Unable to start B&S 12 hp

14 years ago

I have a briggs & stratton 12 hp twin (model 422707-1510-01) that is giving me starting problems. The starter has been cranking it really sluggishly. Sometimes in order to start it, I need to manually assist the starter turn engine over. Sometimes I have to charge the battery more, though this no longer seems to do the trick. The battery tests good. I have removed the starter and found the following: A shiney triangular spot on the inside of the magnet. (approximately the area of a nickel/quarter)

Testing the starter off the mower, it seems to work as it should (using the charger). I noticed that the gear ring has some damage. While no teeth are missing, the stop that prevents the starter from overextending has portions missing at the two places where the engine cycle normally ends. Upon reinstalling the starter, it now whirrs, without engaging. I suspect this may be due to a gummed bendix which will get a shot of WD-40 at first light. The real stumper for me is that when the starter properly engages, it does not seem to have enough ooomph to turn it over. The flywheel advances only an inch or so, unless I give it some help. Now the help I offer it is not enough.

Cost of a starter is $140! That's more than my last auto starter! So trial and error replacement is not the way to approach this.

When I was given this used mower a year or so ago, I attempted to start it. Trying to crank it 4 times, I realized that it had been drained of gas and oil! Could it be that I damaged the engine due to absence of lubrication? If so, how does one confirm this, and what would be the recommended repair options?

Thanks for your consideration.

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Comments (4)

tomplum
14 years ago
Best shop around @ $140... tho they are pricey. These starters get tired. If it won't crank w/ a known good HD battery and known good jumper cables direct then it is likely time for a new starter. I doubt that it was damaged by just cranking w/ the oil drained. How does it crank w/o the spark plugs? Nothing is dragging such as a deck as it is cranking? If it is an oil burner, there could be a build up under the head. Be certain the new starter drive won't go up past the bad spot in the ring gear or get a new one.
rustyj14
14 years ago
You are starting at the wrong place! Do not buy a new starter until you have exhausted all other possible problems!
First: The starter Bendix must be free of any kind of lubrication!
Second. Make sure you haven't installed or connected the battery backwards, i.e. cable connections.
Third: How old is the battery? More than 2 years, you are on the last good life of the battery.
Fourth: Unbolt all cable connections, to battery, starter, and ground cable to frame. Using sand-paper, sand off and clean the cable ends (both ends), the places where they connect to solenoid, starter, frame ground! Use new bolts.
I am hoping that you installed the proper amount of oil in the engine. (Read my previous post on proper reading of the dip-stick)
If the starter gear looks good, use it. If not, you can buy replacement parts reasonably. As for damaging the engine by cranking it without oil in it, i'd say no. If it started and ran, then yes, it might and probably would damage it.
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walt2002
14 years ago
Like Rusty says, plus, several things.

I doubt that a 12 hp horizontally opposed twin is a model 42--, most likely a 40---, but that doesn't matter. This whole series of engines where prone to starting problems when they aged.

The shinny spot in your magnet, sounds to me like the top starter bushing is worn out allowing the armature to drag on the field magnet. Cure, replace the "unreplaceable" top bushing by tapping it with a threading tap and pulling it with a bolt as you would a valve guide. Get new bushing at hardware, farm supply store or auto parts store. The OD will likely need turning or filing down.

Almost any B&S starter will fit this by changing the end plate/mounting bracket. Remove starter gear and bendix ass'y, remove two long bolts holding starter together, hold starter body down so brush ass'y doesn't come apart, remove end/mounting plate, place on "new" starter.

As a last resort, check the Valve clearances. This does not generally need checked UNLESS someone has recently done a "valve job" on it and as often the tenancy, left excessive clearance "just to be sure". The "easy Spin" cam acts off the Intake Valve Cam Lobe to hold the Intake Valve open very late into the compression stroke to relieve some compression for starting ease. The starters on these engines are taxed to near limit when all is ideal.

Almost forgot, often excessive carbon build up in the heads also can cause this condition by increasing the compression ratio, overloading the starter.

Walt Conner
ron_ray
14 years ago
I pulled everything out (including my hair), before doing the sensible things mentioned by the other members. I replaced everything that I shouldn't have on my mower. (Along with the starter and relay, I actually replaced the head gasket too!)

The battery and starter "cable connections" are probably your primary problems. That's not to say that the problem is not the battery and/or starter, but this is the proper sequence in the 'process of elimination'.
Completely remove the cables from the battery AND where they attach to the body and relay. (Where two of my problems were!)
Clean these areas good (sandpaper, wire brush) before reconnecting. Be sure you see "shiny metal" before reattaching.
This sounds overkill, buy is overlooked too often!

Another thing.... (Depending on your model) Be sure there's no pressure on the blade belts or pulleys (safety brake, etc.). This, in combination with the connections, will also cause the symptoms that you described.

Unable to start B&S 12 hp

Comments (4)

tomplum

rustyj14

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walt2002

ron_ray

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