Saturday, 11 August 2018

CBF250 Engine Problem - Part #3 - Putting it back together.

The new valves must be "lapped" into the valves seats. This is a process to ensure a good gas seal. For this I need a lapping tool (a wooden rod with suckers on each end) and some abrasive paste.

I must have bought this grinding paste 25 years ago - I suppose it doesn't go off.

Luckily I've got a factory manual to help me. I bought it as a pdf file when I got the bike. A slight problem - it's in Portuguese - the bike was built in Brazil. Not a problem, Google Translate is my friend. Later I got an English version but it wasn't that good. It looked like it had been translated by a computer or someone who didn't speak English….or Portuguese. All part of the fun, I suppose.

The valve lapping procedure according to my "English" manual. Note "Out of windy" is its translation of the Portuguese "Cabo de Ventosa" = suction cup.

Then,as the manuals are wont to say "reassemble in the reverse order of disassembly"
I had to fit the new valves and I also had to refit the undamaged exhaust valves I removed to fit new oil seal and lap them in. I borrowed a valve spring compressor from my friend Ron (I mean, a man with two Velocettes and a Norton MUST have a valve spring compressor) 
Unfortunately his compressor didn't fit (the prongs were too wide to fit into the bike's head) He said I could modify it as necessary but I didn't want to mutilate his long serving tool. I made one based on Ron's tool out of some scrap steel sections.

The things you can do with a cheapo MIG welder and some scrap steel.
I made a stand from timber to hold the head while I worked on it

Head with new valves

When re-assembling the cams they are timed using the IN & EX marks

Working on the valves throws the clearances out. The CBF uses shims to control the gap. The size marking tend to wear away so a cheapo micrometer is needed.

So did it work after this? - See final enstallment coming soon.

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