Sears lawn tractor starting trouble

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  #1  
Old 04-25-05, 07:12 PM
earth79
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Sears lawn tractor starting trouble

I have a Sears lawn tractor 17hp 42". When I try to start it the engine turns over maybe one or two times then jams. If I manually pull the flywheel around a few inches I can get it to kick over maybe once more. It seems to just jam. If I pull the plug it rotates fine. I checked the connections to the starter including the bolts into the block & made sure they were good. It seems like there's too much compression to turn the engine when the plug is in. I used to be able to get it going after a few tries but now I can't. What should I be looking at?
 
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Old 04-25-05, 08:46 PM
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Hello earth79!

Your valves need adjusting. Set 'em both to .050" and you should be fine.
 
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Old 04-25-05, 11:50 PM
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I'm going to guess you have a problem with the compression release camshaft whereas the lower of the two valves is not opening slightly on the compression stroke. Note that the cam could be OK but you may have excessive clearance on the lower valve. Do as cheese suggested first, but not .050" rather .005". I'm sure cheese's fingers let him down while typing his post.
 
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Old 04-26-05, 05:08 AM
earth79
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Thanks for your replies, I'll definitely check the valves, when I figure out where they are :-) I inherited this from my dear brother and did not get a manual. Any clues?
 
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Old 04-26-05, 11:31 AM
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If you're not sure where the valves are, you better find a friend who has at least some mechanical knowledge if you're going to attempt a valve clearance check/adjustment. Also, it would help us to know what make of engine you have as well as the ID numbers of such. Based on your original post, I'll bet you have a Briggs opposed twin. These engines notoriously have high compression and you may simply have a battery without sufficient cranking amps. Why don't you remove the battery, take it to a battery shop or automotive parts store and have it tested for amperage. If it is the least bit weak, this engine will require a good, solid battery.
 
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Old 04-26-05, 07:56 PM
earth79
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Hi puey61, thanks for the info. I had a look and it's a model 311707 B&S Type 0132. I found an illustrated parts manual on the B&S site so I can see where the valves are located. I've done lots of mechanical stuff but never messed with valves on small engines so not sure what tools or skills I might need but am willing to give it a shot. I live off the beaten track so it's a big deal to haul it into town for service.
 
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Old 04-26-05, 08:15 PM
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YIKES!! Thanks Puey! Yes, I meant .005", not .050". Biiig difference.

The vlaves are at the front of the engine under the stamped silver valve cover that says OHV on it. Remove the four 3/8" head bolts that hold it on, then use a 10mm wrench to loosen the adjusters. There is a T15 torx set screw in the center of the rocker arm nuts. This sets how far the nut will tighten. Use a feeler gauge to set the clearance to .005" with the engine at top dead center. Don't crank down on the adjuster nut when you tighten it. Tighten it snugly enough that it won't come loose, but if you tighten it really hard the nut will break. (vioce of experience), lol.
 
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Old 04-26-05, 11:29 PM
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Note that we have had a dozen or so of these model series engines where the compression release cam has been defective. Once you set the clearances correctly, watch to see if the lower valve (intake, if i'm not mistaken) opens slightly on the compression stroke of the engine when turning over by hand. If not, you'll have to do a tear-down to inspect the cam.
 
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Old 04-27-05, 06:15 AM
Azis
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I am sure Cheese and Puey have you all covered, just thought I would add an experience of mine with the same make of engine. I had replaced the battery and other electrical parts on this mower the year b4 and when it returned acting like a bad battery I naturaly began with the electrical system. Even with a fully charged battrery I had the same symptoms. While under the hood I noticed the cooling fins and shrouds were packed with material of all sorts. When I pulled the dipstick there was a brown sludge abut the consitency of silly puddy.
After flushing the engine and adding new oil it started normally.
 
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Old 05-04-05, 09:56 PM
earth79
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Well I finally got the time to work on the mower and it took me all bloody day but I got it running like a top. I adjusted the valves according to cheese & puey61, .005 each at top dead center. Unfortunately that didn't work. I changed out the crankase oil which was pretty far gone but that didn't work, still kept thinking about the valves and noticed the manual said .005 and 007 max for intake & exhaust respectively, 6mm past top dead center. Tried that, didn't work. So I just kept tweaking the exhaust a little more and finally got it so the starter could turn the engine. But it wouldn't start. Messed with the intake setting some more and thru trial & error finally got them so I had ignition. Seems to be working a-ok now. Thanks for your help & pointing me in the right direction!
 
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Old 05-04-05, 11:29 PM
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Glad you got it. If you had to set the valves tighter than the specs say, then chances are your compression release on the cam is defective as Puey61 suggested. I've seen it a few times, but most of the time just adjusting the valves does the trick.
 
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Old 05-06-05, 11:33 AM
earth79
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Cheese, so if the compression release cam is defective am I causing any long term problems by running with a tighter setting on the valves? It seems to run great, doesn't smoke or anything.
 
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Old 05-08-05, 11:33 PM
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If it's running good, then I'd say you're ok. If the valves are too tight, you will probably burn one in time. If they're too tight, you would probably notice though, because of power loss, backfiring, etc...
 
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