Export thread

Took my mower to local repair shop and he said it needs a new head. Apparently the valve seat came off and bent the valve. He said he replaced the valve seat and put in a new valve but after letting it run it happened again and bent the new valve too. Just curious if this is common or if someone else has had this issue? Just haven’t heard of someone replacing a head on a mower before.

Hmmm, I have already replace a couple Kawasaki heads this year. A Kohler head and three Briggs heads last year.

Usually once an OHV valve seat or valve guide come loose you need a new head.

It is common that when the cylinder head is overheated that the valve guide comes loose, yes. There is no repair procedure for this and the guide is not a replacement part from Kawasaki. I’ve seen many try to get the valve guide back into place. It usually never works. For the few that have made it work, probably invested more time and effort than what it was worth.

StarTech said:

Hmmm, I have already replace a couple Kawasaki heads this year. A Kohler head and three Briggs heads last year.

Usually once an OHV valve seat or valve guide come loose you need a new head.

Click to expand...

I’m not a mechanic by any means just trying to get a better understanding.

txmowman said:

It is common that when the cylinder head is overheated that the valve guide comes loose, yes. There is no repair procedure for this and the guide is not a replacement part from Kawasaki. I’ve seen many try to get the valve guide back into place. It usually never works. For the few that have made it work, probably invested more time and effort than what it was worth.

Click to expand...

Thank you, very helpful!

Mower heads are an Al-Si-Cu alloy
These alloys are heat treated to make them harder ( stiffer actually )
When overheated they revert to full solution soft state and need to be aged to restore their operational hardness
Ageing is done at around 300C to 400C ( depending upon the actual alloy ) for 10 to 40 hours or you can just sit it on the shelf for 2 to 3 years to have them naturally age.

During overheating, only a small section gets damaged but to restore it you first have to fully soften the casting called "solution treating " then age or precipitation harden if you want to do some research
The cost of doing this for 1 head is 5 times the price of a complete replacement head .
If you have access to a good kiln lab oven you can do it yourself but care is needed to ensure that it does not warp .