CB500 rebore/big bore

[Tomb]

My 500 needs a rebore, I have spare barrels that are in poor condition but would bore out, I have two options, go to the first oversize that Cruzinimage do with the barrels on the engine, or using the spare barrels, use a CB550 big bore kit to take it out to 600. A 600 is always something I wanted to do.

My question is - Are the 500 and 550 barrels the same dimensions, obviously not the bore but the sleeve thickness and any other sizes that may be affected, will the 500 barrels take the 550 big bore kit out to 600?

[Seabeowner]

Third option is to bore out to 550 (58.5) or +0.5 (59.00)
Think 550 had bigger crankcase openings, but I,ll let the experts chime in.

[Tomb]

Thanks, yep that's the kind of info I need, I was just looking at more options.

I have a CB550 engine to go in whilst I do the work.

600 big bore clicky

553 big bore clicky

500 +0.50 rebore clicky

550 +0.50 rebore clicky

[philgresty]

Yeah i'm sure Seabeowner is right, id go for the 58.5 550 pistons and overbore as mileage requires.
Using the 61.5 600cc pistons leaves the cylinder liners awfully thin, so overboring isnt possible.

Another option is machine down some 750 pistons "gentlemens express" style to give 590cc

http://www.chinonthetank.com/2012/05/cb550-the-gentlemans-express/

[Bryanj]

You MAY have to open out the crankcase mouths to take the 600 conversion liners and the alloy cylinder has to be bored to take them

[Tomb]

Thanks lads, interesting read. And very similar to what I've already done on my CB72 using 750 liners and pistons with the top edge machined down.

If the crank case needs opening out for the 550 barrels the liners must be thicker on the 550

[Bryanj]

They are but the later 500 cases had bigger holes, the 600 conversion liners are thicker again

[Colonial-Clive (yindi)]

I have bored out a 500 to 605 and that worked out fine and have just bored a 550 out to 600 the bores on that were rusted too f**k but came up fine. These guys did mine and no question very professional.

http://www.sep-kegworth.co.uk/page1.htm

[Bryanj]

You can bore original liners but as stated before the liner gets very thin at the bottom and easily cracks, the 605 kits available come with new thicker liners that need the block boring out and sometimes on 500 cases the crankcase mouths opening out, I know because i have one.

The original Jock Kerr 605 conversion used modified 750 pistons with the liners very thin, i had one of those as well and the liners broke!

[Tomb]

I read the same thing when looking into doing my CB72/CL77 big bore, that if boring the original 305cc barrels bigger then cracking could occur, its why I bored the block and used thicker walled 750 liners, and when speaking to Wiseco they said if I do that I could then take the motor out to 400cc.

The spare barrels I have are rusted to hell too, that why I was thinking go out bigger.

I 'spose the best option would be take it out to 550 using a standard kit from Cruzinimage, or the 500 to 553 big bore kit as it comes with a head gasket, as previously said it gives me more re-bores, and will clean out the rust and they a lot cheaper than the 600cc kit.

I'll still have the original barrels as back up.

Thanks for all the comments lads, much appreciated.

[Rozabikes Tim]

Interesting post, specifically  where case barrel openings are smaller on some 500's versus 550. When I had my  500  in the 80's I fitted it with standard 550 block and pistons....  Barrels did fit cases, just - but engine always ran too hot, so I reverted to standard 500 kit. I always suspected but never knew cases were different in this respect.

[Darkness]

The original Jock Kerr 605 conversion used modified 750 pistons with the liners very thin, i had one of those as well and the liners broke!

My recollection was that he used modified CB 350 K4 pistons?

[Bryanj]

They had too much "dome" i think

[SteveD CB500K0]

Whenever I see the name "Jock Kerr" I cringe at the memory of my room-mates 180cc CB125S in the 70's

It was dreadful...

[hairygit]

Whenever I see the name "Jock Kerr" I cringe at the memory of my room-mates 180cc CB125S in the 70's

It was dreadful...

  I know the feeling well Steve, I remember trying to sort a mates 250 Superdream years ago, it had a Jock Kerr "sleevedown kit" which involved the barrels being fitted with cast iron sleeves to knock the capacity down to 124cc (62cc per cylinder) to make it learner legal after the 125 on "L" plates law came in. Problem was serious overheating due to the thick iron sleeves not transferring heat fast enough to the ally barrels for cooling, plus the gutless performance (A C90 could keep with it on acceleration AND top speed, about 55 M.P.H.) I don't think he sold many of those kits! And he did a conversion for Suzuki GT250 as well which involved having a conrod removed from the crank and running as a 124cc single!