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1940 Allis Chalmers B With Knock And Miss

7K views 30 replies 9 participants last post by  GTTinkerer 
#1 ·
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
 
#5 ·
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.
 
#9 ·
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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#11 · (Edited by Moderator)
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
 
#12 ·
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.
 
#13 · (Edited by Moderator)
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.
 
#15 ·
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
 
#18 · (Edited by Moderator)
Part of the timing process requires the engine to be turned over by hand to bring the #1 piston to be TDC and the mag to fire the plug. Since I don't have the hand crank I drill and tapped a piece of 23/4" rod, ran in a 3/8" bolt and cut off the ends to fit.

I screwed the compression tester into the #1 plug hole to show when I am getting compression which should mean the #1 piston is on the compression stroke and the #1 spark plug will be firing very soon. Problem now is the compression gauge is showing 30PSI when I turn the engine over slowly by hand every engine rotation instead of every other rotation. So now it seems like it could be several things including bent push rod, worn cam lobe, push rod popped out of the rocker arm and ????. At least now the timing will be adjustable in both directions instead of bottomed out on the advanced side.

So off comes the muffler and the hood. Gonna have to change the signature line.

Bill
 
#19 · (Edited by Moderator)
I believe I found the source of the knock. The #1 exhaust push rod was off its seat and I believe it was causing the cylinder pressure to build up high enough every two or three cycles to either self ignite like a diesel or fire off the spark plug. One of the photos shows the the valve "adjustment" on the #1 intake valve. slightly out of spec. The clearance is supposed to be .010" hot so I will set it at .012" cold and then warm it up and readjust.

Still going to have to look at the valve lift to check the cam lobes.

Bill
 

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#22 ·
Turned out that the nut that is supposed to mount the rocker shaft to the head came loose allowing the shaft to raise up enough to cause this problem. The other end was loose also but the two bolted down mounts between them were both still tight. Cleaned them off with some carb cleaner, put on a couple of drops of red Loctite and torqued them down to 15 foot pounds. Set the valves to .010" cold, put the magneto back in, timed it while the engine was warming up, checked the valve clearance again and it was close enough on all eight not to readjust.

Started it and ran it for about 20 minutes and it ran out of gas, put in a couple gallons of the recreational gas and tried to restart. No &%I%^* spark. Boy I haste magnetos, give me a set of points and condenser along with an external coil and distributor any day.

And I still have to rebuild the carb since it won't idle below 800 rpm.

Remove the red if you want.

Thanks,
Bill
 

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#24 · (Edited by Moderator)
Points were a little corroded and I cleaned them up with some 220 grit crocus cloth. Sprayed them off with electric contact cleaner, then ran a clean business card through them and dried them out with air when I had the mag off the first time. Guess I will do it again.

New point set is almost $50 on ebay. Anyone have any other sources for parts?

Thanks,
Bill
 
#27 ·
I found the problem on the no fire side. There is a small spring that carries the fire from the coil to "distributor cap", there is also a brass rod and some other stuff.. The spring is about the size of the one in the old click type ink pens for those old enough to remember them. The spring in this one broke in the middle and just collapsed on itself. The hardware store in town is closed for the owner's daughter's wedding so I have to wait until tomorrow morning to see if they have something close.

Hopefully I can get it running tomorrow so I can pull the carburetor to let it soak in some muratic acid. The carb kit is supposed to be here Monday morning.

Thanks,
Bill
 
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