# Engineers Gone Wild



## hankster (Jan 1, 1998)

Just another update from the daily life of a repair tech. It’s not only fellow workers and customers that can drive you crazy, but engineers too. Let’s see if I can explain this.



Over the past coule years there have been problems with the clutch coming loose on MTD 2-cycle engines (Ryobi design) which causes the flywheel to rotate. Below is an exploded view which shows how a thin wall spacer (#21) goes between the clutch and the flywheel… when you tighten down the clutch on the crankshaft, the spacer presses the flywheel onto the crankshaft.














The flywheels that have been used have a molded-in key. These keys DO NOT hold the flywheel in position during use and their only function is to aid in proper alignment when assembling. The crankshaft and flywheel have a matching taper and the pressure of the tightened clutch is what holds the flywheel in place.



MTD’s solution to the problem has been to use a flywheel with a “real” steel key. While this does sound like a sensible solution to the problem it only makes things worse. Now when the clutch loosens, the flywheel still spins… this results in not only damage to the flywheel but it also now wipes out the crankshaft and crankcase bearing. The previous $28 repair is now a $110 repair as you now have to replace the shortblock (crankcases are not available separately. The picture below is somewhat poor quality but you can make out the damage.












The real issue we have here is that the spacer that is used to hold the flywheel in place is very thin. When you tighten the clutch the spacer digs into the aluminum of the flywheel. During use, the spacer continues to eat into the flywheel because of engine vibration and at some point the clutch loosens up and causes the flywheel to spin. The solution to the problem is to use a steel washer between the spacer and the flywheel which would prevent the spacer from digging into the aluminum flywheel.



We have suggested this solution to the MTD engineers but I guess they think they know better. Let’s increase the damage caused instead of fixing the problem.


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## tommyj3 (Sep 16, 2006)

Hankster I've had the pleasure of working with many engineers in my time, and I have found they look down on the people that work on their designs. (heaven forbid if there is a problem with the design, they never make mistakes) Most have no common sense what so ever. Someone should be listening to you, because you have the fix. Even I can see your logic.


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## cajunh2s (Apr 19, 2007)

hank

you should market your repair idea.....put a steel washer in a small bag....and call it hanks ryobi clutch and flywheel sealer......lol

i'm sure ryobi would love that....and what a way to get even with a smarty pants engineer.....lol

cajun


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## geogrubb (Jul 28, 2006)

I had this happen to a Troy-Bilt 4 cycle trimmer(MTD/Ryobi design I believe), when the flywheel shifted it also throws off the timeing, I wish I had known of Hanksters solution, the little trimmer has since gone to trimmer heaven. Have a good one. Geo


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## hankster (Jan 1, 1998)

If you add a washer, you have to shorten the spacer the same amount as the thickness of the washer. A flywheel washer from a 25cc Poulan engine works perfectly. The ID of a 5/16" washer (I think that is the size) is just a few thousands too large to work properly.

Geo, yep, same basic design. This has only become a real problem since MTD came out with their "spring assist" or "incredipull" recoil. I would guess I've replaced well over 300 flywheels over the past 2 years.


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## pyro_maniac69 (Aug 12, 2007)

I wish I would've know about this steel washer idea, cause I had to give a customer a brand new rototiller because it sheered keys from 4 flywheels that I put on, I could've save my Ace some money


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