Dies under load

Sun Aug 10, 2014 9:44 am

Title says it all. Sorry for such a long post.

Starts, idles, revs, no missing hesitation. Drives fine in 1st gear on the flats. Try to climb a slight hill or engage the PTO and it dies. Fails the 3rd gear test miserably. Things I've tried:

1. Fuel. Drained the fuel tank, cleaned the sediment bowl, put in fresh gas. Disconnected fuel at carb. Constant flow of clean fuel. Disassembled the carb, very clean inside. Sprayed carb cleaner inside jet, ran a wire through, couldn't find any dirt or debris. Bought the carb from TM 5 years ago. I've given up on a fuel problem because, idling in neutral, when you rev up the rpms, and hold it there, no hesitation, stumbling.
2. Ignition. This was my first thought. I don't drive the Cub much in the winter. Primarily in the summer to mow. Over winter, I noticed I had left the Pertronix ignition on. I thought I may have burned it up but, after charging the battery started right up. Now, that I'm down on power, I re-checked. Found a plug wire was loose in the distributor cap which arced pretty bad. That wire read a little high on resistance. Replaced plug wires. Spark plugs were carboned up pretty bad. Replaced with a hotter plug, Champion D21. Checked spark with a Lisle tester. All 4 cylinders jumped a 0.25" gap. Looked like everything was good but, went ahead and put in a new coil. $25 couldn't hurt. No change. Hooked up a timing light. Idled nice at 500-600 rpm but, not at the 400 rpm required for the first mark on the crank pulley. So, I held it at 1600 rpm and eyeballed it for the second mark (my replacement pulley only has 1 mark). Tweaked it a little but, no change in performance.
3. Governor. Don't know much about these but, followed the manual and adjusted the high idle. No change.
4. Compression test. This is where things got really strange. Pulled the air inlet tube. Opened the choke. Set to full throttle. Pulled all 4 plugs. First ran a test with a battery that was tired after all the stalling and re-starting. Numbers were way low (35psi). Read John's compression post about cranking speed so, I repeated the test with a fresh battery. Dry (#1 - 50psi, #2 - 45psi, #3 - 42 psi, #4 - 45psi) Wet (#4 - 45 psi). That seemed low so, I ran a leakdown test. Per Brian's suggestion started at 20psi input. 0 leakage. Increased to 80psi. Again, 0 leakage. All 4 cylinders the same. Listened for air escaping the valves, crankcase, exhaust. Nothing heard. I've leak tested a lot of motors. I've never seen 0 leakage. A fresh rebuild usually leaks 3-10%. A tired motor will leak a lot more.
5. Exhaust. My brother suggest I check for a clogged muffler. Removed the muffler temporarily. No change.

Here's a clip of me starting and letting it run.

I'm completely stumped. I can't live without my Cub. It doesn't rain much in the desert but, during our Monsoon season it rains a lot. Grass will grow to your waist in no time. I mow about 1/2 acre of my 2 acres. What takes the Cub 1.5 hours took me 6 hours with a weedeater on wheels.

Any ideas on what to check next??

Re: Dies under load

Sun Aug 10, 2014 11:14 am

Engine overhaul time. Compression test numbers are very low. Lack of sufficient torque.

Leak down test conducted after the compression wet test?

Re: Dies under load

Sun Aug 10, 2014 11:50 am

Like Eugene says - no compression = no power.

Here's your link https://www.youtube.com/watch?v=NINoV9-V_S4

Re: Dies under load

Sun Aug 10, 2014 1:08 pm

At this point an engine overhaul may be relatively inexpensive. May only need to clean up the cylinders, rering pistons, lap the valves, new rod and main bearing inserts.

Re: Dies under load

Mon Aug 11, 2014 6:57 am

Eugene wrote:Engine overhaul time. Compression test numbers are very low. Lack of sufficient torque.
Yeah, I was afraid of that.

Eugene wrote:Leak down test conducted after the compression wet test?
No, I did the leakdown before the wet compression check. Only did a wet compression check on #4. Puzzles me that the leakdown doesn't show any problems. I expected air to escape somewhere so, I would know what's wrong.

Re: Dies under load

Tue Aug 12, 2014 2:11 pm

45-50 PSI? It must be VERY difficult to start. Usually they won't start at that level unless you drag it at a very high speed or use a lot of starting fluid.

No leakdown... Something's weird here. You sure those compression checks were accurate?

Re: Dies under load

Tue Aug 12, 2014 2:16 pm

Since the dry numbers and the one wet number that you listed are so close together, have you checked the valve tappets for clearance?

Re: Dies under load

Tue Aug 12, 2014 2:51 pm

Compression tester - accurate? Try the compression tests again with a different tester.

Re: Dies under load

Wed Aug 20, 2014 6:42 pm

Eugene wrote:Compression tester - accurate? Try the compression tests again with a different tester.

Once again, this forum helped me solve my problem. I can’t thank you enough. My Cub is back and ready for action. I stumbled across the solution while, re-running my compression and leak down tests. This is a long story so, please bear with me.

After some internet searching on my zero leak down results, I found I did my leak down test with the wrong hose. My leak down tester hose only has the 14mm fitting so, I decided to use the compression tester hose with the 18mm fitting. I didn’t realize the compression tester hose has a Schrader valve in it to hold the pressure in the gauge. For a leak down test, you need an open hose. I removed the Schrader valve and re-ran my test. This time, I had leakage and could hear it escaping out of the crankcase (worn rings). I wrote down all my numbers and proceeded to the compression check. I ran a dry compression test on all 4 cylinders and then began to run a wet compression test. When I got to cylinder number 3, the slowly cranking engine sped up considerably. Whoa. That’s interesting. Then the light bulb went off. My engine is much happier when it gets a little lubrication in the cylinders. Uh Oh. That oil pressure gauge that has never been reliable and is currently reading 0 might be correct after all. I removed the oil pressure gauge, regulated my compressor down to 20 psi, and shot air into the gauge. The gauge reads 20 psi. Wow. The gauge is fine. I really do have no oil pressure. This isn’t good.

I searched the archives on this forum and found a post about priming the oil pump. Pictures and everything. http://www.farmallcub.com/phpBB2/viewtopic.php?f=1&t=82740#p661995 I pulled the cover off my oil filter and there’s my brand new oil filter dry as a bone. I pumped oil in the casting hole until oil came out as shown in the post. Turned it over. It sucked up all the oil. Filled the hole again. Turned it over and it’s gushing oil out of the hole. Put the oil filter cover on and fired the engine up. Good strong oil pressure on the gauge.
Last winter, I drained the oil the last day I used it and put in new oil and new filter. All I can think is the oil pump somehow drained itself over winter. The Cub seems to run fine, now. I just hope I didn’t hurt it too bad in my 2 to 3 hours of testing, tuning, etc.