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Old 08-25-2011, 01:21 PM   post #1 of 27
747driver
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Default flywheel shear pin keeps breaking

I have a 16hp ohv briggs series 28q. I replaced the altenator with a new one as the old one quit charging. I learned I put the wrong style on so I took the new one off and put the old one back on. After taking the new one off I found the flywheel shear pin had broken. So I put the old altenator on and a new shear pin. I adjusted the valves and the engine ran rough for abit then would not start at all. I pulled the flywheel off to check the pin and found it to be sheared again. Now the first new one I put on was not a briggs pin but just key stock from the hardware store, would that make a difference? Can't figure out why the shear pins have broken ? I can understand when the pin shears it throws the timing off which will make it hard to start or not start at all.

Thanks Chuck
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Old 08-25-2011, 01:46 PM   post #2 of 27
tomw0
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Default Re: flywheel shear pin keeps breaking

How much torque did you put on the flywheel nut? The shaft is tapered, and depends on friction to keep the flywheel in 'place'. If the nut is not tight enough, the fly will shear the key as the key is sacrificed if you ever hit a stump... and if the flywheel is not tight enough.
The surfaces should be clean and non-rusty for a good friction contact at the specified torque.
tom
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Old 08-25-2011, 06:22 PM   post #3 of 27
747driver
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Default Re: flywheel shear pin keeps breaking

Thanks Tom...I didn't use a torque wrench, just tightened it by feel to what I thought was tight ! Your right I should have use a torque wrench, it makes sense in your response to my problem. Yes, being a aircraft mechanic we use torque wrenches all the time on critical parts.
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Old 08-25-2011, 08:46 PM   post #4 of 27
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Default Re: flywheel shear pin keeps breaking

And dont use a hard key..
A hard key will mess up you crank and flywheel...
The taper does all the holding...
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Old 08-26-2011, 05:46 AM   post #5 of 27
Mike Milburn
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Default Re: flywheel shear pin keeps breaking

Since the grip is dependant on the taper and the key is just for alignment I'll get some valve lapping compund and use it to true up the flywheel and the shaft. Just be sure to get it all off before you put it back together.....Mike
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Old 08-29-2011, 04:40 PM   post #6 of 27
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Default Re: flywheel shear pin keeps breaking

Ok guys....I put a new key in and torqued the flywheel down to 65 ft. lbs. I adjusted the valves from TDC and the engine started right up but ran rough. It stopped and I couldn't get it started again. So I pulled the flywheel and the key was sheared again. The crank shaft taper is alittle scared from the keys shearing. The flywheel bolt has 4 washers under it, should I remove one to seat the bolt farther on the crank shaft ?
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Old 08-29-2011, 04:47 PM   post #7 of 27
Mike Milburn
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Default Re: flywheel shear pin keeps breaking

Quote:
The crank shaft taper is alittle scared from the keys shearing
Anything other than a clean fit is going to cause the key to shear. Did you get some compound as I suggested and dress up the flywheel and shaft?.....Mike
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Old 08-29-2011, 05:14 PM   post #8 of 27
rscurtis
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Default Re: flywheel shear pin keeps breaking

I've never seen a Briggs with 4 flywheel washers. That could be the crux of your problem.
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Old 08-29-2011, 06:33 PM   post #9 of 27
dc 3mech
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Default Re: flywheel shear pin keeps breaking

Look closely and make sure the flywheel isn't cracked,usually in the keyway,over torquing can split it,and tightening more can cause it to spread.
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Old 08-29-2011, 06:39 PM   post #10 of 27
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Default Re: flywheel shear pin keeps breaking

If the flywheel bore and crank taper aren't clean and dry w/ absolutely no lubricant, the problem won't go away.
Mike
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Old 08-29-2011, 06:51 PM   post #11 of 27
LilysDad
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Default Re: flywheel shear pin keeps breaking

Does this have a dished washer like the old Briggs verts. used to?
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Old 08-29-2011, 07:11 PM   post #12 of 27
747driver
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Default Re: flywheel shear pin keeps breaking

Mike..I had put it all back together before I read your post. Now I will use the compound and dress the shaft and bore. As I said earlier I don't work on small engines much, but with manuals and this forums help I am learning alot !

Thanks again Chuck
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Old 08-30-2011, 01:29 PM   post #13 of 27
BOSMECH
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Default Re: flywheel shear pin keeps breaking

Chuck come on your an A&P mechanic (So am I) so we should never have problems.


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Old 08-30-2011, 10:23 PM   post #14 of 27
dc 3mech
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Default Re: flywheel shear pin keeps breaking

Yeah,me too,A&P IA,DME for a while,lots of piston time, 4&6 cylinder flats,, 9,14&18cylinder rounds,and still I've had these little one lunger's kick my butt.
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Old 08-31-2011, 02:20 PM   post #15 of 27
tomw0
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Default Re: flywheel shear pin keeps breaking

Dad worked on them (Wright Cyclones) for the B29(?) back when at the Chicago (Cicero) Dodge plant, then went on to build R4360's and Pratt J57s, again at the old Chicago Dodge plant, then taken over by Ford AED. Long ago.
Same place Preston Tucker built his 50 Tuckers... Dad said he was put out of business by the Big '4' of the day... Didn't want the competition, and they had a lobby in DC, which Tucker did not. Old f*rt memories, I spoze.
Back OT, if the crankshaft taper is all scored from slippage, what is a possible solution? I have two in mind, but one involves disassembly, and the other involves epoxies...
tom
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