#1 Cylinder TDC Simple Question **Updated**

[ctltmp]

One simple question. When #1 piston is on compression stroke TDC should it be at the top of the stroke or already traveling down in the bore?

Thank you

[Bill Hudson]

TDC = Top Dead Center. At that point the piston is neither travelling up or down, at that brief instant it is stopped.

Bill

[ctltmp]

Thank you Bill. Exact answer I thought I would get.

Therefore, my tractor's TDC is timed to the first notch on the pulley rather than the second since at the second notch the piston is already traveling nearly 1/4" into the bore.

[Bob McCarty]

The first notch is 16* before TDC (BTDC). The second notch is TDC.

Bob

[ctltmp]

Well, had to move the governor a tooth but up and running. Now moving on to fixing the slop in the governor/rockshaft key. Pretty hard to tune much with all that play.

[brewzalot]

At that point the piston is neither travelling up or down, at that brief instant it is stopped

This can be seen/found very accurately with a dial indicator with a long wire tip bent at an angle placed through the spark plug hole on top of the piston.

[ctltmp]

Now hold the horses. Thats what I have been trying to explain to everyone. If you can use a dial indicator to find the top of the stroke as tdc second mark isn't tdc in my case.

Although everything says the second pulley mark is tdc, when I align to that mark the piston has already passed the top its the stroke and is traveling substantially down in the cylinder.

When I align to the first mark the piston is at the top of its stroke. The tractor starts and runs when timed to either mark.

On engines I was taught when you have no reference come up to compression stick a screwdriver in the hole and feel until the piston is at the top. If that rule applies and I think it does the second pulley mark is not tdc on this engine.

[Eugene]

When you worked on the engine did you remove the pulley mounted on the front of the crankshaft?

Possible that during a previous engine overhaul the pulley was incorrectly installed.

[ctltmp]

Eugene,
I did not remove the pulley. Someone overhauled it before (has .010 under bearings).I rolled the crankshaft bearings out and in. My suspicious has always been it wasn't assembled right.

Knowing that should I go back to piston at compression tdc top of stroke (this would be first mark in my case) and reset governor? All timing marks align in this position on the idler and governor.

I know this goes against the book but I don't think it was built by the book either.

[brewzalot]

My new pulley came with just one mark... I did the math and filed the second one in. Is it possible that someone did the same with yours but put it on the wrong side of the first one?

[Eugene]

TDC not only refers to the piston being at the top of the stroke but that the crankshaft journal is at 360 degrees, top of the journal arc. The piston will reach it's highest point slightly before the crankshaft journal reaches it's highest point in the arc. The piston will remain at it's highest point until the crankshaft journal passes the 360 degree point and starts it downward movement.

Couple of ways to accurately determine TDC. Dial indicator, roll engine over until piston is at assumed TDC. Mark pulley. Roll engine over backward until same point is reached on dial indicator, mark pulley. TDC will be exactly half way between both marks.

Since this is a magneto. I would try to accurately determine the TDC mark on the pulley. Then set the governor for timing the magneto.

I don't know if you can do this, never tried. The key way in the crankshaft for installing the pulley is at 360 degrees, crankshaft TDC. Flashlight and mirror, you may be able to see the key way location.

Whole bunch of assumptions. If the idler pulley was correctly installed, the timing marks for the governor should show up centered in the governor installation hole at TDC. Might take two full crankshaft revolutions to find the timing marks.

And an edit: The I&T manuals have a method of determining TDC by measuring the valve to tappet clearance. Haven't tried this method, just read about it years ago.

[ctltmp]

Eugene,
Pricipals you described understood. With pulley on first mark timing marks on idler are centered in the casting hole and line up 2 & 10 exactly. Matter of fact you and I used a picture of it as an example for another member a couple days ago (you resized it for them). That picture was taken at first mark on pulley #1 compression stroke piston at top of stroke.

[Jim Becker]

My new pulley came with just one mark... I did the math and filed the second one in. Is it possible that someone did the same with yours but put it on the wrong side of the first one?

Based on all the information given, either this happened or the pulley is installed out of position. Either it was installed without a key or the key/keyway is damaged.

If you have determined TDC with certainty, use that location to time with and ignore any misplaced marks. Normally I would not give this suggestion, but you seem certain about your TDC measurement.

[ctltmp]

Thanks guys. This cub has had me at wits end from day one. Never had one problem with the 52 cub I did. I'll establish positive tdc (seems like it's going to be first mark or very close to it).

If it wasn't my wife's grandpaps tractor I believe I'd shove it in the weeds or make one of you guys a heck of a deal on it! Comes complete with 3 plows and a set of cultivators!

[ctltmp]

Well I found "this things" tdc, timed it up and it starts up immediately. Much better than before.

The bad news is when I pulled the governor I found a nice chunk out of the new seal. No idea how it got there. This seal has a double lip. I installed it to the 23/32 depth. Before I put the governor back in I went ahead and set it 1/8 deeper as discussed in other posts. Since the seal has a double lip whats the chance of it not leaking by? That thing was a bugger to get in straight.