I know its best to install a blockguard before doing any machine work but is it really necesarry. I just tore my motor down to replace the rings since the oil rings decided to crap out on me and figured that since its all apart I could tap in a guard.

 

reliability-wise, yes. Install the blockguard and then have your machine-work done. Most especially the deck resurfacing.

 

I did mine after. Just tap the guard about 1mm below the top of the deck. No worries.

 

put the blockguard in before all machine work... welding it in as well is also a good idea...