Small engine repair advice

I have a Craftsman mower, 6hp, B&S overhead valve engine. This engine has always started on the first or second pull. Open throttle, close the manual choke, give one or two lazy pulls and it fires right up. It is the easiest starting mower I have ever had!

I ran over a stump that stuck up a few inches - it was in tall grass, I didn't see it, and the blade hit it hard, immediately stopping the engine. Thunk, engine stopped. The plastic cover over the pull starter popped off, it hit so hard.

Now the engine won't start. It pops and sputters and backfires out the carb, but absolutely will not start. Thinking a timing gear (or whatever valve timing mechanism it has) had skipped a gear/notch, I pulled the valve cover, pulled the spark plug, and watched to see if the rockers arms would both rock at TDC, and as far as I can tell they do, though I'm not sure how accurate or reliable of a test that is.

The engine turns over easily, but it always has - if anything it turns over easier than it should, which is what made me think the valve timing was off, though it's hard to tell.

Anyone have enough experience with this engine or type of engine to comment on what might have happened, and availability/cost of parts should I decide to tear the engine down? I don't know if sheared a key, skipped a tooth/cog, bent a valve in the process or what I'll find when I tear it open. It's been a good mower, and it's worth a bit of time and effort to me to fix it.

Reply to
Zootal
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Plus one on that--- Also be sure the blade hasn't come loose. That'll do some odd stuff.

Jim

Reply to
Jim Elbrecht

Almost definite diagnosis - sheared key. A couple of bucks and half an hour's work for a half-handy guy with a few tools

Reply to
clare

So the general consensus is a sheared key - where is this sheared key that it can be fixed in a half hour? I thought I'd have to take the engine apart to get to it? I worked as a mechanic, but I retired my tools in 1984, and haven't been into a lawn mower engine since the early 1970's...(yeah, I know, I'm dating myself....)...

Reply to
Zootal

You pull off the top tin- a 5 minute job for an ex-mechanic with his eyes closed, and remove the flywheel. The key is right there between the tapered shaft and the flywheel. An ex-mechanic knows how to remove the flywheel in about 2 minutes - including finding the hammer. Puting it back together is the reverse - without needing the hammer.

Reply to
clare

And here's a picture to prove that there's one under the nut:

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Jon

Reply to
Jon Danniken

Since you hit a stump, I agree that the flywheel key should be replaced whether it is bad or not. But! FIRST check the blade to see if it is bent and also the crankshaft to see if it is bent. If the crank (shaft) is bent, throw out the mower and go no further.

Hank

Reply to
Hank

I used to have an el-cheapo made-in-China piece-of-crap Wal-Mart lawnmower,

3hp engine. I hit something, and it bent the crank, bad. After pricing parts and finding that they cost more than the mower did, I tossed the entire thing in the trash.

As for this mower - it's an old Craftsman, 6hp engine, built a bit more solid than the made-in-China piece-of-crap mowers Wal-Mart sells.

This picture pretty much says it all:

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My daughter took pics of the entire operation:

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So, yeah, not only did it shear, the flywheel turned almost 180! A quick trip to Ace Hardware, $2.99 buys a 5-pack of flywheel keys that "fit all B&S engines". Had to use a wheel puller on the flywheel - it was very tight. Did a bit of cleaning while I was there. Put it together. Close manual choke, one lazy pull on starter cord, and it fires right up.

So thanks to everyone here - I had not idea the flywheel would shear the key and turn, I was thinking I was going to have tear motor down and good luck finding parts for it.

Reply to
Zootal

It was easy to do - remove a couple of bolts, lift off top cover, air wrench to remove flywheel nut (big old 1/2" impact wrench, never get to use it anymore, why use hand tools when you have huge impact wrench that yeah might be a bit overkill but bzzziippp and it's off in two seconds), wheel puller pulls flywheel right off. Replace key. Clean here and there. Torque flywheel nut. Put everything back together. Started right up.

Reminded me how much I loved working as a mechanic way back when. Kids today couldn't set a point gap to set their lives. And time an engine? Set idle screws? CO2 meter? wtf? I could have a carb off, tanked, cleaned, reassembled and purring like a kitten in nothing flat. Kids today hardly know what a carb is.....ask a so-called mechanic today what a dashpot is, or what a choke pull-off diaphragm is, and watch them give you blank looks.

