with a larger clearance, and it's the only one getting compression.

[salty_monk]

If you're within range it shouldn't make a lot of difference.

Have you tried swapping plug wires over to see what happens? 2&3 would be an easy test as they are on the same coil.

If this bike has sat for a long time it quite possibly has stuck rings, this may well sort itself out when you can get riding it & the compression numbers will go up.

An inline filter is usually not a good idea. The petcock has an integrated filter & inline filters have been known to cause fueling issues. For the sake of ruling it out I would try it without the filter in place.

Are you sure the carb jetting is correct for the pod filters?

Good luck, keep going, you'll get there

[Isoparmesan]

Have you tried swapping plug wires over to see what happens? 2&3 would be an easy test as they are on the same coil.

If this bike has sat for a long time it quite possibly has stuck rings, this may well sort itself out when you can get riding it & the compression numbers will go up.

I get spark on all the wires, so I don't think it has to do with that. all four cylinders are definitely firing as well. If I remove the cylinder 3 plug cap (which is the cylinder with good compression), I can still coax the bike into starting, but it's difficult. Cylinder 3 is definitely doing most of the work.

I'm just not sure about the air blowing out the carbs, and if that for sure means I need to remove the cylinder head and overhaul the valves.

[LAB3]

Air blowing out of the carbs means that pressure is building inside the engine and needs a place to escape.

Try putting about 10cc of motor oil in the cylinder and retry the compression check. If it goes up then it's probably the rings, the extra oil will help seal the cylinder. If it doesn't go up, then it's the valves.

[Isoparmesan]

Air blowing out of the carbs means that pressure is building inside the engine and needs a place to escape.

its not blowing out the carbs randomly though, its on every stroke. you can hear it in this video. https://www.icloud.com/photos/#0Yo1L...QLxdpikgqEMP3g

[LAB3]

its not blowing out the carbs randomly though, its on every stroke. you can hear it in this video. https://www.icloud.com/photos/#0Yo1L...QLxdpikgqEMP3g

When I made my suggestion I failed to notice you already did the wet/dry test. You have one cylinder that's up to par, this leads me to believe that can timing is fine. Based on the wet/dry numbers it's pretty safe to say you need to tear the engine down and deal with your cylinders. You can continue to try this or that or come up with new theories but in the end that engine is toast.

[salty_monk]

How many miles since you started riding it again? I still think you have a decent chance of the rings breaking free with some heat cycles on it...

[Isoparmesan]

I’ve probably ridden it less than 100 miles. And they’ve mostly been low speed. I did take it on the freeway for about 20 miles once, but then got that issue with the front brake where it decided to slowly engage itself because of a clogged return port. At least that issue is solved though

Is it worth doing any of the “drop some *@%^$*@%^$*@%^$*@%^$ in the cylinder overnight” fixes? I park it in a poorly ventilated apartment building garage that’s underground. So it needs to be running to go up the ramp. I’m hesitant to do something that will smoke the whole place up.

[Grimly]

Is it worth doing any of the “drop some *@%^$*@%^$*@%^$*@%^$ in the cylinder overnight” fixes? I park it in a poorly ventilated apartment building garage that’s underground. So it needs to be running to go up the ramp. I’m hesitant to do something that will smoke the whole place up.

Yes. Drench each cylinder with some paint thinners / gunwash / panel wipe (it contains a mixture of xylene, toluene, acetone and other good stuff) and leave it for a week.
I was impressed at how the thinners I'd left the pistons soaking in had thoroughly de-gummed every ringpack by the time I turned my attention to them for putting back into the engine, but several weeks had elapsed. The process might happen quicker - I've a feeling it will do some good in a week. I'd re-drench the bores every day if necessary.
You'll have to drain the oil first if you want to keep it - you might have already put new oil in, so don't waste it.

This stuff - you will have a local equivalent.

https://www.proweld.ie/product/tetrosyl-standard-thinner-5-litre/

http://easy.tetrosyl.com/images/stories/virtuemart/documents/STT025_SDS.pdf

Important: when you come to re-start the engine plop some engine oil down the bores, because that stuff above will have totally removed any trace of lube.

[Steve]

I watched the video (after having to download it), those carbs are not blowing, they are SUCKING. You are hearing the individual pulses that are being drawn by each carb. If you go with pods, you will STILL hear that while riding.

I also heard a bike that is not running on all four cylinders. Could be carb jets are dirty, could be out of sync, but that engine should be purring, not chugging.

.

[Isoparmesan]

I watched the video (after having to download it), those carbs are not blowing, they are SUCKING. You are hearing the individual pulses that are being drawn by each carb. If you go with pods, you will STILL hear that while riding.

I also heard a bike that is not running on all four cylinders. Could be carb jets are dirty, could be out of sync, but that engine should be purring, not chugging.

.

I’m going to do another compression test on Tuesday and do it properly this time (with the throttle all the way open). I’m guessing I’ll still get low readings in cylinders 1,2, and 4. I think the problem is likely stuck rings. I also tuned the carbs with some cheap pods on, and realized after that there’s a lip inside blocking the idle inlet. I’m going to either get different pods or cut channels in the ones I have. I will then retune the carbs. They were completely disassembled and chem dipped a few months ago, and the bike has been run at least once a week since then. If i still have fueling issues I’ll open them and check the jets again.

I’m just hoping that, assuming it’s stuck rings, I can unstick them without pulling the pistons out. The bike has low miles, so I doubt the rings are worn. Makes more sense that they’d be stuck in the grooves.

[Big T]

A bit of Marvel Mystery Oil down the cylinders is the go to for many members.

Let it soak overnight, rotate the engine daily for 4-5 days.
Then start, yes, it will be smokey for a bit.