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Silencer Clamp for an Idiot

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Silencer Clamp for an Idiot

Postby Tonyfitz55 » Thu Oct 29, 2020 1:13 pm

Hi Lads

Bear with me here, I know I'm going to sound like a complete bellend. I posted about oil leaking from the silencer manifold clamp, and thanks for the answers about checking that the clamp is tight. Being Selwyn Froggitt, I tightened the clamp that much, that the single bolt snapped. Rather than order one on line and wait, I bought a U- Shaped exhaust clamp from Halfords used on cars thinking tightening two bolts instead of one bolt will stop a leak, I even put exhaust paste on before I clamped it really tight, Has it stopped it, has it buggery, there's still a slight leak, are there any clamps on the market that anyone has used, looking on-line they are all standard clamps where I snapped the bolt,
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Re: Silencer Clamp for an Idiot

Postby ULC Soulagent » Thu Oct 29, 2020 2:45 pm

Get used too the leaks, commonplace on a Lambretta Engine :mrgreen:
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Re: Silencer Clamp for an Idiot

Postby solostax » Thu Oct 29, 2020 3:24 pm

Tonyfitz55 wrote:Hi Lads

Bear with me here, I know I'm going to sound like a complete bellend. I posted about oil leaking from the silencer manifold clamp, and thanks for the answers about checking that the clamp is tight. Being Selwyn Froggitt, I tightened the clamp that much, that the single bolt snapped. Rather than order one on line and wait, I bought a U- Shaped exhaust clamp from Halfords used on cars thinking tightening two bolts instead of one bolt will stop a leak, I even put exhaust paste on before I clamped it really tight, Has it stopped it, has it buggery, there's still a slight leak, are there any clamps on the market that anyone has used, looking on-line they are all standard clamps where I snapped the bolt,

Hope you get it sorted but having not suffered exactly your symptom did have a gooey discharge :cry: from the cylinder / exhaust manifold joint. Found tightening the Fan side exhaust brass nut impossible with the engine in situ. Ended up removing rear suspension unit,rear foot boards, exhaust box, spark plug ,tilting the engine cylinder down ,removing the cylinder shroud. Wondering if there is a special tool that can access this nut without all that hassle?
Answers on a postcard please :idea: :(
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Re: Silencer Clamp for an Idiot

Postby Warkton Tornado No.1 » Thu Oct 29, 2020 5:04 pm

The 'Golden Rules' that I adhere to on ANY Lambretta large frame engine:

Fit rolled thread M7 studs to maximum depth that cylinder studs allow, Loctited in place

Only use a solid copper gasket. Win-win as they are re-useable & brilliant as templates for porting.

Assemble with a good, flexible sealant. Bathroom silicone works exceptionally well & will take the heat. You don't need high temperature stuff. Silicone is as silica. Ever tried melting sand?

Get some steel M6 extended nuts from the likes of Toolstation & tap through M7 (same pitch as M6) which gives the immediate advantage of being only 10 mm across flats. Cross drill each & lockwire the two nuts together.

Assemble with Copaslip type grease on the threads with good, thick heavy duty washers that just fit. Make them if necessary, although good hard ones are available from t'Internet auction sites.


As for clamping. If a 'U' clamp must be used (rather than a sprung joint) & the joint is still a bit baggy, take the 'box & find some tube or bar the same size as the 'U' pipe. Clamp the 'box onto the bar/tube/1/2" drive socket (or whatever!) undo it, rotate it, clamp again & so on so that a 'swage' is formed of reduced diameter to better fit the 'U' pipe. Then assemble with silicone sealant as above.

I hope that helps...
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Re: Silencer Clamp for an Idiot

Postby gaz_powell » Fri Oct 30, 2020 9:47 am

Use a wide SLJ ali type clamp or a mikalor exhaust clamp, they give the even pressure and don't distort the tube, but best done at day one before any distortortion of the exhaust tube. You might find you "chase" this forever.
Avoid the use the car u type IMHO - although a good tip from WTN1
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