P40 Flywheel broken fin ???

[lesorubcheek]

Hello all. I'm a new member here and want to say up front I've found tons of very useful info about my biggest addiction... chainsaws. I have a P40 that I'm in the process of restoring and wanted to ask advice regarding a broken flywheel fin. Haven't ran it enough to know if this will even be a problem yet. I've searched the forum for suggestions about broken flywheel fins and found recommendations of cutting the opposite one for balancing and of using JB Weld to reattach a broken fin.

The flywheel is a Wico and I've attached a pic. I found a newer style Phelon flywheel on ebay, but just my luck it appears the keyway is located different so the timing will be off and so its not the solution either. Anyone ever try to use aluminum welding to repair a broken fin? Any issues with heating it that may cause fractures? Any tricks to balance a flywheel? Open to any and all suggestions.

Thanks in advance.

 

[Lawn Masters]

AS you've learned, if you remove the fin directly opposite from the already broken one, you've basically rebalanced the flywheel. an off balance flywheel IMO would probably be bad for the crank bearings.

 

[Crofter]

I would not like the possibilty of having a glued fin come off and potentially do a heck of a lot more damage. Take the one off opposite would be my take on that. Welding on a flywheel could have some problems from the heat affecting the magnets but I would worry more about the possibility of crystallising in the weld zone causing a stress raiser. You dont want a flywheel coming apart in your face. Some alloys weld beautifully and some can be pulled apart with your hands leaving a grain structure like rock salt.

 

[ray benson]

Don't want to think about a reattached fin coming off at top rpm. I would try to take off the opposite fin, do some filing or sanding and make them look symmetric. As far as balancing -what about using a mower blade balancer ?
Ray

 

[Pioneer]

I've successfully re-balanced flywheels with one broken fin by drilling out the area of the broken fin, filing it flush with the surface, drilling and tapping and installing a bolt head with locktite. Perfect balance can be achieved by using a hobby magnetic balance setup that is used for propellers. You can probably borrow one from a friend who is heavy into R.C. airplanes. I have done two flywheels this way and have had smooth running on the saws.

 

[glens]

If there are an odd number of fins, you might get by with removing equal parts of the opposite two, but I don't know how much load the fins put into the system as far as moving air.  It's conceivable you could get a static balance that would act like an imbalance in use.

Glen

 

[Greg Carberry]

Just snap the opposite fin off and don't worry about it. I've got several running saws with the same arrangement absolutely no problems. I've just carefully broken the fins off with a small hammer and punch. You need to be extra carefull and just lightly hit it enough to break it off not smack into the other fins. Then file it down like the other side and your done.

 

[lesorubcheek]

Hay everybody, thanks for the great advice. Lots of ideas I'd not considered. Pioneer, I have a prop balancer, but I'll have to fab a spacer to center the flywheel properly. This is a brilliant idea!

I am still a bit concerned about the effect from decreased cooling of breaking the fin opposite, but this may be the best way to go.

 

[trimmmed]

I don't see how breaking off another fin has anything to do with balancing anything circular. I think Pioneer's idea goes more toward balancing.

 

[njforestfire]

Don't worry about the extra cooling you might be losing....don't forget they are all 'air cooled' saws.

 

[glens]

I'm going to say it again even though it may not amount to a hill of beans.&nbsp; If you can put enough weight back at the location of the missing fin to restore proper static balance, don't you think the air load at the perimeter which will now be missing from and/or additional turbulence that will be present at that location might just have some effect on the <i>effective</i> dynamic balance?&nbsp; How much might it vary at different rotational speeds?&nbsp; I'd think your safest bet would be to hope for an even number of vanes so you can fully remove both the remnant of the one and the entire one opposite, providing smooth surfaces for air to contact.

Glen

 

[lesorubcheek]

I think that's a very good point. Uneven loads due to forces excerpted by uneven airflow may cause problems even if static weight balancing is ideal. The flywheel appears very much symmetrical, so breaking off a fin directly opposite would be simple enough.


This is why I love this forum. So many points of view and most are very ingenious!