Small Engine Repair 101

Part 1: Engine siezes

Saturday, Jan 14, my fave machine, our chipper/shredder, quit suddenly. That usually means a branch has wedged in between the rotor and the shroud. Couldn't find any such but the engine would not rotate without great force. Monday, I dismantled the shroud and removed the rotor, still nothing obvious stopping the engine. Oh, oh, engine seized?

I took the engine to Wayne Miller for a consult. Wayne is my mentor in many things a good farm boy should know. He discussed bearings and the possibility that a bearing could seize as the piston doesn't appear seized. In the current state of disassembly, the bearing on the rotor side of the engine is rather easily accessable while the bearing on the other side is behind the flywheel. Wayne suggested checking the easy bearing first and, in my current spate of bad luck, that probably won't be the one.

After returning home, I removed the crankcase casting on the rotor side. Hard to believe that this is the first time in my life I have disassembled an engine, small or large, to the point of being able to peer inside at its working guts. That bearing is a bronze bushing and the casting turns easily on the crankshaft bearing surface. Probablility rules!

Part 2: Accessing the "bearing"

Wednesday, I pulled the flywheel to gain access to the other bearing. Prying with a crowbar and whacking with a hammer did not loosen it. A few years ago, I fabricated a crude flywheel puller for our lawnmower engine. Of course, the diameters of the lawnmower flywheel and the C/S flywheel are not the same so I had to fabricate another crude flywheel puller for the C/S diameter, cannablizing the PVC spacers, bolts, and nuts. Better luck now, a few turns of the center screw and the flywheel popped off.

I knocked the bearing seal out. Now exposed, there appeared to be no bearing. Back to Wayne for a consult. Wayne has the shop manual for a similar Tecumseh engine but OH cam and didn't match up with what we saw. He loaned me his manual and, back home, I surfed and, viola, the manual for my Tecumseh HM80 engine is online in its entirety. Probably Wayne's is too and he paid $5 for it. This manual has no description of the bearing on this side and that should've been a clue. I decided further disassembly was required.

I disconnected the connecting rod at the crankshaft. As shown in the manual, the camshaft drive gear and it's mate on the crankshaft have marks to align them properly, however, in order to remove the camshaft, one has to align them three teeth off those marks. Strange but, so aligned, the camshaft slid right out. Suspicions continuing to be confirmed, didn't see a bearing. I rotated the crankshaft using the flywheel temporarily in place as a lever until the crankshaft had no interference with the connecting rod. Holding the connecting rod out of the way with a DIY keeper, I covered the crankshaft end with a board and whacked it with a hammer and the crankshaft slid out of the crankcase.

Damn! There is no bearing. This must be Tecumseh's saving a dollar or two with a flawed design, running the steel crankshaft in a hole in an aluminum crankcase. Back to Dr. Wayne for consult #3. I'm running up a bill. He'd not seen such prior. We examined scoring in the case and metal buildup on the shaft. We agreed this is as far as DIY Eddy can take repair, time for the experts. Now about 3 PM, I packed the shaft and case in the car and took it to Jeff at Precision on my way to workout at RWC. Damn again! Jeff takes Wed off after 2.

Part 3: Enhancing the engine

Thursday 08:00, I was at Jeff's doorstep when he opened. Well, he doesn't work on engine internals, stops at carb adjustments and such. Recommended Wilson's in central Raleigh. Off to Wilson's, doesn't work on Tecumseh, recommended Arvin's on US-401 six miles south of Raleigh. Off to Arvin's, doesn't do machining, recommended Hamilton Machine Works four miles back closer. Off to Hamilton, viola, owner Lin Hamilton was very helpful, discussed the problem and alternatives for repair. We concurred the best to be boring the case to accommodate an oil impregnated bronze bushing, for ~$100. Will take ~1 week.

Part 4: Reassemble the enhanced engine

Saturday, Feb 4, I fetched the engine from Hamilton Machine with its new bronze bushing installed. $100. I reassembled the engine but certainly not all the C/S shrouds, just enough to stabilize the engine so I could pull-start it. I added oil and gasoline, sprayed a little ether in air filter, and tried to start it. Oh, oh, way to stiff to be readily turned over. This was not an unexpected result, many things could account for it. I'm going to try a few to see if I can't get shaft to turn more freely.

Part 5: Relieving the bushing

Tuesday, Feb 7, Wayne viewed the above blog status report and emailed a suggestion (slightly edited herein). "You can make your own tool to polish the bushing. Use a big drill bit and with a drill, spin on some steel wool until you get to about the size of the hole, then insert the wad into the hole, and then spin on more steel wool until it binds real good in the hole. Hone away."

Off on an errand run to buy steel wool. I'd also surfed "flap wheel sanding bits" and decided one of those would be a good idea, too. Never fails, can't satisfy a simple two item shopping list without visits to four stores. Burke Brothers's Hardware is a Raleigh institution and I found neither item until I got to Burke. First three stores had #3 steel wool but not the coarsest #4, none but Burke had a small sized flap wheel.


Thursday, I disassembled the engine, spun #4 steel wool on a drill bit (see pic), and honed away on the bushing. The flap wheel appeared too large diameter to fit in the hole and I used it only to relieve the milled edge of the bushing. I partly reassembled the engine and, without oil or gasoline, tried to turn it with the pull start. Rotation obviously still not free enough for it to start.

That evening, I asked Wayne to make a house call as, with the engine down in our crawl space to work on it, it was a bother to carry it back to the Trooper to transport it to his "office". He examined my steel wool on drill bit hone, thought it to be satisfactory, could detect some progress in freeing the crankshaft, but obviously not free enough for it to rotate enough to start with a pull. Nothing to do but hone it some more.

Part 6: Success!

Friday, I disassembled the engine one more time. With a second attempt, I was able to fit the flap wheel into the hole, tight fit. The flaps are very abrasive, medium grit, and I ran it only a few seconds not wanting to enlarge the hole too much. I found the strip emory cloth I'd used for my outdoor faucet project and polished the crankshaft bearing surface a bit. I reassembled crank and case just enough to test rotation, finally, it turned freely.

For the second time, I reassembled the engine, added oil and gasoline, sprayed a little ether in air filter, and tried to start it. Viola! It fired up and ran for a few seconds, then quit. I started it again, it quit. I realized the linkage from the governor lever to the carb butterfly didn't appear to be working. Started it again and held the linkage with my fingers. It ran continuously as long as I held the linkage, quit when I let go. OK, with the shaft in case bushing problem solved, enough for the day.

Part 7: Lingage foulup

Didn't get back to engine until Sunday afternoon. I looked at the online manual section on throttle linkage and realized I'd fouled the linkage from the governor lever to the throttle lever, not the one I thought I'd fouled. I fixed that, pulled the start cord, and it ran pretty good. Even started without ether. It hunted speed a little bit, I adjusted an idle screw a 1/4 turn as manual suggested, and that quelled.

Part 8: Let's shred some leaves

Monday, February 13, one full month on this project, I completely reassembled the chipper/shredder shrouds and chute, now in full working dress. I fired up the engine and Jeanne took this pic of leaves being shredded once again. Oh yeah, leaves, do I have leaves? A month out of service at this time of year and I have tons of leaves to shred into mulch.

This was quite a project and I learned a lot. Wish it had occurred many years ago.