I'm guessing my valves are leaking but now I don't know [Help!]

[4strings]

So, for the latter part of the riding season, the bike has always smelled rather rich.  It also was a little hesitant and lurchy starting from a stop with less than 1/4 throttle.  I figured I'd get to that eventually, but for the last 3 weeks, she would smoke blue on a cold start up. 

It used to be for just a couple of seconds.  Then it stayed longer, now I had to ride home in as much of a traffic jam as my 14k pop. town gets and I think i suffocated whomever was driving behind me.  It was smoking like hell and smelled like a two stroke for a good 5 minutes.

I did search and found a decent thread here with some good info
http://gstwins.com/gsboard/index.php?topic=32083

First check for fouled out plugs.
I'm planning on doing a compression check (If low, I'll do a leak down test)
Then valve clearances (I did an adjustment maybe a 1000 miles ago)

Beyond that the whole head is coming off
I'll turn it upside down and put gas in the chamber to see if the valves are leaking and which ones

Good thing the season is coming to an end I guess.  I'm preparing for the worst and hoping for the best.  Not that a head job is the end of the world. 

I've been told I'll need to find valve seals and bring them and the head to the engine shop.  I'll be going to Pakes Engine and Machine (also told it's pretty famous and it's only 20mi away!)
I'm not sure if I'll need new valves but I hope not.  Hopefully I'll get a vid of the thing smoking it up so you guys can check it out.  I also plan to update this with whatever goes down.

Anybody have any other ideas?

[4strings]

So the plugs look ok. 
I got the compression tester out and did the left side, 120. I think i saw somewhere that was roughly normal. I checked the right, 60. The leak down test didn't change anything either
Looks like it's time to check valve shim clearances.  If that checks out, it's time to get handsy and take the head to the engine shop.

[NickyNumbers]

great part about these bikes is all you need are a few hand tools and sockets to get the head off. 


Probably take you about an hour total lol.  Coming from cars, motorcycles are a walk in the park to work on. 

[4strings]

Alright, so I goofed.  I didn't know until looking at some more posts that you must be at WOT when doing the compression test.

I rechecked the compression and at WOT the left side got up to 140 PSI and the right jumped way up to 155 PSI.  This now means:

Throttle closed:
Left - 120
Right - 60

WOT:
Left 140
Right - 155

I plan on checking valve shim clearances tomorrow afternoon.  I'm really confused now because I thought I had it pinned down to the valves leaking.  Ideas?

[burning1]

Have you checked to see if there's any oil in your airbox? The engine breather feeds into the airbox, and when overfilled or tipped over, will leak oil in there. The oil can then be sucked into the intake, and burned.

Other thoughts:

Pour a little oil down each cylinder, and see what that does to your compression numbers. 10-20PSI improvement = normal. Much more than that, and it's an indication of bad rings, which would cause you to burn oil.

If you have a leak-down tester, get a mechanic's stethascope and listen to the engine to see where air is escaping from. Won't really help with the valve guides, but if you have compression problems it can help to pinpoint the source.

[burning1]

FWIW, I don't think filling the chamber with gas will help identify leaking valve stem seals... It will test for bad valve seals, but if your compression numbers are good, I'd expect the valve seals to be good as well.

FWIW, I don't actually know what's normal for the GS, regarding compression.

[4strings]

Searched and found another thread.  Sledge says 142 - 199.  My manual is at home so I cant check.  I'll probably be tearing into it tomorrow so I'll check the airbox then.

Thanks Burning.

What is your compression? Most 4 strokes run about 30-50 depending on the bike. As long as you're not under 30 you should be fine.

30-50 what?? Bar, Psi, kPa......Pink elephants???

Lets assume Psi....Suzuki quote anywhere between 142-199 Psi for a healthy engine, the service limit is 114 Psi and the (often overlooked) maximum allowed difference between cylinders is 28 Psi.

[craigs449]

Valve checks are a normal part of maintenance on any bike.  I would have checked the clearance on the valves long before doing a leak down or compression test.  Is it possible that you overfilled the oil the last oil change and the rings are leaking a bit due to the excess oil?  Although I am new here, I am not new to motor work on bikes.  I was also under the impression that the GS motors were kind of bulletproof and did not know of any problems with the valvetrain.  Also, what year bike?, Mileage?, any mods?

[4strings]

Thanks for the suggestions.  The bike is a 93 with 24k miles.  Again, I did valve adjustment within the last 1000 miles and the last time I added oil was long before the blue smoke started happening.  I plan to check oil level and also see if there is oil in the airbox. I need to find my tiny friggin feeler gauge set and then I'll check the clearances.  Have any ideas why the compression is so crazy when the throttle is closed?  I checked once this started happening and the right side header (Right cylinder had 60psi at closed throttle) is much slower to heat up than the left.  I wonder if that was contributing at all.

[burning1]

A closed throttle doesn't allow the engine to suck in much air. When the piston is at bottom dead center, there will be a vacuum in the cylinder. What little air is in there will be compressed, but since there was less air to begin with, the pressure in the cylinder will be lower, resulting in low compression numbers.

