Having a valve seat insert come loose is usually due to overheating, and the usual cause of overheating is grass or mud blocking the cooling fins, though a roughly-treated engine may have a damaged fan, a tenant's improvement to the cowl, a carburetor malfunction, or an intake air leak, any of which can cause the same outcome. In general, it doesn't happen without overheating of the valve/valve insert, which doesn't happen without there being something wrong with the engine or engine installation.

Briggs approves re-inserting the insert and staking it in place, but warns that it should be classified as a temporary repair rather than a permanent one. Nevertheless I believe it is the usual thing for owner-repairers to do, when the problem arises. That does not mean it is cost-effective to do it at $40 per hour, given Briggs' warning that it is a temporary repair. If you charge the owner say, $120 just to stake the old insert back into place, and it falls out after a couple of hours' use, he may bad-mouth you all over town and ruin your business reputation.

http://www.briggsandstratton.com/us...he-engine-block-how-can-this-be-repaired

Here is the Briggs instruction for installing and staking an insert:

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