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1942 farmall h problem

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Andy(PA)

05-23-2005 06:40:33




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Tractor missing/no power - low compression 3 cylinders at 83lbs one at 60 had head rebuilt by machine shop ie new valves seats etc, new head gasket- corrected low compression. Adjusted valves (before and after head rebuild), replaced distributor cap, points, condenser, plug wires, plugs. Cleaned carb good fuel supply. All this has not changed initial problem. Had freind come over to help trouble shoot and thought maybe manifold has internal crack allowing exhaust gases/intake to be intermittantly mixing causing problem. Anyone have any methods for testing this or had problem occur?

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EricB

05-25-2005 06:22:06




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 Re: 1942 farmall h problem in reply to Andy(PA), 05-23-2005 06:40:33  
If you are running only 83-83-83-60 and have just rebuilt the head I would look seriously at the rings and sleeves.
Have you done a wet dry compression test. ie: checked compression normally then put a 1/2 oz of oil in each cylinder and tested again. If there is a difference then your rings are in question. The oil seals off any small gap along the wall long enough to get a reading. If there is no change I would check the head gasket and speak to the guys that rebuilt your head.

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captaink

05-24-2005 08:18:01




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 Re: 1942 farmall h problem in reply to Andy(PA), 05-23-2005 06:40:33  
It seems to me that there is a vacuum port on the manifold just above the carburetor flange. If there is, get a vacuum gauge, take out the plug and attach the vacuum guage. You should have a steady needle at idle at about 21 inches of vacuum. If it is lower, but steady you have a vacuum leak in the manifold that is affecting all cylinders equally possibly worn piston rings.

If the needle fluctuates somewhat (like between 16 and 23 inches) you have a leak that is affecting cylinders differently like a leaky exhaust valve letting exhaust back into the cylinder on the intake stroke or a leaking intake gasket on one cylinder. If the gauge fluctuates wildly, then you have exhaust getting back into the intake somewhere or have extremely burnt valves.

Vacuum gauge readings can tell a lot, I don’t remember all the things off the top of my head but if you really understand how an engine functions a lot of the diagnosis can be figured out with some thought.

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Hermit

05-23-2005 17:43:00




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 Re: 1942 farmall h problem in reply to Andy(PA), 05-23-2005 06:40:33  
To check if you have an internal manifold leak - Disconnect coil wire so engine won't accidentally start then rotate engine till any cylinder has exhaust valve full open. Remove spark plug from this cylinder and install an adapter which a low pressure air source (compressor) can be connected. Turn on air and cover exhaust pipe. Then listen inside the intake manifold for a leak. A small hose placed up to the ear and the hose moved into various locations inside the manifold will help. Basically, you're pressurizing the exhaust manifold and listening for a leak on the intake side. If you put too much pressure in the cylinder, watch out because the piston will move and rotate the engine. However, as others have said, this type of leak is a rare occurance.

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Janicholson

05-23-2005 07:46:43




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 Re: 1942 farmall h problem in reply to Andy(PA), 05-23-2005 06:40:33  
Step 1} If the miss is irratic, and at all RPM there are two prime suspects one is the manifold leak problem noted in your post, the other quite common issue is with distributor shaft bushing wear. Pull the cap and firmly move the rotor up. down---away and towards block---and diagonally. if it is at all able to be displaced by watching closely with your eye, the dwell variation caused by this slop will change timing and ign. performance enough to cause the symptoms.
I believe a crack between the exhaust side and intake would lead to extreme back firing any leak small enough to limit the flow of exhaust such that sparks and flame were quenched would not likely cause the missing. (my experience, Opinions may vary, I have not heard of this in an H.) to check for vacuume leaks at the manifold, use an un lit propane torch set at a flow that would produce a medium flame if lit, and pass the nozzle around the intake manifold to block area, and carb to manifold joint. If miss goes away, and engine speed increases, you found the leak. Step 2} Put a tachometer on the engine (tach Dwell meter will work). Using a pair of plug wire pliers to limit your personal interception of high voltage, pull plug wires one at a time then replace each (only one off at a time), and note the RPM drop on each cylinder in turn. The throttle may need to be a bit higher than Idle. This will point to a particular cyl.
Sorry the post is long the issue is not easy.
JimN janicholson@stcloudstate.edu

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RustyFarmall

05-23-2005 07:15:37




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 Re: 1942 farmall h problem in reply to Andy(PA), 05-23-2005 06:40:33  
I suppose it is possible that manifold could cracked internally but I've never seen it happen. Are you sure the points are gapped correctly? Is the ignition timing correct? If the timing is way off, either too slow or too fast, you will experience similar symptoms. Are the adjustments on the carb correct? If the load adjustment on the carb is set too lean the engine will miss, but usually this happens only under load. Last thought, are the pushrods bent? Is a lobe worn down on the camshaft?

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Andy Trudeau

05-23-2005 07:49:57




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 Re: 1942 farmall h problem in reply to RustyFarmall, 05-23-2005 07:15:37  
Sounds like the trouble shooting I have already done - had friend go back over everything just to make sure ie point gap, valve adjustment, messed with timing (even move distrubutor gears around just to advance and retard timing past adjustment - got normal indicators such as servere backfiring etc.) Pushrods straight, messed with carb adjustments (got normal tractor reaction you would expect but did not correct problem). Did not check lobes on cam however getting positive pushrod movement on all cylinders(ran with valve cover off). As a side note intake seems to be getting hot along with carb.

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RustyFarmall

05-23-2005 08:59:57




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 Re: 1942 farmall h problem in reply to Andy Trudeau, 05-23-2005 07:49:57  
Intake seems to be getting hot as well as the carb. This does not sound very good, maybe you do have a defective manifold.



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Janicholson

05-23-2005 08:53:34




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 Re: 1942 farmall h problem in reply to Andy Trudeau, 05-23-2005 07:49:57  
If the symptoms are still there after checking with Propane etc. I believe Id check the fuel. Contaminated fuel will do this. run the tractor from a lawnmower tank direct to carb (be careful of spills, and make sure tank is above carb)
LOL X 2 JimN



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