Reply to
Zootal

With fuel injection and electronic ignition, many cars today do not have any of the above. Also not much needs ot be done now. I had a 1991 Toyota that had 200,000 miles on it and only changed the plugs once around 100,000. The old stuff needed them changed about every 20,000. Also the points. I did have to take it to a place to get the timing belt changed.

Atleast you could find the old stuff under the hood. Now it looks like one big mass of steel and hoses.

Reply to
Ralph Mowery

On Sat, 30 Jul 2011 14:30:19 -0500, Zootal wrote:

My oldest daughter - a "poor grad student" at St. Mary's in Halifax, was "babysitting" a 2001 Sunfire for a classmate who was out of the country for a few months. The car was not terribly well maintained, andshe said it "seemed to misfire" and made funny noises - so she didn't drive it much. 2 weeks ago it almost quit on her - would not do more than about 30kph, and barely made it into the parking lot, with check engine and traction control lights on. She called me, in Waterloo Ontario tosee what was wrong with it. I had her pull a couple of plug wires and determined the 1-4 coil was not firing - and told her it needed a new set of plugs and wires and a new coil. She went to Canadian Tire, bought the parts, and borrowed a set of cheap tools from a classmate friend. With some help she got the plugs out, and one bolt out of the coil - but the other one stripped the head - so she had to take the complete coil pack assembly off and take it to Canadian tire where a mechanic drilled the head off for her, and she removed the stuck bolt with her newly purchased vice-grips. No-one in Halifax had the required coil bolt - so she got on the internet and found there was one in Bridgewater - 2 hours away. When I texted her to tell her where to find one, she had already found it (the same one, at the same dealership) She figured out another classmate/friend's parents lived in Bridgewater and, since this is a long weekend in Canada, he could bring it back next week if he went home for the weekend - as long as she could arrange to have it picked up ahead of time. When she called to make the arrangements to havr it picked up the parts gut said one of the mechanics was heading into Halifax the next night - and he dropped it off at her door and she finished putting it back together on Friday and said it "ran like a dream" She was VERY proud of herself.

Her Dad was pretty proud of her too - she's generally not the "handiest" - and had to ask "I know it's right-tighty and lefty loosey

- but thats at the TOP of the swing, right Dad?" For an International Development major she did pretty darn good!!!

There's some hope yet for the younger generation.

Reply to
clare

"Zootal" wrote

Dashpot? I've not heard that term in over 35 years; probably no one under the age of 40, maybe even 50 knows what it is.. I've cleaned many a choke pull off to get it working again too.

Reply to
Ed Pawlowski

6HP Briggs in a Craftsman will NOT have points. Briggs stopped using points long before craftsman started using Briggs instead of "eager 1" branded Tecumseh engines.
Reply to
clare

I didn't bother with the magnets, and left the gap where it was. Is this critical? The engine fires up with the first pull and AFAICT runs just fine.

Reply to
Zootal

But if there was a problem there, the OP would have experienced hard starting before hitting the stump. And "magneto contacts" were mentioned - which do NOT exist on that engine.

Reply to
clare

Rephrase that to:" it is important the gap between the flywheel and ignition coil is correct". If it started and ran properly before the key was sheared, the adjustment is correct. DON"T SCREW WITH IT.

Reply to
clare

You are just digging yourself deeper.

Reply to
clare

No issue with the gap - and as you and I both said - if it ain't broke, don't fix it. But you mentioned contacts. If you mean the bround connections, if it ran before, they are OK - don't touch them. Loosening the attachment screws, in most cases, means losening the coil mounts - which can screw up the magnetic air-gap between the coil and flywheel magnet - which we have pretty well established should not be screwed around with if the engine was starting and running fine before. I've seen too many cases where someone played with the air-gap, without knowing EXACTLY what they were doing, and ended up with the coil catching the magnet, damaging the flywheel, coil, or both, within a short time after re-assebming the assembly.

Reply to
clare

Yeah, small engines don't seem too picky about the gap I've always found

- too wide, and the spark tails off quickly (and is obviously wrong), too close and the flywheel hits the magneto and trashes it, but anything inbetween gives good results (always rotate the engine by hand after changing it to test that it's clear).

cheers

Jules

Reply to
Jules Richardson

Jules Richardson wrote in news:j1665o$tjg$ snipped-for-privacy@dont-email.me:

I finished mowing the back yard today - it is a happy mower. If anything, it runs better now than before, which doesn't really make much sense unless the flywheel had already rotated just a degree or two...I didn't touch anything else (knocks on wood...)...

Reply to
Zootal

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