Briggs Stratton 17.5 Horse engine Questions

I didn't want to hijack Transtar 61's post, so I'll start another. Son has a Yard Machine with a 17.5 hp B & S engine. Model 42A707 Type 2238E1 code 9904225B. It's been a hard starter for him. He said you had to crank it a long time to get it to start and if you shut it off, it wouldn't start again that day. It had a spark plug stripped out and the wrong plugs in it. I rethreaded the spark plug hole and put the right plugs in it, still no start. It has a new battery and I had him take it back and get it checked out, it's good. It cranks slow and stalls on compression stroke. I put a spark plug tester on it and it has very weak spark. I took the plugs out and cranked it over to see if it was the starter and the bendix came apart and broke a piece out of the top of the flywheel right above the teeth. Also, the new spark plug on the left cylinder has the threads on the end boogered up, looks like it's hitting the piston. Can you buy just the bendix, or just get a new starter? I'm thinking a new coil , not sure about the flywheel. Is there a do it yourself Briggs & Stratton website? How do you check the compression release? I'd like to get this fixed so I can get my extra mower back before he tears it up also. Any help appreciated. Chris

The starter gear is part # BSP-695708 Lowes or Home Depot might carry it.

What kind of battery does it use? A regular mower battery or a motorcycle type battery? I would do a voltage drop test to make sure 12Volts is getting to the starter. The starter may be worn out. Maybe someone can post a way to check by measuring AMPs.

If you crank too long on those starters, the magnets break inside the case.

If the plug is in snuggly, then I wouldn't worry about the threads. A plug thread insert would be a good repair. A new head would be best repair.

I would pull shroud off top and make sure there is not a rats nest on plug wires. Wire brush flywheel and coil. Air gap should be .010(thickness of most business cards). Very very rare for shear key to shear on those engines. I would atleast pull flywheel nut off with an impact and make sure shear key is not spun since the starter gear broke.

The coil either stops working and that is it or it stops working when it gets hot and then works again when it cools down.

I would search Ebay for parts instead of going new. Or, find a parts yard near you. I know of a good one in Mi.

pdf of that engine:
http://www.odref.com/briggsandstratton/model-42/42A700-ms0635-0602.pdf
Voltage drop test

The piston should not be able to hit the plug threads. They should be short threads. There could be something in cylinder causing damage tho.

Make sure connecting rod isn't broken on both cylinders. Stick a stick in plug hole and slowly turn engine by hand.

I use Champion RJ19LM in those engines.

I agree with rrobert about checking flywheel key same may be Z bent/sheared changeing ign timeing,this may be the reason starter drive broke if ign timing out it can cause flywheel to kick back against drive.

After that I would goto partstree or jacks small engine online & lookup mod/type# of eng & get pn for a new starter then goto ebay & search briggs+ starter pn,see if anything listed in new aftermarket or used starters as the main problem is to eliminate any internal problems in starter.

From the type# you gave for eng same has magnetron(solid state)ign,all briggs eng with magnetron system must turn a min 350 rpm when cranking or you will get a weak/no spark condition,if starter can't crank eng that fast this may explain weak spark.

As far as damaged plug thread if something hitting threads when plug installed it would also damage/destroy center electrode of plug,the exception being for thread damage as rrobert said something in cyl or if wrong reach/long reach plugs as used in ohv valve eng were previously installed same may have cracked/punched a hole in piston(s) & you now have chunks of piston floating around in cyl or a jagged edge of piston crack/hole hitting plug threads.

An other thing that will help your cranking:

Yard Machines typically have battery cables that are barely adequate when new. That machine is probably 10 yrs. old to have that engine. Larger battery cables will help your starter crank your engine.