Extending a crankshaft - Snowblower Forum : Snow Blower Forums
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post #1 of 4 Old 02-10-2018, 01:51 PM Thread Starter
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Extending a crankshaft

Background on this is last month when we had that big storm I fired the Searsasaurus up and it was just over idle and it threw a rod that ventilated the block. Net result was one dead TEC 10HP. I'm going to describe a modification on how you can use a short crankshaft engine in a long crankshaft situation, which is what I experienced.

The fastest repair would be to find another TEC 10HP and swap out the engine. I found one on a machine I bought for parts. I only checked for spark and compression at the time and it came back to bite me.
The engine had a 2 3/8" x 1" crankshaft while the ventilated one was 2 7/8" x 1". I probably could have just shoved the pulley on but that would have left a lot of space between the end of the crankshaft and the end of the pulley so I made a crankshaft extension instead. The replacement engines pulleys were held on by a bolt threaded in the center of the crankshaft.

First thing was getting some metal. My local metal distributor had some 1" cutoff cold rolled steel. The crankshaft measured 1.01" while the steel measured 1.00", which I decided was close enough. I have a metal lathe so I found the correct size drill bit and drilled a centered hole that the bolt would go through into the center line of that 1" cold rolled steel piece I picked up, I drilled to a depth of about 3/4" so it would be there once I cut off the piece I needed. Next I cut the length of the extension to 1/2" as this was long enough to extend beyond the end of the pulley but allow the bolt head to fit inside the pulley cover. You might have to get a different length bolt, in my case the one in there worked just fine.

At this point the extension would bolt onto the end of the crankshaft but that's it. I then scribed the extension corresponding to slot for the pulley key for both width and depth. I don't have a mill so I took an angle grinder with a cutoff wheel and roughed out where the keyway slot would go. Then using a grinding wheels and some files I finished off cutting the keyway slot to match the crank key slot. I got a longer key (actually it was the one from the original engine), with the extension on the crankshaft slipped on the pulley, fit like a glove. One thing is don't tighten the bolt in the end of the crank till the pulley is aligned with the belts on the blower as it can shift ever so slightly and tighten in the bore of the pulley. The easiest way to tighten up the bolt, remove the recoil starter and you put a socket on the flywheel bolt and the crankshaft bolt. A little Locktite doesn't hurt either.

Before you ask, I could have bored another hole though the extension into the crank and pinned it, but since where the set screw in the pulley sat along with a long key it didn't seem necessary as they held the extension just fine to the crankshaft and aligned well. The bolt and the key seems to just fine.

I took the carb and muffler off the ventilated engine, carb cover (due to modifications made to fit the different muffler) and a decarboned the piston, head and valves. Everything seemed to work just fine with this combination. I also switched the oil to some 5w20 synthetic just to try it out so we'll see how it works out. With this engine on the Searsasaurus it fired right up. All I had to do was some minor adjusting to the high speed jet and it ran like a top. Now to see if we get enough snow to actually try it out, but time will tell.

As a result, the Searsasaurus lives. I have some ultimate painting etc to do on the engine, but who cares if it's snowing a bunch. I'd rather have it working instead of looking pretty.
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Last edited by HCBPH; 02-10-2018 at 03:39 PM.
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post #2 of 4 Old 02-10-2018, 02:33 PM
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I would like to have seen a video of cutting the slot for the key. That seems to have been the hardest. No pics of the keyway slot? I only can think of me doing a sloppy job with that, needing to use a file.

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post #3 of 4 Old 02-10-2018, 03:29 PM Thread Starter
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I didn't take any other pictures or video but it really wasn't that difficult once you figure out the tricks.
I bolted the prepped crankshaft extension onto the crankshaft and snugged it up using the bolt without the large washer shown. Using a straightedge and a scribe I marked down the length of the piece the width of the new keyway to be cut into the extension. I also scribed on the inside the depth of the cut needed, then switched it end for end and marked the other side the depth of the cut. I then carefully darkened the area to be removed with a Sharpie to make it easier to see the area to cut out.
I mounted the piece in a vice with the scribed mark horizontal and carefully cut along the inside of one line using a angle grinder with a cutoff wheel as close to the marked depth of cut as I could. Flipped it over then cut the inside of the other line to the marked depth. Then made multiple cuts through the middle to remove the waste. Once I had enough out I switched the cutoff wheel for a grinding wheel with a square edge. I used that to get most of the waste out. Once I had it close, I'd put the extension on the crankshaft snugged up, and check the key against the slot. Using a variety of metal files I fine tuned the slot till it matched the slot in the crank (in the vice, not on the engine). When I could put the key into the keyway and slide the pulley on with the extension snugged up I figured I was done. When I was ready to put it on the last time, I removed the recoil off the engine and had a breaker bar and socket on it. Slid the pulley and key on with the extension snug but not tight and aligned the pulley. Tightened the pulley set screw then the bolt in the extension. Put the recoil back on and it was done.

If I pull the thing for any reason I'll take some more shots but being it's together I'd really prefer not to.

PS if you know someone with a metal working shop and a mill it would be a snap. I really don't think a machine shop would cost that much to do it either. Just happened I wanted to do it myself so that's how I did it.

Last edited by HCBPH; 02-10-2018 at 03:36 PM.
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post #4 of 4 Old 02-10-2018, 03:34 PM
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