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I've got an old Toro Timecutter 42-Z with a B&S 16HP OHV engine. I was cutting with it and it pretty much sputtered out and died. I tried to start it back and the engine will only go about halfway and seems to hit something preventing it from going further. I can hand turn the flywheel easily either direction about 180 degrees and it stops. I'm pretty sure it's not a valve adjustment. I'm not an engine guy. Does anyone have any thoughts on what to look for before I tear into it? Thanks

Well that don't sound good at all. It acting something on top of the piston like a broken valve seat. There is only two ways of verifying this. One is to use a bore scope and other is to pull the cylinder head. Now something could have failed in the crankcase too.

try it with the spark plug out and report back

So this is spark plug. Never seen this before. I imagine this is very bad news?

You need to pull the cylinder and just how damage has been done. I have seen plugs very close to being that damage.

that happens when something in the cylinder hits it. Pull the head and see what is in there or if you have a borescope use it. There is one on amazon for $17 that can be used with a phone or laptop. https://www.amazon.com/gp/product/B07PBF6DX5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Broken valve. The top of piston is beat up pretty bad. It will rotate all the way now with obstruction removed. Is it repairable?

Top of piston

sgkent said:

that happens when something in the cylinder hits it. Pull the head and see what is in there or if you have a borescope use it. There is one on amazon for $17 that can be used with a phone or laptop. https://www.amazon.com/gp/product/B07PBF6DX5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Click to expand...

Finally one small enough for those 10 mm plugs. Added to my list for the next order.

bummer, cheaper just to get a replacement engine. If you are near any mower salvage yards you might find a good used engine at a reasonable enough cost to chance it. But if the mower is good otherwise, a new engine is often the least costly way to go.

I didn't know if maybe replacing the complete cylinder head might be the way to go. I can find used on Ebay for about $55. Not sure if the dings on top of the piston would be an issue.

and the bent rod?

sgkent said:

and the bent rod?

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Dont think there is a bent rod. Just broken valve and dinged up top of cylinder.

Stick a ruler across the top of the bore
At tdc the piston should just touch the ruler.
If it is short then the con rod is bent .

when one has dings that big in a piston the force has to go somewhere. Usually into the connecting rod. At the least you are looking at a head, connecting rod, piston, rings, and valves. If the guide or seat are damaged, or the bore scored then the engine is junk. By the time you price out all the parts, you are better off with a new engine or a good inexpensive one from a donor. I priced out parts on a high hour engine a while back that still ran. Parts cost too much for a rebuild to be economical. Good luck.