If your throttle bodies are out of sync, I could imagine it resulting in bad compression numbers in one cylinder with the throttle closed. A throttle sync tries to insure that both cylinders are getting the same amount of air while idling.

[craigs449]

Thanks for the suggestions.  The bike is a 93 with 24k miles.  Again, I did valve adjustment within the last 1000 miles and the last time I added oil was long before the blue smoke started happening.  I plan to check oil level and also see if there is oil in the airbox. I need to find my tiny friggin feeler gauge set and then I'll check the clearances.  Have any ideas why the compression is so crazy when the throttle is closed?  I checked once this started happening and the right side header (Right cylinder had 60psi at closed throttle) is much slower to heat up than the left.  I wonder if that was contributing at all.

Is it possible that your fule/air delivery is not synched for both carbs and maybe the one is running lean (causing a much quicker heat buildup than the other side)? As for the smoke....we know it's not antifreeze leaking into the combustion chamber on these bikes

[ohgood]

broken ring/ worn out ring, grooved cylinder, OR possibly a bad valve guide. i'm betting on the first...

if you drop the piston, look for this: (first and second rings)





note, this a drz400 piston, yours will look different. the oil ring is fair, the other two are worn enough to roll over into the grooves, making removal difficult... along with crap gas making a nice glue to hold it in.

post up when you find the root cause, pictures for the other newbies !

[4strings]

Alright guys, I did some more testing and probing  .
First I did another round of compression testing.

                          left side           right side
WOT                   140psi              150psi
Closed Throttle     120psi              70psi
Leak Down           160psi              200psi !!!


That last number is freaking me out.

I took the valve cover off.  Thank you Kerry for the tip of rtv on the valve cover side.  The gasket stayed put.

Clearances are as such:

                     Left                 Right
Exhaust      .127-.152         .102-.127
Intake        .076-.102         .102-.127

Plenty of room so the valves aren't being held open during the cycle.
I plan on swapping out the Right side Intake shim to close that up a little.

I checked the air box and there were marks like something came out of the carbs and ran down the inside of the box, but it didn't look new and it wasn't really wet at all. 
The oil is also definitely not overfilled.

I did do a carb sync with the famed $5 tool a month or two ago aiming to get it synced at about 4k rpm.

Gah!  I might rather a hole in my head than have to take the whole top end off this winter.  I want to get moving on my cb400 powered of-road go kart!

Ohgood, I think I might see what you mean.  The first two rings are nearly flush with the grooves they sit in where the oil ring (two rings and the wavy one sandwiched) does protrude more.

I'm swapping the shim that is too small.
I don't want to but I am prepared to take the head and valves in to have them grind the valves and valve seats.  Also replace valve seals.

What do you guys think I should do now?

[burning1]

It concerns me that you're giving a PSI value for your leakdown test... That's not how it works. Also, leakdown should be used to find the exact source of your problems. You should *know* where the leakage is, rather than having to investigate by digging into the engine.

How many miles on the bike?

[4strings]

Now that I google it, leak down test is not the test I though I was doing  .  I was doing the test where you put a teaspoon of oil in the cylinder and then do the compression test again. 

My gs has 24k miles on the clock.

[burning1]

24K miles shouldn't be so much that you're needing new valve seals, and rings... But it could always be a defect of some sort. If you can get your hands on a compressor and a leakdown tester, those tools are very good ways of investigating this kind of problem without pulling your bike apart.

[4strings]

Could I make one? I do have an air compressor.  Google shows me it looks like an air compressor with a pressure gauge, a valve, another pressure gauge, and a way to connect it to the spark plug port.

I went to a local shop to swap valve shims.  I told him about the issue and he said to check and see if the carbs areletting gas pass when it is off. He said if this happens the gas can get to the cylinders past the rings and into the oil. The fumes would get back through the air box and continually richen the mixture.

I guess I'll give the carbs a once over and see how they are doing.

[burning1]

I've never heard of someone making a leakdown tester, so I don't know, sorry. :\

I realize it's kind of an expensive tool. You've got to determine how useful it will be in the long run, and how much your time is worth.

[The Buddha]

4strings - you plan on doing a 4K throttle synch in a few days ... after that why dont you do the rolling into a ravine test for the bike ? 4K sync ... as useless as that ... synch is for idle. Synch wont make it smoke ... synch isn't obama, synch's not at fault for everything.

Dude ... your motor is fine, these numbers are all cold leakdown and cold compression right ... makes no diff, compression when hot is the deal. You may be leaking @ the rings ... but my 48K mile gs used a qt of oil in 300 miles, yes 300, not 3000, and still ran. You blowing blue smoke

Leakdown is a percentage. Who the Fs^k measured it in psi ... and you set it to ~60-70 psi ... and see what the percentage leak is ...

I have no idea what is going on, but you need a new mechanic I'd bet. You got water in the carbs ... or oil in the air box ... all of those can smoke.

Cool.
Buddha.

[4strings]

Ha ha, funny you should mention I need a new mechanic.  I am my mechanic!

Again, I was mistaken calling the test a leak down test.  I just put a little oil in the cylinder and remeasured the compression.

I've done this stuff with guidance found here.  I'm going to redo the sync at idle and I'll be looking at the carbs soon too.

Thank you for your help