Valve Timing check, 1948 JD A

[MichaelNiemann]

I'm checking the valve timing on my 1948 JD A. (A tractor I inherited from my father-in-law.) I can't find any timing marks on the crank or cam gear. When I roll the flywheel until the left hand exhaust valve has no lash left, the words "LH Exhaust Open" are a good two inches past the mark on the tractor frame. Could timing be this far out and still run?
I am checking the valve timing because a year or so ago I had to lift the governor to get the mag drive slot horizontal so the impulse would fire on time.
I would appreciate any pointers or advice.

 

[Mike(NEOhio)]

Timing marks for the crank to cam are on the crankcase side of the gears. Crankcase cover off and you can see them. Cam to governor marks are on the outer side. You can see them with the left side cover off the governor. First check your valve clearance with the valve closed. Could be way too much.

 

[MichaelNiemann]

That's what's baffling me. I don't see the marks on the crankcase side of the gears. Can the gears be installed "backwards"?
I'll check the valve lash and see if that solves the question.
Thanks for your reply!

 

[Mike(NEOhio)]

That's what's baffling me. I don't see the marks on the crankcase side of the gears. Can the gears be installed "backwards"?
I'll check the valve lash and see if that solves the question.
Thanks for your reply!

No on the backwards gears. The crankshaft gear is also the thrust surface and the cam gear is a three bolt flange and can only got on one way. Look real close with a good light. The marks may be a stamped V or only what looks like a punch mark. Turn the crank so LH piston it just past TDC, the mark should be at the top. If you can't see a mark on the cam gear give it one full turn and check again.

 

[MichaelNiemann]

Finally found my timing marks. With the cam gear "V" over the crank gear "dimple", the left piston is ~3/4 way from TDC. The flywheel is on, or near, "LH Exhaust. Is this correct?

open".

 

[Mike(NEOhio)]

I'm not sure that's correct.. I never went by the LH EXHAUST OPEN mark. Only used LH IMPULSE to set the ignition timing. If your tappet gap is way big it would affect where the mark lands. Look again on the crank gear for something more definite. As I recall my LH rod was in a different position when the marks lined up.

 

[Mike(NEOhio)]

Opened mine up for you. Mine has a V on the crank gear but I think you have the dot.

 

[MichaelNiemann]

Where was the LH crank throw when your marks were together? TDC or somewhere else?
I checked my LH exhaust valve lash and it was good. I turned past TDC until I couldn't spin the exhaust push rod anymore. The LH Exhaust open mark was ~1/2" past the mark on the side of the tractor. (According to my I&T manual within 1" of the mark on the case is good.) So I think my valve timing is good. I'll start putting everything back together. I want to go through the clutch yet. But then I'll put a timing light on it to see what my running timing is.
Thanks for getting a picture of your gears for me. I appreciate the trouble.

 

[Mike(NEOhio)]

Where was the LH crank throw when your marks were together? TDC or somewhere else?
I checked my LH exhaust valve lash and it was good. I turned past TDC until I couldn't spin the exhaust push rod anymore. The LH Exhaust open mark was ~1/2" past the mark on the side of the tractor. (According to m)y I&T manual within 1" of the mark on the case is good.) So I think my valve timing is good. I'll start putting everything back together. I want to go through the clutch yet. But then I'll put a timing light on it to see what my running timing is.
Thanks for getting a picture of your gears for me. I appreciate the trouble.

It was down and to the rear. Turn the picture 90 degrees clockwise. I'm guessing it was about 8 o'clock or 120-130 degrees past TDC. I think you're good. Make sure your flywheel is in the right position. V marks on it and the crankshaft. Don't bother with the timing light, the centrifugal advance may throw it off. Roll the distributor (or mag) forward, put it at TDC, LH IMPULSE mark lined up, then roll the distributor to the rear until you get a spark and tighten it. You want the mag impulse to trip or points to open just at TDC.

 

[Village Blacksmith]

I might not understand. You say you lifted the governor to get the mag slot to horizontal. What does this have to do with the cam to crank gears?

