Bantam Project

Hi all,

As you know ATG student are building a Bantam racer.

One Question

Why was the limit of 190cc set for the 175 class?

Paul Brown
Aylesbury Training Group.

Hi Paul,
Apart from not turning formula bantams into single cyclinder 250 racers, 190 cc allows the use of modern 64mm pistons and oversizes for rebores to 64.5mm. There are pistons on the Wiseco web site with sensible 15 or 16 mm gudgeon pins to fit RD400 conrods or other alternatives. There is no standard arrangement, we all use different configurations.
The latest I heard is RD400 rods TZ350 pistons, this then requires a small packer under a BTW barrel to get the arrangement OK for use.
The choice is yours! Note the 125 engines get very exotic in this department!
Cheers,
Alan

Hi Paul/Alan
I thing most/all? 175 runners use a maico rod(125mm) or a rod sold by T and G motorcyles based at Milton Keynes. Maico rods were in short supply but are now availble again - chat to Tom at Mallory. RD400 rods are I would say to short (115mm eye to eye) so in fitting one you wouldhave to alter crankcases(shorten mouth height) not within rules or shorten barrel extremely? when they need to be externally unaltered.
Standard 175 piston is 61mm there are no decent modern pistons this size but there are pistons of 62 (and oversizes to 64) Suzuki PE 175 : 64 (no oversizes TZ350) :64( +o/s) Suzuki TS185 and a Yamaha DT 175? with 66bore. Rules were to 190cc so people could use 58 stroke and 66 bore pistons so a wider choice of parts ?
Hope this helps
Regards Mike

Hi Mike/Paul,
The 175 motor that I had looked at had a TZ350 piston, the advantage was that the piston has such a high crown height (gudgeon centre to crown) that with an RD400 rod (115mm centres) the throat could be left completely standard, and a 2mm spacer under the barrel gave a perfect match.
I of course presume that the TZ350 pistons are still readily available from somewhere? With the use of a lower crowned piston the choice of rod becomes rather different! Maico Rods appear to be a good choice as well, as they have the standard 125mm centres.
I hope that between Mike an myself that everyone is thoroughly confused!
Good luck with the build,
Alan

Sorry to butt in like this but what happened at Mallory?
We had snow here -- and it was cold enough to freeze
the the things I cannot mention here - of a brass monkey ...

Johannes B...