can i perform a leakdown test on a cold bike,with no oil (without starting it)?? I drained the oil and checked the clutch plates thinking i had a clutch drag problem, but im pretty sure its a compression issue. I dont wanna waste clean oil by filling the bike for a compression test possibly contaminating it with metal bits ect.. jus to drain it and pull the head for a valve job.

You can, you just won't get an accurate reading. Compression tests and leak down tests have to be done at operating temp.

Quote from: Deros514 on July 15, 2010, 07:21:37 PM
You can, you just won't get an accurate reading. Compression tests and leak down tests have to be done at operating temp.

Well, yes, and no.........

I work in an airplane shop.....we do a leakdown test on every airplane once a year.....(you cannot do a compression test like you do on a car, because you would be killed by the rotating propeller lol!)

We normally do the leak down test with the engine cold......if the numbers are within spec....that's it...done.....

If there is too much leak, we try to determine what is leaking by listening.....at the oil filler, or air intake etc.....valves or rings........


Only when the test is beyond spec. , do we warm up the engine and test again.....sometime this will put the test within spec..........

This test is not all that conclusive of a test as some make it out to be..........some freak out if one cylinder is a couple of pounds less than the others.....sometimes the readings will be higher than last year.....this is just a general test of engine condition......

If a cylinder is really messsed up, the reading is way low........not just a little low...

Cookie

I suppose if you do something like that routinely you know an acceptable range when the engine is cold. I'll take your word for it. Anyone that's allowed to work on airplane engines must know what they're doing.

In any case, newly rebuilt engines will hold nearly 100%. When I rebuilt my car engine I got about 2% leak down. This was only with fresh rings to get end gap back in spec and a quick valve lapping. Most service manuals give you an acceptable range for a compression test but not a range for leak down. IIRC 10% leakdown is worn but acceptable, any lower and its time for a rebuild.

Of course with a leakdown tool you can get more valuable info than a compression tester. With some good ears it will tell you pretty much if the valves are leaking, the rings, a gasket, or if you've got a scored cylinder.

You can pull the head off without draining the oil. I'm in the middle of re-ringing my gs right now and tore it apart without draining anything. That way I can start it up for 5 minutes with the old oil, then drain and flush all the crap out of the engine with an oil change. There's nothing that demands you drain your oil to pull your head off.

you might need to rotate the engine to do a leakdown test if one of the cylinders has a valve open.

Quote from: Agent4573 on July 16, 2010, 09:07:37 AM
There's nothing that demands you drain your oil to pull your head off.

+1

I've pulled the head 3-4 times without having to drain the oil.

Quote from: Deros514 on July 16, 2010, 09:03:01 AM
I suppose if you do something like that routinely you know an acceptable range when the engine is cold. I'll take your word for it. Anyone that's allowed to work on airplane engines must know what they're doing.

In any case, newly rebuilt engines will hold nearly 100%. When I rebuilt my car engine I got about 2% leak down. This was only with fresh rings to get end gap back in spec and a quick valve lapping. Most service manuals give you an acceptable range for a compression test but not a range for leak down. IIRC 10% leakdown is worn but acceptable, any lower and its time for a rebuild.

Of course with a leakdown tool you can get more valuable info than a compression tester. With some good ears it will tell you pretty much if the valves are leaking, the rings, a gasket, or if you've got a scored cylinder.

When we do the airplanes we put in 80 psi...........a good engine (cold) will read like 78 psi on the other gauge...

But readings in the 60's are still considered good.........

When there is a "real" leak, like valve or rings, you get like 30 psi......

Sometimes if we get a low reading, we hammer on the valve a little and it will seat and make good compression, or sometimes we rotate the engine back and forth a little and you can hear the rings "seat" and the reading goes way up.......

Cookie

80psi? a good engine should have over 110psi, a great engine will have 160psi-ish.

In a leak down test you pressurize the cylinder with air and measure the amount that leaks out. For example, 80psi goes in, gauge shows cylinder is holding 78psi. Cylinder is leaking 2psi or slightly under 1%.

A compression test measures the pressure the engine is able to build on compression stroke and should be much higher than 100psi

Quote from: black and silver twin on July 17, 2010, 10:12:38 AM
80psi? a good engine should have over 110psi, a great engine will have 160psi-ish.

