Fixing Briggs and Stratton lawn tractor

[John Lawrence]

[PaulD]

Ok, here is the update. I measured the voltage at the starter engine terminal. I did it a bunch of times. I measured sometimes slightly below 9 volts, sometimes slightly above. There was definitely a voltage drop. Was the drop large enough to be significant?

I also noticed that every once in a while I got a voltage spike at about 14 volts for a very brief instance. I am not sure whether the spike was just a multi-meter error or whether it has some significance. I also tested the voltage drop where the starter cable is attached to the solenoid (?). I got similar readings there.

I did your suggestion regarding compression. I got alternating puffs and suction from both cylinders. Its hard to tell whether they were both similar. Seemed like they were.

My son said that the engine slowly faded before stalling out.

Finally, two other things I observed. First, I did try to get multiple readings. As I did so, I noticed that the starter engine casing did get hot to touch. I did not have my helper crank for more than a few seconds at a time. Is this something one would expect when cranking the starter a number of times or is it an indication of a problem. Second, at one point the starter gear stopped popping up to engage the flywheel. I gently moved it by hand a few times. This seemed to resolve the problem.

Ether J> > I've got a busy day ahead so I may not get to this for another day

[MLD]

[Ether Jones]

Substantial drop in voltage at the battery under load is normal. 9 volts is at the low end of acceptable for a 12 volt system but still acceptable.

PaulD already measured the voltage at the battery and gave that info in a prior post. It was 10 volts, which is entirely normal. You might want to read the rest of the thread to catch up on other details. The test he reported on here was the voltage reading at the starter motor. The purpose was to determine if the voltage at the starter motor (under load) was the same as the voltage at the battery (under load). It should be nearly so, if the cabling and connections are in good shape.

10 volts at the battery, and 9 volts at the starter seems to indicate a problem in the cable connections.

[Ether Jones]

By the way, it's a starter motor, not a starter engine.

You ran this test with the plugs installed, is that right? It's important. If you got 9 volts at the starter with the plugs removed, and you got 10 volts at the battery with the plugs installed, then it seems likely that you have a problem of some sort with the cabling between the battery and starter motor.

If the 9 volt reading was with the plugs installed, it's less definitive but still suggests a cable problem. I would have expected the reading to be closer to the same reading you said you got at the battery terminals: slightly over 10 volts. But perhaps you've worn the battery down a bit with all this cranking, and the voltage at the battery is now only 9 volts. It would be good to check it quickly again to make sure it's still 10 volts there. It's the difference between the two readings that's significant.

Assuming the two readings are indeed different, you can try to locate the cable problem. First test the ground half of the battery-to-starter cabling: connect one voltmeter lead to the negative battery post, and the other lead to engine ground (cooling fins). Make sure the plugs are installed. Make sure the voltmeter leads have a clean contact. Crank the engine and note the voltmeter reading. It should be zero or nearly so. If you get a non-zero reading, it indicates abnormal resistance in the ground side of the connection. Make sure your voltmeter leads have good contact. You may get an erroneous "zero" reading if your leads are not firmly in contact with good clean metal.

Second, test the positive half of the battery-to-starter cabling: connect one voltmeter lead to the positive battery post, and the other lead to the starter motor positive terminal. Make sure the plugs are installed. Make sure the voltmeter leads have a clean contact. Crank the engine and note the voltmeter reading. It should be zero or nearly so. If you get a non-zero reading, it indicates abnormal resistance in the positive side of the connection. Make sure your voltmeter leads have good contact. You may get an erroneous "zero" reading if your leads are not firmly in contact with good clean metal.

I have the service manual right here for the model 422707 Briggs engine. The starter motor only has one terminal. I'm not sure what you're referring to.

This is one of those tests where if you did NOT feel alternating compression and suction it would definitely indicate a problem; but if you DO get alternating compression and suction the test is not definitive (there could still be a problem - only by using a compression gauge could you be sure). Let's assume for the time being that the valves are OK, although that's not a sure bet.

That's not what I was asking. I was asking about the starter motor cranking. Were you noticing increasingly "weak" starter motor cranking in the days (or weeks) leading up to the stalling incident, or did the weak cranking manifest itself suddenly right after the stalling incident?

It's probably normal but I wouldn't swear by it. Depends on how many times "a number of times" is, and how long each time lasted. Sounds like the battery was getting quite a workout. In view of this, it might be good to re-check the voltage across the battery to see if it is still 10 volts (engine cranking with plugs installed). Since the whole purpose of measuring the voltage at the starter was to compare it to the voltage reading at the battery, this is important.

Did the starter gear ("pinion gear") spin rapidly during those times when it didn't "pop up"? On an automotive starter motor, this can be indicative of a low battery. I'm not sure about the starter motor design on this Briggs engine in this regard.

[PaulD]

I'll follow up tommorrow or the next. I noted the voltage drop the first time I had the engine cranked so I am fairly certain the battery was still at full charge. As I continued, I did notice the battery power was dropping so I put a jump between a car battery and the lawn mower. Still got a low voltage reading at the starter motor. I'll make sure the battery is fully charged again before proceeding further with your suggestions.

I ran all the tests with the plugs installed.

The starter motor has a wire going from it that is attached at the other end to some type of terminal. Is this the solenoid? I followed the cable from the starter motor to its other end and tested for a voltage drop there. I thought this might indicate whether there is a problem in the cable that leads to the starter motor.

I didn't noticed any problems with slow cranking prior to the stalling incident, except as indicated earlier about the intermittent behavior. In some ways it is hard to know whether there was any gradual deterioation because usually the engine fires up quickly so the starter does not crank that long. After the stalling incident, however, it was noticeably very weak (i.e barely cranking).

