Scooterotica

Can anyone advise please,got a rapido 225 with a black meceur crank standard GP200 size 58.Basically checked it over yesterday as the compression has been woeful of late and the cranks fooked, conrod is out,worn the rings on the one side of the piston,not the first time its happened on this barrel,I know its not the barrel as had it done by a respected tuner this last time and its done it again the only constant is the crank.So I'm after another crank is it worth getting the Meceur crank split? are the webs any good on them? Also what conrod to replace with is it one of these http://www.ebay.co.uk/itm/YAMAHA-RD400- ... 3376aeb4d0 if so do I then need a 1mm packer plate,if I do where do you get them from? and finally any real life experience of who can do this please.Sorry for all the questions.

I've based my assumptions on this old MB page http://www.mbdevelopments.co.uk/lambretta/lt9.html

Is it the black race with shims, or the non-shimmed 'standard' version?

I've just had a black race Mec Eur crank split and 110mm yam rod (from Yambits) fitted by CS Engineering in Norwich. Chris said he would need to machine the webs to get clearance for the shims but when I picked it up he told me the the Mec webs were recessed on the inside to take the shims. Not had a chance to to fit it yet though.

Thank you chaps,Dan the one I have is this one http://www.ebay.co.uk/itm/Lambretta-Mec ... 20cdc473c6 not from this dealer,I got it from sandyscooters about 4 years ago.Is it financially better to go down this route and would I end up with a decent crank,the rapido isn't really a high hp motor.Coaster PM sent

DaveTomo wrote:the rapido isn't really a high hp motor.

OOps....what is wrong there then`? Is there another thread?


unless your habits compete with this that is :

[quote][not the first time its happened on this barrel,/quote]

wouldnt be the first rapido to come with a pissed up bore from new!! dont matter what crank, webs, rod, shimmed or not if the pistons being forced up n down off centre thousands of times a minute somethings gonna give,, get it checked before you re-build or your on a hiding to nothing

tarmac tickler wrote:

[not the first time its happened on this barrel,/quote]

wouldnt be the first rapido to come with a pissed up bore from new!! dont matter what crank, webs, rod, shimmed or not if the pistons being forced up n down off centre thousands of times a minute somethings gonna give,, get it checked before you re-build or your on a hiding to nothing

This is distressing to read and learn about...possibly overlapping with the Rapido 'soft liner' reports that have made it through to the rock that I live under? Spot-On advice above BTW!

Have to confess that I know little about the barrel/cylinder machining sequence post casting. Presumably the spiggot, base and head gasket surfaces are machined prior to the boring bar (never come across a pub with that name yet) and hone?. In which case it is the machinist's fault (else they would all be like that). Depending on the severity of the missalignment the barrel should be recoverable with a re-bore. BUT you will lose the 'edge' on the tuning done when going oversize

If the bore is true to the studs + spiggot, then the gasket faces need re-doing. With the longer rod crank (you need a new crank anyway) this is probbably the better option in this scenario, as you can square the barrel (quite cheaply) and optimise port timings with the packer required (MBD, Scooter Center and LTH have all got a good range of these). If still in spec piston to bore clearance wise you could poss save on new piston and re-bore costs.

Anyhow thst is what my mechanic told me down the 'Bull and Bush' 't other nite disclaimer

i do like the rapido cylinder and what it offers in terms of value for money and tuneability,ive found the base and head gasket faces to be out of square to the bore so skim both off ,but saying that the crankcase base gasket face can be off or uneven too so both can cause a problem ,the overbore wont bother the ex port as much on the rapido as say an rb due to its straight ex outlet
you can check with the cylinder tightened down with no gaskets and normally see daylight through the gap at the base,and with piston and no rings fitted a feeler gauge will not slide down the side evenly until true,also a check for bent conrods(there not all straight)