Help needed with a knocking lawnmower...

[waterinthefuel]

I found a lawnboy self propelled lawnmower sitting roadside, i.e., in the trash, down our street. It was in remarkable condition considering someone was throwing it away, and after taking it apart, changing a few parts in the carb and putting a new brake cable on it, it purrs like a kitten. It even started on the first crank.

However, during hard deceleration, and only during hard deceleration, there is a considerable knocking noise heard until it slows down, then at idle, no noticeable knock, you can even slam the throttle to wide open, no knock at all. Only on hard deceleration. If you decelerate slowly, no knock. Anybody know what could be the problem? We put brand new fresh gas in it (the tank was dry when I found it).

It's a 6.25 HP Tecumseh.

Any suggestions would be greatly appreciated!

 

[eurolarva]

Re: Help needed with a knocking lawnmower...

Most lawnboys are two strokes or at least they used to be. Try running some seafoam in the gas and see if that helps. Also verify if it takes two stroke oil or not.

 

[waterinthefuel]

Re: Help needed with a knocking lawnmower...

Sorry, it's a 4 stroke. I forgot to mention that. We pulled the head and cleaned off the piston and the valves and valve seats looked good.

This is the lawnmower, I guess what it looked like a long long time ago! LOL

 

[eurolarva]

Re: Help needed with a knocking lawnmower...

Amazing what some people will throw away. I am in a small machine forum and they all say lawnboy is the way to go. I am not a mechanic but my guess would be piston slap. For free I would not worry about it but if you dont get any hits here for a good answer try small engine technical forum. I dont want to post a link but google should work

 

[waterinthefuel]

Re: Help needed with a knocking lawnmower...

Thanks for the info. We tried to move the face of the piston around in the cylinder and it had VERY little to no movement. The knock surprised both of us. Rest assured, the lawnmower I got doesn't look nearly as good as the one in the pic, but by no means is it beat to hell.

I mowed his entire back yard as a trial run, and it MANICURED that yard. It was amazing.

 

[KRS]

Re: Help needed with a knocking lawnmower...

Please return my mower... my kid was mowing the lawn and left it by the street to get a drink, when he came back out,.... someone stole it.























KRS

 

[Lone Duck]

Re: Help needed with a knocking lawnmower...

By hard deceleration you mean heavy load that slows it down? Like in tall grass? Or do you mean sudden throttle shut down? In either case it could be a loose blade. It my seem tight but some times the belvile washer gets worn and the blade will make all kinds of queer sounds if it is loose. I am a retired small engine mech.

 

[Scaaty]

Re: Help needed with a knocking lawnmower...

Use it 'till it blows..can't beat the price, right?

 

[kenimpzoom]

Re: Help needed with a knocking lawnmower...

Try the loose blade, my mower was knocking and it was the blade.

Ken

 

[waterinthefuel]

Re: Help needed with a knocking lawnmower...

I meant from a sudden throttle close.

He just sharpened the blade for me yesterday, it might be the blade. But if it's the blade, why does it only do it on sudden throttle closure? It sounds like it's coming from inside the engine, not from under the deck.

 

[Ret USN CPO]

Re: Help needed with a knocking lawnmower...

Well, the blade is attached to the shaft that runs right up into the engine, and sound travels. I would give a try on tightening the blade.

 

[SeaKaye12]

Re: Help needed with a knocking lawnmower...

You could ask over at this forum... They love LB's....

http://forums2.gardenweb.com/forums/lmower/

There's a guy there named Tecuman....guess what brand of engine he likes

Chuck

 

[Drowned Rat]

Re: Help needed with a knocking lawnmower...

The blade can get out of balance too, especially after sharpening it. If tightening it doen't work, try replacing it.

 

[waterinthefuel]

Re: Help needed with a knocking lawnmower...

Excellent thoughts and ideas. I made a small list and will slowly eliminate each one!

 

[Lone Duck]

Re: Help needed with a knocking lawnmower...

One more thing. You would be surprised how many folks put the blade on upside down. Check it.

 

[thefairlaneman]

Re: Help needed with a knocking lawnmower...

That is a 400 buck mower. I checked one recently for a neighbor like it that had the piston stuck in the upper cylinder when the rod broke. I wasnt impressed at all. I believe it has a very exspensive problem to fix. You WILL need a new engine very soon. Plan to throw it away soon. You could remove the blade and run it to rule out a blade issue....those engines suck

 

[Lone Duck]

Re: Help needed with a knocking lawnmower...

Do not run without blade. On those engines the blade acts like a flywheel. it helps to give momentum to get through all its cycles . With out blade it will run like sh-t. And you really could damage it. When you are holding on to the handles at a steady speed is there a lot of vibration? If so the shaft may be slightly bent and the bearing is worn.

 

[waterinthefuel]

Re: Help needed with a knocking lawnmower...

Ok, here is an update. I have a feeling fairlanemen is closest out of everybody, unfortunately.

I put a brand new piston, wrist pin, and connecting rod in it. Although it got quieter, it still knocks, especially at idle. It no longer knocks on deceleration, now it knocks on acceleration and at idle, and even a tad at any throttle setting, but it's barely noticeable. I think the case of the engine is worn. I can't imagine what on it is still knocking. We checked everything, and it looks great.

It gets a bit quieter as it heats up, and I'm running a bunch of Bardol in it to try to get it quieter.

Total spent on this piece of crap: 125 bucks. Costly lesson.

 

[Haut Medoc]

Re: Help needed with a knocking lawnmower...

Don't run over any cats with it......​

 

[thefairlaneman]

Re: Help needed with a knocking lawnmower...

I wont say "I told you so" but you got to admit you would have been better off trashing it from the start. Im not a mower expert but Ive learned the hard way on a few of them myself...... Lawn boys are overpriced and cheap made