Starter, Flywheel or Armature

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  #1  
Old 04-30-09, 09:09 AM
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Question Starter, Flywheel or Armature

I have a craftsman model 917.273881. It has an 18.5 hp Briggs and Stratton engine : model #31P777/type # 0296-E1

I'm having trouble starting this thing. One time it starts just fine, the next time I try it it won't start. I can turn the flywheel by hand and if I manage to stop in the right spot it will start, but if I shut it off it may or may not start again. (Did I mention I had 16 yards of dirt delivered yesterday that I have to move??)

I put a new solenoid on it, thought that was the problem, it wasn't. After a few hundred times of trying to start it the starter gets hot, should it?? (I don't know all that much about small motors) The guy next door said it might be a flat spot on the flywheel, that I should pull it apart and sand it so it makes better contact. Given that his mower runs like crap I decided to bring the problem here.

Any help would be appreciated.
 
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Old 04-30-09, 09:31 AM
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When it isn't starting, check for spark at the plug (ground a good plug and crank it = should have a bright blue spark at the plug. If you're getting it to start and it runs well after starting the compression is likely OK and the problem is in the carburetor getting fuel or passing the fuel into a fuel/air mix.

If you aren't getting a spark at all, go to the coil/module on the flywheel and disconnect the small wire(kill wire). If it starts then, the problem is in a safety switch or the ignition switch. The seat switches are often a problem.
 
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Old 04-30-09, 03:13 PM
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Marbobj
Thanks, I did pick up a new plug today, I wasn't getting much of a spark from the old one. I'm recharging my battery right now. It was a little low on water so I figured I better charge it. Water was covering the plates, just not up to where it should be. As soon as that's charged I'll give your suggestions a shot. I'll post back and let you know how I make out.
The flywheel had a lot of rust on it so I sanded that a little to clean it up, I also recapped the armature to match the new plug. (I hauled dirt via wheelbarrow today and I don't care to try to move all 16 yards that way.)
 
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Old 04-30-09, 04:10 PM
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I'm assuming your reference to "recapped" is in regard to the ignition coil to magnets air gap and, if so, the spark plug should be set at .030" and the coil will be .010", not matching the spark plug. If you set the coil air gap at .030" you will have very weak spark.
 
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Old 04-30-09, 04:41 PM
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Puey61

I knew I should have left that alone. The jackass next door said "oh no that has to match the gap on the plug", so I can tear the cover off that again tomorrow to reset that. Well I'll have plenty of time now, it's supposed to rain for the next 3 days, so much for getting that dirt moved, at least I got a bunch of tarps over it.

Unfortunately the owners manual only gives the plug gap, not the coil gap too. Thank you for the info.
 
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Old 05-01-09, 07:51 AM
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I got the battery charged, re-gapped the armature. Have great spark. Again the same problem. One minute it will start the next it won't.
I did discover one thing, the starter doesn't disengage like it should. The starter get so hot you can't touch it. Could I have a damaged key on the flywheel?? I had the starter checked out and they said it was fine, but the bendix spring seems a little weak. Would that cause the problem?
 
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Old 05-01-09, 08:24 AM
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The times that it will not start, does the engine not turn over?
Sounds like the starter gear might be hanging up on the ring gear and when you turn it by hand sometimes it will release.

If this is the case I would say your original assumption could be correct.
 
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Old 05-01-09, 08:44 AM
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It sounds like the valves need adjusted &/or there is a problem with the compression release. The starter will get hot if you hold it in the start position & the engines not turning.. Is this what is happening?? Does it crank O.K. with the plugs removed?? Roger
 
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Old 05-01-09, 08:52 AM
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The bendix spring would hold the bendix gear out of the flywheel. It sounds like your starter is locking at the gear drive and the flywheel or you have a weak battery.

When you turn the flywheel to a workable location on the revolution it may just be coming off a compression stroke where the engine will turn over a little easier. If you can get it started at all, the flywheel key is likely where it should be - that affects the timing.

The starter would get hot when over used. They aren't designed for extended running = over cranking. But they shouldn't get hot right away and normally get the job done when the rest of things are OK.
 
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Old 05-01-09, 10:37 AM
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I went out to start it and it fired right up. I let it run a few minutes then shut it off. Tried to start it again and it did the same ole hang up. The bendiz gear is not dropping down like it should.
I took the plug out as you suggested and it turns over just fine. With the plug in it doesn't turn over. (guess I should have said that right off the bat, sorry)
When I turn the key it moves just enough to push the bendix gear up to the flywheel gear, then it won't turn any further.
Before I could turn the flywheel by hand and if I was lucky it would start, unfortunately it looks like my luck ran out. I can turn it and turn it and maybe it'll start, but 8 out of 10 times it won't turn over. The battery was new last fall and I charged it over night yesterday, so it should be ok. According to my charger it says it's fully charged.

