Small Engines (Lawn Mowers, etc.): 16.5 hp B&G no turnover - excess compression or weak starter?, compression point, lawnmower engines

Question
Hello,

I've been a quite fan for awhile.  I appreciate your great advice and often search your Q&A’s.  I’m writing because I’m stuck.  I’m a systems engineer by day and a small engine hobbyist by night, often fixing up & selling at cost mowers & blowers other have thrown away.

I’ve a B&G 16.5hp OHV, model 31C707, type 0154E7 mounted on lawn tractor.  I think it was well taken care of until the owner (my boss’s boss’s boss) rolled it and 6 months later this problem came about.  It doesn’t want to turn over, as if the starter isn’t strong enough or the compression just too high.   Otherwise everything seems ok.

Per your posts and the B&G Repair CD, I’ve adjusted the valves (they weren’t that much off; I set both to .004”), checked the full electrical system, tried a car battery (coupled, alone, and direct to the starter), insured the intake & exhaust routes (outside of the valves was unclogged), and knocked all the CD’s other troubleshooting steps.  Haven’t broke open the crankcase, yet.

Without the plug, it spins easy by hand.   With the plug in, it turns quite hard at two points quit near each other, like it has two TDCs.  In other words, it spins easy for 360 300 degrees but then has two tough humps within 60 degrees of each other.  (Yes, I measured it, remember engineer by day?)  Is that normal?  That doesn’t occur on 5 hp lawnmower engines.  I’m able to get over them by turning the flywheel by hand but it isn’t easy.  Is that normal?   Perhaps normal for an engine 3x larger than what I’m used to working on.  It holds the compression well at those times.

I was able to get it to spin and start twice - it ran just fine once started, high & low speed.  Otherwise it spins until it just stops at that high compression point(s), like the starter is not strong enough to get past TDC.

The starter’s brushes are 3/4 left, springs strong, and it’s clean within.  No obvious burns.  It turns ok by hand.  I haven’t taken it in for an amp-volt-rpm test yet, a test shown on the CD).  It connects & disconnects fine w/ the flywheel, but I still spray-greased the teeth.

Thoughts?


Answer
Turn the engine backwards and try to start it. My guess is it will fight through compression and start.
This engine is notoriously know to break compression release springs on the cam.
Don't bother with the amp-volt-yadda,yadda, whatever test.
Take the starter off. attach your jumper cables and see if it spins, if so it's ok.
I'm betting on the acr spring broken, buy a cam.
System engineer eh? I always wondered who designs these products that are impossible to work on. Do you have a second major in pain in the butt to work on.