Newbie here.

Engine is about 4 years old. Ran fine for 3 years of light lawn mowing duties. Last year the engine got noisy and eventually lost power and smokey. Took off the valve cover and the posts had unscrewed. Tightened them up and the engine was fine again. Kind of. It was now difficult to start, and only now am I understanding that it was probably a result of high compression. It needed a jump start even with a new 275cca battery. Anyway, the engine ran fine for another year.

Today the engine lost power and huge smoke out of the muffler. Checked the valves again - they are fine. The engine would sometimes start, but straight away it had no power and huge smoke out the muffler, and cut out after a few seconds. Did that a few times and then a nasty noise from the starter gears and the engine won't turn at all. Starter turns, gears don't mesh.

Took off the starter gear cover and the gears are well chewed and a few missing teeth. Same for the flywheel gear. So I know I need to replace those, but what about the high compression and smokey muffler?

Took out the head bolts and took off the head (28N707 is OHV single). By the way, both bolts holding in the muffler sheared off :( The head gasket is perfect. Engine is easy to turn. Bores are not ridged and look great. This looks like a good candidate to fix and get a few more years out of.

My thoughts - get a new head gasket and reassemble the head. Remove flywheel and replace the plastic gear with the new aluminum kit. Neither of which will solve the high compression problem.

General question - how is the valve gap adjusted? There is no adjuster. What causes the engine to develop high compression, and what is the fix? Would this also cause the smokey muffler, or is that a different problem? Also, the oil is getting pushed back into the air filter and that is a big mess too. Do these engines have crankcase breathers?

Specific question - can someone provide the part number for the head gasket? Also, is there a way to get off the big center nut that holds on the flywheel without buying the $32 B&S holder tool? If I have to buy the tool, what is the right part # for this engine - 750-083 or 750-075?

Thx for your help!

Yes these engines have crankcase breathers...... are you sure in the thin spot it wasn't kinda black? What color smoke is it? (never gave it) A blown headgasket will cause oil consumption (white to blue) or a faulty breather.

http://faqs.custhelp.com/cgi-bin/faqs.cfg/php/enduser/std_adp.php?p_faqid=3441&p_created=1101860144
this is how you adjust the valves...... sounds like you never did adjust them RIGHT so hence the catching on the compression stroke.

For holding the engine..... just put a little rope down the spark plug hole (put the head back on for right now) to lock it.

I ordered a new head gasket and aluminum flywheel kit. Found a "breather hose" in the parts list, but nothing that could be a PCV type of widget.

The smoke was white/grey. I may have skipped a few details because it was already a long story. The engine was running fine, lost power and pushed huge smoke out the muffler. Wouldn't restart. Came back an hour later, engine restarted and ran fine - no smoke at all, oil level where it should be on the dipstick. Finished cutting the grass. Came back many hours later, the engine started once and immediately had no power and smoke. Stalled. After a few restart attempts, the starter gears crunched and now the starter turns but the gears don't engage.

I'm hoping I can replace the flywheel and starter gear, new head gasket, set the valve clearance and it's good for a few more years. From your link I learned that there is a valve adjustment using a torx wrench/screwdriver. I knew the torx was there, but I tried to move it before and it was locked solid. Won't hurt to bathe it in penetrating fluid now the engine is apart.

That torx screw has Locktite on it. You may have to use a ratchet on a
torx bit to loosen it. The valve clearence on the 28N707 is critical.
If the exhaust valve isn't adjusted to .005-.007" with the piston 1/4" past top
dead center (to get off the compression release), the compression will be
high enough damage even the aluminium ring gear.