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kenbow56 
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Location: Lk. George, CO.
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 Topic: have a ihc h4 magneto in allis chalmers b will thi
Posted: 31 Oct 2022 at 8:09pm |
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Hello, question, I have recently purchased a allis chalmers B tractor year 1938. it has a IHC H4 magneto installed on it. will this work correctly? I was told by prior owner it had recently been rebuilt along with the engine. then sat for last 2 years. It shows signs of having been run since with IHC mag installed, but firing order was not correctly wired up. Firing order on the Allis is 1243 correct? I have checked for spark and it has spark all 4 wires, so I brought engine to tdc on #1 cyl. then checked rotor position it was almost 180 degrees out. I re-positioned wires to go 1243 firing order clockwise. am I correct so far? or have I messed up somewhere I dont realize? have not tried to start it yet as I have carb. off to rebuild it, was flooding over big time. I did try pull starting it when first arrived here, only got occasional pop backfire at that time. thats why I have gone into checking it out more Thourouly now. does this sound like i am on the right track? I have many years experiance with repairs but not with a magneto only ignition. Is the IHC h4 magneto ok (compatible) for use on the Allis Chalmers B my main question here I guess? thanks ahead of time for any and all replies, Ken
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steve(ill)
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Posted: 31 Oct 2022 at 9:02pm |
not an expert on the H4, but any mag with 4 wires built for a Straight 4 motor should work.. The only variation is the ADVANCE timing.. The impulse used in the ALLIS "B" mags is 30 degrees... Some others use 25 degrees or 35 degrees.. It will start and run, but ADVANCE might be different than factory..
You change the wires around as you said, depending on the firing order... And you get it to SNAP or fire the plug at the TDC mark.... Top Dead Center.. After running, the springs/ weights in the impulse will back out and you will FIRE at the FIRE mark or 30 degrees BTDC.. you can check that with a timing light if you want......... again, i dont know what the ADVANCE is on the H4.. it may or may not be 30 degrees.
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Like them all, but love the "B"s.
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steve(ill)
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Posted: 31 Oct 2022 at 9:05pm |
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on the left side of the tractor bell housing, there is a 1 inch hole .. You can look thru there to see the TDC mark ... as you rotate the crank to TDC, you should hear the mag SNAP at that point.... loosen the two mounting bolts and turn a couple degrees in or out to get the SNAP right at TDC.
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Like them all, but love the "B"s.
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kenbow56
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Posted: 31 Oct 2022 at 9:32pm |
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Steve, Thanks man, your reply is very helpful and confidence assuring as to what I am looking at and attempting to diagnose and repair to running, working status, I really like this Lil B model. I see you like them too. Thanks again, Ken
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steve(ill)
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Posted: 31 Oct 2022 at 10:04pm |
Fairbanks Morse was a big manufacture of MAGS.. They posted a page for "replacements" if you wanted to buy one to replace on ANY tractor.. The page below is their alternative for the IH/ Farmall tractors.... Note that the ORIGINAL is H4... and the REPLACMENT is a FMJ which was used by ALLIS... but they changed the IMPULSE to 35 degrees for the IH.... So i would guess you H4 is 35 degrees advance and ALLIS was 30..
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Like them all, but love the "B"s.
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cpg
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Posted: 02 Nov 2022 at 9:07am |
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It should work just fine, I have an H4 that is converted to a 12V distributor on my Allis Chalmers WD that used the same magneto as the B. I just set initial timing with the number one plug on the magneto cap firing with the first cylinder at TDC on the compression stroke (set by pulling spark plug and using feeler to set piston to TDC). Then once it is running there is some adjustment forward and backward to tune in the timing to how the engine runs best.
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Boss Man
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Posted: 02 Nov 2022 at 4:01pm |
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Not sure but seems to me some mags turn backwards. If I'm looking at Steves chart right some of the H4's turned clockwise some counterclockwise. You may have screwed up the firing order. Roll the motor over with the cap off to verify if the mag turns clockwise or counterclockwise
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steve(ill)
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Posted: 02 Nov 2022 at 5:31pm |
I think any mag put on the tractor will turn the same direction.. The problem is the IMPULSE has been setup with an anchor bolt to WIND UP and SNAP at TDC... If you turn the mag the wrong way, it should not WIND UP and SNAP.
So if you put a CW mag on a CCW tractor, the mag will still turn CCW... but never engage the impulse and SNAP..
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Like them all, but love the "B"s.
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Steve in NJ
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Posted: 02 Nov 2022 at 6:10pm |
The FMJ and the FMX Mags are CW with a 30 degree lag. The H4 is also a CW Mag with 35 degree lag. Change the H4 to 30 degree lag, and you can set it up the same as a J X or K series Mag in a AC Tractor. Should work fine. Keep in mind, not all AC Tractors are CW. The 20-35 is CCW with a 35 degree lag, and the Model A is CCW with a 30 degree lag if memory serves me correctly..
Steve@B&B
Edited by Steve in NJ - 02 Nov 2022 at 6:12pm
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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TramwayGuy
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Posted: 02 Nov 2022 at 6:56pm |
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When you said the rotor was 180 degrees out, it could be because your TDC was on the wrong stroke!
