Piston Rings? Valves? Timing? All Three?

[Isoparmesan]

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/#0Yo1Lvru2ovQLxdpikgqEMP3g

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.

 

[Isoparmesan]

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.

I was thinking this, or ATF/Acetone mix, or Turpentine like another poster recommended.

Think I should drain the oil if I do MMO?

 

[Big T]

No, just put an ounce or two in each cylinder
MMO is ok in your motor

 

[Isoparmesan]

Interesting development: The bike has also had an issue with the throttle cable sticking. After lubricating the hell out of it, and seeing that have no effect, I discovered that it wasn?t the cable at all, the bolt that holds the slide for carb #3 had come completely loose and was bouncing around inside the top of the carb, and occasionally binding against the slide arm.

this means that carb #3 was pretty wide open at idle. Once I put it back in place, the bike magically started idling normally and that air hiss I was hearing in every stroke is gone. That could also explain why cylinder #3 seemed to be pulling the hardest, and won the compression championship, even with the throttle closed.

still going to do another compression test tomorrow, along with re-balancing/syncing the carbs (will also consider throwing some threadlocker on the slide adjuster bolts). I?m more hopeful for the compression results now though.

 

[Chuck78]

Yes your compression test was definitely biased because only one cylinder was wide open, unbeknownst to you!
Low mileage engines still suffer from severe bore wear or sticking rings, sometimes people just run them out of oil and they run extremely hot and wear things out. other times, people can't get them to run because the carbs are gummed up, and they do a really foolish thing and run them with no air filter at all, and ingest dirt, which will score of the cylinder walls if it is abrasive...
Also, cylinder walls can get rusty from humidity in the air and not being run...rimgs as well, as when the temperature drops, the moisture in the air can condensate on the cylinder walls and run down into the rings.


all that being said, I think you having one cylinder wide-open full-time was the cause of your compression test only accurately being done on one cylinder.


if you still have difficulties, I have had excellent luck with some engines in the past, that have been neglected, and no valve adjustments ever done. On first valve check, I will set the valve shim clearance at the maximum side of Suzuki's tolerances or above, give the valves plenty of room to slam shut and break/wear off any carbon that had formed on the faces of the seats and valves from the valves hanging open (due to neglect) and not shutting fully.
In conjunction with that, I will squirt automatic transmission fluid or acetone ATF mixture in the spark plug holes and cycle the engine over a few times manually with the kickstarter or with the large nut underneath the bolt that holds the ignition parts on the crank. Let that sit overnight, then go run the bike fairly thoroughly. I don't ever baby them! I have even squirted it into the intake ports before just to make sure I got some on the valves to help break up any carbon deposits. If you are exhaust bolts are able to be removed without breaking them in half, I have even done the same on the exhaust side.


When I first met my wife, her bike was the first shim bucket style that I had the opportunity to work on. I did all of the above to that, and the bike had the most power she had ever felt on a motorcycle before, and she commented heavily that she was so happy to as "THIS is how a motorcycle is supposed to ride!"
helping the valves seal better with this technique, and using plenty of ATF persistently on the piston rings restore to the compression to around 130 or 140 PSI, and the bike was very fast again after that. eventually she wore that engine out, and I got a low miles junkyard engine that tested 170 PSI on all cylinders.


Also, thanks for the re-reminder that I need to go out and coat the cylinder walls of all the bikes and spare engines in the garage with some good thick oil for the winter! You don't want the winter warm days humidity condensing in the evenings and fouling up your cylinder walls and rings!

 

[Isoparmesan]

Well, it looks like my compression is actually totally fine. Just redid the dry test (properly) and got 160-170 in every cylinder.

So, here?s another question. If my compression is good, why am I getting such significant blowby out of the breather?