duckwizard Posted January 17, 2008 Report Share Posted January 17, 2008 Help required. After stripping down my B40 i noticed the following. The engine has a high compression piston. Should there be a compression plate fitted ?, as the piston has touched the valves. Any advice on thichness of plate. The bike was always difficult to kick over, which maty explain this. Any advice appreciated. Quote Link to comment Share on other sites More sharing options...
old trials fanatic Posted January 17, 2008 Report Share Posted January 17, 2008 Does your bke have a cast iron barrel or an alloy one? Some alloy ones are machined from B25 barrels and may require a plateunder the bottom. If its a std cast iron barrel then a high comp piston shouldnt be a problem unless the cam has been mistimed or oversize valves fitted. Had aB40 myself and sometimes the marks on the cam are out. May be worth checking. One tooth is all it would take. Then again could just be tired valve springs and a bit too much revs? I used a std piston with an alloy barrel and two paper gaskets on the base. Std copper head gasket is fine. One other thing to check are the pushrods. Make sure they are not bent after the valves met the piston also that they are the correct ones as a lot of these engines have been rebuilt in their time from various parts which all look similar but vary slghtly i.e. C15, B25, B40, B44, B50 etc etc Best source of information i found was Rupert Ratios book which comes up regularly on e bay. Quote Link to comment Share on other sites More sharing options...
slinny Posted January 17, 2008 Report Share Posted January 17, 2008 If there has been no machining to the crankcase, cylinder barrel or cylinder, head even with a H C piston and MX cam shaft there should be plenty of room between the valves and piston. Check that everything is standard, including the valve timing. A "physical" check on the valve timing may be needed to verify that the dots on the camshaft pinion & the half time pinion are correct, ( they have been known to be wrong.) Does it seem that the valves have been "kissing" the piston or been giving the piston a big whack.? When you find the problem i would be interested to know what the problem was. Regards, Slinny, Pat. Quote Link to comment Share on other sites More sharing options...
duckwizard Posted January 18, 2008 Author Report Share Posted January 18, 2008 Thanks for info. The barrel is std. The piston is only slightly marked, possibly with over reving, will check springs & rods against rupert ratio book. Thanks again Kenny Quote Link to comment Share on other sites More sharing options...
charlie prescott Posted January 18, 2008 Report Share Posted January 18, 2008 Hi Guy's Hi DW. Take note as to what "Slinny" says, as this guy is Mr BSA, and knows more about race engines than i will ever learn. Regards Charlie. Quote Link to comment Share on other sites More sharing options...
charlie prescott Posted January 19, 2008 Report Share Posted January 19, 2008 Hi Guy's Just checked this out this morning, BSA C15 B40 valve timing, this is a guide you can try. If there is a Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 17, 2009 Report Share Posted November 17, 2009 did you ever get this running ? Ross Quote Link to comment Share on other sites More sharing options...
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