Finding TDC

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Baxter28
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Tractors Owned: 1953 F-Cub Serial No. 160499JL

Finding TDC

Postby Baxter28 » Wed Jun 21, 2017 10:41 pm

I tried finding TDC by putting my finger over the #1 sparkplug hole but no luck feeling the compression. I even tried putting motor oil on top of the piston for a better seal. So I made a bubbler using a cork, a 3' piece of small diameter plastic tubing, and a pint mason jar half full of water. Very easy to tell when #1 piston is on the compression stroke.

I also removed the governor so I need to get it back in time. The manual shows removing the distributor drive to observe the distributor drive lug. Why can't I just mark the #1 terminal location on the distributor housing, remove the cap, and make sure the rotor is in the correct position when the governor is installed?

Jackman
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Re: Finding TDC

Postby Jackman » Thu Jun 22, 2017 6:31 am

I believe you can do it that way, another way is just line up the dampner timing mark with the pointer and you'll be either TDC or 180 out on the wrong stroke.
, you should have compression so maybe something else is going on too

staninlowerAL
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Re: Finding TDC

Postby staninlowerAL » Thu Jun 22, 2017 6:34 am

Possible stuck open or not properly seated valve on #1 piston.

Eugene
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Re: Finding TDC

Postby Eugene » Thu Jun 22, 2017 7:12 am

Baxter28 wrote:Why can't I just mark the #1 terminal location on the distributor housing, remove the cap, and make sure the rotor is in the correct position when the governor is installed?
That will work. Once the governor is installed you will probably have to time the distributor to the engine then static time the ignition.

Suggest conducting compression tests before proceding much further.
I have an excuse. CRS.

ParlowMillFarm
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Re: Finding TDC

Postby ParlowMillFarm » Thu Jun 22, 2017 12:48 pm

Hey Baxter28,

I had the same problem. Timing check lead to a compression check - and no compression.

First check for a stuck valve by removing the valve cover. If you are lucky this will be the problem. (you will probably need a new valve cover gasket)

If not a stuck valve, do dry and wet compression tests. Taken together they will indicate whether it's a valve or ring problem. (although others will have to tell you which as I can't remember)

John

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Re: Finding TDC

Postby Urbish » Thu Jun 22, 2017 2:00 pm

Big change in compression between wet and dry indicates rings. Little change indicates valves.
Jim

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Ohiowoodchuck
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Re: Finding TDC

Postby Ohiowoodchuck » Thu Jun 22, 2017 3:42 pm

A easy way I have found is to tighten down the intake about 5-6 full turns after taking out the slack and roll the motor over clockwise slowly until you feel it touch the valve. I then put a mark on the balancer where the pointer is. I then roll it over in a counter clockwise direction until I feel it touch and put a mark there. Half way between those two marks is true top dead center. don't forget to readjust your lash. As long as you go easy you won't hurt a thing.

Jim Becker
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Re: Finding TDC

Postby Jim Becker » Thu Jun 22, 2017 4:38 pm

Ohiowoodchuck wrote:A easy way I have found is to tighten down the intake about 5-6 full turns after taking out the slack and roll the motor over clockwise slowly until you feel it touch the valve. . . .

Are you talking about the piston touching the valve? If so, never going to happen on an L-head engine like the Cub. Cub pulleys should all have a notch for TDC so all that shouldn't be necessary anyway.

I believe this whole discussion has revolved around the question of telling the difference between #1 TDC and #4 TDC. If you go to all the trouble of pulling the valve cover, you can tell which it is by just looking at the valves. Turn the engine until the notch is at the pointer. If valves 1, 2, 3, and 5 are closed, you are on #1. If valves 4, 6, 7, and 8 are closed, you are on #4.

Ohiowoodchuck
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Re: Finding TDC

Postby Ohiowoodchuck » Thu Jun 22, 2017 6:59 pm

Jim Becker wrote:
Ohiowoodchuck wrote:A easy way I have found is to tighten down the intake about 5-6 full turns after taking out the slack and roll the motor over clockwise slowly until you feel it touch the valve. . . .

Are you talking about the piston touching the valve? If so, never going to happen on an L-head engine like the Cub. Cub pulleys should all have a notch for TDC so all that shouldn't be necessary anyway.

I believe this whole discussion has revolved around the question of telling the difference between #1 TDC and #4 TDC. If you go to all the trouble of pulling the valve cover, you can tell which it is by just looking at the valves. Turn the engine until the notch is at the pointer. If valves 1, 2, 3, and 5 are closed, you are on #1. If valves 4, 6, 7, and 8 are closed, you are on #4.

You are correct. My apologies, I was thinking of a overhead valve engine.

Baxter28
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Tractors Owned: 1953 F-Cub Serial No. 160499JL

Re: Finding TDC

Postby Baxter28 » Fri Jun 23, 2017 11:31 am

I reinstalled the governor and the tractor fired right up. The only things left to do is the adjust the valves, check the timing, and set the idle and max RPMs.

Baxter28
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Tractors Owned: 1953 F-Cub Serial No. 160499JL

Re: Finding TDC

Postby Baxter28 » Tue Jun 27, 2017 6:03 am

Finally got to adjust the valves on my F-Cub. Whoever was in here before used gobs, literally, of gasket sealer instead of using a new gasket. There were gobs of sealant laying in the lifter galley. In addition, all the valves were adjusted to .010". Everything I have seen says to adjust to .015".

Why would somebody set all the valves to .010"? More power?

Scrivet
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Re: Finding TDC

Postby Scrivet » Wed Jun 28, 2017 7:26 am

Baxter28 wrote:..........Why would somebody set all the valves to .010"? .......
Because he is living in the dark ages and has never heard of farmallcub.com and that's what their brother in law's friend, who knows a guy, that lives down the road from a guy that restores old tractors, and really knows his stuff, said it should be. :D :lol:

Could be a thousand reasons actually. At this point set em right, clean off the gobs of sealer, put on a new gasket and give it a pat on the hood and say there that's better isn't it? Smile a little smug smile to yourself and then brace yourself for the next unorthodox repair you're going to find.

Ohiowoodchuck
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Re: Finding TDC

Postby Ohiowoodchuck » Wed Jun 28, 2017 8:47 pm

People do it to add lift to the cam or take it away. Adding lift would get a little more air same as subtracting lift or bigger clearance. Take a little air out of the motor. I know a lot of the old school drag racers done this to fine tune a engine as they call it.

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Ken (48 Cub)
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Re: Finding TDC

Postby Ken (48 Cub) » Thu Jun 29, 2017 9:00 am

Hey Scrivet...I know THAT guy :)
Ken, Annie the '48 Cub & Marie the '57 Loboy.

I think we gotter if'n she don't kick, Andy Griffith.


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