076 Flywheel comes loose...

[cbfarmall]

Never had this happen before, but I had pulled and reinstalled the flywheel on a recently acquired 076. Tightened the nut as much as I dare with 10mm threads. Started and revved it a couple times and was tuning the carb when saw shut down. Of course, I found the flywheel had come loose and sheared the key and loosened the nut. As first inspection, there doesn't appear to be any damage, grooving, or anything of the sort and the keyways are intact. I dug up a new key but have yet to reassemble.

Anyway, my thought is to lap the tapers with some valve grinding compound and put it back together. I have no idea why it originally came apart. I've put together many, many saws and this is a first. Must have been something in there I didn't see.

Chris B.

 

[Lakeside53]

Weird... yep, try lapping...

any chance the flywheel or the crank has a crack?

 

[cbfarmall]

Andy,

I'll look closer in the morning. I've got spare flywheels, so I'm sure the crank is messed up.

I did have (and still have) a Briggs engine that kept spinning the flywheel loose. The crank keyway was slogged out and no amount of BS I did would keep it tight. So I just lock-tited the sucker on, and used the crap out of it. If I ever need to adjust the points, however, I'll be out of luck. On the other hand, I have a Homelite 650 with a messed up crank taper, like a chunk missing out of it. I just made sure the nut was tight and forgot about it.

Funny how these things are.

Chris B.

 

[THALL10326]

Never had this happen before, but I had pulled and reinstalled the flywheel on a recently acquired 076. Tightened the nut as much as I dare with 10mm threads. Started and revved it a couple times and was tuning the carb when saw shut down. Of course, I found the flywheel had come loose and sheared the key and loosened the nut. As first inspection, there doesn't appear to be any damage, grooving, or anything of the sort and the keyways are intact. I dug up a new key but have yet to reassemble.

Anyway, my thought is to lap the tapers with some valve grinding compound and put it back together. I have no idea why it originally came apart. I've put together many, many saws and this is a first. Must have been something in there I didn't see.

Chris B.

Don't know if this had anything to do with your flywheel coming loose but we're told to make dayumm sure there is no oil on the crank taper or the flywheel hole. Seems any oil between the fit puts stress on the flywheel and Stihl claims it can cause one to burst. Yours may have just come loose because of it. I say may because I don't know.

 

[RaisedByWolves]

Any proper locking taper (like this) should not come loose even if the nut were to be removed. The key is for alignment, the nut is to draw the tapers up (tite) and friction does the rest.



Make sure both tapers are clean and not gouged and that the key is not interfearing and preventing the two tapers from meet fully. Also try to tighten the nut and then remove it to check that it is not bottomed on the shafts sholder where the taper begins.



Ive seen where the wheel gets so fagged out that it seats too far on the taper resulting in problems.



.

 

[RaisedByWolves]

Don't know if this had anything to do with your flywheel coming loose but we're told to make dayumm sure there is no oil on the crank taper or the flywheel hole. Seems any oil between the fit puts stress on the flywheel and Stihl claims it can cause one to burst. Yours may have just come loose because of it. I say may because I don't know.

True, oil on the tapers can cause the flywheel taper to become over stressed, Good call Tom!

 

[cbfarmall]

Thall,

I thought about that, but I'm usually pretty careful about making sure the tapers are clean. Maybe I overlooked that last time, but I darn sure won't do it again. I'm just glad the renegade flywheel didn't take out the coil or the starter.

Have a Mac 125 that once had the flywheel dogs grab the recoil and try to go running while standing still. Saw was sitting at my feet and pieces went flying everywhere. Flywheel, starter, shroud, and coil were all trashed. I still don't know how a dog caught the starter as they are thrown out of the way by centrifugal force.

Chris B.

 

[THALL10326]

Thall,

I thought about that, but I'm usually pretty careful about making sure the tapers are clean. Maybe I overlooked that last time, but I darn sure won't do it again. I'm just glad the renegade flywheel didn't take out the coil or the starter.

Have a Mac 125 that once had the flywheel dogs grab the recoil and try to go running while standing still. Saw was sitting at my feet and pieces went flying everywhere. Flywheel, starter, shroud, and coil were all trashed. I still don't know how a dog caught the starter as they are thrown out of the way by centrifugal force.

