Briggs 17.5hp 31c707-3346-g6

[arch252]

Need help, I'm at a loss. Picked up a freebie Troy Bilt Pony rider, no history on it. Valve cover was missing, not sure if they tinkered with the valves. Starter was fried internally and carb was trashed. I had a replacement carb with a fixed air mixture screw, used it just to get it running. Replaced the valve cover, starter, fuel lines, fuel filter, new spark plug (RC12YC), oil change and new battery. It started but seemed to have too much compression and struggled to get "over the hump" but then it did crank and ran strong but it was surging.

I ordered a new carb with adjustable air mixture screw. Put the new carb on, didn't change anything else, now it is extremely difficult to get it to turn a full rotation. I took the plug out and it spun freely. It was not hydrolocked. Checked the valves, still set at .004/.006. Checked the push rods, they are both straight. After I put the plug back in I put a spark tester on and it started first crank. I turned it off and removed the spark tester and connected the plug wire and tried to start it. It backfired and then the compression was again too strong to allow the engine to turn over. I pulled the flywheel and checked the key, it was good. I have tried jumping it off the battery on my JD LX279, no difference so battery is not the issue.


Any ideas???

 

[Scrubcadet10]

Willing to bet the 793880 camshaft Automatic compression relief is bad.
take the spark plug out and the valve cover off, turn the engine over by hand, check for the intake valve to bump open slightly on the "compression" stroke.
if that is the issue, the cam P/N is superseded to this, https://www.jackssmallengines.com/jacks-parts-lookup/part/84005207

 

[arch252]

Just checked, no bump for the compression relief. I tightened the intake clearance down to a snug .003 and still no bump. I'm in it this far, guess I'll have to open it up. Thanks!

 

[Scrubcadet10]

Just checked, no bump for the compression relief. I tightened the intake clearance down to a snug .003 and still no bump. I'm in it this far, guess I'll have to open it up. Thanks!

do me a favor and check one more time, that it doesn't bump the exhaust valve either.

 

[StarTech]

Scrub, the 310000 series uses a cross flow head and the ACR bump is on the intake valve (lower rocker when looking down from the flywheel side).

 

[arch252]

Opened up the engine and the compression release was in pieces. Unfortunately when inpicked up this mower the valve cover was missing so I have no engine code. This engine does not have an oil pump. The only camshaft I have found is 793880 but it has the grooves for an oil pump. I believe I need the cam with the flat head, no grooves. Anyone have the part number for that? Briggs 17.5 hp Powerbuilt 500cc.

 

[Scrubcadet10]

https://www.jackssmallengines.com/jacks-parts-lookup/part/briggs-stratton/84005207

As far as i know, you still use the same cam, Star Tech, Rivets or Ilengine might know for sure.

31B700, 21A800, 210700, 212700, 212900, 215700, 215900, 216900, 217800, 219800, 21B800, 28BH00, 31A500, 31A700, 31C700, 31E500, 31E700, 31G700, 31K700, 31M700, 31M900, 31N800, 31P700, 31P900, 31Q700, 282H00, 31E877 Small Engine 4 Cycle

 

[ILENGINE]

it is the same came with or without the oil pump and the 793880 camshaft has been superceded to a new part number that I don't remember.

 

[arch252]

Thanks! I couldn't fine the one without the groove and I see no reason why it would matter if there is a groove but no oil pump.

 

[Scrubcadet10]

it is the same came with or without the oil pump and the 793880 camshaft has been superceded to a new part number that I don't remember.

84005207