Finding TDC of compression stroke when no help available

Duanes · Aug 12, 2011

I"m timing a magneto on a Farmall Regular and need to find TDC of the compression stroke. Problem is I have no one available to crank tractor while I place my thumb over spark plug hole to feel compression. What is another way to determine the compression stroke?
Thanks!

old · Aug 12, 2011

First off can you see the piston with the spark plug out?? If you can then pull the valve cover and watch for the piston to be up top. When it is up top and the valves are both closed your at TDC

Duanes · Aug 12, 2011

I can't see the piston but, I assume I can put a long straw in there or wire? Long enough not to drop in of course.
Valves are closed when I can spin them by the stem correct?

Anonymous-0 · Aug 12, 2011

Set your timing mark to TDC on the pointer. At this point, you're either on TDC, or 180 distributor degrees/360 crankshaft degrees out. Then remove the valve cover and see if the valves on #1 are open or closed. If they're open, you're 180 out; if not, you've found TDC.

JRSutton · Aug 12, 2011

Another way is to get a cheap compression guage. You can watch the compression build when it's on the compression stroke. If you go slow, you can even get a pretty good estimate on TDC by watching for the moment that the compression reverses. Go back and forth a bit and you can zero right in on it.

Get a guage with a long hose to the spark plug hole and you should be able to position the guage where you can read it while hand cranking.

By the way, if you can spin your valve stems I'm thinking you either need to adjust your valve lash because they're not seating properly - or you have very very weak springs. But that's a different issue.

JRSutton · Aug 12, 2011

Sorry, I just re-thought your question on the valve stems - perhaps you meant the lift rods? Yes, those you can spin when the vale is closed.

old · Aug 12, 2011

Can not spin the valves but can the push rods. You should also be able to rock the rocker arms so as o see if both more freely just enough to be able to feel the gap that should be there. Yes a straw like a soda straw will work be I would slip it in feel for the piston then pull it out and turn it a bit more and recheck not leave it in

Anonymous-0 · Aug 12, 2011

I have a hand crank Farmall H and I have the same problem of having short arms. On the H I put the belt pulley in gear and turn the engine with a socket bad on one of the pulley bolts. MJ

Janicholson · Aug 12, 2011

A piece of vinyl hose or small garden hose stuck in the spark plug hole, and put into a quart jar of water will bubble easily on compression, when bubbles stop, look at the timing marks, should be very close! don't suck water out of the jar!! Jim

Anonymous-0 · Aug 12, 2011

I pull all the spark plugs then put a plug back in #1 a couple of turns. One, it makes the engine turn over really easy, two, when it comes up on compression on #1 it will make a noise when the compression leaks past the loose spark plug. Then you know you are close and you can look for the timing marks.

Duanes · Aug 12, 2011

I meant push rods. Thanks Old and everyone else for the help!

F-Dean · Aug 12, 2011

On a Regular, you can take the cover off the front "Crankcase Viewing Hole" and and see the crank and rod. This should allow you to get very close to TDC.

teddy52food · Aug 12, 2011

The valves on #4 will be closed too, between ex and in. at TDC.

Super-H-Mike · Aug 12, 2011

I once worked with a guy who had soldered or brazed an old time metal whistle onto a hollowed out spark plug just for this very purpose, I thought it was pretty clever !

sflem849 · Aug 12, 2011

You can hear them push the air pretty easily. I like the comment about putting it at the timing mark and checking the valves as well. It is pretty tough to find the timing marks with all the dirt and grime many times. It is really a PITA when it is in a hole on the flywheel.

Tom Fleming · Aug 12, 2011

Get a 18" - 24" piece of flexible hose that has an outside diameter of 7/8". Put it in #1 plug hole and keep the other end up front by you.

OR

buy a case of beer. Offer to friends. You will have plenty of help!

OR if you are under 21

Tell your friends that the high school cheer leading squad is coming over to see your new tractor and take pics for the yearbook.

any of these will produce good results!

davediehl@hotmail.com · Aug 12, 2011

I took the lower cover off my H so I could rotate the engine by hand while my finger was in the plug hole. I also took a wire brush to the crank pulley so I could see the marks.
Someone had posted a link to a video that helped a bunch.
Timing

rustred · Aug 12, 2011

with valve cover of, watch the valves on #6 cyl.WHICH IS THE RUNNING MATE when they are on the rock you are on TDC.on #1 cyl. no need to even remove plugs.
ROCK means one valve is closing other one is opening.

rustred · Aug 12, 2011

thats for a six cyl. running mates for inline engines is the last cyl.
if firing order is 153624 then spit it like this 153
624, 1 and 6
5 and 2
3 and 4 are running mates.

Rumplestiltskin · Aug 13, 2011

That's a great idea! Or how about some flexible tubing with the spark plug threads on one end and a balloon on the other?

Mark W. in MI

Janicholson · Aug 13, 2011

But on either Compression, or Exhaust, the cam position might be tough to assess. Jim

Finding TDC of compression stroke when no help available

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