It's unlikely the keeper rings "just fell off". If you did something extreme, they could have come off. (Only you can judge that.)

There is a valve spring compression tool, however even using that, it would probably work best with the head off. I don't even know if it's possible to compress the spring and get the keeper on with the head on. ??

Try pulling the valve stem out from the top (thinking maybe, the valve head popped off. I don't even know if this ever happens.) Maybe, if the keeper ring came off very easily, it might indicate that.

"Blown engine" would usually mean something serious in the bottom end, I would think. If the pistons and push rods go up and down, I'd tackle the valves first.

Let's see what the pros have to say.

Engine Model & Type numbers are always handy so we know exactly which engine you have.

Without looking at the engine, it's hard to know exactly what "blown" means. It might be as minor as a "blown" head gasket (not uncommon) or very major damage to the internal parts.
Why not ask the "mechanic"?

You pretty much have to remove the head to reinstall the valve keepers. Not a major job if you have some mechanical aptitude. You could probably do it without the valve spring compressor if you have strong fingers and a 3rd hand.

You can down load a pdf IPL from Briggs at the link below.

BTW, on Briggs OHV engines, the valve lash is checked with the piston 1/4" PAST TDC.

I can't speak for Sears how they would deal with the situation. You might ask them or Briggs, since it is an engine issue.

Here is a link that might be useful: Link

Now that you have given a brief description of the scenario, it would be appropriate to post the engine model # and type # from the engine itself.

Sorry the engine type is 18.5hp, OHV INTEK PLUS.

I'm surprised at how quickly and willingly people are at answering my e-mails.

Anything to help me out would be good.

Model number 917.273642

That engine should be a-
31P777-0348-E1

SAME engine as in the "Valve lash adjusting" thread!
Hmmmm

Yes, it is the 31P777-0348-E1. Can someone link me into that thread? I'm new to garden web and I'm afraid I'm not that good at navigating. Sounds like I might be on to something though......

It's down the list about 5 threads.

Here is a link that might be useful: Valves adjusting