there is a famous saying ..
there is no replacement for displacement ..
while this hero is 72cc and its short stroke as opposed to chondas .. the only thing u can do is to increase its bore . by boring it to 50mm instead of 47mm u will get some more displacement i.e. cc .. or u can use a 52.4mm bore by having it resleved ..
personally i wont recomend modding these 72cc as they require a lot of work .. like replacing con rod .. relacing engine mounting studs .. relacing timing chain and girariz.. and opening of entire crankcase .. and widening of teh cylinder hole in crankcase to accept the bigger dia cylinder .. all in all its not worth the effort .. wheareas in 78cc its just swap cylinder at minmum .. and re jet carb .. no timing chain change .. no opening of crankcase .. all will work ..
now regarding the issue of heatup ..
first which jali does the mechanic says is closed ? is it the oil filter screen ?
if its that then u can do it ur self . just drain the engine oil.. then open the nuts on clutch side .. (remove the clutch cable from its lever near the case aram sa nikal atha ha .. ) then just buy new chalni which costs 35rs and fit that .. but u will need a gasket for clutch side as well .. this doesnt requres u to remove the head /cylinder ... or carb ..
before doing that i would recomend u to check if there is sufficient quantity of engine oil present ? verify from dipstick reading ..
if yes .. then remove the tappet cover which need i think 17mm hex .. just remove the inlet tappet/valve cover .. jo upar ki side pa hotha ha .. now u start ur bike .. if there is a stream of oil oozing out through that tappet cover then i dont think that oil screen is clogged .. it may be some issue afterwards it ..
oh haaan tappet cover ko us ka upar rak laina hath sa pakar ka .. taka jo engine oil bahr nikal wo cap pa lag ka wapas us usi tappet cover ma giray .. and dont run ur bike for long duration of time like this .. this only checks /verifies if oil is flowing to head ...
what is the issue with tappets ? have u set the clearance ?they wont need replacement .. may be just refacing it from kharadia will do the job .. wo srf is ka surface ko smooth kar daithay hain ..and new tappets cost 90 rs for janyaan .. i think ....
kia duvan mar rahi ha bike ?
is there any oil spot on air filter ?
kia engine oil kam ho raha ha ?
i think only opening the head will tell the real story .. ka kider oil ki blockade ho rahi ha ..