KDXRIDER.NET

Hi, i'm having some trouble with a top end rebuild on my 220 and was hoping some folks with more engine building experience can chime in.
I just finished reassembling the engine and pressure testing it @ 5 psi. Unfortunately i have some serious air leakage from the head gasket and nuts, the base gasket, and the reed block gasket- or maybe the rubber boot/reed block interface. It should go without saying that everything was assembled squeaky clean and torqued to spec.

Here's what i'm wondering- do i need to do a few break-in cycles with the engine followed by a retorque session before i can expect it to seal up and hold 5 psi? Or is this something i need to sort out on the bench before putting the engine back in the frame?

Oh,I should have mentioned, this is a 220 engine in a 2003 KX125 chassis- so that's why the engine has to come out for a top end replacement.

Thanks to anyone who can weigh in!

Freshly assembled motor should not be leaking from those locations. Did you use aftermarket or OEM gaskets? Was it holding air prior to the top end rebuild? How are you sealing the engine (your pressure test setup)? I know that when I rebuilt my KLX and used aftermarket gaskets it leaked like a sieve. When I redid my KDX220 motor I used a Cometic kit and had zero issues (it now has well over 100 hours on it and still has the same compression and leakdown numbers as when freshly done.

Lastly, pics! My hybrid is a 220 motor in a 2001 KX125 chassis with KX250 suspension. Love it!

The head gasket was oem, the paper gaskets were aftermarket, not sure what brand as i've had them in a box for about a year.
It was holding air prior to top end rebuild with the exception of a leak from the powervalve actuator shaft cover, but no leaks from base or head that i could see. The bike had 178psi before tear down on a 110hr top end.
My pressure test setup consists of an expandable rubber plug in the intake boot and one in the exhaust port. I then pressurize the engine at BDC Through the spark plug hole. No leaks from any of the test equipment.

Maybe the paper gaskets are just crappy? but why is the OEM steel gasket leaking?!
For what it's worth, i put a thin coating of grease on the paper gaskets- something i haven't done before but was recommended by an experienced engine builder. Even if that were to blame, it still doesn't explain the leaky steel gasket...

I would love to post some pics for ya, but i can't figure it out...

Hi. The link to picture info is in my signature.

Thanks for the tutorial! Here’s some photos of the bike from an enduro I raced a couple weeks ago. In a sea of orange, someone has to bring the green!

PS- I ordered a cometic gasket set. The last gaskets I used were from a wiseco top end kit, and they worked well for over 100 hrs, so I’m thinking cheap paper gaskets are likely the culprit here. Will report back

Cosmetic gasket kit came in today. The gaskets are much different than the cheap paper gaskets I had on hand- they’re all a steel core with some kind of coating. Buttoned everything up and the carb boot still leaked like crazy. A little smear of yamabond set it right and the rest of the motor held pressure nicely.

Great to hear!

Nice, good result.