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I have a Toro 20330 22" rotary mower with a B&S engine. It really runs nice except that under certain load conditions, I hear what sounds like a rod knock. It's been going on for a while and wonder if substituting SAE 40 oil for the 30 thats in there will quiet things down.

Post Model xxxxxx, Type xxxx, Trim xx, & Code Numbers xxxxxxxx from B&S Engine. With engine cold, adjust intake & exhaust valves to specs. in Operators Manual.

I know that it's not valve noise because it's a knock, not a tap. I am using 20 ounces of SAE 30 oil as per the Toro instruction manual.

Rod knocks don't come and go, if it's really a rod you're hearing you need to open the case and inspect the internals or the rod will work loose and come through the block

I am curious, this SAE 30 oil...
Is it a detergent oil?
Because it's easy to purchase NON-detergent SAE 30 without realizing it, and for gasoline engines it is essential to use a detergent oil.

Also SAE 30 is really thick...
Especially conventional oil, even if that's what the manual says.
I would try some full synthetic 10w-40 myself.

Most oils now days are detergent.
Take it from a vintage motorcycle rider who needs non detergent oils so the vintage oil cleansing systems can work properly .
Rule of thumb is detergent oils were an external replaceabe filter is used
Non detergent oils for engine that use sludging tanks and no removable filters .
At operating temperatures 30W , 10W/30, 5W/30 or even 0W/30 are all the same thickness
The only difference happens at 25 deg C

sidemouse said:

I am curious, this SAE 30 oil...
Is it a detergent oil?
Because it's easy to purchase NON-detergent SAE 30 without realizing it, and for gasoline engines it is essential to use a detergent oil.

Also SAE 30 is really thick...
Especially conventional oil, even if that's what the manual says.
I would try some full synthetic 10w-40 myself.

Click to expand...

Oil used is Penzoil SAE 30. If I remember correctly, there is no stipulation in Toro manual regarding deterent or non-detergent. The knock is audible only under load and gets louder under heavy load. Otherwise its a good running lawn mower. I keep the blade sharpended and it does a great job on my el toro zoyshia lawn.

As stated, rod knocks don’t come and go. Have you checked the blade for looseness? I would remove the blade and clean everything up good. Reinstall the blade, making sure it is tight and test run. Also, make sure that all engine to deck mounting bolts are tight.

First off all the engine is most likely the 126T02-3206-B1, which is the number we need if we're working on the engine.
The model number of the mower is good to have, but it's the engine we're working on and Toro doesn't make the engine, Briggs does.

You only stated the engine had a "rod knock" and that you ran SAE 30 in it.
That doesn't say much...
It doesn't specify if it's truly a rod knocking, it could be but in my years I've ran across many a misdiagnosis. I always start with the basics, the engine has a knocking sound... Could it be oil related? Not sure, but we also don't know what kind of SAE 30 you're running and yes, I've seen people run all sorts of "oil" in their engines over the years, even 2-cycle mix; lets keep in mind most people wouldn't change their lawn mower oil hardly ever and they will let that stuff get black as soot and even claim that to be normal but when I switched it to what I run (which is 5w-20 full synthetic) all their problems went away.

Non detergent oils are good for air compressors and such things, maybe certain hydraulic drive systems, but in today's gasoline engines it is always best to run a multi-grade full synthetic oil. This covers you for summer, winter, and for home owner use on a lawn mower you can go a year or two between oil changes.

The manuals can be found on this page:

The actual manual for this particular engine can be found here:

And on page 10 of that manual it states to use

Briggs & Stratton 100005 SAE 30W 4-Cycle Engine Oil, 18 oz. Bottle​

So I have to guess that is the actual oil you are using.
You didn't per chance go by Dollar General or some auto parts store and buy just any bottle of SAE 30...

That being said, I would personally still run a Full Synthetic 10w-30 or 10w-40 in it.
But, if you're going strictly by manufacturer's recommendations and what the manual states, then yes you should use the

Briggs & Stratton 100005 SAE 30W 4-Cycle Engine Oil, 18 oz. Bottle​

Oil will not cure a rod knock , if in fact it is a rod knock which I seriously doubt that it is because rod knocks are loudest when backing off , not under load.
Add to that the engine has a full splash lubrication so heavier oils just make it worse.
Even if it quietens down an audible knock, it will still be there and quietly flog the big ends oval till they go bang & break .

As you say it gets worse under load then it is most likely detonation or a broken governor ( if yours is internal )
A loose flywheel will also cause a knock that gets worse under load .

There is only 2 options
1) pull it apart and find the problem
2) use it as is till it becomes scrap metal

As for synthetic oils, a total waste of money in an engine that is not designed to run with synthetic oil, same as putting 110 octane avgas in a low compression side valve engine .

As for detergent / non detergent oil, totally irrelevant when we are talking about the low tech lazy governed engines that are used in lawn mowers .
Now if we are talking about a NASCAR engine then there is relevance but not in a mower.
People who have not had the education needed so they can actually understand oils adsorb all of the total bull that oil companies put out and it sinks into their brains till they become religious deciples of the oil companies.
If synthetics were 1/10 as magnificant as the oil companies claim , they would not be spending the millions that they do to brain wash Joe Public into using them.
Remember
Quality products sell themselves
Trash has to be sold .
Remember all the hype about exotic metal spark plugs ?
remember how those $ 20 -$ 50 plugs were going to give your engine more power , more MPG , cleaner exhausts & increases engine life ?
Did they do any of that ?
Nope
In a few very high performance engines they make a difference in the bulk of real life engines they make not difference to anything other than your wallet .
To make an analogy $ 1000 running shoes do make a difference to Eugine Bolt's performance & might drop a few tenths of a second of his times.
Will they make YOU run faster ? not a chance in hell but we buy them because we think they will .

Rivets said:

As stated, rod knocks don’t come and go. Have you checked the blade for looseness? I would remove the blade and clean everything up good. Reinstall the blade, making sure it is tight and test run. Also, make sure that all engine to deck mounting bolts are tight.

Click to expand...

It's not the blade. I recently sharpened and retorqued the blade to the recommended 60 ft. lbs.