Continuing my theme of daft questions ... Look at another Derbi Senda (97 'R' Plate) but the seller is being less than clear about whether it is a 50 or 70 (he has both sets of "bits" apparently!) ... last response was that bike was quite slow so "might have 50 kit on it" ... answer to what is fitted seems to depend on what I want Q1: If I go to look at bike is there an easy way to distinguish between a 50 and 70cc Q2: If (as stated) the difference is just "a barrel and head" REALISTICALLY how easy a swap is it assuming he does have all of the "bits" ... have done a little work on cars and bikes but usually pads, shocks, starter motors and a bit of electrics rather than engine. Q3: bike has 9000 miles but no current MOT ... not sure how long it has sat - is this likely to be an issue with a bike of this age? Sorry if these are obvious questions but don't have any experience with this sort of bike!
Dunno about Q1. Q2...if not had a Derbi senda but i've replaced a piston on a KMX125 which would be the same amount of work as a Senda. I'd say if you're happy enough swpping shox and starters on cars you'll have no problem doing the head on a 2 stroke as long as you follow the basics - i.e. clean gasket faces, fit new gaskets, fit new piston/rings (no need but may as well if you've got the head off) and torque things down correctly. Thats assuming he actually does has all the bits...if not you're at the mercy of finding a supplier and i don't know how easy it is to get parts for these. Q3...don't see it as an issue but obviously if you turn up and it looks a complete nail then that might change!
Thanks u33db ... I have had the head off of a Sierra many years ago so happy with the gaskets and torqueing up etc. Does teh engine need to be pulled for this or is it a matter of yanking the top half off (stop me if I start getting too technical). I can't get my head around what "just a barrel and head" means ... I assume that the head is replaced with a bigger (deeper) one to provide a deeper chamber for the combustion to take place in (i.e. 20cc more space) but would have thought if that was the case that the carb would need to be modified to allow more fuel. No idea what the "barrel" means in this respect. Anyone point me at an idiots guide somewhere on the net?
The cylinder bore (barrel) of the 70 will have a wider diameter hole than the 50...thats the only difference as to Q1, the standard barrel 50CC usually has the CC stated on the side of the barrell like this The 70cc probably wont have. Most of the time folk dont bother to upgrade the size of the carb due to expense but its not guarenteed He states that he has ALL the parts, he'd need the piston, little end (ideally) with circlips, gudgeon pin, head and base gaskets, cylinder barrel and cylinder head swapping is easy...drain coolant if liquid cooled, undo the head bolts which usually hold the barrel too, remove exhaust bolts and carb inlet rubber...lift the barrel and support the piston as it appears out the bottom of the barrel. Pack the case opening to save dropping things in and then remove the piston circlip to remove the gudgeon pin and piston...reassemble with new gaskets and clean surfaces
Cheers Stig, That makes sense ... I guess it should all fall into place if I do it I did have a look at some 70cc conversion kits so I get the idea about all of the bits. I need to have a think about the bike generally but this is good info for this or another bike!
