leakdown test on a Commando

What tricks are there to hold the engine from turning while doing a leakdown test? I've tried applying the rear brake but there's enough slack in all the chains such that the pistons move when air is applied. The amount of crank rotation where both valves are closed is rather small.

I know I can put a wrench on the crankshaft nut, but I don't wanna open the primary cover if I can avoid it.

Thanks

There is the Hindu rope trick, stuffing cord in one side so it jams up and can be pulled out later, but hicks like me put it in 4th and run a stick through through the shocks to bind on a spoke nipple. Another way is use metal block, plate, wedge to jam a sprocket tooth on a cast boss in inner case. Maybe bungee cord the rear wheel to keep some tension on the jammer while fiddling the pressure test.

I've always used a long breaker bar and socket on the end of the crank. Even then, you have to be pretty careful to get it right at TDC, or the air pressure will drive the piston down. There are probably other ways, but I never found them.

Ken

This is not a perfect test, but I have done it several times when I'm working by myself and have trouble keeping the crank from turning. Back off the valve adjusters and take the test at BDC. The problem with doing the test this way is that the piston/ring /cylinder leakage reading will not be correct because most cylinder wear takes place at the top of the cylinder. (where the test should be taken) However, if you happen to have a leaky valve, or headgasket problem, you should be able to determine that. Also, a hole in a piston, scored cylinder, or major cylinder leakage would also be noticeable. I have never done this on a Norton, but I would think you should be able to back off the intake valve adjuster enough at the bottom of the intake stroke to get everything closed. Better than nothing.

Mike Wolf

It sounds like the options avoiding the primary cover off are more of a PITA than actually taking the cover off?

What's the problem doing this, it's a 1 minute job?

You're right, Rich. It's time to clean out the chaincase anyway...

Thanks guys.