[kyle_blake]

Hi

I can find tdc on #1 based on rotor and then lining up timing mark.

Curious, I don't want to take valve covers off to see both valves closed.

I know firing order.

Can I move from cylinder 1, then turn crank 1/4 turn to get TDC on number 8? And repeat for rest? Just make some marks on balancer using straight edge, type thing?

[steve25]

Pull all the plugs out and have a helper bar the motor over while you place a finger over number 1 plug hole.

When you feel pressure on your finger tip, then your coming up on # 1 TDC .

Finding TDC exactly will be a different story however!

[tstroud]

A plastic drinking straw in the spark plug hole on top of the piston will get you close enough to do a leak down test.


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[AG]

I use the screw in TDC finder that goes into the spark plug hole which works well.

[track73]

Some times the air pressure will push the piston back down. It's better if you have a stick shift so you can put into gear.

[shaker455]

Originally Posted by kyle_blake

Hi

I can find tdc on #1 based on rotor and then lining up timing mark.

Curious, I don't want to take valve covers off to see both valves closed.

I know firing order.

Can I move from cylinder 1, then turn crank 1/4 turn to get TDC on number 8? And repeat for rest? Just make some marks on balancer using straight edge, type thing?

Kyle,
Your initial timing is not @ zero so the rotor is not going to line exactly up.
That's where the timing mark on balancer falls onto play
Jeff

[MrWrestlingII]

Good timing for this post, I did a leakdown test for the 1st time just yesterday.

When building the motor a few years back I verified TDC on #1 lined up with the 0 mark on the balancer. So I pulled the plugs and turned the motor by hand to the 0 mark. When doing this I could hear compression on #6 and started the leakdown test there, moving thru the firing order by turning the motor to the 90, 180 270, 0, 90, 180, 270 degree marks on the balancer. The motor was cold and I was consistently losing about 3% at each cylinder. This loss was thru the rings as I could hear it at the valve cover breather and dipstick tube for each cylinder with no sound at the carb, exhaust tips or radiator. The next time I've got the motor warmed up I'll run thru the test again to see if there's any difference.

It was a pretty easy deal. I don't think I spent much more the 45 min from start to finish.

[Schurkey]

Looking at the rotor, looking at the damper (unless it's already marked at 90, 180, 270 and, of course, 0), looking at a piston stop = TOTAL WASTE OF YOUR TIME.

The leakdown tester is it's own TDC indicator, used with a long-handled ratchet and whatever socket fits the crank bolt of the engine you're working on. I have, when I was younger and stronger and fiercely angry, turned the crank by pulling on the alternator or PS belt, when the crank didn't have a bolt in the front.

Dial the regulator for some low air-pressure value. Five, ten, fifteen PSI. I can't really tell you because I don't check the dial on mine. It's not a critical value--you need "some" pressure, but "too much" pressure makes it harder to turn the crank. (The leakdown tester I've used since 1988 or so isn't calibrated in PSI, it's calibrated in percent of leakage. I have a second leakdown tester that's calibrated in PSI, but I haven't used it much.) Plug the hose into the cylinder as if you're doing the test. If the valves are open, you hear hissing at the tailpipe or at the carb, or both if they're on overlap, and the gauge shows ZERO pressure. Start turning the crank somewhat rapidly--whatever is comfortable--in the direction of normal rotation. At some point, you'll hit the compression stroke and the gauge shows whatever pressure you've dialed-in, and NOW you're ready to look for TDC.

BUMP the crank by hand--not with the starter. Try to turn the crank the minimum amount each time. Every time you bump the crank and it pushes the piston UP, you'll see a jump in pressure on the gauge, which will almost immediately decrease to the regulated pressure. When you get very near the top of the stroke, the jump in pressure will minimize AND you'll feel that the crank is easier to turn when you bump it.. When you can bump the crank and the pressure doesn't rise and the ratchet is really easy to move--you're at TDC.

If you go too far, so that bumping the crank is pulling the piston DOWN, the gauge pressure will DROP momentarily, and then recover. If you see that, back up a little bit and re-try.

For the purposes of leakdown testing, everything you need to know about TDC is indicated on the gauge (the second gauge, on a two-gauge tester) and felt on the ratchet. As there is some amount of skill development in judging the "feel", expect this procedure to require a little practice. Won't take much, though.

Practically all leakdown testers have a quick-connect in-line with the spark-plug-hole adapter. When you've got TDC by looking at the pressure changes on the gauge vs. crankshaft motion, you pop the quick-coupler, dial up the regulated pressure to whatever your testing pressure is, and connect the quick-coupler. Depending on your method, you either read your leakage or you re-adjust the regulator to the nominal test pressure and then read your leakage.

Point being, you don't need any special tools and you don't need to count degrees or mark the balancer (unless you want to.) You don't "need" to go in the normal firing order, because it's no big deal to find TDC accurately enough to do a leakdown test, from any random crankshaft position.

[tom s]

I do it by myself.I pull all the plugs,put a cork in #1,turn with breaker bar until the cork goes across the garage.Tom

[kyle_blake]

Perfect, thanks everyone again for helping out. Really neat on how to use the gauge as the tool to find it.

[72LuxuryLeMansLa.]

Originally Posted by tom s

I do it by myself.I pull all the plugs,put a cork in #1,turn with breaker bar until the cork goes across the garage.Tom

Does it make that cool sound like when you pop a cork on wine?

[tom s]

YEP!I now use the tapered rubber ones I steal out of my wifes chard bottle!Tom

[Jack Gifford]

Originally Posted by track73

... Some times the air pressure will push the piston back down...

It's a good idea to get in the habit of removing the wrench from the balancer bolt before applying air. Ask me how I know...

[kyle_blake]

Hi,

I was able to find the TDC on #1 using rotor position and little camera in the cylinder. Everything lined up and saw piston come right to top. So all was good!

Started off with my tiny compressor which built a big 90 psi. Set the dual gauge to "set" and then plugged it in. 20% leakage. I left it and as the pressure dropped to the gauge the leakage % went up. Eventually little compressor kicked on which can't keep up with anything... mins went by, second gauge was almost at like 50% at 30 psi.

I can hear through dip stick and valve cover grommet so assume rings. Didn't run back to exhaust , I flipped carb throttle to see if i could hear anything, but i didn't . Not that I gave it enough time.

Should I be concerned or is the fact the compressor sucks ass the reason it goes from 20%-50% after several mins? I don't think piston went down?

[kyle_blake]

I think it's the compressor that is the issue, weak cfm and it couldn't maintain 90 psi if it tried. I'm going to run with the first 15 seconds. you can clearly see as you get the gauge to "set" that the total psi has to be up near 90 to even get there. So when it can't maintain it it just flows through gauges. Certainly would be nice to real compressor and see if it does stay steady at the 15%-20% leakage seen in first 10 seconds.