Avanti woes

[coaster]

Thanks Jazzy, hopefully Chris Sadd can oblige but should I be able to check it myself in situ with a dial gauge?

[Lambretta Sash]

Not far wrong with blow back from lack off seal on inlet side diagnosis, You can check insitu with dial gauge but make sure it's solidy mounted. I would take crank out nd check tbh as you will find tiny specs of nikasil all over internals of engine especially seals.

[coaster]

Thanks Sash, I will take it out anyway but I don't have any 'V' blocks for checking it out of the case but I do have a dial gauge and can fabricate a bracket. It would help to give me some peace of mind for the crank in the TS1 as well.

[coaster]

the area at the top of the barrel roughly 45 degrees from the centre of extra transfer "W" port looks like wear. is this directly opposite the area of damage at the exhaust. Both areas appear non- central to their respective ports.
if so I would seriously check the crank for true before fitting a new top end.
one theory is its pushing the piston hard on the inlet side resulting in the worn out plating. and on the down stroke its forcing the piston rings into the exhaust. resulting in either heat build up and resulting "seize" or the ring lifting the plating (did you smooth off the rings) and this getting chewed up on the side of the piston.
The other theory, a bit more left field, is something has entered from the exhaust, flake of rust if old pipe or swarf if new (remember gases flow in both directions through the ex port in 2 strokes)
this has caused the damage and pushed the piston over causing the wear above the inlet.

The down pipe is dented at the bottom and I think I did 'clunk' it on a speed bump shortly before this happened. Perhaps that dislodged some weld?. Apart from the lack of tickover and increased bogginess, it was still running a smoothly as the day I first built it so the entry of a foreign body makes more sense than a twisted crank.

Cheers

Colin

[coaster]

I have just measured the runout on the crank and get a reading of 0.06mm (6 of the outer dial marks), is that out of tolerance?

Cheers

Colin

[psychedelicropcircle]

Here's mine as a comparison coaster. Now on eBay no reserve!

[Adam_Winstone]

What an odd place for the plating to lift!

[eden]

Here's mine as a comparison coaster. Now on eBay no reserve!

Is that an early one? By early I mean one of the 1st batch?

[mick1]

There appears to be a "ring" around the top where the plating lifted.

How many miles had the barrel done ?

Could the Nicasil have worn leaving a ridge (the ring) which caused it to de-plate ?

just a thought................

[ducksta]

recall them all i say