Dear Ole Mechanic;

I have a 1935 Allis-Chalmers crawler with a six-cylinder gas engine and electric starter.  I was turning it over trying to get it started after it had been sitting unused for a very long time, and the engine locked up.  I removed the starter and plugs which didn’t help.  Any idea what’s going on?

Old Crawler Guy 

Dear Old Crawler;AC Model L Crawler

Since I am not all that familiar with the pre WW II Allis line, the 6-cylinder engine just didn’t sound quite right, so I did my homework.  Sure enough, the Allis-Chalmers Model L crawler had a big 844 cubic inch displacement 6 cylinder engine.  It needed a big engine because the crawler weighted over 22,000 pounds.

My first thought was that someone forgot to put a tin can over the exhaust, and the engine had become a big cast iron rain gauge.  With water in a cylinder you would get a hydraulic lock up when the piston came up on compression.  But you have already taken care of that by removing the spark plugs.  While a piston could have jammed into rust in a cylinder, you said that you had the engine turning over, so that is not a likely problem.  In case a water pump bearing came apart and jammed up, don’t forget to loosen the fan belt to make sure th water pump is not binding things up.

The next thing I would check for is to see if a mouse nest got sucked into a cylinder from the intake manifold as the engine turned over.  Those little critters build nests in the most unlikely places.  While a mouse’s nest is usually made of soft shredded material, a big nest could put enough material into a cylinder that it would prevent the piston from reaching top dead center and would lock things up.  The key thing here is that you should be able to turn the engine backwards.  Also, by carefully looking in the spark plug holes you should be able to see the material in the cylinder.  I am not sure how much room there is in the combustion chamber so a stuck open valve could be hitting the piston and keeping it from turning over.  But once again you should be able to turn the engine backwards.  You could also see a stuck valve problem by removing the rocker cover.  Correcting the nest problem or the stuck valve problem may require the removal of the cylinder head or heads.  I say heads (plural) because some of the older engines had heads cast in pairs and there would be three heads on a six-cylinder engine.  Before removing the head(s), I would strongly recommend getting a shop service repair manual and do some reading to see just what you are getting into.  I know that removing the head retaining nuts on some older engines would allow the crankshaft main bearing cap to drop into the bottom of the oil pan, as the bolts ran all the way through the engine from top to bottom.

Still stuck?  I have seen a big rat’s nest in the flywheel area get caught in the starter gear teeth and jam things up.  While less likely. the same thing could happen in the crankshaft to camshaft gears or in the crankshaft to governor/magneto gears.  How something big enough to jam up the crankshaft in the crankcase would get in crankcase I have no idea, but I have seen stranger things in my lifetime.  If none of the above are causing the problem, then it is time to get way down in the dirty bottom end.  You will need to check for a broken crankshaft or camshaft.  Also check for spun insert-bearings or bearing Babbitt material that has come loose and jammed things up.  And last, but not least, check for a locked up pilot bearing between the crankshaft and the transmission input shaft.

I know that I have covered a lot of hard work in a short column, but working on the old tractors and implements is a labor of love for some of us. 

Holler if you need help.

Herr Professor Nuzanbolts