Chris B.

Well I'm not saying oil on the fit was the cause, just saying it may have something to do with it. All the schools I go to they keep beating that issue in our heads. I always spray my flywheels and crank ends with degreaser and whip it super dry like they tell us. To date and many many flywheels later I've never had one come loose. Yours may have other issues but the oil thing is a big deal with Stihl so it won't hurt to look yours over to be sure..

 

[Lakeside53]

Ive seen where the wheel gets so fagged out that it seats too far on the taper resulting in problems.



.

Now PAS is gone (again, for now..), I'll need you to explain this...:monkey:

 

[huskydave]

My take would be you could have a problem with the fit or your threads could be damaged most likely on the nut. I would use an emery cloth on the shaft using a fine grit 250 maybe and use a light oil under the emery cloth and check your bore on your flywheel for any lines grooves or pitting. if they are present make a tool using 1/4" rod maybe 2"-3" long find a die grinder and cut a slit in the center of a 1/4" shaft for about 3" long using a hacksaw. Iinstall that rod into your die grinder , Now you can put a small piece of emery cloth in this section and use the die grinder to claen out the bore this tool will work on any bore so keep it handy and if you don't have a die grinder (air powered) go and buy one and a die grinder and a air compressor as it will pay for itself in no time! or see a friend who has one. Make sure the shaft is clean and free of oil dirt grit and check the bore for dirt grit etc.. and reassemble using a new nut just to make sure the threads are not stripped or damaged. If it backs off again you most likely have aproblem with the threads why? The other boys have stated that with the taper you should have the power to keep the flywheel in place but if the locknut backs off due to a damaged thread the vibration of the saw will work that loose in no time so try all of this and get back to us. If worst comes to worst you can loctite the new nut onto the crank and there is a good chance that will not break loose.

 

[Al Smith]

The taper does the holding.Lapping most likely would be the best solution .

I don't know about Stihl but on Harley crank pins we used acetone to clean up the taper.

I doubt the nut is bottoming out but if so use a machine shim,which is just a special ground washer to space it off the shoulder just an RCH.

I had a stubborn flywheel on a little Mac 6-10.It most likey became loose as a goose because I had it off about a zillion times tweeking the timing.Never the less I lapped it and heated that rascal up a tad with a heat gun and shrunk fit that pot licker.

 

[cbfarmall]

Snapped a couple pics of the tapers. Interesting note, last night I set the flywheel back on the crank and hand-tightened the nut (just to keep the parts from bouncing around.) Left the saw in the back of my truck and drove to town. This morning when I took it back apart I had to give the flywheel a rap with the screwdriver to pop it loose. Seems like the taper is still doing its job.

Chris B.

Crank looks good.

Flywheel, not so nice but certainly not bad. Maybe I'll check out my spares.

 

[Lakeside53]

Maybe a illusion, but there looks to be a horizontal crack in the crank just below the taper?

If not the crank looks fine.

 

[cbfarmall]

Maybe a illusion, but there looks to be a horizontal crack in the crank just below the taper?

If not the crank looks fine.

Thankfully just an illusion.

I looked over my spare flywheels and decided the original one was the best. So, I lapped the tapers, replaced the key, and reinstalled the flywheel. Just to eliminate questions, I used the torque value Stihl gave in the repair manual--35 N*m. I removed the nut and confirmed it was not bottoming out on the crank shoulder. Saw started right up.

Additionally, I dumped the decomp valve and replaced it with a plug. The old girl found a lot of lost compression. Save for a few minor parts and a thorough cleaning, this saw is field ready. Screws holes are not wallowed out so bad as my 075 was. Not too shabby for a $150 E-bay special. It helps to have a supply of parts saws.

Chris B.

 

[Lakeside53]

There was an old tech note about stihl discontinuing the decomp on the 076, and inserting the plug to increase the compression. I know a guy that does that on 044's.. but inserts a slightly longer bolt..

 

[cbfarmall]

Well, I never thought a decomp plug would actually raise compression. I got rid of the valve because it was a POS. The stem was bent and wouldn't move without a lot of force and, it was leaking significantly when closed. I know I have an 084 decomp somewhere and would install it if I could find it. At least this saw doesn't kick like the 084.

Chris B.