Lawnmower knock

[GMFan]

Our church has a ~5 yr old Toro lawnmower - Tecumesh engine I believe.

I went to mow on Friday and I had a bear of a time starting this mower. I primed the engine and pulled but it didn't want to start. It would poof out a bit of smoke but not start.

After 10 minutes of frustration I finally got it to start. First it started spewing oil out of the exhaust in a spray. It then blew huge amounts of white smoke. I shut off the mower due to the smoke show.

I try starting 5 minutes later. It does the same smoke show and the engine knocked loudly for about 15 seconds while smoking. After the engine stopped knocking and the smoke died down after a few minutes it ran ok.

I usually don't do the mowing so I don't really have any idea what the deal is with this mower, but it seems to have major issues. Bent rod from hitting a rock? Could I have flooded the engine and it knocked because of the excess gas?

The oil was full but did look gray.

I am going to try to change the spark plug first.

Any ideas? I do recall I mowed a few months ago and it did aggressively smoke on start up as well.

 

[AlanJW]

did the lawn mower ever get left on its side? or matbe ever flooded? I know that when ever I tilt mine on its side to clean it, it usually smokes a little bit. Also overfilling the oil will make it smoke. And you said the oilo was Grey? did it smell like gas?

 

[mechjames]

Grey? Maybe break in metals? Has the oil ever been changed? That would explain the knock.

 

[GMFan]

I do recall the oil being overfilled. I saw an empty container of Napa 10w40 but I don't know how old it is. For all I know, that is what was used from when the mower was bought. I may give it an oil change.

The oil was overfilled by about an inch on the stick.

 

[greenaccord02]

Probably just overfilled though like GM says. Change and remember to add no more than 20oz to the empty engine.

 

[Johnny]

If the oil was overfilled by an inch on the stick, that is your problem. That is causing the knock plus the oil spraying out of the exhaust. Do what greenaccord suggested, drain and fill with no more than 20 oz of oil. Probably also needs a new spark plug from oil fouling. Go to your local parts store or mower shop and get a quart of straight 30W to put in that thing.

 

[Turk]

While you're at it, clean out the air filter, or just get a new one.....

 

[3311]

I was getting a terrible knock out of my 3 YR OLD Toro/Tecunseh 6.5hp mower, it was so bad I thought that it was going to come apart every time I started it up during the first 10 seconds. Switching to heavier (Delo15w40 from Mobil 5000 5w30 )made the knock go away, significantly reduced the start up smoke. Mobil is great oil but I think this Tecumseh needs a much thicker oil. This is my first and last Tecumseh.

The levels were/are fine on both fills.

 

[Steve S]

Tip the lawn mover on its side to drain the oil out of the fill hole and add the required amount of oil . Straight 30 or 15w-40 . Try to start it. My techemse is a 1998 model gets used a half hour ten monthe out of the year and gets what ever oil is sitting left over in the shop 5w-20 to 15w-40 the oil gets changes once a year and the air filter every couple of years , The bad thing about the internet is it would be easy to say I'll be ther later to see what I can do. N.Y. is a little far to do that.Gray is the oil never been changed or water .

 

[Papa Bear]

Clean the air filter...

 

[GMFan]

I worked on the lawnmower last friday. I cleaned the (filthy) air filter, changed the dirty (and overfilled) engine oil and using Exxon 10w30. After the filter was somewhat clean and the engine oil was changed, I checked the spark plug. The spark plug looked like it was oil coated.

I didn't have a new sparkplug with me, but I bought one yesterday and plan on changing it this week.

For the record, after the oil change and air filter cleaning the mower started up a lot better and easier. It did not blow nearly as much smoke as before. It DID however knock slightly in the beginning for a few seconds.

The shed it is stored in is quite humid and damp. I'm wondering if that is adding moisture to the gas. I also bet that whoever gets the gas isn't using premium (which I believe premium should always be used in small engines).

I will update after the sparkplug is changed.

Everyone's help is greatly appreciated.

edit: And I was wrong in my first post... The mower is closer to 8 yrs old and (obviously) abused.

Our commercial grade Lawnboy with a Briggs engine still runs like new after 13 years...but then again I maintain it every spring.

 

[lexus114]

Why do you believe premium fuel must be used in small engines ??

 

[3311]

Make sure the blade is tight as well. The first time I sharpened mine I didn't tight because of the pulley(self propelled) and it sounded horrible for a few minutes until I shut it off and put a wrench back on it.