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Mower: Troy Bilt Pony 42"
Engine: Briggs Intek 17.5HP
Engine model: 31C707-3346-G6

Backstory: I got this mower for free, in pretty good shape! The guy I got it from told me he was mowing on a hill, it smoked and died. Apparently he tried to crank it again (a LOT), and was unsuccessful at that. It was an older gentleman and he didn't want to mess with it so he got a new one and gave the old one to me.

When I got the mower I replaced the battery, starter, starter solenoid, and starter cable. It cranked, and then hung up on the compression stroke. I checked the valves and they were in spec, so I went ahead and ordered a camshaft and gasket kit.

So I tore apart the engine, and the compression release mechanism on the camshaft was broken and in the bottom of the sump. But after doing the engine teardown and rebuild, the thing STILL won't start. It pushes past the compression stroke a lot better, notice I didn't say perfectly, but STILL won't start. I even removed the carburetor and sprayed in ether. Had a small fire, but still no start. What in the world have I missed?? I am at my wit's end with this thing.

List of things I've done/replaced:
- New valve cover gasket
- Adjusted valves
- Cleaned valves and valve seats to a shine
- Cleaned under valve cover, removed lots of carbon
- I noticed the intake valve wasn't seating all that well. Lots of carbon buildup in the intake port under the valve. On the exhaust side, it was clean (in the port, under the valve, that is)
- Lapped valves
- Cleaned head surface
- Cleaned piston, removed carbon
- New head gasket
- Compression test (125psi if I remember correctly)
- New camshaft
- New sump cover gasket
- Cleaned sump religiously (I'd eat out of it, seriously)
- New valve tappets
- Used assembly lube where needed
- New PTO seal
- Cleaned up ignition coil (removed rust)
- Cleaned up flywheel magnet (removed rust)
- Oil change
- New spark plug
- Spark test (passed)
- Cleaned carb fuel bowl, float, with carb cleaner
- Sprayed carb cleaner through each end of carb
- New air filter
- New battery
- New starter
- New starter solenoid
- New starter cable and lug

is the flywheel key in tact in the flywheel and crank groove?
It should make a perfect square.

did you line up the timing marks on crank and cam

I have not checked the flywheel key, I'll rent a flywheel puller tomorrow and check this out. Hopefully the local parts stores rental tool will work on this motor.

Yes, the crank and cam timing marks are lined up.

I couldn't wait until tomorrow; had to take the flywheel fan off and have a peak. It looks like the key is okay, but I'll still rent a flywheel puller and have a closer look.

key looks fine to me.

Just remember to re-torque that retaining screw to 110 ft-lbs.; no guessing, use torque wrench.

Now have you tested to isolate if it is fuel supply problem or other problem? Otherwords have you tried induce fuel to if it will start up or not?

Whe you checked for spark did you remove the plug and check that the spark will jump a 1/4" gap?

@StarTech I've somewhat tested for a fuel problem. I removed the carb and sprayed starting fluid in the intake port. Had a small fire, so I've got spark! But no start. I could spray fuel in the intake port to see how that works. What else can I do to test for a fuel supply problem?

@Hammermechanicman I removed the plug and just grounded it to the block. I did see a spark but I didn't test to see if it would jump a gap. I'll definitely try this later.

Sorry I miss that in the long read.

That tells me that you an internal problem with the engine and not a carburetor problem; although, there is still a chance you need to work on the carburetor later.

As Hammer said check spark jumping nearly .130" - .250". Also double check you mechanical timing of the camshaft and valve adjustments. Plus a known good spark plug as just new doesn't mean it is okay. I have gotten plugs that were bad right out the box.

One last thought, you did install the coil the right way and not upside down?

Good Afternoon,

I confirmed that the ignition coil is on the correct way. I was also able to get the spark plug to jump a .25in gap.

I also gapped the valves again (to .006), and made a quick video of the valves as the motor tried to crank (with the fuel shut off). At the beginning of the video, you hear it hit the compression release hard, pause, then resume cranking.


I also noticed that the exhaust pushrod is spinning. If you look closely in the video below you'll notice it spin as the compression releases. Is this normal?


I've pretty much accepted the fact that I am going to have to tear apart this motor again.

.06? Do you mean .006 (inches)?

Well just a couple thing I notice here that is incorrect.

First that lower rocker and valve is the intake and not the exhaust.

Second you got the push backwards as the aluminum goes on the intake and the steel one on the exhaust. Won't prevent he engine from starting but will cause problems later.

cpurvis said:

.06? Do you mean .006 (inches)?

Click to expand...

Oops missed a digit, yes .006. I corrected that in my post.

Good Morning Guys,

So I've got the engine off the mower, and the timing appears to be correct. The camshaft is still in tact (intake & exhaust lobes, compression release). I've attached a few pictures just to confirm the timing is right.

I also switched the push rods.

Is there anything else in particular I need to take a look at while I have the case cracked?

I see a key on crank i don't see a dot on the crank gear tooth
dot to dot must line up

I think you're one tooth off... I zoomed in on the picture and it looks like the gear tooth on the crank below the key and dot on the cam has a round dot on it.

I might have figured it out. There are two very tiny dots on the crank, one on the left and one on the right. Apparently I chose the wrong tiny dot? Maybe it's the one on the left and not the one by the key?

Here is a picture of where I'm at now. How can I confirm this is the right timing before putting it all back together?

By rotating the crank and watching the valves. The exhaust valve should just be closing and the intake valve starting to open when the piston is at top dead center.

StarTech said:

Well just a couple thing I notice here that is incorrect.

First that lower rocker and valve is the intake and not the exhaust.

Second you got the push backwards as the aluminum goes on the intake and the steel one on the exhaust. Won't prevent he engine from starting but will cause problems later.

Click to expand...

Taryl said you can run 2 steel push rods if you want. Actually he said he prefers it, won't hurt anything. So the push rods should be interchangeable. Just typing out loud here.

Yes later on someone might get confused in or ex.

slomo

Scrubcadet10 said:

I think you're one tooth off... I zoomed in on the picture and it looks like the gear tooth on the crank below the key and dot on the cam has a round dot on it.

View attachment 53035

Click to expand...

Scrub, how the heck did you catch that one? Freaking super eagle eyes LOL.

slomo