Gravely L repower
I received a PM from a member months ago about a repower I had done to my Gravely L wanting more details and an update. So here it is:
Honda clone Gravely Conversion
Gear 6325k5 Steel Plain Bore 14-1/2 Deg Spur Gear, 10 Pitch, 15 Teeth, 1.5" Pitch Diameter, 3/4" Bore from McMaster Carr
Hub W series weld on hub from Tractor supply or Burden Surplus center 1 shaft diameter
¾ Cold rolled steel shaft, few inches long
¼ inch plate for transmission, engine plates, and gussets
1/8 inch plate for handlebar support
Misc steel pieces
The transmission plate was cut using the transmission as a pattern. The center was marked based on the locations of the various bolt holes and a 2/1/2 inch hole drilled. The inside outline of the transmission was marked using the old transmission gasket. A ¼ inch rod was welded and bent along the inside of the markings from the transmission gasket. This ¼ inch rod simulates the lip that was on the original engine case. This lip fits tightly inside the transmission edge and keeps the clutch from coming too far towards the rear of the transmission. The transmission plate is a piece of ¼ inch plate with the necessary bolt holes, a large 2 ½ inch hole in the center and a ¼ inch high lip. A gasket has to be cut to fit.
The engine plate is just a square piece of ¼ inch plate big enough to fit on the engine face plate with the required 4 holes to mount the engine. The engine plate has the same 2 ½ inch hole cut in the center.
The engine hub is just a gear with a ¾ inch bore. The gear hub was turned to a outside diameter of 1 inch. The gear hub then has a 1 OD and a ¾ ID. The gear hub should be a tight fit into the 1 ID of the weld on hub. The ¾ inch shaft is placed inside the gear hub so it protrudes from the gear side the necessary amount. Measure the original engine but ¾ of an inch should be enough to function as a pilot shaft. Weld the shaft into place on the hub side of the gear not the gear (tooth) side of the gear. The gear now has a short shaft protruding from the one side and a 1OD hub on the other. The weld on hub gets a taper turned on the outside to facilitate welding. Place the gear hub into the weld on hub and weld the two together. When all is done you should have a ¾ inch smooth pilot shaft with a gear and a 1 ID keyed hub to fit the engine shaft.
The engine shaft can be cut shorter if possible.
A piece of pipe will form the spacer between the engine and transmission plate. You will have to measure the length based on the length of the engine shaft and the finished gear hub assemble. Cut the pipe to the correct length so when placed together with the engine and transmission plate, the gear and pilot shaft will protrude the same amount as the original engine. Weld the pipe in place. Now you should have a weldment consisting of a transmission plate, engine plate, center pipe spacer such that the gear and engine shaft will fit through the center of the pipe and protrude the correct length. Weld in the gussets spaced so as to not interfere with placement of the engine plate bolt holes.
I wanted a strong handlebar support so drill the handlebar plate on the bottom so it will match the top 3 bolts on the transmission. Weld on 2 angle iron pieces on the left and right sides of the plate. Bolt the spacer weldment in place leaving out the top 3 bolts. Place those bolts through the handlebar plate, transmission plate, and into the transmission. Pull the handlebars to the height you want them, drill the bars and the handlebar mounting plate angle irons to anchor the handle bars. You should be able to pull the tractor around by the handlebars without any force being transmitted to the engine itself.
The whole assembly, engine and spacer, will likely be slightly longer so you will need a longer hitch plate. I used a piece of 1 inch pipe bent to fit and mount into the differential bolts like the original. I mounted the hitch ball and then made a steel cage to go over the top of the hitch ball. That cage attaches to a U shaped bracket that hangs from the handlebars at the rear of the engine. That bracket attached to the top of the hitch ball cage to provide support to the hitch ball through the handle bars. I wanted no weight supported by the engine.
The original setup had the transmission lubed by the engine oil pump. Prior to mounting the spacer weldment, I leveled the tractor and filled with oil until the oil level was about to run out the transmission opening. I pulled the dipstick and made a mark at that level with a marker. I estimated by looking at the transmission and the planet gears that another inch or so of oil height would be more than enough to let the gears splash lubricate. So I pulled the dipstick again and made a scratch mark one inch about the current oil level. That was my new FULL mark.
Gaskets for the engine mount side, locktite on the shaft and hub screw, and bolted everything together. I used an 11 hp electric start engine but have not used the electric start option, it starts easily. It has a lever for the throttle that is in perfect position to move with my toe so I have not converted to a handlebar throttle lever. It has plenty of power so I have be able to run the engine at a speed which give a similar ground speed as the original engine. Of course at 3600 rpm it would be much faster than the original but I have not needed to do that.
I have used it mostly for grass cutting and rotary plow work, 30-40 hours since conversion. Works great so far. I am very happy with the conversion. The original hood will fit but I decided to just leave it off for now. There are many ways to mount an engine to a L model Gravely but I liked the minimal machining method I have used for my conversion. Not counting the engine, the cost should be $50-$60.