Ether J>

[Ether Jones]

It is the relay. When you turn the key, the electrical switch in the key activates the relay, which completes the circuit to provide power to the starter motor. The relay is designed to handle the large current; the key switch is not.

If you test the ground side of the circuit as described in the prior post, and you get a zero reading, and then you test the positive side and get a non-zero reading, then you can start working your voltmeter lead backwards from the starter motor terminal until you cease to get a non-zero reading (with the other voltmeter lead always on the battery positive terminal post). That will isolate where the problem is. It could be a bad relay, or a loose or corroded connection, or a wire with several strands broken internally.

Again, this only addresses the weak cranking. It doesn't address why the engine stalled. The stalled engine could be due to spark, fuel, or compression (bad plugs, bad ignition system, clogged fuel filter, clogged air filter, carburetor problem, bad gasoline, valves, etc). Once you get the engine cranking properly, you can troubleshoot that.

[PaulD]

[Rich256]

Is it turning fast enough to start? Getting a spark? \\ Jumper in a car battery. Don't tackle the starter until you totally eliminate that it might be battery.

If it is spinning fast enough to start try the suggestion of squirting in some starter fluid. Personally I just use carburetor cleaner for that task.

[Don Young]

I would suggest that you remove the plugs and check that the engine spins over easily. If it does that but turns over too slowly with the plugs in and

9.5 volts across the starter, the starter is very likely not performing properly.

D>>

[Ether Jones]

Read the rest of the thread, Rich.

[Ether Jones]

Read the rest of the thread, Don. The OP stated that the engine slowly stalled out while his son was mowing the lawn. Then when he tried to re-start, the cranking was slow. We're trying to determine if the two are related. Very few single failure modes could cause both problems. But a valve problem could cause both problems. If compression differs greatly between the two cylinders it could indicate a valve problem. So it's worth checking.

The compression doesn't have to be "too high" to cause a cranking problem. If the exhaust valve is stuck shut in one cylinder, for example (broken valve stem?), the starter motor has to work harder because it's compressing on the exhaust stroke. This would cause slower cranking.

He already did that. It's described in an earlier post in this thread.

That's the current most likely answer (for the cranking problem) based on the tests run so far. But before he runs out and buys and installs a new starter motor, it was suggested that he rule out a valve problem (which could cause the engine to crank slower, and would ALSO explain the stalling described in the original post).

[Rich256]

I think I did. He seems to be centered on heading for the starter motor.

I would prefer doing the test with a hefty battery that can take long term cranking.

More important, I haven't seen anything about the engine firing when he is doing those tests. Seems to me that regardless of how it cranks that is what is important.

I would like to pull the head. Just wonder if that is difficult on that engine. Usually pretty easy.

Since it died early, like you, I just can't believe it is the starter.

[PaulD]

I spent some more time trying to figure this thing out and now I find we need to backtrack again.

I tried the test aga> D>

[Rich256]

Is it easy to pull the heads? Usually just a few bolts. Then you could see the valves working.

[PaulD]

[Rich256]

With the head off, turning the engine over slowly you will see the valves open and close. All closed during the compression and power stroke. Only one open at a time during the intake and exhaust. Both closed during the compression and power.

I once saw a valve stuck open to where just some penetrating oil and twisting got it working again. And I have had them stuck open due to carbon. A wire brushing fixed that one.

Your problem of getting suction but not exhaust sort of rules out an open valve. More like one is permanently closed and that would likely be something broke. If one is open you probably would not notice either suction or puff.

Anyway, I have found it is normally a very easy task on a small engine. And if nothing else gives me a chance to clean off any accumulated carbon.

How about spark? I have not noticed any mention of that.

I had an different problem just a short time ago. An old engine was surging. Thought it might be ready for the scrap heap. The wire to the kill switch ran through a little support hole on the casting. The wire looked rather old and the cover brittle. Moving it around seemed to change the surging. I put a good insulated sleeve over the wire and it runs like normal again.

[PaulD]

I haven't checked for spark yet because I really would not expect the engine to start at its current cranking speed. Once I get the cranking problem fixed, I'll trouble shoot any remaining problems.

Rich256 wrote: >Your problem of getting suction but not exhaust sort of rules out an

Actually, I am getting exhaust, but not suction. Is that likely caused by an permanently closed valve also?

I suppose the next step is to open up the head. When you say that something is likely broke in the valves, is that a problem caused by wear or am I going to need to look for another problem that might have caused something to break? Could it be something as simple as a broken spring? The engine was made in 1993 so I am not sure that I want to invest alot of money in it. That is why I am trying to repair this on my own, even though I am not much of a mechanic. I do think with some help I could replace a broken spring or valve.

Ether or anyone else who can answer: Do you think the possible valve problem is causing the cranking problem? Or do I still maybe need a new starter?

[Ether Jones]

Re-read his post. It's the other way around. He said there's a "puff" but "little or no suction". Could be a broken valve spring.

A broken valve spring could make that valve open during the power stroke when he is turning the engine, thus no suction. During the compression stroke, the pressure pushes the valve closed and he feels the compression. Just a working hypothesis. On this engine, the valves are oriented in the horizontal direction and are driven directly from the camshaft.

With the right tools maybe.

[Ether Jones]

It's difficult to say without quantitative information. Can you quantify how fast the engine is cranking? Put a piece of masking tape on the rotating screen. Is it slow enough that you can count the revs while somebody else keeps time?

Or, how difficult is it to pull the starter? Your local parts store that charges batteries for free sounds helpful. Do they have a test stand for testing small engine starter motors?