Try moving them back to where they were.
Edited by TramwayGuy - 02 Nov 2022 at 6:58pm
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steve(ill)
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Posted: 02 Nov 2022 at 7:54pm |
ken, i have an old spark plug that i have broken the ceramic out of it and soldered a 1/4 inch copper tube in place of that, sticking out 3 inches... I have a rubber hose 3 ft long that slides over the copper tube.. i put the other end in my mouth (!!!) When i crank the engine with the hand crank, i can feel the air when it comes up on compression stroke..
if your hand crank is not BENT, you should have the handle "about" Horizontal when you are at TDC, and hear the mag SNAP.
Edited by steve(ill) - 02 Nov 2022 at 7:56pm
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Like them all, but love the "B"s.
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kenbow56
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Posted: 02 Nov 2022 at 8:02pm |
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CPG- Yes I did that made sure it was on compression stroke not exaust stroke. Rotor turning clockwise. Thanks for your comment.
Edited by kenbow56 - 02 Nov 2022 at 8:03pm
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kenbow56
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Posted: 02 Nov 2022 at 8:38pm |
Steve Ill , your hard core man !!! that one with the hose on plug makeup made me bust out laughing. Your advice and comments were all helpful and good. Today I got it running, Mag was out 180 set for exaust stroke on the #1 cyl. Plug wires were mis-connected. Carb flooding issue fixed, was washer under needle seat leaking, got to make sure needle seat is tight to carb. body, (Details Man!) Inspected needle viton tip with magnifying glass, looked good no ring around it from seat . Bottle fed carb. on bench- knocked it around tilted up and down, alas no more flooding. all back together and voila! pull started it today, pop pop pop, running lil B. Engine recently rebuilt high compression for hand cranking. I tried but couldn't hand crank it. When trying to it just popped backwards and I could not get it to rotate past compression by hand. got it running adjusted timing, adjusted idle mixture screw and main jet needle adjustment. I had prior to today pulled valve cover and checked that all valves were opening and closing and also set clearance to .012 cold since I couldn't at the time set hot. you think i should recheck them when engine is hot ? or close enough with cold setting? ran it around today put a couple miles on it. Yes I already checked all gearboxes and lubed it up. Clutch T.O. brng. as well. A little goof on me. sitting on a hill here in Colorado, had my son push me a bit so i could pop clutch and get it running.... tried 3rd gear.... whoa nellie....... it started right off,,,, trees around me on hill.... Hand brakes funny I never had anything with hand brakes before, whewww it goes fast in 3rd at half throttle, wheres the brakes my foots trying to apply..... rushing past and weaving through trees. boucncing about. holy crap..... !!!!! well missed all trees thank the Lord for being with me. Will try 2nd from now on. with timing light now, should I set it for right on TDC or advance it for best starting? , I reckon the 25-35 degrees advance mentioned above, in Magneto is centrifugal-right? I am at an elevation here of 8500 ft. we always advance spark on automobiles to 18-20 degrees up here at idle speed. Thank You all for your replies and comments here. most helpful to me being ignorant on the magneto, IHC versus FM ect... Yes a IHC H4 mag will work on the Allis B when all is set correctly. I will post a picture when I figure out the hyperlink thing. I am 66 I didn't grow up on a PC. we had 3 channels on tv, no video games and played outside, making up our own adventures. From the High Country in Colorado. Thanks again to all, Great Group here , Ken
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steve(ill)
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Posted: 02 Nov 2022 at 8:54pm |
CONGRATS !!! .......... I have never used a timing light to check the FIRE mark.. I just set static at TDC and go with that.. If your mag is 35 degree, then you will not see it on the FIRE mark unless you move the STATIC to 5 degrees AFTER TDC.... I would leave it alone.
The timing is not an ADVANCE system like a car... The IMPULSE is a spring and weight that actually CATCH on a pin and RETARD the timing 30 degrees so you see it and hear the SNAP at TDC.. Once the engine hits a couple hundred RPM, the weights fly out and take the IMPULSE out of the system and the mag fires at the FIRE mark at all rpms.
Edited by steve(ill) - 02 Nov 2022 at 8:54pm
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Like them all, but love the "B"s.
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steve(ill)
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Posted: 02 Nov 2022 at 8:56pm |
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Ii dont redo the valves when hot either... Just set them COLD and go for it..
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Like them all, but love the "B"s.
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Les Kerf
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Posted: 03 Nov 2022 at 6:53am |
 steve(ill) wrote:
ken, i have an old spark plug that i have broken the ceramic out of it and soldered a 1/4 inch copper tube in place of that, sticking out 3 inches... I have a rubber hose 3 ft long that slides over the copper tube.. i put the other end in my mouth (!!!) When i crank the engine with the hand crank, i can feel the air when it comes up on compression stroke...
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I do something similar but I use a toy balloon to indicate TDC; the balloon will inflate, then begin to deflate as the piston passes TDC on the compression stroke. By rocking the crankshaft back-and-forth past TDC you can get quite close to actual TDC. Definitely close enough to set the initial timing to get an engine started.
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