1940 John Deere B Timing+

Well, since I have searched the internet long enough without getting the answers I need, I figured it was time to try asking someone here. I'm hoping there is a big enough 2 cylinder fan club on here so I can get somewhere with my 1940 B (s/n# 95050). this is my first "gasser" restoration. I've done a handful of diesels, and after this B, I might just keep it that way. but I must say, parts are waaayyyy cheaper for B's compared to my 820. But, anyways, I found 2 B's sitting in the weeds, bought them figuring i could get them running and make a few bucks. Pretty sure I'll be lucky to break even after this one. Cylinder block had a major hole in it so i machined a plug and brazed it shut, then had it honed. The block has new valves, and has been surfaced, put the stock pistons back in with new rings. I went through the carb and completely revamped it with Steiner's deluxe carb kit. bought a new magneto, and put a new radiator core in it. ever want to pull your hair out, try resealing the cooling system on that thing... I have another question pertaining to that topic too, but firstly, this whole timing issue is making me want to part this thing out and give up.

So, for the real question, who knows which timing cup my B needs and where the impulse mark needs to be at inside the Magneto? bought a refurbished WICO C Magneto off eBay. has a short lug 25 degree drive cup on it(says 25 degree with the part #6274 i believe), but there is no part number on the old one(also a short lug), and I'm wondering if it is a 35. when I timed the mag and got it running it did run, but not great, it sputtered and missed. But did not backfire to the best of my recollection. Watched a lot of "justtinkering" on YouTube. afterwards it was suggested that I rotate my governor gear one tooth backwards, or clockwise. tractor did run better, but still not great, went another tooth and it couldn't get it to start. went back to one tooth and fired up to run half way decent. while it was running, I twisted the mag clockwise(top of mag towards front of tractor) and it seemed to run slightly better yet. this has led me to believe that i have the wrong drive cup on my Magneto. When starting it currently, it doesn't take much to get it fired up, about 4 pulls on the flywheel. Does anyone have any better insights? Love testing out ideas and fixing it all myself, but I'm starting to get tired of getting nowhere.

First things first, when you timed the mag, was the mag impulse tripping when the LH Impulse mark on the flywheel was aligned with the timing mark on the crankcase? If so, then it should be timed right and you might be chasing ghosts trying to get the tractor to run better by messing around with the timing.

You say you put in one of Steiner's premium carb kits, but did you clean out the passageways with aircraft drill bits? These are notorious for fouling with rust and they need to be drilled out by hand with the appropriate drill bit. If these are plugged or fouled you can fiddle with timing until doomsday and it will never run right.

Yup, I timed the mag correctly, may have gotten shocked a time or 2 doing it, but its right. and also yes, I bought the drill bits to clean all the ports. I ran into issues there too where it wanted to run for the first 5 seconds an then it died. carb is not the issue and the mag isn't 180 off. once i try to rev it up, it definitely comes to life, just not smoothly. Im trying to get it to run smoothly enough to get it to idle nice and low at like 150-175 rpms.

I had a D that ran like that and it turned out to be a bad condenser in the magneto. Worth a look

By rotating the mag clockwise it retarded the timing. I would be checking the
condenser & get the timing back where it belongs. I think the short lug were 25 & the
long lug were 35.?

Just curious but you said you got a short lug magneto? The
39 and 40 Bs all used long lug mags like the unstyled
tractors. That may be the issue too.

Best I recall the 6274 drive cup was a 25 Degree. AFTER about 250 RPM when the impulse drops out RUN
timing depends on the drive cup (like your 25),,,,,,the points gap,,,,,,,,,and the mags rotation in the
governor housing,,,,,,Forward CW retards, backwards CCW advances.

I have used a timing light and on the open flywheel tractors made marks at 0, 20 and 30 BTDC to time them
based on governors rotation. For gas (unlike dual fuel when on Distillate drip fuel or kerosene) I think
25 BTDC is plenty fast enough.

In addition to timing of course the points and condensor as well as the carb affects smooth running

John T

Ok, so I'll try to reply to everyone here in one post...
Mark- I can look into the condenser to see if that might be an issue, but i just bought that mag completely rebuilt and it was labeled "hot" which I was just assuming it meant it had a hot spark. I do find it highly unlikely that the condenser is bad being brand new, but it very well could be a possibility and I will check it out after I find out how to do so. thanks for the tip!
Teddy- if I put the governor gear back it will run worse, but if what's wrong that I think is wrong, I will definitely have to put it back. Were all short lugs 25 and all long lugs 35? i think this is my problem.
JD39B- That's what I was wondering, it does run with the short lug in it, but the old mag I pulled out was a short lug too, but that's not to say that it was the original either. how deep are the cog holes on the governor gear side to fit the long lugs? I think your on to something. I was wondering what years had which lugs and which mags as well.
John- Your correct on the 6274 cup with the 25 degree. I checked mine and it has both the degree and number stamped on the cup. I know it might be a long shot to get it to idle that low, but why not give it a try. I turned the governor gear CW 1 tooth, so that would retard it, and then CW on the mag to retard it even more right? I did see someone use a timing light on the Tube, I might have to find and borrow one of these timing lights to see exactly where its firing at. I do remember seeing the formula on that "Justtinkering" guys YouTube video on how to mark the degrees. I most likely will be trying this idea out as well. As long as I find a timing light... thanks for all the insights so far fella's!

This post was edited by armbru37 on 02/25/2023 at 06:06 pm.

