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Order Farmall Cub Parts Online

HELP!!! CUB PROBLEMS

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Mike Johnson

04-25-2001 06:23:24




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I did a compression test and got these results! #1 cyl - 80 lbs.
#2 cyl - 65 lbs.
#3 cyl - 110 lbs.
#4 cyl - 100 lbs.
What would you recommend doing first, and what do you think is the likely culprit. It does not smoke but has lost a lot of power.




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Red Dave

04-25-2001 11:19:57




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 Re: HELP!!! CUB PROBLEMS in reply to Mike Johnson, 04-25-2001 06:23:24  
I agree with Bill, it seems odd that 2 cylinders are so much lower than the other 2. Valves not seating or a head gasket problem seem like good suspects to me too.



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Mike Johnson

04-25-2001 12:28:51




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 Re: Re: HELP!!! CUB PROBLEMS in reply to Red Dave, 04-25-2001 11:19:57  
Thanks for your help. I will let you know what I come up with.



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Bill {Antique Acres}

04-25-2001 07:14:07




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 Re: HELP!!! CUB PROBLEMS in reply to Mike Johnson, 04-25-2001 06:23:24  
That is a pretty broad array of numbers. It seems odd that 1&2 are that much lower thatn 3&4. It would probably be ok with the numbers you got of 1,3,&4. I would pull the inspection plate off behind the carb and check for a sticking valve. Also when you checked the compression did you do it with the choke off and the throttle wide open? If you see nothing with the valves, I would maybe suspect something with the head gasket around the front to cylinders where the compression is lower. I would maybe check the torque on your head bolts. If that does not help then it is probably time for a rebuild. Are you noticing any water in the oil or the coolant level dropping? Did it loose power all the sudden? The reason I ask is because this happend to me and a head bolt broke and it took a while before it started to leak antifreeze. If you do have to do a rebuild that is a perfect engine to learn on, really simple and easy to do. Also check the vent tube from the front of the block to the air cleaner. Bill {Antique Acres}

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Mike Johnson

04-25-2001 07:27:15




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 Re: Re: HELP!!! CUB PROBLEMS in reply to Bill {Antique Acres}, 04-25-2001 07:14:07  
When I checked the compression, the choke was off, but I don't remember the setting for the throttle. I will check the valves. Do I need to remove the exahaust to check the valves? I did add some antifreeze a couple of weeks ago, but not a whole lot. There is no trace of water in the oil. We use the cub for mowing, and noticed the loss of power last summer, but I am now just getting the opportunity to really get to fixing it. I appreciate your advice. Any more information is welcomed. Thanks.

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Havin Fun in Mo

04-25-2001 16:27:15




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 Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Mike Johnson, 04-25-2001 07:27:15  
The advice that "p" offers below is good. The trick he mentions is a real easy way to determine the cause of a leak. A couple of squirts of oil is enough to fill the gap of worn/weak rings but will not fill the gap of worn/burnt valves. This can be done in a few minutes without having to take any major components off the engine. Be sure to work quickly after inserting the oil and only let the motor crank a rotation or two if possible as the oil will disperse.

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Bill {Antique Acres}

04-25-2001 12:01:35




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 Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Mike Johnson, 04-25-2001 07:27:15  
You do not have to remove the manifold to get the cover off. I also failed to mention that the fuel supply from the tank to the cylinders is extremley important on these Cubs. I would first make sure to find out why those 2 cylinders are so low. After that I would make sure that you have good fuel supply to the carburetor and that the carburetor is good and clean. Your readings should be all within 10 pounds or so from each other. all four at 80 would be on the low side, but it would still run. The last 2 are right up where they should be, but 1 is way off. Check the valve clearences and make sure everything is opening and closing. You could have developed some bad seats in the top of the block also. When you check your readings again make sure you have the throttle wide open and the choke off. Bill {Antique Acres}

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Mike Johnson

04-25-2001 12:31:51




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 Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Bill {Antique Acres}, 04-25-2001 12:01:35  
Thanks Bill.



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p

04-25-2001 08:14:06




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 Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Mike Johnson, 04-25-2001 07:27:15  
when you have the inspection plate off you should also check valve clearances. Any good manual will walk you through the steps and have the tolerances.

If the engine is not smoking and the spark plugs are not developing deposits, then I would suspect the valves are shot. If you have been running unleaded fuel without a lead substitute then you may have destroyed the valve seats. The seats are not hard enough for modern gasoline. If you were running the motor hard the seats will heat up and small amounts of metal will stick to the valve and remove itself from the seat. This will cause pitting on the seats and eventually result in lower compression. I don't think pulling the head and lapping the valves will do enough to clear this up. The block will have to be machined to accept new hardened valve seats. At this point it only makes sense to do a quicky rebuild to ensure proper ring pressures.

I have heard that adding a few squirts of oil to each cylinder before performing a compression test will help diagnose worn rings. I heard that if the pressure increases after the oil is added if proves a bad ring and bore fit. The oil fills the voids left due to imperfections. I have not tried this but it makes sense.

let us know what you find.

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Mike Johnson

04-27-2001 07:42:48




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 Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to p, 04-25-2001 08:14:06  
I removed the head, and the valves appears to be the main problem. They were severely covered with carbon, and were not seating properly. Some of the head bolts were hard to break loose, but a few were too easy, probably explaining why the compression was so off in the first two cylinders. The head is in the machine shop now, to ensure it is in good shape. By replacing the head gasket and installing new valves correctly, this cub should perform much better. It may take a week or so to get it complete due to my honey do list. Thanks for the help.

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Jimmy Brumit Jr.

04-25-2001 10:44:13




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 Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to p, 04-25-2001 08:14:06  
I have a similar loss of power. I have good comp on all cylinders 125lbs but it runs very rough skips and will NOT run off choke. I noticed my spark was red and cleaned the neck of the coil replaced the + wire from the coil to the distributer and reset the points to 20 thousands, and it still will not run right. I have replaced the fuel and filter. I am just before pulling out the rest of my hair. HELP!!

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Red Dave

04-25-2001 11:11:24




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 Re: Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Jimmy Brumit Jr., 04-25-2001 10:44:13  
Jimmy, If it won't run without the choke, it sounds like a carburator or vacuum leak problem. Maybe you could check all over the intake side of the manifold and the carb for leaks. I don't know if dirt in the carb would cause those symptoms, but, it wouldn't hurt to clean it out good and make sure the float level is set right.



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Jimmy

04-25-2001 12:27:22




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 Re: Re: Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Red Dave, 04-25-2001 11:11:24  
O.K. I'll check that but it is still only running on 3 cyl. plugs are new and cap is less than 1 yr old. How can I tell if a plug is bad ? and how would I know if the cap itself is bad ? I have an inline spark tester, one of those that you pass over the wire and all are firing, when I have them out and laying on the head(the plugs) they are all firing. ??



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Jimmy Brumit Jr

04-25-2001 18:38:49




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 Re: Re: Re: Re: Re: Re: Re: HELP!!! CUB PROBLEMS in reply to Jimmy, 04-25-2001 12:27:22  
O.K. Fellows here is what was wrong. No. 2 plug no good. spark was jumping out of the neck of the coil and jumping to the + side of the coil. I replaced the plug put a dab of electrical grease on the neck of the coil and cleaned the connection at the coil and distributor. The old gal started right up and ran fine. I still have a little carb problem but I found a rebuild kit at Miles Tractor in Baxley Ga. Thanks to all for the great suggestions.

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