SOHC.co.uk Forums > CB350/400

Addressing the smoking

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Johndoc:
Cheers Bryan, two of the pistons are 50.5 and the other two are 51 dead! Yea a real botch up, was thinking the big bore kit might be the best and most economical way to go? I do want to keep the bike as original as possible.

Chris400F:
A big bore kit seems slightly at odds with keeping the bike as original as possible.
I concede that the Cruzinimage kit looks good value, don't know why they don't seem to have non big bore pistons any more.
Not sure if carburation changes are needed if you go down the big bore route, someone on here will tell you.
Standard bore is 51mm; if you could get away with 2nd oversize (+0.5mm) then DS have pistons to suit (coincidentally they show 4 in stock right now).
Guess that may be a question for a machine shop.
I have seen larger pistons available but they are more expensive and you need to search, but there are some out there.

Johndoc:
Thanks Chris, good to hear from you. I will have a look at DSS, yes it seems strange that the Cruzinimage do not do a non big bore kit. I have read good reviews on the big bore kit, little or no other changes needed, would be good to hear from someone who has carried this out and what their thoughts are on it. It works out far less to do it this way and if what I am reading is correct the engine feels the better for it. The other problem it solves for me is to get the cylinders in balance as I am not sure what has gone on exactly with them. I am taking a guess that two of the bores have been taken out to the first oversize and the other two are standard, but I am just not sure.
Incidentally does anyone know of a machine shop in Central Scotland or a mail order company who could do this work?

Johndoc:
Finally got it all sorted out. Turns out the bores were all standard size and in really good condition, machine shop honed the barrels and new Honda piston rings fitted, even the last washer from the head turn up, it was lying on the ramp!. Bike now back together and sounds as sweet as a nut. Just some minor jobs to do and then up for an MOT. Thank you guys for your input.

mike the bike:
That's good to hear, I'm glad it all went to plan in the end.

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