My 40B had an original mag in it and that was an AP.
Since parts were no longer available for that style mag I
changed to a Wico X which is a more reliable unit. Tom in
Mn

John- Your correct on the 6274 cup with the 25 degree. I checked mine and it has both the degree and
number stamped on the cup. I know it might be a long shot to get it to idle that low, but why not give it
a try. I turned the governor gear CW 1 tooth, so that would retard it, and then CW on the mag to retard it
even more right? I did see someone use a timing light on the Tube, I might have to find and borrow one of
these timing lights to see exactly where its firing at. I do remember seeing the formula on that
Justtinkering guys YouTube video on how to mark the degrees. I most likely will be trying this idea out
as well. As long as I find a timing light... thanks for all the insights so far fella's!

IFFFFFF the flywheels on the correct crank spline and iffffffffffffff the cam to crank,,,,, and cam to
Governor are allllllllllllll in correct time, when the Flywheels LHI Left Hand Impulse mark is at 3 o
clock in line with a mark on side of tractor (thats TDC of left piston),,,,,,,,,the female horizontal
drive slot in governor shaft end (where mag mates) should be flat horizontal fore n aft. Then rotate the
mag in housing forward CW to retard or backwards CCW to advance and with a 25 cup running she should fire
No 1 around 25 BTDC. Then if the lag angle is set correct she should fire at TDC when slow
cranking/starting when the impulse assembly is working

For a good slow idle the carb needs absolutely correct also

John T

PS If I recall correctly the mags impulse assembly stops functioning around 250 RPM ???? NO Warranty and
its NOT good to idle so slow it has to keep winding up and tripping over and over which can happen if idle
is too slow. If theres any air leaks in the carb such as throttle shaft bushings it leans out at idle. I
couldnt get any of my B's to idle as slow and sweet an A or G, if it idles at say just over 250 RPM thats
decent in my opinion. If you get run timing in the 20 to 30 BTDC thats prob good enough for good idle and
performance. Here are a few pics of my carb n mag on my 1938

John T

Knowing now that the goal is an exceptionally low and smooth idle speed, I'm going to say something that is not a mechanical fact, but is true nonetheless. I can get my '44 A running really pretty sweet, but when I take to the show at Rollag, sometimes driving it the 35 miles there and back, along with running it pretty much all day for 4 days, when I finally get home, that tractor is running far, far better than it did when I left with no changes made to it at all. I can idle it down to a speed that that would have killed it before, not so slow that it runs on the mag's impulse, but pretty darn close.

Which is to say, that sometimes all the tinkering in the world cannot do as much for how one of these engines runs, than just taking it out and running the snot out of it for a few days.

There is something advantageous in running a good volume of clean fuel through all the passages at varying loads. It certainly can't hurt to remove deposits, debris, and moisture.

Getting the whole assembly to a good operating temperature not only aids that function, but assures the clearances of rings, expanded pistons, rod caps and wrist pins, and the valve train are at optimal points.

Extended running can also help to exercise the mechanical parts of a mag/distributor, but also helps reform the oxide layer in the condenser. That's maybe a bit more important than some might understand, since capacitors don't do well if they sit dormant for extended periods without voltage applied. If one has lost capacitance it not only stresses the points, but also slows the collapse of the magnetic field in the coil primary, thereby reducing the secondary output voltage. That's usually not a good thing.

These things were built to work and move, not sit and shine.

''capacitors don't do well if they sit dormant for extended periods without voltage applied''

That is TRUE for ''electrolytic capacitors'', but I don't think it applies to the tinfoil and wax paper caps used in old mags and distributors.

Moisture creeping in is their biggest cause of failure, IMHO.

Thank you John for the info and pictures, I figured 175 was a long shot, and I definitely don't want to wreck the mag, so I can settle for 250, that would still be nice, as long as I can get it to do so smoothly. I have located a timing light and hopefully I can get to that part of the testing process soon. Getting pounded with snow, so I haven't had much time to do anything other than plow snow and work this week though, so I'm shooting for this weekend, as long as we don't get another foot like their calling for...
NoDakInMN and Watthour- I couldn't agree more! I know after I give any of my diesels a "healthy" workout with either plowing all day or a good run on our dyno, they run smoother, slower, and better than before. My brother and I have neve had any intention to buy our 2 cylinders to let them collect dust sitting in the shed, we thoroughly enjoy getting them out and giving them a workout. John Deere never made tractors to sit and look pretty their whole lives, they were ment to be used!!
so, this leads me to another question, What mag should be on my B? a C or an X? is there an "era correct" mag? does it really matter?

(quoted from post at 21:11:35 02/28/23) What mag should be on my B? a C or an X? is there an "era correct" mag? does it really matter?

Click to expand...

In my world it doesn't matter one bit. But maybe the correct police have other ideas.

So, I was looking on Steiners website, and its showing me that the long lugged drive cup goes in B s/n 0-89999 and the short lug goes in s/n 90000 and up. (mine is 95050). So, if so facto, I should technically have the right lug, unless I have an all fuel?(I will be looking up to see what I have. I am definitely a rookie at identifying B types and models) Or possibly Steiner has the s/n wrong. the correct number break for most of the parts on the B's is after 96000. I did see the lug depth on the long lug, so I do plan on checking to see if it will fit in the governor housing side cogs after I check the timing. And, maybe I wont have to after I check the timing. It may be off in the wrong direction possibly? Just some thinking and looking that I've been doing. Not sure if im on the right track here or if I need to just spend the money and try it. Just don't want to waste every last dime I've got on trying to make this thing run right.

Has nothing to do with the correct police. It has everything
to do with the correct serial number break when the short
lug replaced the long lug. If the long lug governor is needed
a short lug mag will slip and cause erratic running. In my
experience the break is at 96000 was the change between
the short and long lug. According to the parts book the last
long lug was used at 95999.

I said in a response earlier that I have a 40B and it came
with an AP477 mag in it which was the factory mag for it.
AP477 are obsolete and parts are no longer available so I
installed a Wico X 477 which is the correct replacement.
Tom in Mn