Lawn tractor starting problem

It may have a compression relief valves so the starter can turn the engine over. There ARE engines like that but Sears? I don't know.

There's not any riding mowers with compression relief valves.

snipped-for-privacy@optonline.net wrote: ...

If far enough out, sure...if the exhaust valve doesn't open to allow compression gas to escape, it'll build enough pressure the starter won't have the torque to spin it...

If he kept the old starter, I'll bet if you test it on the bench it'll show it was (and still is) just fine.... :)

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Remove the spark plug(s). Does the starter moter go like it should?

If so, I would think the motor doesn't have enough oomph to get past the compression. Just guessing, the spark plug is not firing when it should.

How could an exhaust valve possibly be so far out that it doesn't let exhaust gas escape and the mower run, cut grass and work perfectly fine when it does start. Sometimes it would spin over and then start.

I don't know how you'd test it without some kind of test jig. Even if it spins up under no load on the bench doesn't mean much because it has no load against it.

A non sealing carb float flooding the cilinder? Take out plug see if its wet and turns over and check oil for gas in it. Bypass the battery and hook the positive to the starter and clean something for a good ground, a bad connection or battery might be found, but a newly purchased starter could be a rebuild, not new and worthless, once my car mechanic went through about 4 , then he just bought a new one. So I gues not enought volts, bad starter or flooded motor.

I agree, bad valves are not a cranking problem. Bad timing can "stop" a starter but usually it continues to crank after the plug fires. When you say you hooked the positive up to the starter terminal you do mean the terminal directly on the starter? Both cables? To insure that a bad connection is not the culprit you need to clamp the negative on the starter preferrably like where it bolts to the block. Then hit the positive terminal directly on the starter. And make completely sure you are using battery that you know will crank a car. If there is any doubt, use a car. Make sure the clamps on the battery are well dug into the lead of the battery terminals.

After it quit cranking did the lead spark when you took it off? If it's not sparking then check all your other connections and try again. A battery tester that also shows cranking amps would be handy for this problem.

That has nothing to do with the starter failing to spin the engine.

I posted that I had connected both the lawn tractor's own battery and a fully charged car battery directly to the starter with car jumper cables and the starter would only move little and NOT spin the engine.

Yes, the new one could be bad, except that after the "valve adjustment" by Sears, the new starter does start the motor. The only problem he now has is that he says sometimes it doesn't start it immediately, ie the starter still hesitates at least some of the time.

I'm wondering if there is another problem in the starter circuit, eg bad cable, solenoid, etc, that was not delivering full current to the old starter and eventually over time caused it to fail. With a new starter, maybe it's on the same path, but the starter still works most of the time, but is still marginal because it's not getting full power? Since it's not mine and I didn't get to try any testing with the new starter, really don't know at this point.

Yes. As I described, I hooked the jumper cables from both the lawn tractor battery and a 1 year old car battery that came right off a battery tender from my garage. In both cases I connected the negative to a large bolt right on the motor close to where the starter is bolted on. I held the positive cable jaw firmly against the starter connection bolt. Got a good spark with initial contact, then only a little bit of rotation. Exactly the same results as turning the key.

Yes got a good spark both on connection and removal.

interesting thing is

On some models, if the battery isn't at FULL voltage, you will exhibit these problems. Check battery voltage. They should be at least 12.8 volts.

Another thing to check is the belts that go to the crankshaft pulley. If they are not completely loose when the clutch is disengaged or the mower deck is disengaged, they may be grabbing. This may be just enough to cause your symptoms.

Hank

You know, that's an excellent suggestion. I just assumed that with the mower in neutral, no blades engaged, that the engine was free to spin. Never considered that something it's CONNECTED to could be holding it back.

Bad solenoid can cause that as can loose or corroded cable connections, even the key switch. Another cause can be a clutch that is dragging or not fully disengaging or the mower deck clutch and binding of the flyhweel itself because of a misplaced cowling cover.

MANY of them have an automatic compression release feature built into the camshaft/valve-train. It is dependent to some extent on the valve adjustment

If the exhaust valve never opens the compessed air just pushes the piston back down and the intake valve opens again - the compression pressure NEVER gets significantly higher than if the valve was opening properly.

I'd be checking the ground, myself.

That's how I normally start my mower anyway :-) I get tired of those crappy little batteries.

Bad ground between engine and starter seems unlikely (but maybe worth a check that your ground from your battery wasn't connected to a bolt on the engine which was painted).

Did you disconnect the normal positive line to the starter (from the mower's solenoid) when you tried these tests? If not, maybe there's a short to ground somewhere in the solenoid or wiring (or even something of low enough resistance to cause problems).

If you can turn the engine by hand, I can't see a reason why a *good* starter shouldn't be able to turn it over, too. The sort of symptoms you're seeing do sound like a bad starter, though (my old mower one was the same, and sometimes I'd have to rotate the starter by hand a few degrees just to get it to spin when power was applied) - I suppose there's the possibility that Sears gave out a bad starter, but it seems pretty unlikely.

cheers

Jules

My two 1970 husky bolens 12HP (Wisconsin Engines) have compression relief valves. I believe it is the exaust valve which doesn't close as long during slow starting speeds. Then again they were clasified as "garden tractors", not lawn mowers. There equal if made today would cost about $7,000 new with a couple attachments.

It doesn't take much. Maybe only a hundredth of an inch. It just lowers the compression when it's turning that slow. My one that has the same problem I can start by clicking the key off and on and stopping it at top dead center. From that point it will have enough speed built up to make it past that point again and hopefully fire. One of these days I'll fix it, I have to remove the valve to do it.

Years ago my girlfriend at the time had a similar problem with her truck. I pulled the starter, took it apart and cleaned the carbon off the brushes and commutator; it worked fine thereafter.

Paul