Neighbors Troy Bilt Pony cranks slow then kicks back, think its the ACR?

[BackyardBrian]

Hey fellas, Brian again. Neighbor heard I been wrenchin on my X350 and asked if I'd look at his Troy Bilt Pony before winter. 17.5 Intek, bout 10 years old n 300 hrs.
Ran through everything you guys walked me through on my own stuff. Fresh battery, cleaned grounds, starter bench tests fine, strong blue spark, fresh gas, carb clean, valve lash set. Fires on starting fluid for half a sec then dies.
Heres the weird part. Plug out it spins beautiful. Plug in n the starter grunts, slows way down right before TDC on compression, sometimes kicks back hard enough you hear the bendix clack.
From what I been readin this screams sheared ACR tab on the cam. Pulled the valve cover n dont see the little pushrod bump before TDC either.
Am I readin this right before I crack it open? Whats the compression number im lookin for to confirm? TIA

 

[Bertrrr]

Your battery maybe weak , with no plug it will spin freely as there is no compression , make sure you have a good battery then see how it turn over for starting ,if it kicks off with starting fluid , it's a fuel problem not fire. Also too much starting fluid can make it kick back like your saying. I think it sort of advances timing because the flash point of starting fluid is so low ,

 

[ILENGINE]

Hey fellas, Brian again. Neighbor heard I been wrenchin on my X350 and asked if I'd look at his Troy Bilt Pony before winter. 17.5 Intek, bout 10 years old n 300 hrs.
Ran through everything you guys walked me through on my own stuff. Fresh battery, cleaned grounds, starter bench tests fine, strong blue spark, fresh gas, carb clean, valve lash set. Fires on starting fluid for half a sec then dies.
Heres the weird part. Plug out it spins beautiful. Plug in n the starter grunts, slows way down right before TDC on compression, sometimes kicks back hard enough you hear the bendix clack.
From what I been readin this screams sheared ACR tab on the cam. Pulled the valve cover n dont see the little pushrod bump before TDC either.
Am I readin this right before I crack it open? Whats the compression number im lookin for to confirm? TIA

If the valve clearances are set correctly, and I would double check. And still no decompression bump on the intake valve which in this engine is the bottom valve I would highly suspect broken ACR.

 

[BackyardBrian]

Thanks guys. I double checked the lash and it is dead on. Still no bump on the lower valve. I ran a compression test and it pumped up to 145 psi cold. That is way too high for a working ACR so the cam is definitely toast.
OEM 793880 is about 80 bucks on its own. By the time I buy the gasket, seals, and tappets, I am looking at over 120. I found a complete kit on FridayParts for about 33 dollars that has the whole supersession chain and includes the gasket and seal.
I bought a blade balancer from them back in July for my X350 and it showed up fast. I will give their Briggs parts a shot and report back once I get the engine opened up.

 

[Auto Doc's]

Everything points to a broken ACR.

 

[sgkent]

that said, put a volt meter on the battery and see how far down the voltage is dropping. Although it may have a bad AC, starter motors turn engines over all the time that are in the 140 compression range.

 

[slomo]

Fresh battery

Means zero to me. Battery needs to be LOAD tested to confirm. Find someone with a real carbon pile tester. Call all the auto parts stores and ask if they have one. It's the only real, accurate way, to test a battery.

strong blue spark

How far, does it jump in free air? How big of a gap till it starts sputtering from the lack of fire? Strong blue means zero again.

fresh gas

What about the sludge in the bottom of the tank and the probable stock OEM fuel lines that have degraded internally? Things to check out. Solid fuel flow AT the carb inlet hose?

carb clean

Is the emulsion tube clean as a new one is? Float height set proper?

valve lash set

There are two TDC strokes on a 4 smoke engine. Recheck the valves using the heel of the cam method. Toe of the cam is the lobe lifting point. Heel is the back side with no lift and duration ON the valves.

Fires on starting fluid for half a sec then dies.

What does this tell you? Engine needs air, fuel, spark (at the correct time) and compression to run. She is thirsty........

 

[BackyardBrian]

Good points guys. Went back through it today. Battery load tested good and I saw 10.8v lowest at the starter post to block while crankin with the plug in, so the starter is gettin plenty of juice. Solid fuel flow at the carb inlet and the bowl had gas.
Rechecked lash on the heel of the cam on the compression stroke, still no ACR bump on the lower valve and 145 psi cold. Might still need some carb tuning after but the hard crank and kickback sure look like a bad cam/ACR to me.

 

[Auto Doc's]

Per internet search:​

Briggs & Stratton Intek Engine — Compression Release Failure​

A broken compression release on a Briggs & Stratton Intek engine is a common failure that makes the engine extremely hard to turn over, often mimicking a dead battery or seized starter YouTube+1.

How the Compression Release Works​

The Automatic Compression Release (ACR) is built into the Intek’s camshaft. During the compression stroke, it momentarily lifts the exhaust valve slightly to vent cylinder pressure, making starting possible without excessive force homeexparts.com+1. If the ACR’s flyweight or return spring fails, the valve never opens, and the engine resists cranking.