How to change o ring in control valve in a timberjack skidder

The error code "ER20" on a Franklin Log Skidder Q90 likely indicates an issue with the transmission. The exact meaning of this error code may vary depending on the specific skidder model and manufacturer, but it typically indicates a problem with the transmission control system or a sensor within the transmission.
If the transmission will not take gear, this is a clear indication that there is a problem that needs to be addressed. The issue could be with the transmission control system, the transmission itself, or even with the engine.
If you're experiencing this issue, it's recommended to have the skidder inspected by a qualified mechanic or dealership as soon as possible. They will be able to diagnose the problem, determine the cause of the error code, and repair the transmission to ensure it is functioning properly.
If the problem is not addressed, it may cause further damage to the transmission and result in more expensive repairs. Additionally, operating a skidder with a transmission issue can also pose a safety risk to the operator and anyone nearby.

contact the manufacturer on line and quote the machine serial number and ask for an engine serial number that engine.

Not sure if you mean engine size or not . Each engine has it's own serial number. Anyway the Duetz engines were 130 HP 6 Cylinders. Now Duetz had 912 and 913 engines the 913 was the model with a turbo and they produced these engines in 3,4,5,and 6 cylinders. Most of what I've seen is the 6 - 130 HP. This particular unit was built in the mid 80's or so. Other Timberjacks different models/years, etc, also had 4 cylinder cummings, then some John Deere also. If my memory serves me correct it seems like I ran up on an old Timberjack in the woods hunting one day and it had a Detroit 353 in it. Great little engines.

Engine should have data plate

Friction is usually the cause of hydraulic overheating. Every time the hydraulic oil moves through the system the moving of the hydraulic fluid against the hoses,pumps, cylinders , etc. creates friction. Any restrictions such as valves or filters can be hot spots because of the friction created as the passages get smaller the fluid moves faster creating more friction. Friction = Heat.
I would check the filters to make sure they are clean. Check the valves to make sure they are opening fully. Check hoses for any kinks or pinched spots.Try to operate the skidder at the lowest r.p.m. need for the work being done. Over revving can also cause heat buildup.
Hope this helps.
Bob

Is the control valve leaking internally? Might need new o rings or replaced.

my timberjack 360 wont shift into 3and4 but will shift into 1256. any people know whats wrong

In order to get the best gas mileage the Honda motors only have one compression ring and a oil control ring on the pistons. If the oil wasn't changed regularlly then it's time for rings after about 120 thousand miles. they all use a little oil because of this one ring system, about a quart in 1000 miles, even when new. When doing your work did you clean the valve cover real good? the cover has the baffles for the oil control of crankcase blowby and as they fill up with carbonized oil the baffles in the valve cover instead of separteing the air and the oil start passing oil into the PCV systema and into the air cleaner and into the air entering the air intake of the engine gets burned in the combustion gases and out the tailpipe.