Topic: andrews cam help ????

[fastsmoker]

i think i need help dont know much about cb 750
was given 3 of them in a huge pile made nice calf racer out of the 3 in about a week
rode it almost every day for months no problems
now i blow the head gaskit well any way when i tore it down i find out it has big bore kit monster cam
heads been ported and polished at one time all the trick stuff they did back in the days
ok when i pulled the head i noticed two rings on the top of most of the pistons but they looked old so i didnt realy trip
yesterday i got it all slapped back in the frame it started right up sounded grate i ran in the house to grab my helmet to take it for
a little test run i came out of house helmet in hand smile from ear to ear get to the bike "#$%*!!!!!" whats that noise
i shut it down fast as i can i looked over at my wife "what did you do" i yelled at her had to blame it on someone right
trying to figure it out the only thing i could think of the valves smacking the top of the pistons
so today i tear it back down again there gos my $60 head gaskit i just mail ordered
now that i have it in million pieces i cant find any thing wrong
could it of been the valves hitting top of piston
or ?? the cam is a andrews ep-13 i think other markings are C 25
thanks for any help    vince

[quietlikeachurch]

Calf racer??

[750goes]

sorry I can't help with the cam information

but

CALF RACER

that's half a cafe  right ??


I don't use the spell checker ethier

[Terry in Australia]

Moooooooo! 

Seriously though, when you say you saw two "rings" on the top of the pistons, do you mean you saw two marks on each of the pistons where the valves were contacting them?

I'm guessing that the valve to piston clearance was minimal, and when you re-fitted the head you might have set the valve timing out by a tooth on the cam sprocket, and as the engine warmed up the valves have "kissed" the pistons? Not necessarily bending them, but it must have come close?

Have you noticed any more "rings" on the tops of the pistons since you pulled it apart again? Did you remember to properly adjust the cam chain when you put it back together? Could be the cam chain adjuster wasn't properly engaged and the chain jumped a tooth? Either way, you'll need to drop your valves outta the guides and check that they're not bent mate, and look after that engine, it sounds like someone put a lot of time and money into that gem! Cheers, Terry.