gents,
building my first lambretta engine, so forgive any stupid questions
i have a mec crank with shimmed big end. I'm using a 185 SR (sort of) kit that a local lad (with a good reputation) has tuned for me.
I have a 22mm small end bearing but there is still room (about 2.4mm) left on the gudgeon pin, so the bearing is free to float about to some extent.
this is not the kind of s**t that i dig
i want to fit 2 x 1mm shims on my small end but have read that there aren't any decent ones available and they will probably fail. also, I've read that they aren't really necessary
what's a chap to do gentlemen?
piston/gudgeon shims
Hi hendy,
You need to fit a longer small end bearing so there is no side float.Dont use shims.
You need to fit a longer small end bearing so there is no side float.Dont use shims.
Lambrettas are for life!
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hendy
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Does anyone sell a 24mm small end bearing?Boo wrote:Hi hendy,
You need to fit a longer small end bearing so there is no side float.Dont use shims.
I've only managed to find 22mm
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Adam_Winstone
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MB sells Jap bearings that are wider than normal, to take up excessive float of the bearing.
As the crank is shimmed at the big end, there is no need to shim at the small end to control rod float. However, as you've picked up on, it is worth having a bearing that fits pretty well at the small end so that the bearing cannot slop too far to one side and run on the ends of the rollers, rather than the flat sides.
Do watch out for a bearing too tight a fit though as there needs to be a little room for expansion when the motor comes up to running temp. I've experienced 2 pistons cracking in half along the gudgeon pin bosses, literally breaking the piston in half and buggering up the motor. In both of these cases, a wider big end bearing was used.
Adam
As the crank is shimmed at the big end, there is no need to shim at the small end to control rod float. However, as you've picked up on, it is worth having a bearing that fits pretty well at the small end so that the bearing cannot slop too far to one side and run on the ends of the rollers, rather than the flat sides.
Do watch out for a bearing too tight a fit though as there needs to be a little room for expansion when the motor comes up to running temp. I've experienced 2 pistons cracking in half along the gudgeon pin bosses, literally breaking the piston in half and buggering up the motor. In both of these cases, a wider big end bearing was used.
Adam