Leakdown test - assistance

[shawski]

Well thanks to a few of you guys out there I'm on to my next test on my new '68 U15 with original 289...the leak down test.

Discovering from the compression test cylinder 3 is at 35psi, and 6 is at 60. the rest of the cylinders are averaging 152.

I understand the concept behind the process, but I can't figure out on the 289 how to get these two specific cylinders to TDC.

Can someone please help me with the first step of finding TDC?

thank you much!

Shaw

 

[Pedestrian]

Pull the valve covers, locate the cylinder you want to test, remove the spark plugs from these cylinders, unplug the power wire to the coil, using a jumper wire from the positive side of the starter solenoid touch it to the start terminal of the solenoid to "bump" the motor over. Using this method keep bumping the motor over watching the valves on the cylinder to be tested, till both valves are closed. This should be close enough to TDC to perform a leakdown test. If you want to be exact, insert a screwdriver into the spark plug hole and turn the motor over with a wrench till you feel the piston at TDC.

Note a leakdown requires low air pressure (50psi or less), too much pressure can spin the motor over.

 

[DirtDonk]

If you have the valve covers off, you can watch the rocker arms. if not, and presumably you have the plugs out still, you can keep rotating the engine until the particular cylinder you're interested in comes around to TDC and pressure starts pushing your finger off the plug hole.
In your case, the 289's firing order is 15426378. So cylinders 3 and 6 are going to come around one right after the other. And, theoretically at least, right about the time that the timing marks come around to TDC on the damper.

Remember the crank makes two complete turns to make one full engine cycle of 720° of rotation. So cylinders 1, 5, 4 and 2 are on the first rotation, 6, 3, 7 and 8 are on the second.
Put your finger over the hole of each one as the damper comes up to the TDC mark and see when #6 starts to push.

Paul

 

[DirtDonk]

Beat me by "that" much...

Paul

 

[av bronco]

Find TDC on your harmonic balancer, mark it on the balancer, then directly across from tdc (180)make another mark, now make two marks so you have a 4 slice pie. the reason you do this is so when you rotate the engine every 1/4 turn (as marked) this is when the correct cyl. to firing order will come up. now start at no.1 on tdc, ( you can pop the dist. off to verify it's on #1)then every 1/4 of a turn on the crank will be the next cyl. on your firing order. ie-if your firing order is 15426378 then at #1 tdc when you rotate the engine 1/4 turn you will be at #5 and so on.

 

[Viperwolf1]

#6 is at TDC at the same time #1 is but it needs one more complete revolution to get the valves closed. #3 is at TDC exactly 90 crankshaft degrees later.

 

[shawski]

You guys are all great! Thanks again!

I'm off to the garage!

Shaw