Like the other post said....

A leak down test is NOT a compression test.........A compression test is the compression generated by the piston...(with the engine turning )   so with a 9:1 compression ratio  you should get 9 x atmosphere or like 132 psi


A leak down test is done with the piston TDC and valves closed..engine no turning ......pressureized air is introduced into the hole where the spark plug used to be.............this is the reference pressure     we use 80 PSi

We then measure the actual pressure in the clyinder.....it will be lower than 80 psi due to leaking around rings, thru ring gaps and around valve..........so maybe it will read 78 psi......this would be very good with almost no leak

If it reads low like 40 psi, you have a big leak...valves and or rings

Cookie

cool thanks for tha help, as for the oil it was already drained from a previous service i just didnt want to refill it to check tha leak down. I just noticed that i may have a head gasket leak and the heads probly gonna have to come off anyways, would it be a good idea to rehone and rering it at that time since ive got 25K miles on it and its already apart?

Here's a thread I posted comparing hot/cold wet/dry compression test results for a 2004 Suzuki GSX-R 600 with 35000 miles.

http://www.bayarearidersforum.com/forums/showthread.php?t=298719

Quote from: burning1 on July 19, 2010, 02:45:42 PM
Here's a thread I posted comparing hot/cold wet/dry compression test results for a 2004 Suzuki GSX-R 600 with 35000 miles.

http://www.bayarearidersforum.com/forums/showthread.php?t=298719

I can't find what you are talking about in that thread....can you post the data here?

Cookie

its on page two bro, its jus says what variations he had between the tests

Not if the ring end gap is in spec and there are no obvious defects on the cylinder walls or pistons. Just clean off the carbon and varnish from the pistons and ring lands and you're good to go.

Quote from: da602krew on July 19, 2010, 03:49:34 PM
its on page two bro, its jus says what variations he had between the tests

OK  I found two posts referring to taking compression test cold, warm, and "wet"

Interesting that readings of 240 PSI were taken...this implies 14:1 compression......not a gs 500 I assume?

Anyway, I thought we were talking about a leak down test, not a compression test.....

Either test is just a general condition test......if the readings are fairly high, the engine is good........doesn't really matter if hot or cold,,, or wet.....its all relative...

A stuck or burnt valve will give a really low reading in all tests, as will bad rings......

In the airplane world we just have to meet a minimum spec.......its pass or fail.......

If we do the leak down cold and it meets the spec................good we're done!

If it does not meet the spec, we then warm up the engine..........usually better reading when hot...if this meets the spec....done........

Many times a cylinder will read higher this year than it did last year! 

If it does not meet the spec.......we must diagnose and repair...


Cookie

Cookie,

That was my post, based on a series of tests I took on a Suzuki GSX-R 600. I'll summarize the results here, later.

Basically, there was about a 20PSI difference hot/cold.

A wet test is a test performed with some oil poured into the cylinder.

Quote from: burning1 on July 20, 2010, 12:50:34 AM
Cookie,

That was my post, based on a series of tests I took on a Suzuki GSX-R 600. I'll summarize the results here, later.

Basically, there was about a 20PSI difference hot/cold.

A wet test is a test performed with some oil poured into the cylinder.

Compression test is mostly a diagnostic tool......

A 20 psi difference between hot and cold is insignificant...........

If you get a too low reading cold, then get an acceptible reading hot, the engine is still good...

If the cold reading was low, and the hot reading stayed low, then engine has problem....

The wet test is more for diagnosis after a low reading on dry test..like bad rings ....reading will come up if oil is added....

Cookie

Well i decided not to do to the test mainly because i didnt want to spend the money on the tester when i was pretty sure i had a fudged valve. So i pulled the haed and what do you know... theres a BIG hole melted through the #2 exhaust valve, it probly took out the valve seat and im pretty sure messed up the head to the point of it needing to be machined. ive decided to pick up a head from my freindly neighborhood motorcycle salvage yard, i found a 1999 gs500e head that looks pretty good has a little surface rust on a few valves but overall is in good condition. Will a gs500e head work on a f model