As JMOR stated, you need to perform the HYDRAULIC LEAK DOWN TEST before you do anything. What were you trying to lift? N's have a 500 pound capacity safely. It does sound like you have a worn cylinder though. Be prepared for a time consuming job. It isn't difficult, just takes time as so much has to be removed -pulling the top cover included. HYD system is different for the 9N/2N vs the 8N. The 9N/2N uses a 'wishbone' bracket linkage that must be manually disconnected before thru inspection covers BEFORE you pull the top cover. ALL use 4 four square head bolts to fasten the cylinder onto the the top cover and do not get removed until cover is off and on the bench. Square head bolts are used as they help dog the bolts to the milled bosse on the cylinder so you won't see the heads from the top of cover. Four bolts are easy to identify from under the seat. NEW parts you'll need are: cylinder, piston, O-Ring or neoprene wiper, gasket kit, torque wrench, and 5 gals of fresh oil. READ THE CHAPTERS IN THE MANUALS.
Remove side inspection plates. Hitch a load to 3-pt like a 2-bottom plow or a back blade or raise up and chain down arms. SHUT OFF motor, leave raised, and observe up to the lift cylinder underneath top cover. Look closely, use a good Mini-Mag, and for several minutes. If you see oil seeping down from the piston/ram, the piston and/or cylinder are worn and need replacing. If so, while at it, may want to clean pump chambers and entire system. That may require dropping pump to do a thorough job. If no oil leaking down, try replacing the safety relief valve. You need an 11/16 STUB OPEN END WRENCH or cut down one in your tool box with not too much sentimental value. Pulling the top cover on the N has to be done a certain way. READ MANUALS FIRST. The Hydraulic Cylinder is bolted to the Top Cover with four square bolts accessible under the seat. DO NOT REMOVE THE 4 BOLTS UNTIL YOU HAVE THE TOP COVER ON YOUR BENCH. When you replace the cylinder and piston, I advise you use the NAA-530 piston that uses the rubber O-RING. It is a better system than the prior 3-Steel Ring Piston used '39-'52. Invest in a new cylinder as well; honing or trying to rebore is a waste of time. NOTE: The 8N Cylinder has a cast or milled scallop clearance divot on the bottom 7 O'Clock position as it must have relief for the control rod. Understand the control rod must be inserted into the base when reinstalling top cover. The 8N uses a control rod to shift between DRAFT and POSITION CONTROL. 9N/2N models do not have the control rod, they have the 'wishbone bracket' and thus do not need/have the scallop clearance. Some new cylinders sold today do not have the clearance either so you'd have to grind or mill clearance on it yourself. Note my original 9N-510 cylinder that I modified with the clearance to fit my 8N top cover. See the 8N top cover and control rod? Note also the clearance on cylinder and top cover -not much there. Finally, once cover is back on and ready to secure, you will want to torque the bolts down. The I&T FO-4 Manual states bolts to be torqued at 53-60 Foot/Pounds. I use the mean value of 57 ft/lbs. There are two short (3/4) bolts and two long (1-1/2) bolts so use your MPC and diagram for proper position. Email to see my article on Rebuilding the 8N Hydraulic System if you need help.
OEM 9N-510-D CYLINDER left, & MODIFIED 9N-510-B, right, WITH MACHINED SCALLOP FOR 8N CLEARANCE:
OEM 9N TOP COVER w/WISHBONE FORK LINKAGE:
8N TOP COVER w/OEM 9N-510-B CYLINDER, MODIFIED:
8N TOP COVER w/CONTROL ROD & OEM 9N-510-D CYLINDER w/SCALLOP:
FORD 8N TOP COVER TORQUE: