• Hi everyone,

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How to lock engine at TDC for leak down?

Mucci

Mucci

Husqvarna
AA Class
Trying to lock my 570 at TDC for a leak down test and I can't get it to stay there. It won't even hold 10PSI.

- Can't put a wrench on the crank bolt because it's reverse thread.
- Tried putting the bike in 5th, rotating the engine to TDC with the rear wheel and standing on the brake but it still gives. I'm guessing its the clutch that slips because the tire is locked. Clutch is brand new though and has great bite on the road.

Any other tricks?
 
It does. I've tried for 2 hours setting it at TDC and it moves every time. Tried very small increments before and after TDC as well. As soon as air is introduced it builds up and rotates the motor.
 
I tried over the winter to do a leak down also. I had the exact same problems of rotating off TDC. Eventually gave up and just did a compression test instead and everything pressure wise was fine. Good luck, post up if you figure out a successful way of locking it so it doesn't rotate.
 
It's like trying to balance a bowling ball on the tip of a pencil ...and then blowing 100psi at it.
 
Just spoke to a tech at Hall's Cycles and he said to put the piston at the bottom of the compression stroke then back off the valve /tappet adjusters so they stay closed. Run the rest and reset the valve clearances when you're done.

Haven't tried it yet but sounds ingenious to me :) ...to the garage!
 
Mucci said:
Trying to lock my 570 at TDC for a leak down test and I can't get it to stay there. It won't even hold 10PSI.

- Can't put a wrench on the crank bolt because it's reverse thread.
- Tried putting the bike in 5th, rotating the engine to TDC with the rear wheel and standing on the brake but it still gives. I'm guessing its the clutch that slips because the tire is locked. Clutch is brand new though and has great bite on the road.

Any other tricks?
Click to expand...

Test with 1 gear and not with 5 gear.
In this way should not slip the clutch
 
Ok , how about this idea . Clutch cover off , figure out rotation of primary and clutch gears and slip a small piece of soft metal in between the 2 gears to stop rotation . Wouldn't this take both the clutch and rear brake out of the picture ? I don't know if your bike has this but on my Honda 450 , the crank is offset from the cylinder bore , because of that the piston could be at tdc and the crank still be slightly rotated .
 
The timing mark might not be exactly TDC. True TDC is found by measuring or using a piston stop to mark a spot before and after TDC and then marking it in the middle of the marks. A degree wheel on the crankshaft with an adjustable pointer is the best way. Depending on rod length and stroke the piston can dwell at the top of the stroke for 7-14 degrees.

Another trick is to use a gear jammer in the primary or balance shaft (if it has one) to lock it up close to TDC so it wont rotate. If you don't have one a penny works good because is is soft and won't damage the gears.
 
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