Head scratching and no bright spark.

My new exhaust valve guide and it’s spare had arrived so I knocked that job off quickly this evening. Of course having a spare meant the first slipped in easily. Still it is done now.

Now whilst looking at the head in detail I started to consider if it was a 7:1 or 8:1 compression ratio. There is a flat on which an 8 should be stamped if it is the latter. Now I guess the guy in charge of stamping mine was having a bad day.

However a quick check tells me that all castings HRC1303 are 8:1.

Now whilst pondering this I had a spark of inspiration – check the plugs! Now I have looked at this before and understand the following to be the plugs needed:

7:1 Champion N5C
8:1 Champion RN12YC
7:1 NGK B6ES
8:1 NGK BPR5EIX

Now this is based on what manufacturers’ websites say and check on forum. Of course this is somewhat metered by the fact that these engines will run (maybe not well) on anything.

I checked mine. BPR6ES. So basically the same as that for a 7:1 save for a projecting insulator. Halfords (Half ords as I was taught to say) list this plug thus: