OT, tractor not running /starting

JST · Sep 26, 2016

Father in law has a tractor with a 9 or 10 HP Briggs. originally a coil and points engine, with a 3 leg coil. Coil was supposedly bad when his friend rebuilt it (friend is VERY good with engines, rebuilds Cushmans, good guy), and since those are no longer available, an electronic system from the dealer was put in.

The engine initially appeared to run. But subsequently would not start, kicked back instead of starting forward, etc. FIL thinks it should not be a wasted spark engine, as it has a pushrod for the points, and presumably works off the camshaft

My understanding is that the electronic ignition HAS TO be a wasted spark system, since it has only the crankshaft as a reference. But if timed right, that should not be an issue, it would spark advanced enough to be in the exhaust stroke.

He's disgusted and doesnlt even want to fiddle with it, and I don't have any good ideas that he hasn't got an answer (right or wrong) for.

Is it possible to put in the electronic unit in such a way as to mess up the timing that badly? Flipped over comes to mind, but they usually have a specific orientation that is pretty clearly explained.

Is it possible for the thing to spark late if the electronic unit has a fault? I'd not think so, but......

Any other good reasion for it to do that?

My one thought is that it may actually not be firing backwards, but might have a sticking valve that causes it to act like a kick back, but I am not sure.

I recall when they installed the motor, I seem to recall having some concerns from looking at the actual install vs the instructions, but as usual "they knew better", and I let them do whatever. It did seem to work initially, until after the friend left.

I'm looking for any idea that makes it worth while to get into the thing.

He wants to put it back to points and coil, but never seems to want to get into it that far, since the pushrod needs work. So if the electronic system can be made to work, that is the best.

TDegenhart · Sep 26, 2016

Sounds to me like the rebuilder has valve timing off, assuming the electronic ignition module came from B&S for that engine. Those engines has the ignition timed off the crankshaft, not the cam shaft. Easy to check, either pull the head or observe through the spark plug hole or take the tappet cover off.

Tom

Brianison · Sep 26, 2016

If it's kicking back, the first thing I would check is the flywheel key. (used to work on them for a living)The key on most Briggs motors is aluminum, so that a backfire, or hitting a rock with the mower will shear the key instead of twisting the crankshaft. The mounting area for the flywheel is tapered, and if you don't get the wheel back on tight enough, they will partially shear the key just by running. That's usually what happens when they kick back.

moonlight machine · Sep 26, 2016

JST said:
Father in law has a tractor with a 9 or 10 HP Briggs. originally a coil and points engine, with a 3 leg coil. Coil was supposedly bad when his friend rebuilt it (friend is VERY good with engines, rebuilds Cushmans, good guy), and since those are no longer available, an electronic system from the dealer was put in.

The engine initially appeared to run. But subsequently would not start, kicked back instead of starting forward, etc. FIL thinks it should not be a wasted spark engine, as it has a pushrod for the points, and presumably works off the camshaft

My understanding is that the electronic ignition HAS TO be a wasted spark system, since it has only the crankshaft as a reference. But if timed right, that should not be an issue, it would spark advanced enough to be in the exhaust stroke.

He's disgusted and doesnlt even want to fiddle with it, and I don't have any good ideas that he hasn't got an answer (right or wrong) for.

Is it possible to put in the electronic unit in such a way as to mess up the timing that badly? Flipped over comes to mind, but they usually have a specific orientation that is pretty clearly explained.

Is it possible for the thing to spark late if the electronic unit has a fault? I'd not think so, but......

Any other good reasion for it to do that?

My one thought is that it may actually not be firing backwards, but might have a sticking valve that causes it to act like a kick back, but I am not sure.

I recall when they installed the motor, I seem to recall having some concerns from looking at the actual install vs the instructions, but as usual "they knew better", and I let them do whatever. It did seem to work initially, until after the friend left.

I'm looking for any idea that makes it worth while to get into the thing.

He wants to put it back to points and coil, but never seems to want to get into it that far, since the pushrod needs work. So if the electronic system can be made to work, that is the best.

The point pushrod on the old aluminum Brigs under the flywheel works off the crankshaft. The really old cast iron brigs with the points on the side of the block worked off the cam. No matter it will run fine with a wasted spark. does it have compression? Is there a key in the flywheel to crankshaft connection?

JST · Sep 26, 2016

This is, remember, not a little Briggs on a mower. It's an older horizontal shaft of 9 or 10 HP (I forget the sizes they had). And the guy who did the work knows what to do, so that should be OK.

I suppose it could have been fouled up later, if taken off and on. Usually if it hits something, which this would have had belts in the way of anyhow, the flywheel ADVANCES. To kick back I think this would have had to be retarded, not advanced. I suppose if it went far enough, but......

I have not see it in action, can't get him to get it out,and won't be back there for a while. Thought there would be something specific to the electronic modules that might be the issue.

if the points are off the crankshaft, then this is ALWAYS a wasted spark engine, so the module, which my FIL is blaming the problems on, may not be the issue at all. I'll have to see if I have any manuals to cover those. I may, but don't have the model number. Have to ask him,and he's too mad at it to look.

Still bugs me that I recall thinking the module should go on the other way........

JST · Sep 26, 2016

moonlight machine said:
The point pushrod on the old aluminum Brigs under the flywheel works off the crankshaft. The really old cast iron brigs with the points on the side of the block worked off the cam. No matter it will run fine with a wasted spark. does it have compression? Is there a key in the flywheel to crankshaft connection?

Got lots of compression. Almost stalls the starter sometimes I am told. As for key, I assume so, wasn't there when it was put together.

David J. · Sep 26, 2016

Post the model, type and serial numbers. ( it matters )
Some of the old Briggs required the flywheel magnets to be re-polarized
when switching to the Magnatron type coils.
Briggs has always done this for free if you shipped them the flywheel.
Need the numbers to know.
If the point opening lobe on the cam and points plunger are good, you
could also switch it to a 12 volt type coil. We've used a Kohler coil and condenser
in conjunction with the stock Briggs points, works well on applications with 12 volts
avail.
David
Edit....forgot to mention the old cast iron flywheels needed to be pretty tight
or they would partially shear the flywheel keys. Don't remember the torque
spec. Was a somewhat narrow window between flywheel moving and
snapping the weak end of the cast iron crankshaft. We resorted to prick
punching the od. of the crank taper on some of them.

JST · Sep 26, 2016

Ah. Well I don't know the numbers, but I may be able to get them.

Did not know about the repolarizing, no idea if that was done.

Was that actually changing the poles from N to S, or changing the strength? Presumably actually changing N to S, if described as "repolarizing". And that would definitely have a big influence on timing. The wonder is that it ran to begin with, although there was something about starting it with a faster starter, which might also be in-line with a timing problem of that type.

I can charge some magnets, but probably not those.

The plunger... that's the issue, it seems to be jammed, possibly bent just enough to jam it, so the whole thing would need to come apart to get it out and either clean it up or replace. THAT is the part that has my FIL de-motivated, he doesn't want to get started with it, due to space problems and other projects in the shop. He has a coil and so forth ready if that is done..

But much simpler if it is a magnet issue.

moonlight machine · Sep 26, 2016

That plunger only moves .020 or so, your not using it anyway I'd just leave it alone.

lars66 · Sep 26, 2016

First thing I would check is the KEY. Got a mower that has sheared it 3-4 times and never hit anything.

JST · Sep 26, 2016

It's a decent bet, if it has kicked back a few times. But I'm trying to get the numbers, to see if there is anything else going on. I'm confident the key was OK originally, and it didn't like to start then, so my money is on there being a spark timing issue, with maybe the key NOW being an added problem.

A very good mechanic told me his rule is "Fix what you KNOW is wrong". At least do that first, and then see what else may be still wrong.

TDegenhart · Sep 26, 2016

Keep in mind that if the ignition module is a direct replacement for that engine, it is highly unlikely that anything needs to be changed but the module. If you know the module number and/or the engine number, you should be able to go to the B&S web site and get installation instructions. If not there, how about where you got the module.

Tom

Danny VanVoorn · Sep 26, 2016

Don't know about the Briggs module update so won't comment on that. If the fly wheel key sheared even partially it could cause the kick back described, the advanced timing is what causes it. I remember the old Harleys with the manual advance, if you forgot to retard the timing when starting them the kick starter could throw the rider over the handlebars or worse.
Dan

PDW · Sep 26, 2016

Anything fitted with a Briggs & Stratton gas engine is NOT a tractor.

That's like describing one of those 7" swing lathe-shaped objects as a lathe.

Get something with a diesel engine.... Kubota & Kioti come to mind.

PDW

CalG · Sep 26, 2016

the aftermarket (and OEM) pointless ignitions sense the changing phase of the current generated by the fly wheel magnets. the units position or orientation has nothing to do with the timing.

Check the flywheel key. If there have been multiple "back fires", that key is likely displaced. Those flywheels are heavy!

JST · Sep 26, 2016

PDW said:
Anything fitted with a Briggs & Stratton gas engine is NOT a tractor.

That's like describing one of those 7" swing lathe-shaped objects as a lathe.

Get something with a diesel engine.... Kubota & Kioti come to mind.

PDW

'
Hey, I read it off the nameplate,it cant be wrong......!

Das macht Nichts. The "object"will run a blade, or a mower deck, etc, and is sitting there in the shed, next to the Grasshopper, so it should oughtta run, or else why is it around? it's not a little garden "tractor shaped object", its actually good sized, but, no, it ain't a Kubota....

He already has it, and I know he got it used for not a lot. can't say that for Kubota.

moonlight machine · Sep 29, 2016

JST said:
Father in law has a tractor with a 9 or 10 HP Briggs. originally a coil and points engine, with a 3 leg coil. Coil was supposedly bad when his friend rebuilt it (friend is VERY good with engines, rebuilds Cushmans, good guy), and since those are no longer available, an electronic system from the dealer was put in.

The engine initially appeared to run. But subsequently would not start, kicked back instead of starting forward, etc. FIL thinks it should not be a wasted spark engine, as it has a pushrod for the points, and presumably works off the camshaft

My understanding is that the electronic ignition HAS TO be a wasted spark system, since it has only the crankshaft as a reference. But if timed right, that should not be an issue, it would spark advanced enough to be in the exhaust stroke.

He's disgusted and doesnlt even want to fiddle with it, and I don't have any good ideas that he hasn't got an answer (right or wrong) for.

Is it possible to put in the electronic unit in such a way as to mess up the timing that badly? Flipped over comes to mind, but they usually have a specific orientation that is pretty clearly explained.

Is it possible for the thing to spark late if the electronic unit has a fault? I'd not think so, but......

Any other good reasion for it to do that?

My one thought is that it may actually not be firing backwards, but might have a sticking valve that causes it to act like a kick back, but I am not sure.

I recall when they installed the motor, I seem to recall having some concerns from looking at the actual install vs the instructions, but as usual "they knew better", and I let them do whatever. It did seem to work initially, until after the friend left.

I'm looking for any idea that makes it worth while to get into the thing.

He wants to put it back to points and coil, but never seems to want to get into it that far, since the pushrod needs work. So if the electronic system can be made to work, that is the best.

The electronic ignition coil sold by Briggs & Stratton is labeled for correct installation. Look on the coil, It's hard to see, but it is marked "this side out" on one side and "cyl side" on the other side. Flip it over and the timing changes about 20-25 degrees and it won't run.....

JST · Sep 29, 2016

If it is enough that it flat will not run, that's one thing. If it may "keep running" once it starts, that's another, and might fit what I recall from back when they were messing with it. And, it could be.

It should backfire like crazy and not start if it gets advanced when reversed, but if you spun it fast and then tried, it might run. If it is retarded when reversed, then I expect it would just pop and not run. No idea what the issue would be if it was supposed to be re-polarized to run, probably similar to the over-retarded scenario.

There was indeed something about it being OK if started when spinning fast, otherwise not, so upsy down could be the problem. I won't see it for a few weeks, anyhow..

OT, tractor not running /starting

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