Difficult cold starting and no compression

[LakesideElectronics]

Hi All,

I have been plagued with difficult cold starting on my 2004 GS500F since I bought it last year.  With the late start to the Michigan summer I decided to dig into this problem. Another symptom I experienced was a gradual loss of power.  I have only ridden it twice this year but in 6th gear I cannot maintain 80 mph and at the end of last year I vaguely recall an inkling of reduced power.

In the process I have discovered that the tappet clearance on one cylinders exhaust valve is out of spec.  There was no clearance what so ever.  I ordered a compression gauge, but in the mean time just put my thumb over the spark plug hole and cannot detect any compression or vacuum.

Using a surface grinder I took 0.00275" off of that shim and re-installed - still no clearance.  I am going to continue grinding this tappet shim in 3 thou increments until I achieve spec.  Hopefully my compression tester will come in by then and I can quantify the subjective thumb test to see if the valve is burnt from hanging open.

-Pete

[LakesideElectronics]

I took another 3 thou off and still no clearance and consequently still no compression.  I'm up to 6 thou now and i'm beginning to wonder if I should just pull the head and take a look.  I would have thought the valve would have seated by now if it weren't burnt...

Since I may be in the market for valves and or a head, does anybody have any recommendations on where to buy?

-Pete

[Big Rich]

Wait for the compression tester first - once you pull the head apart, it's worthless.

Sounds to me like something is definitely going to need fixed / replaced. Posting a "WTB" thread around here would probably get you what you need.

[gsJack]

How thick was that shim after you took approx .006" off of it?  How did the bike run after it was warmed up, valve clearance increases a considerable amount as the bike warms.  Did you try the thumb over the hole compression test with a hot engine?

When you took the shim out to grind it did you try to turn the bucket with your fingertip?  My 02 had a sticking bucket when I got it and the valve would stick open when cold.  It would start up idling rough and smooth out within a minute as it warmed and the bucket freed, would run fine all day after that.

[LakesideElectronics]

Hi gsJack,

Thanks for the reply.  I only checked for compression with the engine cold.  After the bike was warmed up I could not maintain freeway speed in 6th gear.  5th gear was ok.  The bike had a few misses, but not persistent only notable.

The left exhaust shim in question is now 0.105" or 2.67 mm.  I did not try rotating the tappet after removing the shim because I did not release it from the depressed state.  However, when I replaced the reduced thickness shim the tappet to cam clearance was zero - I could not measure it with a feeler gauge and the shim will not rotate.  This leads me to believe that the tappet is not currently stuck or a bent valve etc.

Perhaps I can turn up a measurement shim - maybe 2.20 mm thick.  This would not be run, but  I can insert and measure the required shim thickness.

[gsJack]

At 267 that's still a big shim, a tad bigger than I've ever had. You're probably close to getting some clearance now.  My 97 came new with 265 and 262 exhaust shims and my 02 came new with two 265 and two 258 shims.  Never had the intake shims out of the 97 GS in the 80k miles I ran it.  Since it presented no running problem after the first warming minute I let my 02 go for 20k miles with the tight bucket I mentioned above hoping it would free up and one freezing cold morning it stuck wide open and broke the valve off while cranking.   Here's my whole record of valve checks:

http://www.gs500.net/gallery/data/500/GSvalvelogs.jpg

GS500 exhaust valves are set too tight using the Suzuki .001-.003" spec and they will begin receeding into the seats if run at a minimum clearance too long.  My one tighter exhaust valve on the 97 was down to a minimum 215 shim by 80k miles after repeated changes.  When my 02 started the same process with a couple shim changes between 30-40k miles I bumped it up to .005" clearance and it then went another 40-50k miles without a shim change.  I set GS500 exhaust valves at .003-.005" clearance now.

I've never used a measuring shim but many do and that's probably a good idea for you now unless you want to take another shot or two at getting clearance grinding off a little at a time.  You need to get some clearance to get a meaningful compression check when you get your gage.  How many miles are on that engine now? 

[LakesideElectronics]

Thanks gsJack. Good info. It would seem at this point I should adjust both exhaust valves for .003-.005" as you suggest. Not sure, but I'll probably use the measurement shim method. I have about 21,000 miles on this bike.

