How to shave fins on briggs flywheel?

If you shaved them even it should not be out of balance. If you broke one then it would be and you have to break one just the opp asset side to balance. One way is to take a grinder and while it is running, the other is to put it in a lathe and turn them down..........Curt

I just did some final balancing work on my flywheel yesterday, a five horse Tecumseh flathead with cast iron flywheel... very heavy. This had deep fins and I knocked off some of the excess with a ball peen hammer (tapping, not whacking) and then used my side grinder to take them down further and more evenly. Can't remember if I used the grinding disc first or not as this was some time ago, but I know that the latter part of the dressing down was with a flap disc attachment on the side grinder. Yesterday I did the final dressing and balancing using the flap disc and checking for balance with a little tool from the hardware store made for balancing mower blades. You can do it...

If you don't have a side grinder one from Harbor Freight is good enough. I have one and also a DeWalt and most of the time use the lighter HF which costs a lot less.
SB

This is from Briggs guru Msrfan:

"I break the fins off with a hammer, then grind them down on a pedestel grinder, and finish it off on a lathe. I have a stub shaft from a junk crank I put into the lathe chuck and bolt the flywheel to it. It will need to be re-balanced , so I use a lawnmower blade balancer."

Of course a lathe would be ideal. Don't have one, so I have done all mine with an angle grinder clamped to a flat surface - usually my table saw top.

In the pic it's clamped to a normal table to show up better, and the duct tape represents the flywheel.

It's easy to find a combination of flat stock (plywood, books, metal plate) that will raise the grinder the desired height off the table top. Or under the flywheel to get the fins cut right where you want.
I use a thin metal cutting disk. Try to get the disk as level and parallel to the table as possible. And of course clamp the grinder tight enough so it will stay put and not vibrate loose - but not too tight to damage your grinder.

Then you just hand feed the flywheel into the disk, fins facing up. I like to cut in about a quarter inch and rotate the flywheel (against the disk rotation to lessen chance of grabbing); when cut all around feed in another 1/4 inch and continue till fins are all gone.
My grinder and disk gives me about 1 1/2 inches cutting depth, a bigger disk will give more.

Make sure the back of the flywheel is flat. I've had some with a bit of casting flash that needed a quick cleanup before doing the fin grinding.

http://motorbicycling.com/showthread.php?t=49177&page=24

Posts 237 & 238 show photos of the fins being taken down on my Tecumseh. This flywheel had very deep fins and not all were of the same depth, so I did not take them down all the way, but most of the way and reduced the width of the engine by a good bit. To dress up the engine and protect my leg I covered it with a shallow copper bottomed steel frying pan with the handle cut off and center drilled for the flywheel bolt. I think it turned out nicely. I took the fins down by eye and as mentioned did the final balancing with a mower blade balance tool... available at any hardware for a few dollars.
Good luck and give us a picture or two when you're done.
SB

That looks good, silverbear!

I see you wanted the fins cut down following the contour of the flywheel, not just straight across (flat). The small 2-stroke flywheels I've done were all flat.

That shaved flywheel looked pretty good bare, but the "pot" cover is extra sweet. Great minds think alike. I've got a collection of discarded cookware for future projects. Some nice thick aluminum pieces and a big 18/10 stainless skillet with a bottom about 1/4 inch thick that I'm sure will come in handy someday.

Thank you a_dam,
When I started looking for a cover for the flywheel I had no idea anything would look as good or work as well as that frying pan. Who'dathunkit? Nice when something turns out better than you thought it would. Usually it's the other way around. Fun repurposing things, eh?
SB

a_dam- That's good thinkin! Thanks for sharing that technique.

SB- I've been following "kinda..." and I missed that somehow. Kewel!

falcondave- Are you still with us? You're getting super good guidance.

Hi falcondave

Sorry, this not my work.
Here is a link to the post:

http://motorbicycling.com/showpost.php?p=316744&postcount=16

Thanks mat_man. Yes, I removed the magnets for the lathe work. Use a punch to push the 2 roll pins out and then replace them when you're ready. You will be removing some overall weight from the flywheel, so you may want to add some to the light side when balancing.

Some have a flat cut out on the light side and I have fitted a piece of steel onto it with machine screws after drilling and tapping the flywheel. What you don't want to do is take too much off around the magnet mounting area. My grandson's bike threw a magnet off at speed and could have hurt, but it went down and broke a chunk out of the case. We were able to patch the hole and attach the magnet back on with extra bolts. We didn't trust it after that and were more careful on the next flywheel. I like to make custom guards to fit snugly over it when I can. Another way to add weight is on the inside. I use machine screws after making a half moon piece to fit. The centrifugal force keeps it tight. Lightening the flywheel lets the engine rev faster, but there's trade offs. Like more impulse feel and rougher idling. It's worth it to have it narrowed though. I used a 3hp flywheel on my race bike and it revs a lot faster. You need to use a 3hp magneto and re-locate it lower as it's an inch smaller in diameter then the 5hp.