Katana Owners Club U.K.

Looking at the piston crowns I would say you have some detonation problems caused by either lean running due to air leaks/jetting etc (confirmed by the valves) or maybe ignition timing issues.

Have you tried blocking the barrels with lumps of wood & GENTLY turning the crank with a spanner, this should pull the pistons down, keep the block level & watch the 2 pistons going up don't catch the bottom of the sleeves.

Did you have a new head gasket fitted? From the photos I would suggest you are getting oil from the oil feeds to the rocker or chain tunnel, the underside of the head doesn't look very clean & flat, as long as you are running std pistons then there should be a bit of clearance to flatten the underside of the head, 1000 grit wet & dry paper on a FLAT surface (Glass / mirror on a work surface) or pay an engineering firm to skim the head, just a tiny bit.
Mine runs hi compression pistons so very little clearance, also use Cometic Head Gasket.

Steve

Ok now I've had a proper look at home on my tablet I can see its not detonation but carbon build up which is soaked in oil! Bloody phone pics are rubbish
It will be interesting to see what my motor looks like when I strip it

have you changed the valve stem oil seals yet? take some pics up the inlet ports showing the valve stems, im willing to guess that the inlet valve stems will be wet with engine oil being pulled down into the combustion chamber.

You can buy these or similar off eBay for not a lot of money.

https://rover.ebay.com/rover/0/0/0?mpre ... 3365619320

The club should have a valve Spring compressor in the loan dept... But we don't ....but we will.
Blisters matey should you feel the need to buy such an item we will reimburse you and keep it with the other tools we carry .
I shall make a list a put it on here in the next few ........ Then if anyone can contact me and borrow what we have for postage.

strange one, but when it was built up, the piston rings were put in the right way up werent they? its possible to put them upside down and they will cause the problems you have experienced. there should be lettering or some marks etched onto the top edge of the ring, if th ring gets put in with this at the bottom, it will drag oil into the combustion chamber.

You can borrow my set but I don't know where your based?

johnr wrote:strange one, but when it was built up, the piston rings were put in the right way up werent they? its possible to put them upside down and they will cause the problems you have experienced. there should be lettering or some marks etched onto the top edge of the ring, if th ring gets put in with this at the bottom, it will drag oil into the combustion chamber.

I mentioned the same after the motor was initially started up and smoked like it does... sounded to me like a scraper was upside down so instead of clearing it was pushing oil around

Top 2 rings 2 check... the oil rings (bottom set with zig zag bit) unlikely the issue