Avanti woes

[storkfoot]

I'm off on a mini tour of Europe next Friday so I'll have to borrow the TS1 engine in my other scoot which'll mean cutting the battery tray

Oh dear, mate. Just focus on getting the TS1 sorted and leave stressing about the Avanti until our return. There'll always be a space on the back of my Rally

[coaster]

There'll always be a space on the back of my Rally

I did warn you about the Rally, I COULD remove all stress and take the GTS thus keeping it an all Piagio tour or maybe Adele's ET4 (50cc) would be more suited

I will be putting the TS1 in the Jet so will have to take the angle grinder to the battery tray which is something I have always been resisting. I would have loved to put a GT200 kit on but can't get one delivered for Saturday

[storkfoot]

I have my GT186 engine that would be plug and play but it is ts1 side manifold

You'll be surprised how the Rally shifts. Trust me

[Adam_Winstone]

The only time I've managed to damage an Avanti in this way (very similar marks on piston and damage to plating above the exhaust port) was when I seized it when holding it had prolonged high speeds in order to assess the setup. In my case I had already picked up on fuel starvation symptoms at prolonged high speed runs, which I was trying to resolve, forgetting that the carb type that I was using is well documented as having fuel starvation issues unless the carb is 'blueprinted' (enough of a clue for some of you).

Since the above issue I have modified the carb according and cured the fuel starvation issue. Frustrating that I only thought about it after the damage was done

You say that you held it open for a long period before the event happened, has the same setup been ridden like this without issue before? Any reason why you might be suffering fuel starvation? Anything changed from previous good running, just filled up, etc?

Regardless of the piston marks and plating damage near exhaust port, which are similar to the state of mine after the seizure, the wear to top of plating bore is odd (?).

Adam

[coaster]

Hi Adam, no fuel starvation issues and I had been using the thumb choke to check every few minutes and it ran boggy every time. No changes to set up apart from the super tourer,

PS 30 ph have fitted

[Rick]

Seized mine with that pipe at high revs... A dyno operates didn't think he could get that pipe to work with that kit at high revs I'm not so sure.. Adams seems to work well

[Adam_Winstone]

Although my layshaft sheared (!) my Avanti was perfectly happy sitting at speed on the French motorway and German autobahn, without so much as a peep from the top end.

As far as pipes, rev range and suitability of high revving pipe for the conservative exhaust duration is concerned, the older thinking of duration = operating rev range has, in more recent years, been replaced by port-time-area = power spread and operating rpm. I was shocked by the Avanti's ability to rev when using a revvy pipe, with both the Fran Race (as per Ron's demonstrator) and the Supertourer (as fitted to mine) working very well with the standard kit.

Adam

[Jazzy]

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.

[coaster]

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 crank was put together by the late Dave Betts but has been in the engine for several years now albeit with bearings and seal replaced a couple of times. During that time it has had 4 different barrels on it an has seized solid 3 times with holed Pistons so I guess it is possible that the crank is bent would that be enough to bend the rod? The engine has always run very smooth so I wouldn't think it was twisted

[Jazzy]

in my opinion, its unlikely that the rod is bent, but a solid seize is a pretty good way to twist a crank.
trying to kick over a solid seize is another good way.
so is dropping into second when wanting fourth. done that
with the history of the crank, getting it checked over would be a good investment.
if you do a google search for crank truing you'll see how little force is required to knock a crank back into true and therefore how little to knock it out.