engine knock

[cyrusyn]

2000 Suzuki GS500E

I hear loud engine knock during idle. Starts right away when engine is cold. It goes away as soon as I throttle. What am I supposed to do? This started to happen after I went low side about 3 weeks ago and prior to the fall there was a very small tick tick noise that happened irregularly. Engine compression for both cylinders are at around 110psi.


Should I adjust the valve only or do both valve job and cam chain job?

[yamahonkawazuki]

check oil first. cold/hot

[cyrusyn]

Oil? I don't get it. Please be more specific? Half of oil is moto 10W40 and the other half quantity is auto 10W40.

[joshr08]

engines knock when they dont have enough oil.   you can tell alot by looking at your oil.  if its black change it.  if it looks like a nice metal flake paint job time to rip the motor down.  if its low add some .

[ATLRIDER]

Just curious cause the compression is too low.  Did you do the test with throttle fully open? 

Start simple and check valve clearances b4 a valve job or chain.

What kind of fuel you using?  Try some high octane gas and see what happens.

[sledge]

110psi is bang on the service limit. If this is an accurate figure it indicates your engine has suffered some serious wear, particularly as both pots are the same so its no surprise things are banging and rattling. When it went over was the engine running? Something could have been starved of oil.
Rather than guessing at whats wrong an oil-pressure test is the next logical step and the results will indicate the overall condition of the engine. If its good and you are up to it, it could worth pulling the engine and looking for the problems, if its bad you may as well look for a new mill.
Unfortunately unless you have access to the equipment needed to do a pressure test you will have to visit a shop and...."adopt the position"

[bill14224]

I'm picturing a GS with at least one side wiped-out and 110psi compression when the lower limit is 142.  Sounds to me like it's time to part it out.

[cyrusyn]

ATLRIDER>> I did the comp test with throttle closed. Should I leave it open? I am using "regular" 89 at Chevron.

joshr08>> I did oil change little more than a month ago. It is slightly above F mark on the dip stick.

sledge>> Engine was running when it went over.

Guys, I found last night that my left cylinder spark is really weak. When I pulled spark plug off the right cylinder, the motor dies. When I pull left side, motor runs strong.
I hear the knocking (clacking) noise from the top portion of the right cylinder.

When the engine is cold, I don't hear this but as it gets warmed up and hotter, it gets louder.

[sledge]

I'm picturing a GS with at least one side wiped-out and 110psi compression when the lower limit is 142.  Sounds to me like it's time to part it out.

Bill,
Service limit is 114psi with a max difference between pots of 28psi (Suzuki factory service manual section 13.3).

[ATLRIDER]

Yes, you need to hold the throttle wide fully open (WFO) when performing this test.  I can almost assure you the numbers will be higher and feel confident they'll both be within spec since they're currently reading the same.  Let us know what the numbers come back at.

89 is fine.  I use 87 with no problems.

The engine is only running on that right cylinder. First try to swap plugs.  If no change see if you're getting 12v to the left coil and check for loose connectors there.  The fall may have knocked something loose or busted something.  If all checks good, try swapping coils.

[cyrusyn]

Thanks a lot for your help.
I checked the things you recommanded.

Compression: both cylinders got 158psi.
Both ignition coils: primary & secondary resistance are all within spec.
Spark plugs: both sides produce fat orange to white sparks.

I haven't checked what voltage left ignition coil is getting.
I haven't swapped the spark plugs yet.

I will get back with those two things.

New discovery: I was listening to the left cylinder with my ear literally on the surface and I was able to hear very very faint ping. So faint that you can't hear if you take your ear off the block.

With pinging on the left cylinder, knocking or clackking sound on the right cylinder, I feel like this might be a valve adjustment issue. For the pinging on the left cylinder, I will carb sync again. This time I will set the mercury for the left cylinder a little higher than the right one and see what happens.

Yes, you need to hold the throttle wide fully open (WFO) when performing this test.  I can almost assure you the numbers will be higher and feel confident they'll both be within spec since they're currently reading the same.  Let us know what the numbers come back at.

89 is fine.  I use 87 with no problems.

The engine is only running on that right cylinder. First try to swap plugs.  If no change see if you're getting 12v to the left coil and check for loose connectors there.  The fall may have knocked something loose or busted something.  If all checks good, try swapping coils.

[bill14224]

Sledge:

Yes, indeed it is.  He said both cylinders were at 110 and he needs at least one at minimum 142 and the other within 28, so that would indicate excessive wear, but now he says he has 158 from both cylinders, which is wonderful! 

Cyrusyn:

You didn't say if your plugs are new or old.  Put some new ones in there, they're cheap.  If the spark is still weak, make sure the ignition wires have good connections to the coils.  The wire at the end can become corroded from all that sparking.  If that's good, see that your coils are getting around 14 volts when it's running.  And regular gas is fine.  Your bike has 9 to 1 compression.  It doesn't need premium any more than your lawnmower.

[ATLRIDER]

That's good to hear the compression is good and yeah plugs are cheap.  Couldn't hurt to check your valve clearances to get a better picture about what ur dealing with.  Bring everything up to spec, sync the carbs and see what ur left with.  Good luck