Friday 10 August 2018

CBF250 Engine Problem - Part #2 - Planning the fix

The damage to my CBF 250's engine seems fixable at a reasonable cost.

I was keen to attempt a repair because the engine is in surprisingly good condition for a 250cc that has done 65,000 miles. Remember that at its normal cruising speed it's spinning at 7,000 rpm. 

The parts - two inlet valves, cylinder head gasket, valve stem oil seals x4, exhaust gasket.
The oil seals aren’t essential but it seems a good idea to replace these while the bike is apart. They are very cheap items. The CBF's oil consumption has increased recently and it's likely that oil is being lost through these seals. As it turns out it looks to me that the old seals are worn (the hole is bigger) Remember that the valves have moved up and down inside that seal 300 million times (give or take) 

valve guide oil seals - old & new
Also I have to repair or replace the tensioner. The spring is not available as a spare - it comes as part of the tensioner unit. The cost isn't prohibitive but I didn't feel like giving Honda the cash for the unit that had failed and caused the problem. Luckily a search on eBay came up with a solution - a manual tensioner. This is just a plate with a bolt & lock nut. You set the tension manually. There is nothing to fail. I was surprised that this was available for the CBF, these are usually fitted to competition machines but I realised that the CBF's engine was similar to the enduro XR250.

Tensioner old & new

Tensioner fitted

Also I need stick with suckers on the ends……see next instalment

1 comment:

  1. Do you have the part numbers for the Prox valves, and can you advise where you bought them from?