John Deere MC

[BIGNASTY]

Running a cylinder leak down what is an expectable % to assume that head gasket, Valves, Rings are in decent shape?

Thanks Big

 

[Bill Stockard]

Are you referring to a John Deere Model MC crawler tractor? If you are... WOW! that's an antique!

Bill

 

[BIGNASTY]

Ya that's it Bill only not as clean as that one pictured. Its dent free but the paint is dull and it needs some TLC.

My Aunt recently passed away and when Penny & I were back settling her affairs I noticed it sitting in a shed barn on a farm on the way to my Families Property left to us. I stopped and talked to the owner he had parked it and bought a new Row Crop JD tractor and basically just parked the Crawler.

In North Platte Nebraska everyone knows everyone, we went to breakfast in town and at the café the owner said that he had thought about it and decided to sell it. We put a fresh battery in it took out the spark plugs (this is a gas crawler not diesel) put some oil down in the cylinders and it spun over easily so that was good enough for me.

I've since got it home have ordered the carb rebuild kit and some other parts for a tune up basically, just haven't found the time to get after this project. I've been sort of occupied with some rehab and getting ready for Winter precludes pretty much EVERYTHING.

I was just wondering about a cylinder leak down test and what constitutes a Good To Go Motor, I need to get it running and change all the fluids. The tracts are like new from what I've seen on other Crawlers but have been told, Above all take the tracks apart and clean and lube EVERYTHING they don't make to many parts for them and if you should break things it most generally involves someone making the part.

 

[Bill Stockard]

You can do a lot of work with it if you are patient. It isn't a D8...

Bill

 

[fest3er]

Some quick math. Suppose it turns 1200 RPM, rated. That's 20 rev./sec., or 50msec/rev., or 25msec/stroke. It'd still run well enough if you lost 10% of total cylinder pressure in the last half of the compress stroke and the the first half of the power stroke (25ms total).

Going on some very old, very fuzzy memories, if you lose 10% of total pressure in one second, you probably want to do the rings and valves. Or if, cranking by starter, you only reach 90% of expected PSI, freshen the engine. Some of those old engines will run for years with one end of the head torqued finger tight and a couple broken valve springs.

As long as the engine starts easy, sounds smooth, feels smooth, gives acceptable torque, the top end sounds quiet, and a borescope reveals nothing alarming in the cylinders, the motor's good to go for moderate duty.

In human terms, you aren't good to go full bore 18 hours a day any more. That old motor likely isn't either. At ½ duty, it might just run another 20 years as-is.

If you're taking the tracks apart to clean and lube, you should consider a lube that resists pound-out. Amsoil makes a good one.

 

[fest3er]

Some quick math. Suppose it turns 1200 RPM, rated. That's 20 rev./sec., or 50msec/rev., or 25msec/stroke. It'd still run well enough if you lost 10% of total cylinder pressure in the last half of the compress stroke and the the first half of the power stroke (25ms total).

Going on some very old, very fuzzy memories, if you lose 10% of total pressure in one second, you probably want to do the rings and valves. Or if, cranking by starter, you only reach 90% of expected PSI, freshen the engine. Some of those old engines will run for years with one end of the head torqued finger tight and a couple broken valve springs.

As long as the engine starts easy, sounds smooth, feels smooth, gives acceptable torque, the top end sounds quiet, and a borescope reveals nothing alarming in the cylinders, the motor's good to go for moderate duty.

In human terms, you aren't good to go full bore 18 hours a day any more. That old motor likely isn't either. At ½ duty, it might just run another 20 years as-is.

If you're taking the tracks apart to clean and lube, you should consider a lube that resists pound-out. Amsoil makes a good one.

 

[fest3er]

Or if you want seat-of-the-pants tests:

• hand-crank each cylinder to TDC-compression. If you hear leakage (faint high frequency: slow leak, louder mid-frequency: rapid leak), fix the head.
• Tie a balloon/condom/latex glove onto the crankcase vent. Set the blade against an immovable object and push. If the balloon inflates moderately or rapidly, fix the cylinders.

 

[Blu-meanie]

Or if you want seat-of-the-pants tests:

• 
  [*]Tie a balloon/condom/latex glove onto the crankcase vent. Set the blade against an immovable object and push. If the balloon inflates moderately or rapidly, fix the cylinders.
  

Now that's a great idea. Could have used that in the "old" days when cars had crankcase vents.

 

[BIGNASTY]

Not sure if it will EVER WORK on our place. I had initially bought it to drag dead fall and felled trees so we can grind the sumps and create more usable pasture land. The more I see it and tinker on it (when I can) I think that its going to be enough to clean it up and Gramps and his Grandsons just move some dirt around once in a while. To many old things are cast aside for new, I'd just like to keep a few things older than I am running.

Thanks for the thoughts

BIG

 

[DonFitzwater]

FYI- any engine that has been sitting for an extended period with out running will give false leak down readings. They will almost always show high leak down. Also, adding oil to the cylinders will create a false reading as well. The best thing you could do is to get it running and then do a leak down test.

 

[AnOldBiker]

May I ask why not the old style wet / dry compression test ? It wil show how close each cylinder is to each other and if one is way off, it will somewhat indicate how much work is needed. This was what was done on the old cars, since this is a gas tractor, why not here ?