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I'm borrowing a compression tester from a friend and was wondering what "good" compression would be for a KDX200?

Help on the actual procedure, (besides sticking the gauge in the spark plug hole and kicking over a few times) would be helpful too.

Thanks!

I think 100-150 is the normal range. The one time I checked mine it was 147 and that was right after a rebuild. I think all you do is stick in the gauge and keep kicking it until the needle stops going up. I am not aware of anything else you need to do.

Yeah I heard 100 is death's doorstep.

The procedure I read was ground the plug, hold the throttle wide open and kick 4 or 5 times. I'd just like a confirmation before I do it.

Thanks!

Some say to check with the engine warmed up...Throttle open, and kick until needle stops.

Ron Black Said:

Accurate Compression Testing


First you need to get a hold of a "GOOD" known compression gauge. I recommend something like a SNAP-ON or MAC TOOLS. Start the bike and run it until it is at full operating temperature. Then do a compression check on your engine. This is performed by installing the compression gauge into the spark plug hole. Then hold the throttle wide open and kick the engine over vigorously several times until the gauge needle no longer moves. Record the gauge reading, do this two to three times. With the spark plug removed, squirt a little WD-40 down the spark plug hole, then kick the engine over several times. This compensates for ring wear. Now re-install the compression gauge and repeat the compression test two to three times and record these numbers.

Thanks kdxquebec! What are the "awesome", "good", "ok", and "oh sh#t" numbers? Or is there just "awesome" and "oh sh#t"?

I just got 150 psi (average of three readings) on my 2001 220. Have maybe 40 days of riding in the 5 years I've owned it. From the records, I'd say that I'm still on the OEM piston. Looking through the ports on the intake and exhaust side, piston looks like new.

Guess I'm good for a while on the top end.

Kaw manual says: Usable range 655 ~ 1040 kPA (6.7 ~ 10.6 kg/cm2, 95 ~ 151 psi).

Too high : carbon or wrong gasket
Too low: piston clearance, head leakage, rings, ring grooves, or crank seals.

Oh oh....

A KDX220 with a stock piston?

Not good.........

Search there buddy, that piston is a known hand grenade ready to go off any time.

I wish I knew if my piston was stock. I don't want to do a rebuild because it hasn't been that many miles (previous owner did it) and the compression is still great. But I don't want the piston to blow. Is there any way to tell?

Re: 'Guess I'm good for a while on the top end.'

No. You're not. Mr. Pro3 is right about that.

If you had read the stories we've heard over the years...you would order a piston for your bike today.

If 10 out of 100 220 pistons blow up..that's not real bad odds for you to gamble on.

If you're one of the 10...your failure rate is 100%

Re: 'Is there any way to tell?'

The Wiseco/Pro-X pistons don't look the same out of the box.

But...what you can see from the exhaust port? I don't know that, but bet there's something you could see.

How about some 220 riders that've swapped their pistons out and took pics of the both of 'em share!!

Can you ask the PO?

canyncarvr wrote:Re: 'Guess I'm good for a while on the top end.'

No. You're not. Mr. Pro3 is right about that.

If you had read the stories we've heard over the years...you would order a piston for your bike today.

If 10 out of 100 220 pistons blow up..that's not real bad odds for you to gamble on.

If you're one of the 10...your failure rate is 100%

Yah, your right (as ususal).
I've rethought my original opinion ( I must have been impeded by the thought process) and will be getting an order off to FRP soon.

(back to the original thread ) Is the consensus that a PSI of 150 is good to go?

Yes

Re: (back to the original thread )

Sorry 'bout that.


A couple things to keep in mind about compression testing in general:

For one thing...it generally doesn't mean a whole lot. KDXQs quote from Ron notes that having a GOOD guage is the place to start. A lot of guages AREN'T any good..and multiple tests will get you multiply (-ee) different results. How warm the bike is matters. Basically, lots of things matter.

For the purpose of any comparisons, use the same guage and the same method of test.

That said...it's when you're at the margins that all the little things are more likely to add up to what may be an incorrect diagnosis.

150psi should be fine, though.

Consider what you would get with some leaky rings and a fat layer of carbon on your piston/head! Maybe 150!!

Seems to me (not that anyone asked..so sue me) that the value of a compression test is largely in a comparative situation..like with a multiple cylinder engine. If seven of eight cylinders are 240..and one is 150...that's a problem no matter HOW you slice it.

I replace top-ends 'cuz it's time...or when I feel like it. What the compression is or isn't is not something I've even tested.

I've got a good guage. Maybe I'll check it just for fun.

...it'll give me something else to worry about.......

Yeah, I didn't get into details Other than very rough measurements I consider comp testing on a 2T pretty worthless unless you've tested it since a new top-end, the same way every time, just to measure the loss. Pour a shot of castor in that sucker and watch what happens. Pulling the jug and looking for any blowby/etc is the best way...For the KDX...If it idles well, pulls well off idle, it's got enough compression to not worry about it. This is where you'll see the degredation first.

Thanks fuzzy. The bike rips, wheelies through the gears, and idles like a champ right after start-up, no choke. I love this bike and want to keep it in tip-top shape. Guess I'm just trying to be proactive with my maintenance.

Re: 'Guess I'm just trying to be proactive with my maintenance.'

Suspension/bearing maintenance, suspension fluid changes are a couple of places 'proactive maintenance' will be a big help.

If you're looking for things to do.........


A BTW...but a bike that idles 'like a champ' with no choke on a cold-iron start needs some carburetor tuning. That's not an example of things being 'right', it's a surefire symptom of something NOT being right.

Let me elaborate... I'm in the NE, Connecticut to be exact. My season is May 1, to Nov 1. (for legal riding) The bike has been sitting since Dec. I busted it out the first time this weekend; first start in 4 months. Started on third kick. Warmed it up for 5-10 minutes and rode in my neighborhood. The first 1/5 of the throttle (putting around) felt "chunky", a little hesitant, but from there on out it moves. Then I ran it Sunday for 2 hours and it was great. Just chugging through some tight stuff and in the sand winding through the gears. Suspension felt good... Loved it. I am new to the bike but once it's hot it's awesome; all the way through the throttle, even putting around. I ain't complainin'...

btw, per this forum suggestions, I have replaced/greased the swingarm bearings, and greased the steering.

I am no motorcycle expert by any means! Still learning and you guys are a great help.

Be sure to look at the rear shock rocker arm bearings too. My swingarm pivot bearings looked great, but the rocker bearings were just ok and the small one was pure rust. I don't think it had been greased since the bike was new.


BTW, speaking of proactive maintenance.....where do you guys go to get new nitrogen for the rear shock following dissassembling to replace the oil?