 

[MichaelNiemann]

Since I had to "retime" the governor to cam gears, it made me suspect of the cam to crank timing. When my dad-in-law first got this tractor it shook like crazy when the engine was running. Whomever worked on it before my dad-in-law had put the clutch back wrong. Made me question the skill/knowledge level of the previous owner.

 

[Mike(NEOhio)]

Since I had to "retime" the governor to cam gears, it made me suspect of the cam to crank timing. When my dad-in-law first got this tractor it shook like crazy when the engine was running. Whomever worked on it before my dad-in-law had put the clutch back wrong. Made me question the skill/knowledge level of the previous owner.

I got to thinking today as I was putting my flywheel back on. Have you checked the marks on the flywheel and crank end? Could be off a tooth. Also, look for a letter/number stamped on the crank and flywheel. Mine is W29, on crank, flywheel and the clutch driver. Don't know for sure but it leads me to believe they were balanced as a unit. My A was my father-in-law's too. He had someone work on it a long time ago and it too was shaking badly. The clutch driver was installed wrong. I fixed it for him and back then I knew almost nothing about Deeres but it was pretty obvious. The dust plate behind the pulley was loose as well so I slid the pulley back to tighten and rewire the bolts.

 

[MichaelNiemann]

I might not understand. You say you lifted the governor to get the mag slot to horizontal. What does this have to do with the cam to crank gears?

At the time, I assumed the crank to cam gears were correct but I needed the governor's mag slot to be horizontal - and it wasn't. So I lifted the governor just enough to disengage it from the cam gear, and move the slot where I wanted it.

 

[560Dennis]

Question, why are the gears teeth only engaged 75 percent of the gear surface, shouldn’t they be like mikes photo?

 

[rustred]

Question, why are the gears teeth only engaged 75 percent of the gear surface, shouldn’t they be like mikes photo?

My same question also ! Saw that right away. What are them teeth worn like that ? I know it’s an old post.

 

[560Dennis]

My same question also ! Saw that right away. What are them teeth worn like that ? I know it’s an old post.

Old post ,new post doesn’t matter , interesting observation , why is it set up like that and wearing like that ?

 

[used red MN]

What are them teeth worn like that ?

The teeth are not worn unusually. Due to the top gear being back and the angle of the camera the lower gear teeth are blocking or shadowing the upper teeth tricking your eyes into thinking there is odd notching off of the top teeth. I tried to mark the edges of the teeth in the attached photo. If you think about it how could only two be worn and the rest aren’t? Yes, they should probably align better than that. And the thread was revived today (2/9/26) by the OP, absolutely nothing wrong with that.

 

[rustred]

Exactly that is why I asked your question , how can only two be worn. And just noted it was an old post and the op probably not even see our questions. Geez no matter what post or ask u always have some sort of comeback, like I’m a dummy.

 

[used red MN]

how can only two be worn.

The teeth are NOT worn! Read what I wrote. I am just trying to explain it nicely. But you think I am jumping on you. I comment/ challenge/ correct others posts as well. Maybe I will have to start sending you a PM when I do so you don’t feel singled out. These are discussions forums, one person gives a comment, suggestion or fix. Others may have a different way or point of view so they interject that into the discussion. The photo fooled your eyes, so I just tried to point out in what way you were seeing it incorrectly.

 

[rustred]

The teeth are NOT worn! Read what I wrote. I am just trying to explain it nicely. But you think I am jumping on you. I comment/ challenge/ correct others posts as well. Maybe I will have to start sending you a PM when I do so you don’t feel singled out. These are discussions forums, one person gives a comment, suggestion or fix. Others may have a different way or point of view so they interject that into the discussion. The photo fooled your eyes, so I just tried to point out in what way you were seeing it incorrectly.

I am not saying there are worn after your explanation ! I said that is why I asked why they are worn that way in my first post. After 560 asked also. That is all. See how texting gets everybody all mixed up.