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Chris Huber
Chris Huber, Small Engine Technician
Category: Small Engine
Satisfied Customers: 624
Experience:  20 years experience. Briggs and Stratton Master Service Technician. Dealer for most engine lines.
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B/S 16 HP V Twin engine model 30-3777, type 1147-e1 on a JDeere

Customer Question

B/S 16 HP V Twin engine model 30-3777, type 1147-e1 on a JDeere LT166 mower tractor. Starts easy, runs fine @ idle, seemingly forever. When mowing, will suddenly kill with wisp of white smoke. Will kill on slope, when turning or just cruising straight & flat. (used to use a Craftsman mower w/ BS 18 hp mower, without problems on the terrain). Restarts very easily, but with huge cloud of white smoke with underlying black smoke, presume from kill & excess fuel. Have replaced most fuel line, fuel filter, & fuel is fresh. Recent oil chx (SAE 30W), level is at lower mark on dipstick (=add pint) to keep level from too high. Carb removed, sprayed, and bowl cleaned, float works fine, fuel pump seems OK, no excess crap in head fins, Oil breather is clean and works fine, air filter & secondary filter are ok, clean, & LIGHTLY oiled. Head bolts are tight. Plugs were a little fouled, but not bad - have cycled engine without plugs to blow out excess oil - there was none. Nothing helps - WTF?
Submitted: 4 years ago.
Category: Small Engine
Expert:  Chris Huber replied 4 years ago.
Interesting. You have cover most of the bases, I am thinking maybe a valve seal is allowing oil passed a guide and getting into the cylinder, but normally it wouldn't kill the engine, white smoke is oil, excess fuel is usually black smoke. Any time you are troubleshooting a twin, isolate each cylinder and troubleshoot it as if it were an engine all by itself. Does 1 plug look worse than the other? Is there different compression in each cylinder? Perform a cylinder balance test. With needle nose pliers disconnect 1 spark plug wire at a time with the engine running, note the change in RPM. Do the same with the other side. If 1 cylinder is doing all the work, the engine will probably die when you disconnect that wire. Let me know what you find out.



Customer: replied 4 years ago.
Interestingly, when I blew out the cylinders without the plugs, I inadvertantly left off one of the plug wires when I restarted, and the motor started and ran 'fine'. I neglected to try the other cylinder. I just went outside and did the wire test again. Initial cylinder wire had no effect when disconnected. Second wire not only gave me a nice zap through the boot, but killed the motor immediately. So I'm guessing that next I pull off the shrouds and make sure the first wire is intact and not chewed off by a rodent or something, and/or grounding. Wire boots seem OK. I'll also check gap between coil armature and flywheel to see if it's even. Without looking up the air gap, I don't recall what it is supposed to be, but it's usually standard and fairly forgiving. If that all checks out, I suppose the coil is the culprit? Will the twin cylinder B/S coil be the same for most engines, as I do have a leftover coil from when I rebuilt an 18 hp horizontal shaft motor. The other question I have is why did it kill? Flooding in one cylinder until it couldn't run anymore? Where does the excess fuel get dumped? That might explain the black smoke when restarting, but why white smoke - where's the oil coming from? It doesn't seem to be dumping out the muffler, which is bottom-mounted. Is it bypassing the rings, and so when fixed the oil should be changed again? I have not checked compression yet.
Customer: replied 4 years ago.

Addendum to my previous reply - I removed blower shroud, and saw that there are two separate coils for this motor, rather than the duplex coil that was on my other engine. Any way to check for a bad coil, other than visually noticing a severely delaminated armature or burst winding casing?

 

I also looked up the air gap (.20 - .30 mm), which seemed OK on the motor.

 

I checked compression - 115 lbs on dead cylinder, 215 lbs on hot cylinder. I squirted some Marvel Mystery Top Oil into the dead cylinder in case of a stuck ring. This time, when I only ran the motor enough to back up the tractor, I found the dead plug very wet, and the hot plug full of black carbon.

Customer: replied 4 years ago.
I suppose I could swap coils to see if hot / dead plugs swap as well?
Expert:  Chris Huber replied 4 years ago.
Mystery solved. Check the dead coil by disconnecting the little wire that connects to it and check for spark. If there is no spark, the coil is bad. If the coil is good, the prblem is in the head or cylinder, which I suspect due to the severe difference in compression readings. Check for a bent pushrod or valve train issue on the dead cylinder before removing the head. Let me know what you find.
Customer: replied 4 years ago.
OK, maybe not solved...before I disconnected the small wire from the coil, I pulled both plugs out of the head & grounded them against blower shrouds to check for spark from the plugs. The Dead cylinder had a GREAT spark, and burned off any excess fuel that was on the plug. The live cylinder was still a clear spark, but not so bright as the other. I reinstalled the plugs, both together & singly. The motor would still run with the live cylinder alone, but the dead cylinder was still dead. Run the engine with live cylinder only & dead cylinder plug removed but grounded again, and the 'dead' cylinder plug was still bright! Gap on both plugs is still .30, but I'm really confused now. Could it be a grounding issue with the head, that the plug isn't firing when installed? That doesn't seem possible. Is the small wire from the coil just a common ground? Or does it provide a different function?
Customer: replied 4 years ago.
Double-checked compression. Dead cylinder doesn't even register anymore. I guess I'm looking at a broken valve spring, valve seat, valve seal, head gasket, burnt piston or bad/broken rings. But wouldn't the engine even try to chug a little on the dead cylinder alone, even with low or intermmittent compression? Or am I still not clear of the electrical issue?
Expert:  Chris Huber replied 4 years ago.
You have a dead cylinder due to mechanical failure. If the dead cylinder has spark, yet 0 compression, the problem lies in the valve train or cylinder itself. Pull the valve cover, loosen the rockers and pull the pushrods to see if one is bent. If not check for a stuck open valve. That's pretty common on your model when the engine may have overheated. You should be able to push on the valves and feel them open and close.
Chris Huber, Small Engine Technician
Category: Small Engine
Satisfied Customers: 624
Experience: 20 years experience. Briggs and Stratton Master Service Technician. Dealer for most engine lines.
Chris Huber and other Small Engine Specialists are ready to help you
Customer: replied 4 years ago.
Popped off the Valve cover, and both push rods were lying on the bottom of the head. Exhaust valve was a little sticky (understandable, but popped loose fairly quickly). Push rods were bent just a few ths", not bad and easily corrected. Ends were good. Reassembled rods, cleaned area, and reassembled cover. Compression came up to about 195 lbs before running and burning off crud, so I anticipate it will get better. Added some SeaFoam to crankcase oil, as well as into the fuel tank. Engine started easily and ran very smoothly, even as it burned off a white cloud for about 3-5 minutes. Throttle was responsive after burning off the crud out of the exhaust manifold & muffler. When plug wires were disconnected one at a time, motor speed would drop slightly, but continued to run on both cylinders. Cleaned out cooling fins and reassembled Blower housing. Took mower out to the lawn for a shakeout performance cruise, and mower steepest terrain, dropped cutting height an additional 1/2" and put the mower under a heavy cutting load - Mowed about 2 Acres and it never skipped a beat. Problem solved, thanks for your help!

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