1976 CB550F1 (what have I let myself in for) Project

[eight0]

They are aftermarket, but he rebored each one to match each piston so the clearance was to the spec in the manual.

Or am I not following you..

[Nurse Julie]

They are aftermarket, but he rebored each one to match each piston so the clearance was to the spec in the manual.

Or am I not following you..

Different piston manufacturers have different specifications for their piston to bore clearance depending on alloy / silicone ratio. But, it really should only be evident when the engine is hot for the 1st time after rebore. This is when the engine will seize due to not enough piston / bore clearance when everything expands. Have you checked that you have the con rods on the crank the correct way round?.

[eight0]

I really hope so. I put them back on the same way they were on. Letters facing forward, numbers backwards.

You can just make it out in this photo.

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[philward]

Conrods should be installed with 'bearing key' facing forward - 'bearing key' is the bearing locating notches

[eight0]

I can't say for certain then. I put them on how they were but as I bought the replacement crank from DK maybe they had removed them and put them back on the other way around.

Guess that means I'll have to split the cases again.

[philward]

If they had been messed with prior to you getting them, the people who messed with them would have had to have put all 4 rods on 180 degrees wrong as you say the letters were all facing forward - ie, all 4 are either all facing right way or all 4 all facing wrong way.
I have just done my 500 (that is I have just fitted barrel) and can't remember whether letters were forward or back facing - only that the letters were all facing the same way.
I would suspect the piston/barrel tolerances and take piston off and insert pistom/rings into the barrel off the rod to check for tightness - that will isolate the source of the tightness. You can check tolerances at this stage either way

[eight0]

Hang on. I've just found a photo from when i received the crank. I think I've messed up. This would be numbers forward wouldn't it?
It's been a long week.

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[eight0]

Thanks for the help so far everyone.

Yes it span smoothly without resistance. I'll check end gap tomorrow and post the results.

[eight0]

Thanks for the help so far everyone.

Yes it span smoothly without resistance. I'll check end gap tomorrow and post the results.

The odd thing is the fact the outer pistons don't seem centered to the bores

[eight0]

Yeah, seriously regretting it now.
They were piston kits from DS, including the rings, pin and circlips.

[eight0]

The rings are marked R 25.

Just checked the ring gap and it's .30 on all cylinders

[eight0]

Mm

[Bryanj]

Thats right Ken, i inherited a Van Norman and bought  an SPS. Both fit on the same table but cutters are different

[eight0]

Ok I'll remove the pistons and see what they're like in the bores without the rings.

I'm at a loss for what to do here now to be honest.

[eight0]

I've pulled the head again and checked the piston that was hanging up the most.

Without the rings it drops through. With the rings it's really tight, but maybe it's supposed to be this tight?

https://youtu.be/glUKwGO5nxU