Topic: CB500 four K1 0.5mm over-bore

[Register]

Hi, I need a bit of help please.

As part of a necessary 0.5mm rebore I have purchased the related pistons from David Silver Spares.

The machine shop need to know the tolerance required for these pistons.

The response from DSS is - these are pattern parts, we don't know.

Haynes says max piston to bore clearance of 0.050mm.

Is this the max wear befor a rebore is required, or the new installed dimension.

Any help appreciated.

I don't want a rebore that's worn out on day one.

Thanks.

Pete

[bryanj]

The clearances are in the manual for both bore and piston so you just add the 1mm to the standard bore of 56mm. If the machinist is asking YOU what the clearance is find another one who is used to Japanese multis.

[Register]

Bryan

Thanks for the advice. That was my logic, but the point the machinist makes is expansion of the piston is a factor of the material and therefore must come from the manufacturer/supplier.

The logic of Honda’s tolerances is they knew the piston characteristics and sized to suit.

For non-OE pistons, with no data, am I left guessing?

Pete

[bryanj]

When i was working in the trade we had many twins and several fours rebored using none genuine pistons and all to Honda specs with never a problem especialy if it said ART somewhere on the piston as they were Honda's suppliers. In todays world i could not guarantee anything cast or embossed on anything anymore but as you have no hope of finding the manufacturer i would bore to 56.5mm EXACTLY (after honing) as that is 0.5 o/s for a 500, in fact as my local bike shop was selling up i tried to buy his boring bar but the new owners wanted it and i just did not have time before he closes tomorrow to go in and bore a couple of blocks "on spec" as it were.
I know lots are going to shout at me telling each bore needs to done for a specific piston and 40 years ago in the car world i would agree but having checked a lot of Honda pistons i have yet to find a new one that varies in any way from the size it is supposed to be.

[dave500]

i used a david silvers 550 kit,i had the bores done for each piston,these aren't genuine even if they were it would be done this way.

[trigger]

Honda pistons are 98% spot on but, aftermarket ones can be a little up and down on the size. Always be very careful of anyone that does this work, tell them that you want 1 thou clearance on the aftermarket DSS pistons. If they say that it is too tight and it should be 3 thou, then look for a machinist that will do it right.
As Dave has said, each piston to be matched to each bore 

[Register]

Dave, Bryan, Trigger,

thanks for your informed responses.

I think I've got what I need thanks. I'll brief the machinist and let you know.

Pete

[dave500]

ive been thrashing that rebore for a few years now and its fine,dont baby it on the break in just ride it normally,dont let it idle,dont lug the engine but do load it a little.