Allis B quitting after 10 minutes

I finally got to my 47 Allis B after it sat for the winter. I needed to replace a spindle on my Woods belly mower so it sat since putting it away last fall. I only use it for mowing. In the spring I noticed it froze the radiator so I pulled it to see if I could have it repaired. It was too far gone so I put in a new Chinese version. I also noticed the thermostat housing cracked and replaced that and the thermostat. I did put in a new water pump last season so this all should take care of the entire cooling system. She started up as usual and I mowed for 10-15 minutes when the rpms dropped, she knocked a bit, then quit. I was just outside the yard so I was going to get my truck to pull it back in and got distracted so she sat for 45 minutes or more. When I went back to it, she started right up so I got her back in the yard and mowed around close for awhile. After 15 minutes or so she did the same thing, almost sounding like it was locking up. I did look at the temps and oil pressure this time and temps never made it to the normal range so it didn"t overheat. My oil pressure was right where it has been for years. I recently changed it and it is clear and clean. You can read through it. I spoke with my tractor repair man who said he never heard of this happening because once it starts knocking, like a bearing spun, I should lose oil pressure ad the knock should still be there on start up, which it is not. It doesn"t come back for 10-15 minutes of mowing after a cool down. He said it could be a coil in the mag getting hot. I should add that it is still 6 volts and has a magneto. Would that cause a knock? What happened? Where should I begin?

First check to see if you have spark. Condensers can go bad when hot.

Second check for good gas flow. Take of the line going to the carb and run it into a pail for 5 minutes, you should have a good flow. Sometimes crud in the bottom of the gas tank restricts gas flow.

Oil pressure is not made at the bearings on this engine. The bearings can all be shot and still have full pressure. The relief valve is in the stem of the oil pump leading to the center of the camshaft. No pressure is built in the camshaft. The cam bearings and main bearings are oiled by the spinning of the cam shaft forcing the oil out holes in the camshaft but centrifugal force. The oil pipe you see leading to the filter and head is where the pressure is built between the relief valve and the resistance thru the oil filter. The spinning of the crankshaft causes the little funnels in the top of the rods to catch oil being spun out to the camshaft holes that are in line with the rods. The oil is forced into the rod bearings thru centrifugal force.
That be the oil systems operation in this engine.



The red wire is thru the oil path from the cam bearings to the main bearings and thru the cam shaft.

but if the bearings were all shot causing the knock, wouldn't that be there all the time?

OK. I'll try the gas first. I don't want to take the mag apart just yet. Not sure how to check a condenser but it may be time for new points and condenser anyhow. Thanks. I'll let you know what I find.

I was not trying to diagnose your problem just explaining that you can not tell if a bearing if bad by the oil pressure on this type of engine.
You have to remove the pan, inspect the bearings and measure the bearings as well as the crankshaft. With x-ray vision not being possible you are left with guessing which both fall into the same category when trying to diagnosing engine noise problems verses engine running problems.

thank you both for the info. I pulled the gas line at the carb and blew air back through the sediment bowl. Cleaned the bowl, ran gas without the bowl into a gallon jug. Filled it half way in less than two minutes. Then put the bowl back on and ran gas through the pipe and caught it just in front of the carb. The only sediment I found was already in the bowl. After putting it back together and adding some sea foam to the gas, I mowed for 90 minutes and turned it off. It did not repeat my problem. Whether or not it is fixed will be determined later. Thank you.

I have used it three times since trying the gas solution. All three times were uneventful. Hard to imagine a simple gas restriction could have caused the symptoms I had but in all three cases I used it for at least 90 minutes without quitting. While it did take more than one pass, I was mowing grass as high as the top of the radiator. Thanks again for your suggestions.