Is adjusting the valves a hard thing to do? If I take it to the mower shop they will tie it up for weeks. I not only have dirt to move, I have over an acre of grass to mow
 
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Old 05-01-09, 11:57 AM
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If the starter is spinning, but not engaging the flywheel....

You may have some crud on the starter shaft. The bendix drive slides up a little spiral groove in those things. If the groove gets gummed up the drive can't go up the shaft.

If you take a good penetrating oil with a lubricant (like teflon) in it and spray the starter shaft it'll often fix it. Sometimes they have a little lube hole in the end of the starter casing that makes that easier to do.
 
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Old 05-01-09, 02:58 PM
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Marbobj

The problem isn't that the starter doesn't engage the flywheel, the problem is that once it tries to turn over, the bendix gear doesn't drop down. I did lubricate it, used WD40.
Given the thing turns over freely with the plug out I suspect that the problem is compression, or decompression.

If I get it started will it damage the mower if I use it and just not shut it off until I'm done??
I'm going to pick up a new filter and a quart of Castrol 30wt. and change the oil tomorrow morning. I didn't change it this spring like I normally do. Probably won't make a difference but it needs doing anyway.
 
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Old 05-01-09, 03:13 PM
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Pull the rocker cover off the cylinder head, remove the spark plug, turn the engine over, by hand, until the piston is at 1/4" down the bore before top dead center (TDC) on the compression stroke (just before the power stroke), set both valve clearances at .005". After completed and before you wrap it back up turn the engine over completely, by hand, through its 4 cycles (two complete revolutions of the crankshaft) and watch the lowest valve to lift SLIGHTLY as the piston approaches (just before) TDC on the compression stroke. This tells you whether or not the MCR (mechanical compression release) mechanism is functional.
 
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Old 05-01-09, 03:21 PM
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Ok, I reread your posts and you said it wasn't disengaging the flywheel - sorry.

If that is the case - no you can't run it like that. The bendix will drive the starter motor and burn it up.

The spring you're talking about will hold the bendix out of the flywheel, but it only helps to disengage it from the flywheel. When the engine starts the flywheel spins the bendix gear in the opposite direction and throws it off the flywheel and down the shaft.
 
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Old 05-01-09, 03:31 PM
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Marbobj

The starter disengages once it starts it getting it started that is the headache. The problem doesn't seem to be the starter, but rather compression.

Puey
I'm checking out a schematic for that motor right now. Want to see whats involved before I get in over my head
 
  #16  
Old 05-01-09, 03:32 PM
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Whoa, brain fart. Sorry! The piston must be 1/4" PAST TDC on the power stroke to ensure the MCR doesn't come into play while adjusting the valve clearances...not before TDC!!!
 
  #17  
Old 05-01-09, 03:53 PM
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Puey
Do you know where I can find a decent schematic of this thing? I've done a search and the 2 sites I found were not all that informative
 
  #18  
Old 05-01-09, 06:14 PM
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If you're wanting a parts breakdown you can go to one of the parts online (like Sears) and look up the engine with your model and serial number.

For a service manual on a Briggs you would probably have to buy that. A lot of Tecumseh stuff is on line free.

All considered setting the valves is well within a DIY'er talents.
You wouldn't have any problems.
 
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Old 05-01-09, 08:14 PM
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It doesn't sound like you have any starter problems at all. The bendix gear doesn't necessarily drop out from the flywheel until the engine STARTS. That's when the gear drops back down. If you crank it, but it never starts, there is no force to kick the gear back down, and it can be stuck in the flywheel gear until you crank it again...no problem.

Adjust the valves and you should be fine.
 
  #20  
Old 05-02-09, 10:38 AM
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I just want to thank you all for the help.
The valves were clear out to .011. I still have a bit too much compression if it stops at the top of the stroke, but I can turn the flywheel once in awhile if I need to.
So here's to youBeer 4U2Beer 4U2 Thanks again!
 
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Old 05-02-09, 05:10 PM
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The valve clearance is important for the compression release to work.. Glad it's working now & Thanks for the Feedback... Roger
 
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Old 05-02-09, 05:14 PM
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Roger
Does the fact that I still have a little too much compression mean I don't have them adjusted dead on? How tight on the feeler gage should they be?
 
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Old 05-02-09, 06:14 PM
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The feeler gauge should slide between the tappet and rocker arm with light resistance. Not freely, but not hard to move either.
 
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Old 05-02-09, 07:00 PM
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Cheese is right... With the piston 1/4'' past T.D.C. the feeler gage should have a drag to it. Not too much, but still some..Hold the center stud while you Tighten the locknuts & try again. Sometimes it takes several tries as when you tighten the locknuts, the clearance will change... Be sure to hold the center stud still when tightening the locknut.. After you have everything perfect, rotate the engine several turns, till 1/4'' past T.D.C. & check them again,,, Just to recheck!!! Thanks,,, Roger
 
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Old 05-03-09, 04:57 PM
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You were right something must have moved when I tightened the nut, got it reset and it runs like the day I bought it.

Now I have no excuse not to move that ton of dirt
Thanks again
George
 
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