Which engine cone?

[Triffid]

Hi folks! I'm hoping for some opinions to shed light on an issue that came up recently. Basically, its to do with the engine mounting cones - specifically, the Li type that goes into the frame when fitted with the smaller engine mounts and short engine bar. Is it ok to retain the Li type engine cones when converting to the SX/TV/GP type silent bush engine mount and longer engine bar rather than changing them to the later SX type cone? I know in Stickys book it identifies the two types but why, if at all, might it be necessary to change the cones along with the other obvious change such as the longer engine bar? What is the reason Innocenti changed the engine cones from Li-type to SX? Thanking you in advance

[L111amo]

Don’t see it would make any difference

[Adam_Winstone]

The LI type sit deeper into the frame tube. As such, when using larger mounts with LI cones, the bolt/nuts stretch the mount's rubber insert as the inner tubes are pulled in further to close the gap.

If the gap isn't closed then the engine is sloppy and handling is poor. If it does close the gap then the rubber is strained and fails early.

[Triffid]

Hi Adam! Thank you for the enlightenment - that makes perfect sense! Its observable that the SX type cones are a millimetre or so taller and so using Li cones with the SX silent blocks would, as you say, pull the central tube of the silent block mount towards the centre of the bike, putting strain on the rubber. Every day is a school day with Lambrettas! Cheers!

[Adam_Winstone]

I only know from doing it myself, then suffering the poor results.

One giveaway to the different depths of cones is that you can sometimes find that some aftermarket mounts are made with poorly positioned inner tubes that can catch on the correct 'big mount' cones. In this case the Li type small mount cones could actually be beneficial! However, using the correct type of mount and cone (of accurate manufacturer) should be beneficial for both handling and longevity.

All the best.

[Warkton Tornado No.1]

As Adam has said, the variation in cones is due to the redesign of the mounts, resulting in the larger mounts. Obviously, the larger mounts move the mass of the moulding outboard to increase the absorption of vibration whilst also increasing the amount the engine can move relative to the frame. The mounts that SIL manufactured for a while were like a combination of the Innocenti small & large mounts but the ones I had only had two voids, as opposed to Innocenti’s three. They must have also been a softer moulding not to have vibrated the bike to bits…..

The correct moulding process will produce stressed components which means the designer can tune things to reach the desired characteristics. Ultimately, there must be a compromise between comfort & handling.

Now, it has just occurred to me that any type of engine mount must twist through some degrees whilst the machine is ridden. So, at which point should the through bolt be tightened to pull the inner sleeves of the mounts tight to the frame? Should it be with the shock absorber on, off, or on with the rider sat upon the bike with feet up?

My guess would be the latter but I can’t say I’ve ever done that. I wonder if anybody has