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1940 Allis Chalmers B With Knock And Miss


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#1 GTTinkerer OFFLINE  

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Posted July 13, 2012 - 06:39 AM

I picked up a 1940 Allis Chambers B tractor yesterday to repair a hard starting problem. When loading it on the trailer it was "knocking" and missing and the owner said it had been doing that for quite awhile. When I got it home I drove it off the trailer and put it in the shop.

This morning I started pulling the spark plug wires to find where the miss was. When I pulled off the front spark plug wire there was no change in rpm and the knock went away, put it back on and the knock came back. Pulled the rest of the wires one at a time and rpm dropped as it should. Changed the front spark plug and replaced it twice with new plugs and no change was found.

I figure it has either a stuck or burnt valve but wanted to get opinions before I tore it apart.

I made a short video and put it on You Tube.



Thanks in advance,
Bill

#2 MH81 ONLINE  

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Posted July 13, 2012 - 07:02 AM

Check your cap and rotor first, if there's so much junk in there that it's pre/post firing...

Do you have a compression tester handy?

Edit: oh, and cam lobes, check them too.
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#3 jms180 ONLINE  

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Posted July 13, 2012 - 07:10 AM

I agree check the compression of all 4 cylinders and compare
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#4 MH81 ONLINE  

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Posted July 13, 2012 - 07:23 AM

I just watched that in a bigger screen, is that seepage at the head gasket above the carb or is it just a reflection?

#5 JD DANNELS OFFLINE  

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Posted July 13, 2012 - 08:14 AM

I don't have audio on my computer at work. But I would wonder based on your description if there is a bad rod bearing on that cylinder? That's a nice looking B and definately worth fixing. Parts are easy to come by and they are not complicated or hard to work on. They make a great Mower matched up with a 5" Woods mower.
And would do well in a large garden. Back in 1969 between High School and Colledge I worked at a small town factory Midwest Manufacturing in Kellog Iowa,(They made the One Minute Washing Machines and back when Service Stations washed windows their machines were on every island) as a custodian and yard maintenence man. That was a Typical Company town, I did chores around the grounds and picked up alll the trash at the executives homes. I had a C to use for pulling a wagon to remove trash around the grounds, and a B with Woods Mower to mow the 5 acre park around the "Clubhouse" where the Company had parties.
The Allis Chalmers have always had a special place in my heart.
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#6 timtractor OFFLINE  

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Posted July 13, 2012 - 08:16 AM

If you think it could be the spark plug wire move the wire to a different cylinder to see if the problems moves also.
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#7 SimplicitySwede OFFLINE  

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Posted July 13, 2012 - 08:35 AM

Ive had bad luck with champion spark plugs in my Farmalls. If it's getting ran low on oil it can foul a plug. It's a weird knock like more of a click sounds could be camera. I'm just. Saying the simple things. Most the time a knock is vEry serious.

Edited by SimplicitySwede, July 13, 2012 - 08:36 AM.


#8 GTTinkerer OFFLINE  

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Posted July 13, 2012 - 09:52 AM

I just watched that in a bigger screen, is that seepage at the head gasket above the carb or is it just a reflection?


It looks like it is coming from the tappet cover gasket not the head

Thanks,
Bill

#9 GTTinkerer OFFLINE  

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Posted July 13, 2012 - 10:01 AM

Definitely does not sound like a rod or main and I don't think it is happening every time the plug is firing but it is pretty evenly spaced between the knocks. The engine was running at about 800 rpm and there was not 400 knocks a minute.

Had to go out to my SIL to get the compression gauge so back to the shop to finish the TB tiller carb rebuild so I can pull the tractor back in.

This being retired stuff sucks.

Bill
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#10 JDBrian OFFLINE  

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Posted July 13, 2012 - 10:03 AM

I would eliminate ignition problems for that cylinder first before going to other causes. You may have a weak spark on that cylinder only.
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#11 GTTinkerer OFFLINE  

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Posted July 13, 2012 - 01:14 PM

Did a compression check and #1 was 115, #2 was 110, #3 was 110 and #4 was 115. Moved the plug wires around and same dead cylinder. Moved spark plugs around no help. #1 plug is pretty carboned up. Starts just like it should but #1 still popping and no RPM change when the wire is pulled

Opened the spark plug gap to about 3/16" and good blue spark jumped the gap. Going to pull the mag cap and see if maybe there is some moisture in there later since the outside temp is 90* and inside the shop about 110*.

Downloaded the service manual that achomesteader uploaded and it will help a bunch. Turned out the manual was for the B series lawn and garden tractors.

Thanks for the replies.
Bill

Edited by GTTinkerer, July 13, 2012 - 02:30 PM.


#12 olcowhand ONLINE  

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Posted July 13, 2012 - 02:29 PM

That's weird Bill. Definitely goes completely away when you pull the wire. Compression fine, good spark.....maybe it is something in the mag cap. Could be it's jumping from the other cylinder's terminal, firing it at the wrong time, causing the knock much like pre-ignition.
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#13 Cvans ONLINE  

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Posted July 13, 2012 - 05:32 PM

Just from the sounds of the video I'm thinking that #1 cylinder is tying to fire too soon. It almost sounds like the engine is trying to kick back a little bit when that cylinder is firing. The odd part is that it sounds like it is knocking on every other firing cycle of that cylinder. Rod would knock under load and a piston under no load.
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#14 MH81 ONLINE  

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Posted July 13, 2012 - 05:43 PM

Bill, mark where the timing is now, then retard it 5 degrees. See if it changes. I'm wondering if it got advanced and it's showing up on number one first.
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#15 GTTinkerer OFFLINE  

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Posted July 13, 2012 - 05:51 PM

I found a web site that goes into timing the engine and when I checked it with a timing light I found that it could not be adjusted because it was right up against the bottom locking bolt. So I pulled it off and will clean and adjust the points ad set the timing by the information on the web site. I still am not sure it isn't in the valve train but first things first.

The tractor has been sitting for a couple of years and the owner rebuilt the card about the time he stopped using it. It does have fresh 91 octane gasoline without the ethanol in it. I told the owner when I agreed to do the job that I was doing this part time but he was here before noon checking to see when it would be done.

Thanks,
Bill




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