[LakesideElectronics]

So tonight I took out the valve shim in anticipation of taking 4 thou off tomorrow and had an idea to test if my exhaust valve will ever seat.  With the shim out I removed the tappet depressor.  The tappet stopped short of the cam shaft so the valve should be on its seat now.  I previously rotated the engine so that the cams were off both the inlet and exhaust tappets and I blew shop air into the spark plug hole with a rubber nozzle air gun.  Since my exhaust headers were off I was able to stick my fingers in the exhaust port and felt air leaking by the exhaust valve seat.  I am reasonably confident now that I should pull the head to take a look.

[gsJack]

Can you turn that tappet now with your finger tip?  Still a possibility of a tight tappet holding that exhaust valve open if it's not free to turn.  My tight exhaust bucket (tappet) would hold the valve open on a cold engine.

[LakesideElectronics]

Yes, I am able to rotate the tappet with the shim removed. 

[gsJack]

Now I too am reasonably confident that you'll need to pull the head. You've got a good start with the exhaust headers and valve cover off.  Good idea checking it with the compressed air that way.     

[LakesideElectronics]

Thanks!  We will see how it goes tonight.  Have to do some "real" work first...

[LakesideElectronics]

I found the head removal with engine in frame to be far less difficult than I anticipated.  Even before removing the offending exhaust valve it was immediately apparent that it had begun to burn.  The valve will need to be replaced, but the seat looks like it is repairable.



The burnt exhaust valve.



The head with valves removed



The other exhaust valve

[gsJack]

Not too hard to pull the head in frame it's just a tight squeeze getting it out once it's loose.  Good nights work, you'll probably be running again in a couple days.  Nice pics Pete but I need a bigger screen.   

This the GS we're talking about:

[LakesideElectronics]

Yup, that's the one! 

I placed an order at online for a head gasket, a couple oil filters, an air filter and an exhaust valve.  I'll have the other valves cleaned up and seats ground and hopefully be back on the road soon like you say.  I imagine she'll feel pretty zippy after the repair too!

I was wondering about the copper head stud washers.  Do people typically re-anneal them before reinstalling them?

[bombsquad83]

Just order new copper washers for the head.  That way you won't have to deal with chasing down an oil leak later.  If they haven't shipped your other parts yet you can probably add them to the order.

[LakesideElectronics]

Thanks, bombsquad83. Ill give them a call the see if I can add to the order.

[LakesideElectronics]

Still waiting for parts to come in.  I wasn't able to add the copper washers to my original order, so I just placed another order.  Hopefully next week.  The head is about done.  Had the seats ground, head stud bosses ( where the copper washers go ) spot faced and some very mild porting.  The valves that will be reused had some mild pitting and are being ground too.

[LakesideElectronics]

So, my parts came in, head was machined, everything was reassembled and valve clearances set by grinding shims.  I checked the compression with the engine cold and it was ~130 psi on each cylinder.  The bike fired right up - something that never happened since I've owned it, I set the idle and went for a low RPM test ride.  Everything seems to be working great - except I now have an oil leak between the crank case and cylinder at the front.  I guess i will be tearing it down again today to investigate...

[gsJack]

Some say you should always replace the cylinder base gasket as well as the head gasket when the head is off since they are apt to leak once disturbed.  I have only pulled 2 heads in all my years and bikes of riding and on the first, a CM400, I didn't replace it and it seeped oil the next 60k miles that I had it.  When I pulled the head on my current 02 GS to replace the broken valve I did replace the cylinder base gasket and it too has seeped oil for the 70k miles and counting since.   My interest in bikes started, years before I started riding, back when both the Harleys and Bonnies left a puddle of oil to mark their spot everywhere they stopped.  No puddle no fix I guess.   

Got me a bit curious, you ground both valves and seats and then ground shims to adjust clearances, how thin did the shims get?  Hopefully still thicker than the Suzuki min 2.15 mm shim if you went with the wider .003-.005" exhaust valve gaps.  On the old 30's and 40's flat head Ford V-8 engines after grinding valves and seats we ground the valve stems for clearance adjustment. 

Sounds like a good job all around, there's always something more to fix.