Subject pretty much says all.

Basically, I'm trying to do a leak-down test on my L98 engine, and I heard that, ideally, each cylinder ought to be tested at TDC (and with the valves closed, obviously). I've got the tester made and ready to go; now I just need to run the test...

I should add that my intake manifold is off and thus I have full sight of the lifter valley, so if that will help me find TDC any easier...

Thanks!

 

Unless you lock the crank from turning, it will likely rotate
from tdc to bdc during the leakdown test.
Keep your fingers out of the way of the fan and pulleys!
You can find tdc on #1 cylinder by using a "piston stop"
TDC "firing" will be 90 degrees further in rotation for each
progressive cylinder in the normal firing order in the normal direction of engine rotation.
So do #1 at tdc then rotate the crank 90deg and do #8
and so on through the fireing order.

Again if you don't want the crank to rotate during the test you'll have to lock it some how.

 

F-BIRD'88: Thanks for the reply.

Couple of things, though... First, what's a "piston stop"?

Also, about the crank rotating... What if I just left the plugs in the other cylinders? Wouldn't that create enough compression to keep the crank from moving?

 

1. Search the internet Keyword : piston stop crank

2. not likely.... watch your fingers..!!!

 

A piston stop screws into the spark-plug hole. It protrudes into the cyl. When the piston comes up, it will hit the stop.
If you have a degree wheel, you note where the crank stopped. Turn eng the other way till the piston hits the stop again. Note degree wheel. Find the point half-way between the the two points on the degree wheel. Remove stop. Turn crank to the half-way point. That's TDC.

You could stick something thru the spark plug hole and "feel"
the piston. A soda straw works well. Don't stick anything in the cyl that will break off and/or damage the piston. If you get it perfectly at TDC, the crank won't turn when cyl is pressurized. It may take a few tries. Having the plugs in the other cyls won't help much. Once it's off TDC, and air press is applied (50-75 psi in the cyl) the crank will still turn.
Stay out of its' way!!

 

get a 6 dollar timing tape, put #1 on tdc compression. it probably won't move if you have it right at the top, i've done this before, then rotate the engine 90 degrees ( the tape has 90 deg marks on it), and go top the #8 cylinder, then 4,3,6,5,7,2. you might also want to do the test and BDC so you can get an average reading, very few people actually do it at TDC its a real bitch!

 

Thanks for the replies; I know what I'm going to do now.

I just hope that either AutoZone or O'Reilly has the piston stop, timing wheel, and/or the timing tape, because I don't know of anybody else who would (locally anyway--I know I could always order the stuff, but I want to get this done today)...

 

your balancer is marker for tdc, just wrap a tape measure around it( measure circumference, pie x diameter, pie is 3.14) and divide by 4 then make 4 marks equally spaced around the wheel, at every 90 degrees. each mark is a piston at tdc following the firing order 1-8-4-3-6-5-7-2