Anyway, I found a brand new Honda 18hp v-twin at a decent price and I thought it would be better to start this new thread to describe the install. The engine came with no muffler and no fuel tank. It did have a fuel pump, electric start, and a 20 amp charging circuit. The following is a list of issues I ran into during the install and how I dealt with each of them.
1. The crankshaft on the Honda was only 1" diameter and the Onan was 1 1/8" diameter, so the Onan drive pulley would not fit. To address this issue, I made a bushing out of 1/16" sheet metal and made a new key that was 1/4" by 5/16" because with the bushing, the key in the crank was 1/16" deeper than ¼". When installed with this bushing, the pulley fit snugly with absolutely no play. I think it will work OK but I plan to keep an eye on it. I may eventually have to buy new pulleys for a 1" shaft.
2. The Honda crankshaft is about 1 1/8" lower in horizontal height than the Onan. If I raised the Honda enough to make the horizontal heights the same, I was afraid I would have trouble with the tractor hood closing properly. This turned out to not be an issue when you see what I did in item # 5 below.
3. The gas line for the Honda was originally positioned out of the opposite side of the engine from where I needed it so that I could easily connect to my existing gas line. Fairly easy fix. I initially re-positioned the gas line out the side only to find out that the tractor hood wouldn't fit in that position, so I re-positioned it out the back of the engine. Since the Honda has a plastic shroud this was easy to do. In addition, there was also an additional tube on the Honda that was attached to the carburetor intake manifold. I couldn't see any need for this tube other than possibly connecting a vacuum gauge so I plugged it.
4. The Honda has a front and rear oil drain plug that would be difficult to access unless the engine was raised slightly. I had some ½" thick steel bar that I drilled to match the engine mount holes and placed under the front and back to raise the engine.
5. I could not position the new Honda so that the existing drive belt would fit because the rear spark plug would be too close to the battery holder and couldn't be removed. I felt like I only had two options here, I could re-work the battery holder or move the engine forward. Re-working the battery holder would be very difficult because the clutch pulley is welded underneath. I chose moving the engine forward enough to provide clearance for the spark plug. I knew that if I moved the engine forward, I would definitely have to buy a new drive belt and probably a new mower belt. The engine was moved forward till the base of the engine just touched the bottom portion of the hood support, and then moved the engine to the left (as viewed from the driver's seat) so that the pulleys would be in line. This gave me enough clearance for the spark plug and I didn't have to re-position any of the hood mounting parts. To determine the size of the new drive belt I would need, I measured the distance I had moved the engine forward and added double that distance to the length of my existing belt. That worked fairly well and I changed from an initial 84" drive belt to an 86" belt. The 86" belt worked OK, after adjusting the clutch linkage, but is a little tight. Probably an 87" would work better. See photo for engine position.
6. I considered two options to mount the Honda to the tractor frame. I could either drill through the frame and mount directly, or I could use the existing Onan mounting holes for a large steel plate and weld stud bolts to this steel plate in the proper position for the Honda. I decided to mount directly to the tractor frame with new drilled holes. After positioning the engine where I needed it to be, I started drilling the mounting holes. On the last hole that I drilled, I hit a cross brace under the frame which prevented a mounting bolt in the tractor frame there. To deal with this, I welded an extension to the ½" steel plate that I had used to raise the engine so that the plate would extend to one of the original Onan engine mounting holes. I then welded a stud bolt into the ½" plate for the mounting position that I couldn't drill. The Honda was then bolted down with three bolts through the tractor frame and one stud bolt welded to the ½" steel plate.
7. The old ignition switch on my tractor has a position to apply voltage to the ignition coil to run the engine and shuts off the voltage to stop the engine. The Honda did not require voltage to be applied to the ignition coils to run. However, when the ignition switch is turned off the coils are to be grounded to stop the engine. My old ignition switch either didn't have that option or I couldn't figure out how to do it. The Honda also has a fuel cutoff solenoid attached to the carburetor. For the engine to run, this solenoid has to have voltage applied. I ran the wire from the switch, that had previously applied voltage to the ignition coils, to the fuel cutoff solenoid and omitted the grounding of the coils. The engine will shut off when the ignition key is turned off but it's delayed because it shuts off the fuel and not the spark. I may need to add a separate cutoff switch later to ground the coils.
8. I didn't want to spend $160 for a new Honda muffler so I decided to see if I could make my own. I didn't have any way to drill a 1" hole needed for the mounting flange, but going through my scrap pile, I found a couple of old ¼" thick steel brackets that already had a 1 1/8" hole. I used the Honda muffler gasket to center the 1 1/8" hole and to locate and drill the flange mounting holes The gasket was also used to outline the general shape of the exhaust flange. After I cut out the general shape of the flange and drilled mounting holes, I welded a piece of 1" ID black pipe (NPT threaded on the other end) to the flange. I added a universal NPT threaded muffler to the threaded end of the black pipe. I used 1" angle iron to help support the pipe and muffler I know the angle iron support doesn't look good but it will do for now.
The pictures below show the tractor with the completed install.
Another thing I forgot to mention. When I removed the old drive belt, I took the idler pulley for that belt completely off. When I re-installed the idler pulley, I somehow put a washer on the wrong side of the pulley and when bolted down, the pulley was locked and wouldn't turn. When I took the tractor for a test drive with my new drive belt installed, I soon saw blue smoke coming out from under the tractor with the odor of burnt rubber. Not a good feeling when you've spent several days working on mounting the engine only to burn it up on the first trial run. I soon found the problem though and corrected it and everything is fine now. The new drive belt was damaged a little but is usable.
All my pictures didn't show up exactly where I wanted them in the text but maybe you can figure it out. I'm still learning. If some of the steps I have described are not clear, or If you have any questions or would like to see additional pictures, let me know.
Craig., akretowicz, twowheeler63 and 7 others have said thanks