Finding TDC the easy way

[Dave Neptune]

Tom, I just could not resist .

Dave Neptune

[joe_db]

A while back we had a tool concept for finding the compression stroke in a cylinder, critical when setting timing from scratch, without peering or inserting anything into the spark plug hole. Remember this?

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Well it struck me as a pretty cool idea so I finally got around to making one and testing it out. I sacrificed an old spark plug by breaking off the porcelain, drilling out the electrode and grinding off the arm on the bottom, added a balloon to the top, threaded it into the #1 spark plug hole finger tight only and turned the engine over by hand. Once you know you're on the compression stroke you view the crankshaft roll pin for vertical alignment.

Way cool.

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That looks like a fun project It certainly will keep you from finding TDC on the exhaust stroke

[Al Schober]

Well, this has been an amusing thread!
Just what I needed during this isolation. Spring trip to NOLA cancelled, instead we got to visit Loch Down. I hear that even Nessie is now in Loch Down.
So, all this is just to keep from putting your thumb over the spark plug hole?
No, the idea of acetylene balloons is new to me. Haven't tried one. Do they make your voice funny??
Another week or two of this and we can start a thread on vegetable guns. I've still got my potato cannon out in the shed - SpudZooka! I had the design for a radish pistol, but never made one.

[ndutton]

One thing I noticed with the balloon indicator - - you can turn the engine very slowly by hand and still get a good indication. Oh yeah, you can turn the engine with TWO hands.

[joe_db]

Well, this has been an amusing thread!
Just what I needed during this isolation. Spring trip to NOLA cancelled, instead we got to visit Loch Down. I hear that even Nessie is now in Loch Down.
So, all this is just to keep from putting your thumb over the spark plug hole?
No, the idea of acetylene balloons is new to me. Haven't tried one. Do they make your voice funny??
Another week or two of this and we can start a thread on vegetable guns. I've still got my potato cannon out in the shed - SpudZooka! I had the design for a radish pistol, but never made one.

Acetylene balloons explode We made some at random torch settings when we were teenagers. Then we got the bright idea to use a big gallon jug and set the mix just right. My friend's father ended up falling off his chair on the front porch and further use of his welding tanks was curtailed

[ndutton]

Interesting glitch

With this foolproof compression stroke indicator I recently performed a from-scratch timing exercise that was 180° out. Embarrassed, how could I have possibly messed up something as simple as this? I removed the spark plugs, installed the balloon indicator in cylinder #1, turned the crank by hand CCW facing the flywheel, balloon inflated, continued turning the crank until the roll pin was vertical, set the distributor rotor to #1. What could be easier?

Babbling in disbelief it took me an hour to figure it out. The engine had not run in a very long time, like years. The crank was not frozen, compression test showed good numbers on all cylinders, water jacket pressure test was successful so the conclusion was we had a viable block and air pump worthy of an effort to get her to run again.

After replacement and rebuilding of several components, with the coil wire removed I cranked for about 30 seconds to get some oil pressure without combustion. This cranking was done with the raw water intake thru-hull open. In a perfect world I would not have done that but the thru-hull valve was stuck open and I did not want to risk a bigger problem by breaking it trying to close. [Mis]setting the timing as described above followed.

It turned out that there was enough water in the waterlift muffler to seal off the muffler exit. This caused a backpressure to develop in the cylinder on the exhaust stroke thereby inflating the balloon indicator and a false result. I removed the water hose to the exhaust water injection fitting and extended it into a bucket to stop the waterlift from filling any more until I had the engine running. This also vented the exhaust so an accurate TDC could be determined and the timing reset.

I therefore recommend removing the water injection hose to vent the exhaust when using the balloon indicator to avoid the mistake I made.