I’ve been trying to perform a leak down test on my 07 Softail and I’ve been trying to keep the pistons at TDC in order to do this . But by putting it in high gear and holding the brake, the pistons seem to drop from tdc before the brake actually can stabilize them.. Theres the play between the compensator and the tranny causing me grief here... lol .. There’s gotta be a better way than this to hold everything in place .. Do I have to pull the primary cover and chock the chain to hold this or does anyone know of a better way .Ive been wrenching for a living forever, but not on HD . So I’m learning as I go . Any help from you guys would be appreciated.. Thanks in advance...

 

Not an answer but I have been able to successfully run leak down tests on my bikes by putting the trans in first gear, rotating the rear wheel to tack out any slack and using a ratcheting tie down to lock down the rear brake. Even if the piston moves a tad from TDC, you should be able to get accurate readings once the piston is locked in position. You can always lower the input PSI; if using 100psi, try it at 90? JMHO.

 

There is a stop you can buy that fits into the crank sensor hole to hold the crank in place. IIRC Jims makes one. IMO the piston does not have to be exactly at tdc to do the leakage measurement. The important part is that both valves are closed. A little down in the cylinder may be even better as the piston may **** less with the rod pushing the piston to the side of the cylinder. The straighter piston means less leakage past the rings.

@djl Why not put the bike in top gear instead of first?

 

^^^^^^ What Max said....... The difference between TDC and BTC in terms of leakdown wont be very much if any at all.

 

Were you able to keep the pistons at TDC .. I kinda thought that was really important ..

 

While it shouldn't one thing to note is that at BDC, either the intake valve or exhaust valve will typically be open. You can remove the pushrods and perform the test at BDC. Another issue is cylinder wear. It's possible for the cylinder to leak more at one location than the other. Ideally and with a tight motor, it shouldn't.

 

I was under the impression that the motor would be easier to hold in place with the brake . A taller gear should require more energy to push down on the pistons..I believe I saw this somewhere in a video on doing leak down tests..

 

I would think that the exhaust valve would be partially Open . Then the test is worthless.. not accurate...

 

No particular reason; just the way I have done it. I have the Jim's stop but completely forgot that I had one and I used it for the last leak down test I did. Actually, performing leak down tests is why I bought the stop. It's like you say, getting old sucks but better than the alternative.

 

You are correct if trying to use the rear brake to hold crank position. Pressure on the piston puts less torque on the crank close to TDC. Taller gear reduces torque applied to the rear wheel.