Finding TDC the easy way
 

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?

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.

Neil-
IF you decide to mass produce...
can we have a variety of color choices on the balloons? :p

Yes, you may . . .

I'm ALL IN!

Very cool. Only thing I can add is that on this site you will either "learn" or get "entertained".

And that is why they call it enterlearnment!
:D

You must also consider the oxygen permability of the rubber as to the accuracy of the device. More or less rubber thickness may distort the results.









:-)

Yes I'm kidding.

TDC
 

If a Vee drive prevents a visual of TDC there is a notch in the Accessory Drive that tells TDC too-

I hope that forum members will appreciate the engineering complexities at work with Neil's device.

1. The size of the balloon at various inflated pressures/volumes. A weather balloon won't work.
2. The elasticity of the balloon. A stainless steel balloon won't work.
3. The influence of color. Beyond my bachelor's degree in engineering.
4. The influence of atmospheric pressure. Ditto.
5. The influence of oxygen permeability, as pointed out by Spike. Way beyond.

All this stuff makes my head hurt, but kudos once again to Neil.

Bill

On your last two considerations:

4. There is zero atmospheric influence on the indicator short of being in a perfect vacuum. It reads only the pressure delta above ambient created by the moving piston in a closed cylinder.

5. Nitrogen permeability would be a 4X greater concern considering the chemical composition of air.

for durability we would probably need to develop a balloon resistance test to Marvel Mistery Oil vapors too!

Since the air in the balloon has come thru the carb, it just might be flammable. Gives me all sorts of thoughts...

Probably shouldn't go there
 

Al, Have you ever heard of an acetylene bomb?
Tom

Tom, my dad made acetylene balloons for parties. Only he knew which ones were which on the patio. Mom would get mad so he'd blow one up near her and the laughs would start.

I did some torch silver soldering for a while. we had coffee cans on the bench with water for keeping our "prods" clean of flux. If someone was bothering me I would fill a can upside-down and when they'd come back to annoy me I'd wave the torch past a hole. After the second time I moved the fluorescent lights a foot or so.:o Lots of can dents over my bench!

Dave Neptune :cool:

Dave, I was pretty sure that you would have played with them.
Tom

Tom, I just could not resist :p.

Dave Neptune :cool:

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

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.

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.

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.

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."

TDC demonstration by the Master

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

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 :cool:

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.

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