Briggs 12.5HP engine problems

[StarTech]

Sounds like just another person using a flex hone to do the work of a rigid hone. Just makes things worst.

If the cylinder is either ovaled or tapered (usually both) a flex just makes both these worst. Besides if you were able to hang a finger nail on grooves the cylinder should be rigid hone to .020"over as there is no .030 piston supplied anymore. If you got go over .020" then the engine is a basket case. I have seen cylinders tapered that only clean up within the last .002"

As for valve clearance on L-head (side valve) engine I always grind for the max clearance spec as the these engines tend to close up valve clearances over time. This is so I don't need to redo the valves as often. Right the opposite with OHV engine where I do the minimum settings.

 

[SmallTimeMowerGuy]

There was nothing that hung a nail on, just some glazing from the engine sitting with old oil/water in it. the cylinder wall was clean when I finished and the new rings seemed to seal well, when I installed them on the piston and then into the cylinder id didn't appear to have any ovaling to my eye and again the rings seemingly were contacting the walls well. it was a pressure hone I used, a $25 one from local Canadian tire store.

I'm no technician and this is only the second time I've repaired a lawn mower engine, first one was on a OHV Briggs that had a broken push rod which runs like a champ now

 

[SmallTimeMowerGuy]

minor update on this. I just pulled it out again and started working on this "winter" project.
both valve clearance were 0.00 I couldn't fit anything between the tappet and valve with the engine at TDC.

I've curious now though about how this might effect my slow turning over problem? it seems like there is too much compression in the engine and that the cam lobe relief is the problem, I would think that a 0 gap would mean a bigger lift meaning loss of compression rather then the other way around....maybe I'mma missing something?

Thoughts?

 

[Rivets]

Couple of questions. When you rotate the flywheel by hand do the valves open and close properly? When you checked the clearance were the rocker arms snug against the valves and pushrods? The last time you set the valve clearance, are you sure the locking set screw was very tight? Finally, have you pulled the head and checked the valve faces and seats? Sorry, but it will be hard for me to state possible causes until I have a better picture of what you have going on.

 

[SmallTimeMowerGuy]

Thanks for the reply!
it's a Briggs L-Head, with the side Valve cover off and the top of the head removed to expose the Piston and valves I rotate the engine and the valves go in and out as normal as the piston cycles though it's stroke. The rocker arms were snug against the intake valve stem, on the exhaust it was .004 I believe. I adjusted Intake to .005 and Exhausts to .006 I believe. I don't know what the "locking set screw" is and there was no screw in the valve area that I can identify. I cleaned up the lip and seats for the valves and lapped them in prior to setting the clearances above.

 

[Rivets]

Sorry, I thought I read you have an OHV engine, L-head changes everything I posted. Two different questions now. How did you adjust the valve clearance last time? How did you lap the valves and how long ago did you do this service? I need all engine numbers, model, type and code please.

 

[SmallTimeMowerGuy]

This is my first time adjusting the valves.
I removed the valve springs, removed the valves, cleaned them with wire wheel, cleaned up the seats with emery cloth. Once everything looked clean...
I lapped them in with lapping compound and a lapping tool but doing the quick back and forth in my hands and rotating 1/4 turn and repeating.

It appears I have a good seat now. then I pushed them in with my thumb and checked for clearance with a feeler gauge, adjusted to the lower end of the specs I found, I think .005 intake and .006 exhaust.

I've yet to put the machine back together now after doing this part. I'm having problems getting the Exhaust valve spring and retainer in place, it has the 2x half circle lock bits for it and my make shift spring compressor I made isn't working well for it.

 

[StarTech]

Don't to check the valve guides especially the exhaust. A worn exhaust valve will cause one to smoke like a freight train.

Also hopefully you used a ridge hone as flex hone only breaks the glaze and make things worst if the cylinder is ready ovaled and/or tapered. Plus if the cylinder needed honing it is possible that cylinder worn to a point that over sizing is required.

 

[SmallTimeMowerGuy]

I used a flex hone...I think. the arms were not rigid, there was nothing in the cylinder that looked bad, nothing that was pitted, gouges, nothing to catch a finger nail on or anything. it seems to seal well with the new rings installed, but also seems to build compression to the point of limiting the machine from turning over, I'm hoping that the valve adjustment will help and the machine will at least turn over well now.

the guides seem to be a good snug fit, no play in the valves when installed, and a seemingly good fit overall.

I'm not expert though....lol

 

[slomo]

Guy used a flex hone. He doesn't have a machine shop at home so lighten up on the poor fella' LOL

That large HP engine must have some form of compression release.

Like some mentioned but funky wording. Open the valve clearance gap to the widest, in spec value. Example an EX valve specs out at 0.004" to 0.008" gap. Set clearance at 0.008". As one said above, gap will shrink over time and operation.

Too late but when honing or boring, you need to scrub the crap out of the cylinder when done with HOT soapy water and brushes. And do it again and again until a white paper towel stays white on a bore scrub. Think hospital clean here.

slomo