MTD Tractor Starting problem

[bgsengine]

I'd suggest compression test, see what PSI it can develop with valves set properly, and then again with valve clearances backed off to eliminate compression release.... and go from there..

[38racing]

I'd suggest compression test, see what PSI it can develop with valves set properly, and then again with valve clearances backed off to eliminate compression release.... and go from there..

Interesting thought. We all sort of say compression test meaningless because of release but in fact honda pushmower engine manuals actually tell you how to test compression by disabling the release by disabling the exhaust valve completely. Obviously can't do that on the intake valve except by increasing the clearance.
Edited last sentence to correct to intake.

[KE4AVB]

I'd suggest compression test, see what PSI it can develop with valves set properly, and then again with valve clearances backed off to eliminate compression release.... and go from there..

Interesting thought. We all sort of say compression test meaningless because of release but in fact honda pushmower engine manuals actually tell you how to test compression by disabling the release by disabling the exhaust valve completely. Obviously can't do that on exhaust valve except by increasing the clearance.

Only one problem with that idea the ACR on the 793880 camshaft is on the intake valve.

But yes on an OHV you can disable one way for compression test or for an overall leak down test you can just remove both push rods. That way you can test the whole cylinder stroke while checking for tapered and oval cylinders.

Now this something you can't do on L-heads (side valve) engines.

[lefty]

At .009ish on the intake, I got 120 PSI

At .005 I got 95 PSI

[bgsengine]

At .009ish on the intake, I got 120 PSI

At .005 I got 95 PSI

Hmm OK.. so that does prove compression release works, and also shows quite good compression, so likely is not the issue.. and unlikely to be a valve issue - Since it seems to start better when compression release is not active (in your testing) , and your leakdown tests seem fine, compression seems pretty good, I'd have to wonder if it isn't just a combination of little things - lower than new compression (not unexpected), plus possibly a choke plate not closing 100% (Have you tried starting while manually making sure choke plate is forced completely closed?) , plus a slightly lean fuel mix (carburetion issue) .. or maybe a weak ignition system (they may not fire the plug under compression on a slightly lean mixture) thrown in the mix.. - any one of those things may not be a problem by itself, but all added up, they can cause a hard start.. if one or two of the issues were repaired or improved, the problem may go away.. IN short, you may have several small minor issues that all stack up on top of each other causing your hard starting.. However if you have tested before by "forcing rich" (squirt a bit of raw gas in the air intake while cranking, perhaps, or block off air intake with palm of your hand if possible?) and still have a hard start, I'd be at my wits end as well.. (Though I'd be tempted to go back and check flywheel key at that point..)

[lefty]

While preparing to go after the flywheel key, I checked torque specs for flywheel torque and found two different spec for the exhaust valve. .003-.005 on one doc, and .005-.007 on another. I could try to dial that in as well if anyone can help me decide. Or maybe that's inconsequential to the problem. My brain is in a knot.

[lefty]

This is so embarrassing BG. Looks like we have a partially sheared flywheel key. It's not bad but it's definitely off.

[bgsengine]

This is so embarrassing BG. Looks like we have a partially sheared flywheel key. It's not bad but it's definitely off.

Don't feel bad.. took upmteen experts 8 pages worth of posts to get there..

[tuffnell]

Has been interesting following the answers to the problem.

[Arkie]

You may know this but:

Couple things to check to save you some time later. this is not about hard start issue, it's to reduce chance of go back repairs around the flywheel area.

Take little extra precaution around the ALUMINUM flywheel ring. They are easily damaged and not available as a separate part from the flywheel.
While you have that OLD BRIGGS flywheel off the engine put it on the work bench and carefully inspect the ALUMINUM flywheel starter ring. Look at ALL the teeth. Also pay attention to the little thin stop ring just above the teeth, If a piece or chunk of the little thin piece above the aluminum teeth is missing it allows the starter FIBER bendix gear on some types of starters to go up too high in that one place while cranking and the starter fiber gear teeth get chewed at their top portion of the fiber gear teeth and it's teeth life is shortened. Also while the flywheel is off is a good time to carefully inspect the starter's gear also. Some of them single cylinder Briggs engines have a steel flywheel ring though instead o0f aluminum..
You have to keep a heads up when removing the short bolts that hold the starter bracket, one bolt is somewhat behind the bendix gear and can be easily stripped out when removing or installing in the aluminum block if using a socket is trying to be used instead of a end wrench.

Next clean the crankshaft taper good and the taper inside the flywheel so as to remove any lube or foreign material. They aluminum key is only used for timing the flywheel, not for securely holding the flywheel in place and any lube on the taper will allow the flywheel to distort the aluminum key again even though you torque it correctly..