weak compresion on 1&2 cylinders

[jlfcub50]

My initial problem we thought was electrical on tractor with a J4 magneto. We have resolved those issues, replaced rotor, coil, points ,condenser, plugs and wires and it's producing a good spark and timing is correct. Now even though we sprayed ether in the cylinders it still will not fire (cylinders 1&4), upon further checking it was determined that 1&2 cylinders have virtually no compression 3&4 measure around 60. Could this be a head gasket problem?, looking for some clues ideas on how to proceed.
Thanks

Men are apt to settle a question rightly when it's discussed freely.

[Mike in Louisiana]

Have you checked for stuck valves, has it been sitting for a long time?

[Eugene]

What is the history on this tractor? Been setting for some time? Outside?

Could be head gasket, worn rings, sticking valves. My guess is valves.

Try a wet compression test. This will isolate the problem to rings, valves, or head gasket.

[Larry in WNY]

Remove the tappet cover and rotate the engine. You'll see if the valves are stuck or moving up and down with the cam. If not moving use penetrating oil or WD40 and try to get them loose.
Larry

[ScottyD'sdad]

I lean towards valves, first. Could be other issues, mentioned, or stuck rings. I've had to chip the stuck rings out of the groves, on a couple of engines. (Sat a long time). I generally say valves, since the last valve job it had, was probably during the Eisenhower administration.
Ed

[Bigdog]

At best, the 60 pound compression readings on the other two cylinders is poor. Probably not enough to start the engine. I agree with the others that it is probably valves. Squirt a little penetrating oil in each spark plug hole and let it soak a couple of days. Then re-check compression. If you have not already considered it, you could try pull starting the tractor. You might be able to build enough compression to get it to start.

[jlfcub50]

Thanks for all the suggestions as always they are greatly appreciated. The tractor has not been sitting for a long time last run in mid November. Pulled the head off this afternoon and it's gunked up with carbon as is the top of the pistons. I am not familiar with a "wet compression" test could you please elaborate.

[Eugene]

Pulled the head off this afternoon and it's gunked up with carbon as is the top of the pistons. I am not familiar with a "wet compression" test could you please elaborate.

Same as the dry compression test. The idea of adding oil to each cylinder is to help locate cause of the problem. Oil seals up the gap between the piston and cylinder wall.

Since you have removed the engine head and found the cylinders filled with crud, suggest at a minimum an in tractor over haul. Meaning new rings, lap valves, and new rod and main bearings.

[jlfcub50]

Once the head was removed turned hand crank and all the valves are opening and closing as they should, not an expert at these matters but the cylinder walls don't appear to be scored either. Is it worth replacing head gasket and seeing if that resolves the problem? (after cleaning the carbon residue off of the head and the tops of the cylinders)
Thanks again for all the help

[Eugene]

I would pull the engine and rebuild.

[staninlowerAL]

Now that you have the head off and see that the valves are moving as they should, might consider lapping the valves to the seats. You can then determine if they are sealing, check for seats that might need work, etc. and eleminate the valve issue. If you want to reinstall and seal up the head and check for compression after seating the valves and still have low/no compression on the two cylinders, the only other place it could be loosing it is worn/bad rings.

[Eugene]

(after cleaning the carbon residue off of the head and the tops of the cylinders)

Due to the engine design, carbon residue on top of pistons is the result of worn or stuck piston rings.

While some engine oil is able to be sucked into the combustion chamber past the valve stems and guides, it's minimal.

[BigBill]

Do take another compression test with the throttle on the carb and choke wide open.

If it doesn't improve remove the side valve cover to see if there stuck open or not adjusted correctly.

This will tell you what to do next.

It's a good thing to use seafoam in your crankcase and gas tank on every running tractor at least once per year. To be positive the valves are lubed and free plus you don't have any stuck rings.

When cleaning your carbon build up remove the intake and exhaust manifold to make sure the ports are free from all blockages from the carbon build up that could exists that's caused by a bad carb.

Spraying either can be like flooding the engine with gas. It can wash the oil film from the cylinder walls so the piston rings are not sealing. They will notice not produce compression. The gas mixture is blowing by the rings into the crankcase. You need to wet the cylinders with a little oil now so the rings can seal.

[jlfcub50]

Does anyone have any good tricks for compressing valve springs? I have the tool we used on the cub cadet but it's seems hard to get it on top of the spring. As suggested earlier we are going to lap the valves, did take the tappet cover off and everything seems to be moving freely. Anyone have another suggestion outside of the traditional lapping tool?, it seems oversized for this application. Thanks to all for making this a good learning experience.

[Eugene]

Sears has an inexpensive valve spring compressor with adjustable jaws and adjustable deck height. It takes a 2 x 4 block of wood on the head to work on the Cub engine.

I think you are spinning your wheels. Go for a total engine rebuild.