New to me Craftsman rider with a knock?

[hansj3]

I have been gifted a used Craftsman 917.270532,with a Briggs Ic gold, 14.5 hp engine, riding mower. The previous owner let the head gasket blow, and with a quick replacement she fired right up.
After the initial joy of hearing it pop over, I idled it down, and surprise, a knock at idle. Anything I should look for?
I set the intake to .004 and the exhaust to .006. the valves were free, and clear of carbon, the pushrods ended up in the right area, and the cylinder bore still had crosshatch marks

It did it cold and warm. All I had on hand was a Mobil synthetic fleet 5w30 oil.

 

[hansj3]

Here is a picture of the engine placard for those who need it

 

[Lubener]

I would use heavier oil. The knock may be more pronounced after the headgasket change because of the added stress on the rod. Otherwise I would just run it and not abuse it. Only choice you have is a new rod, wristpin, gasket set and maybe a piston. Probably not worth it. I have been running a knocking engine for several years now.

 

[demarpaint]

I agree with Lubener. I would give a good 5W40 a try. Mobil 1 TDT comes to mind.

 

[Silverado12]

The knock could be an internal balancer.

 

[Donald]

A Husqvarna model by the 917.

 

[danez_yoda]

Sound like a candidate for STP or lucas miracle motor fixer.


https://www.youtube.com/watch?v=r2OP7KlHQLw

 

[jeepman3071]

Originally Posted by Silverado12
The knock could be an internal balancer.


This.

Those engines have a bad habit of breaking the balancer. I don't think the bad head gasket itself was the cause. I've repaired many head gaskets on these engines, some which also had the bad float needle problem causing the crankcase to fill with fuel, and they still ran fine after.

I'd say either the balancer broke, or with the bad head gasket it was run low on oil and the rod is knocking. Those seem to be the main causes of engine failure on these from what I've experienced. If it was mine I'd probably find a used engine that runs good to swap.

 

[wayne50]

For the heck of it, I would check the tightness of the engine mounting bolts.

 

[Lubener]

Pull the cover and spark plug, rotate the flywheel back and forth. If it is the rod, you will hear it.

 

[JTK]

To me, some of these Briggs OHV singles can sound a little knocky at certain RPM ranges in these riding mower applications even when they're good. Like said, could be a lot of things. If it runs good, the cylinder and valvetrain looked good and you need it to cut grass, I'd run it as-is and would probably use an inexpensive 15w40 in it.

 

[bubbatime]

Run it at the normal mowing RPM. Does it knock or sound normal? If normal, then dont worry about it. Its splash lube, and they can make a racket at lower RPM's.

 

[repairman54]

I will second the sounding a little knocky at certain RPMs especially low RPM. I have the same motor in my 1995 Craftsman mower and it's always sounded that way since day one. It's always been run on synthetic oils since the original fill was drained. And this tractor gets year-round use between Mowing and plowing. Other than the float needle issues every few years it's been flawless

 

[JTK]

Originally Posted by repairman54
... I have the same motor in my 1995 Craftsman mower and it's always sounded that way since day one.


Same here, except my Sears LT2000 rider has the 18.5hp version "with AVS". Mine is a ~2005-ish range that I bought used in 2011.