Question on performing a cylinder leak down

[elan666]

What's the best way to hold the crank in place at TDC while pressurizing the cylinder?

[Tacomaman87]

try putting it in gear? prob wont work but its worth a shot.

[elan666]

Nah, don't think so. Maybe with a 300lb guy sitting on it in 5th gear holding both brakes ?

Most people seem to recommend 100psi in the cyl for the test, but I can't get much more than 30 in there before the bike wants to walk away

[i4bikes]

Sometimes I use a socket on a braker bar. You need to make sure your realy at TDC and not just close or there will be a lot of force as you have found out. Some guys will check at BDC because it is easer. You will learn more about ring seal at TDC IMO but if it's wore out or has a leaky valve it will show up in either case.

[Tacomaman87]

like I4 says you have to be at true tdc or its going to try and move. I looked in my manual and it looks like you can remove the crankshaft cap that is just in front of your rear brake lever and use a hex socket or allen wrench to hold the crank while you pressure test. are you doing this as pm or are you having issues with the bike?

[elan666]

Well, the bike's using a little oil (exactly how much, not sure yet). I know this is pretty common on CRFs, but I'd like to find out exactly where it's coming from.

I bought the bike second hand, and the guy said he had about 300 miles on it. I've put about 400 on it. I've been good about oil changes and valve adjustments (shimmed one exhaust when I got it, but nothing else has moved since).

I'm probably just worrying myself, but I figured since I have the tools, I might as well do the test.

Thanks for the help btw

[jross]

you could try puting a aluminum washer between he front sproket and chain to hold it. not sure how good it will hold it but worth a try,make sure it isnt a metal washer you dont want hert your sprocket.

[apriliarsvr]

Possible solution....

http://www.motionpro.com/motorcycle/partno/08-0437/

[Tacomaman87]

elan666 please be sure to update us with your numbers and what you figure is going on. as for aprillarsvrs possible solution it would most likley work but i would be concernd as to how much stress you would be putting on on the chain. imo you would be better off holding the crank but maybe im just paranoid

[elan666]

I was actually looking at the motion pro tool last night. Looks handy, but 1, I'm not sure if it'll fit my 08 with the different decompression mechanism ("Allows you to easily torque the cam gear bolts on a 2002-2006 CRF450R/X"), and 2, I'm not sure if it would be totally safe to use the cam gear in order to lock the crank.

Either way though, looks like a nifty tool to have for tightening down the cam gear bolts.

They also make a tool called a "gear jammer" (I think that's what it's called), but you'd have to pull the right side case off in order to use it. http://www.motionpro.com/motorcycle/partno/08-0427/