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Allis Chalmers Discussion Forum
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Allis B timing and Rough Running

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Nicholas Stanle

05-03-2005 19:48:49




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Hello all, I've got a 1946 B with FMJ mag and electric start. It has ALWAYS missed under no load at idle and even at higher throttle, so I retimed the mag and the mag to the tractor. I set the timing statically first using th e"FIRE" marks, and was unsure of this so I checked it dynamically with a light, it was DEAD ON! I also checked that the impulse was tripping at TDC, which it is. Now, this tractor has had valve and rings done, and the carb has been apart and rebuilt twice about 4 years ago, as was the mag. Even with the timing at the factory setting it still misses when not under load, UNLESS I retard the time about 15-20 degrees, at which point it purs like a kitten, but it is hard to start because the impulse coupling is retarding the timing TOO FAR! Did the mag tractors do this when new??? What am I doing wrong? BTW- Intake gaskets are not leaking as far as I can tell with the ether test.Thanks
-Nick Stanley

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Chuck in Tejas

05-03-2005 23:21:46




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 Re: Allis B timing and Rough Running in reply to Nicholas Stanley, 05-03-2005 19:48:49  
first off,be REAL careful using ether around a hot manifold...i suggest a non environmentally friendly carb cleaner like Super Tech from wally world or Berryman's...theyre not as likely to BBQ ya.

hows the compression? sounds like you mite have a valve adjusted too tight or if the motor was completely apart during the ring job its possibly a tooth off on the timing gears [crankshaft/cam sprockets]

point gap or maybe a bent eccentric on mag could cause probs you describe too...check point gap on all 4 lobes and make sure theyre even.

thats all i can think of right now...good luck

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Nicholas Stanley

05-04-2005 06:50:34




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 Re: Allis B timing and Rough Running in reply to Chuck in Tejas, 05-03-2005 23:21:46  
It is not compression, as it seems fine to me. I doubt that it is valve clearances either, because I set the valves while hot to factory specs be my self, so I know they were correct, and it also did the same things before the rebuild. The timing of the valves or camshaft geartrain should not be off, because I did not mess with the geartrain or camshaft, crankshaft, at all, although it could have been fudged before we bought it. Should I check the other 3 cylinders with the timing light too, all I did was the No. 1 cylinder. Also, how can I check my valve timing without removing the front cover?
BTW- The I&T Shop Manual must be INCORRECT with the timing view hole, it clearly says that on the B's and C's the timing hole is on the bottom of the clutch housing, while my rig runs (though not well) when timing through the hole in the side of the housing. I can't imagine it would run if the timing was 90 degrees off?!? And if it is off 90, they could not have adjusted it that far by just turning the mag? They must have move the governor gear several teeth? How do I check that? Thanks.
-Nick Stanley

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Dick L

05-04-2005 13:23:34




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 Re: Allis B timing and Rough Running in reply to Nicholas Stanley, 05-04-2005 06:50:34  
I would re look at my I&T manual. My manual calls out the hole on the left side. This hole is located between the two 5/8" implement mounting holes on the side of the bell housing. It is just hard to tell what is going on with your tractor with out being there. Even though most will say to use the fire mark on the flywheel, I have always used the TDC line when replacing a magneto. I always use a timing light after starting the engine and most of the time the FIRE line is within a Nat"s hair from dead center thru the hole on the left side.
I will put a link to some pictures that might help. Pictures 19,20,21,and 22. With your mag off and the TDC line in the center of the hole, The drive groove that your mag mounts into should be horizontal. If you find your tractor set up like this, the timing inside the engine will be alright. It will line up that way even if you are off 180 degrees. Make you (reset/replace) the magneto on the tractor with the compression stroke for number one cylinder.

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steve(ill)

05-04-2005 20:02:52




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 Re: Allis B timing and Rough Running in reply to Dick L, 05-04-2005 13:23:34  
Dick is the expert here. i also install the mag with #1 TDC. impulse will advance to the FIRE after running. Maybe your impulse is bad if you got FIRE at static and dynamic?---- you can install 180 degrees out, but NO, motor will not run on the exhaust stroke, only the compression, so you are not off 90 or 180.



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Chuck in Tejas

05-05-2005 07:48:37




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 180* out 101... in reply to steve(ill), 05-04-2005 20:02:52  
Steve...if you dance the wires to the opposite towers on cap it WILL run perfectly if the mag is 180* out...that applies to crank/cam timing also.



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Chuck in Tejas

05-04-2005 09:38:25




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 Re: Allis B timing and Rough Running in reply to Nicholas Stanley, 05-04-2005 06:50:34  
let me clarify i dont know much about AC tractors...i been turnin wrenches professionally for the last 40 years tho and i'm basing diagnosis on knowledge of 4 cycle engines.

as far as i know you cant check crankshaft/camshaft timing without removing the timing cover unless theres a sight hole that no engine i've worked on has had...low compression readings would indicate timing off among other things...its also possible for it to run if timing is off 90* very well...one tooth off will make it run like you describe tho.

dont bother using timing light on all 4 cylinders...they will all show same readings.

humor me and do a wet and dry compression check and post readings.

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Chuck in Tejas

05-04-2005 14:24:21




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 ooooops...meant 180* in reply to Chuck in Tejas, 05-04-2005 09:38:25  
on timing



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