OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs 90112 misfire

Hi Guys,
Having issues with this engine. Used to run fine but a little smokey until I removed it from a mower. My son tried to start it in the garage one day and reported a big misfire with a flash of flame coming out the exhaust and a big hiss of fuel blown from the air intake with the air filter removed. Also has the occasional backfire when trying to start. Decided it may be time to investigate and use the opportunity to hone, slip in some new piston rings and oil seals and lap the valves. After reassembly the engine is exactly the same. What have I missed? Have double checked cam and crankshaft timing and all is good.
Briggs 90112
0007 01
9602116FA

Check the flywheel key and the blade plate boss key to see if either of them have sheared.

Yep. Forgot to mention that! When I pulled engine down it had a split key and again now. But whats the cause?

Hello Mr Jones,

Mate, the causes may be different.
The No. 1 cause of a sheared key after a rebuild is insufficient
torque applied to the flywheel nut.

Hope this helps.
________________________
JACK.

Insufficient torque is the usual suspect and also check the boss key as this could be a cause of the flywheel key shearing as there might be insufficient torque there as well causing the flywheel key to shear over and over again .

Cheers Guys,
Salvaged a key and really tightened the starter clutch and she runs. Now need to stock up on some keys and keep that clutch tight!

Here is a picture the correct tool for removing, installing and torquing these starter clutches. The torque spec is 55 ft-lbs. If over torque you risk damaging the flywheel taper or splitting it.

I haven't found the flywheel attaching nut to need a lot of torque unless there is a keyway burr on either the crankshaft or flywheel - which there usually is if it has sheared a key. Most people either don't deburr the flywheel bore at all, or do a sloppy job of it. You usually need to use blue and find out how much contact area you have. If you find a non-contact area close to the keyway on each side of it, you can be sure you have a keyway burr. And remember, always do a final bluing test with the key in place: a key that is too high, or can't get to the bottom of the keyway due to an internal burr, will deform the bore near the keyway, making repeated key failures inevitable.

+1 to grumpy here. Many folk just assume that the Briggs soft alloy key won't do any damage when it gets sheared, e.g. by a bar blade hitting a solid object, but this is by no means always true.

This key should never be replaced with anything other than a genuine Briggs part, or a reputable clone. It's a designed 'weak point', which fails in order to prevent damage to major components.

This is true for most of Briggs vertical engines especially for those design for walk behind use. This is to try to prevent internal damage to the engine and the PTO end. I still get them in the shop sometimes with bent crankshafts even with the Briggs aluminum keys.

There is one set exceptions to use of the aluminum key made in 2012 to the 210000, 280000, 310000, and 330000 verticals where there was undue shearing of the key. Briggs changed those engines flywheel key to a steel key PN 796335 and increased the torque spec to 110 ft-lbs.

This was mainly due to a flywheel key-way design problem which Brigg redesign starting with date code 120630*******. The flywheels and crankshafts of these engines are not interchangeable. There was no mention of going back to aluminum key but they may have after the redesign.

References ASPI 82 and ASPI 89

Thanks AVB, I'd never heard of that limited use of steel keys - now I just hope I remember it if we ever have a case involving one of those engines.

Is it possible for you to post how people can get access to the Briggs service notices? If they are restricted to approved workshops only, of course you can't - we understand that.

I have access to the Briggs Power Portal website. I had ask for access to it through their contact page. Since I am am independent repair shop they granted me access to the site.

I did have nearly full access until a recent change to their system which it now only allows me to access the engine related info only and not the generators, the Murray, or Snapper equipment. I haven't had the time or the need to access those lines lately but I do need work on regaining access to these areas.

You can ask for access but it is up to them to approve or not your request. Here is the link to their contact page.
[url=http://www.thepowerportal.com/PowerPortalPublic/PowerPortalContactUsByUser.htm][/url]

Thank you for that AVB. I'll have to look into it.