Growing stator laminations on Tecumseh HM80 internal ignition.

[BOBTHEBOPPER]

Here is a real puzzle on an old Tecumseh HM80 with internal ignition coil. I have a Craftsman snow blower (late 70s vintage) which has always been kept outside and kept covered, and each year around November I uncover to ready it for the winter season. Usually my only problems are pulling the flywheel, removing the mouse nests, cleaning and resetting the points and changing the oil. I have been doing this for the last 18 years since getting the oldie but goodie. Here begins the mystery of the growing stator laminations, After cleaning and gapping the points (never checked the engine timing in about 6 years) replacing the flywheel and rotating the flywheel by hand I noticed it would hit something, rotated it backwards and noticed it was hitting something way short of 360 degrees, pulled the flywheel again and through careful examination noticed the magnet assembly on the flywheel was striking the stator laminations (both directions of rotation). Examined the flywheel magnets and they were screwed tight to the flywheel, no play. My next thought was maybe a bent magneto end on the crankshaft, checked by rotation and no deflection there. My next thought was to check the lamination assembly riveted to the stator base plate to see if it was lose or bent, everything was tight not bent or deformed. Then I checked the stator assembly to see if it could have slipped out of position in relation to the crankshaft but noticed the stator assembly fits on a boss on the engine magneto case (no adjustment there except for timing). All checked out OK. Now what to check? Magneto assembly in fixed position in relation to the crankshaft and magneto engine cover, all parts of stator assembly tight and not deformed, flywheel magnet assembly tight to flywheel and not distorted, crankshaft not bent and flywheel not distorted and fits tight to crankshaft. The only other issue could be a worn main crankshaft bushing on engine magneto case and that was checked (no slop in crankshaft at magneto end). In order to solve the laminations hitting the flywheel I had no choice but to file down the laminations to get clearance to the flywheel magnets. Being the stator assembly is internal to the flywheel this was a trial and error procedure to get a close fit to the flywheel magnets as possible (external stator clearance to the flywheel magnets is about .013 clearance) but no way to check internal magneto clearance. After much filing and measuring with putty I was able to obtain a fairly accurate fit. Assembled everything and ran engine. seems to run fine but my question is WHAT COULD HAVE CAUSED THIS PROBLEM, I AM STUMPED. Can someone explain this phenomenon? Metal does not grow (AT LEAST ON THIS PLANET). Would appreciate any comments. BOBTHEBOPPER 60 years of engine repairing.

 

[ILENGINE]

I would suspect growth due to metal corrosion between the laminations. I have seen ignition module laminations almost double in size due to corrosion between the metal plates.

 

[Rivets]

IL hit it on the head. Corrosion will cause metal to grow, think about trying to get a wheel off an axle. It can rust so much that the two metal parts will grow together. Even lube and heat can break that bond.

 

[BOBTHEBOPPER]

I would suspect growth due to metal corrosion between the laminations. I have seen ignition module laminations almost double in size due to corrosion between the metal plates.

 

[BOBTHEBOPPER]

Thanks for the reply ILENGINE. I do agree about the corrosion between the laminations since I worked on outboard engines that were run in salt water however my observation has been the thickness of the lamination stack increases due to the corrosion between them. In my case the length of the lamination stack increased perpendicular to any corrosion (I had none). I should have taken a picture before I assembled the flywheel but did not think it necessary. The lamination stack had no corrosion between the plates and the blueing was still visible, the only sign of any corrosion was surface rust on the lamination stack ends. This was easily removed with some sand paper, but in order to get the stator to clear the flywheel magnets I must have filed off about 10 to 20 thousandths or slightly more. Thanks again.

 

[BOBTHEBOPPER]

IL hit it on the head. Corrosion will cause metal to grow, think about trying to get a wheel off an axle. It can rust so much that the two metal parts will grow together. Even lube and heat can break that bond.

Thanks Rivets for your reply. I do agree about the corrosion between the laminations since I worked on outboard engines that were run in salt water however my observation has been the thickness of the lamination stack increases due to the corrosion between them. In my case the length of the lamination stack increased perpendicular to any corrosion (I had none). I should have taken a picture before I assembled the flywheel but did not think it necessary. The lamination stack had no corrosion between the plates and the blueing was still visible, the only sign of any corrosion was surface rust on the lamination stack ends. This was easily removed with some sand paper, but in order to get the stator to clear the flywheel magnets I must have filed off about 10 to 20 thousandths or slightly more. Thanks again.

 

[Gregory5]

I have an H70 I am rebuilding with the same problem. It only took a few swipes with a file to correct it, but I can't figure out what caused it in the first place. The only explanation I can come up with on my motor, is a bent crank. When I got this motor, it did not run,(still doesn't) and I knew nothing of it's past, so I have no idea what it's been through. I am currently waiting on parts.

 

[BOBTHEBOPPER]

I think I solved my problem with the growing lamination stack on the tecumseh HM80 internal magnito. I uncovered my snowblower this year and guess what? The same problem existed Flywhell hitting lamination stack.
As stated the magnet assembly appeared tight to the flywheel however I noticed when viewing the magnet assembly it is held on with 2 screws which are accessible only under the ring gear. If you look at the ring gear you can see the 2 screws but can not get to them with the ring gear on. Anyway looking at the magnet assembly which is aluminum on the left hand side where the screw holds it in place WALA, there is the problem. the aluminum has corroded so bad on the left side it has pushed the magnet assembly away from the flywheel (inward). With this corrosion buildup the magnet assembly appeared tight to the flywheel. I measured it with calipers from the outside of the flywheel to each magnet surface and there was the problem. 1/8 inch due to the aluminum corrosion. Now was my next problem since I was filing the lamination stack down to obtain clearance I now had a short lamination stack and could not use it with a different flywheel. So to finalize and fix my dilemma I was able to obtain a used flywheel in good condition and a used magnito frame. Both parts I found on EBAY and am waitng for delivery as of this writing. Lesson to be learned leaving power equipment outside covered in the north east is a disaster . I hope if someone else has a similar problem this post help. BOBTHEBOPPER 12/21

 

[BOBTHEBOPPER]

I have an H70 I am rebuilding with the same problem. It only took a few swipes with a file to correct it, but I can't figure out what caused it in the first place. The only explanation I can come up with on my motor, is a bent crank. When I got this motor, it did not run,(still doesn't) and I knew nothing of it's past, so I have no idea what it's been through. I am currently waiting on parts.

Gregory5, If you have not found the reason for your problem check my latest post. This might be the cause. Hope it helps