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.

[Theodore]

Atomic 4 compression

Good Neil

Very interesting post a learning experience, thank you.

Question:
So once the balloon has expanded you are/may be at Top Dead Center with the #1 piston, what I want to confirm is are you on the compression stroke?

I just replace all the valves on my atomic 4 and I have little to zero compression. Before I did this job I had (70, 80, 70,60) so I am trying to find out if since I have re-adjusted the valves on the compression stroke which I am having a difficult time trying to figure out, that I have or have not set the valves on the compression stroke.

When I first set the valves I use a pencil in the #1 sparkplug hole to find (top dead center) TDC but didn't know if I were on the compression stroke.

[jcwright]

Hello Theodore.

Here are Don Moyer's instructions for finding TDC, from one of his FAQ documents.

Jack

"The TDC position of the No. 1 cylinder is most easily found by holding a finger over the spark plug hole in the first cylinder, while manually turning the flywheel counterclockwise. As soon as compression is felt, stop turning and look at the position of the roll pin in front of the crankshaft. Continue turning until the roll pin is perfectly vertical. The piston will then be at TDC."

[Surcouf]

TDC demonstration by the Master

https://www.youtube.com/watch?v=2ysFGcm8oNo&t=531s

[Dave Neptune]

Theodore, first welcome to the MMI Afourian forum.

Note that if the valves a to tight from your adjustment position of the crank & cam the valves may not be seating and thus no compression. Finding TDC without the valves seating for compression can still be done. It is a bit more "engaging" but doable by watching the valves through the side plate.

Dave Neptune

[ndutton]

Question:
So once the balloon has expanded you are/may be at Top Dead Center with the #1 piston, what I want to confirm is are you on the compression stroke

The balloon is not an accurate enough method to be a TDC finder but more of a compression stroke indicator. If you have no compression on #1 you can use it on any of the remaining 3 cylinders to find their respective compression stroke, just be sure to set the timing on the corresponding distributor position.

If you have zero compression on all 4 cylinders, the balloon tool is worthless.

[Theodore]

Atomic 4 compression

Hello jcwright,

Unfortunately I can't do both at the same time but I will see if I can incorporate a friend to assist me with doing this procedure. I email back forth with Don Moyer in finding the TDC, by putting a pencil in the #1 sparkplug and watch the pencil rise to confirmed TDC, then set the valves to spec. Which I did but not knowing if I am on the compression stroke or not. I am going to contact Don again after I check the compression once again since I got the engine timed. I thought that maybe I tried to adjust the distributer while I have the engine in forward gear and get RPM up and I might get some compression because I have zero rise RPM when in forward gear when I put the throttle full open, which why I think my compression or valves may not be correct, unless I have a whole different issue.

Thanks for your advice.
Ted Gladden

[ronstory]

Ted--

I would be good to follow Dave N's advice above and if the valves are to tight, they will never fully seat and you will get low/no compression.

The trick is remove the side plate and watch the valves on each cylinder. When both the intake and exhaust valves are in the closed position (valve stems are most visible), you are on the compression stroke. This is also when the cam is on the bottom of the lobe, and you will have the maximum gap between the lifter and the valve stem.

Just check the gap and cold the intake should be 0.010" and the exhaust should be 0.012". Then rotate the crank shaft by half a revolution and look for the next cylinder with both valves closed... and do the same adjustment.

As a bit of foreshadowing... the cylinders will follow 1-2-4-3 in the order.

Good luck!

[Dave Neptune]

Indicator balloon use

Ted, when the balloon "starts" to expand you are on the compression stroke. As soon as the balloon starts to expand stop turning. Now look to the flywheel so you can see the "pin" in the center. When this pin ti "vertical" you are ready to check the adjustment. Rotate the engine another 90* and you are ready for the next cylinders valves. Repeat this for all 4 cylinders and you have turned the engine 2 full revolutions.

If you error on adjusting error to the loose side of the adjustment not tight.

If the balloon does not inflate we will need to look to the valves for TDC so they can be adjusted.

Dave Neptune