Avanti

[Captain Pugwash]

My mate blew his piston so guessing it has leaned out we checked every thing all we found was the needle in his was oversized at its thickest point.
Should have been 2.5mm but it wasn't.

[rossclark]

So that would have affected it at low throttle opening till just when it came on the taper? Up to about a 1/3 throttle?

Was the rest of the taper right?

[Captain Pugwash]

So that would have affected it at low throttle opening till just when it came on the taper? Up to about a 1/3 throttle?

Was the rest of the taper right?

Yes it seemed close to right except the widest part was making it lean coming off throttle, on original set up and Dyno it didn't show up.
But it was an inertia Dyno so won't allow for constant low throttle loading which I think it would have on a brake loaded Dyno. But I might be wrong.

The needle wasn't checked prior to assembly because it came with the pre jetted new Dellorto. we just believed it to be what it was supposed to be, that's until we measured it later.

It's a wile ago now but from memory it was an X7 needle and measured over 2.52.

[Fat Trucker]

FYI - My Avanti TT3 top end didn't miss a beat during my 900 miles in 4 days of getting to Mannheim (Germany) before I decided to call it a day and return home (450 there and 450 back). We spent a number of hours at 70+ on motorways, holding that speed as a constant cruising speed with plenty left for overtaking.

I ended up wimping out after shearing a layshaft and hub, which I replaced for the return leg, but it was nice to have absolute confidence in the top end. I only had the plug out once to check colour and it was a glorious chocolate brown

Great kit!

Adam

I agree with everything you've said about the kit Adam. Unfortunately I hole'd the piston in mine on the way to ebensee. I didn't even make it out of the country.
I tried everything possible to get it set up right for the trip, dyno, loads of high speed motorway miles, cht gauge, check, check check. Unfortunately it hole'd at 65mph doing 5,900 revs (I've done over a dozen runs of 10 miles at 7,000 revs, 77mph with no problems what so ever)
Ah well, new piston and barrel re-line then I can start again.

Mark what exhaust are you using?

[mark1]

FYI - My Avanti TT3 top end didn't miss a beat during my 900 miles in 4 days of getting to Mannheim (Germany) before I decided to call it a day and return home (450 there and 450 back). We spent a number of hours at 70+ on motorways, holding that speed as a constant cruising speed with plenty left for overtaking.

I ended up wimping out after shearing a layshaft and hub, which I replaced for the return leg, but it was nice to have absolute confidence in the top end. I only had the plug out once to check colour and it was a glorious chocolate brown

Great kit!

Adam

I agree with everything you've said about the kit Adam. Unfortunately I hole'd the piston in mine on the way to ebensee. I didn't even make it out of the country.
I tried everything possible to get it set up right for the trip, dyno, loads of high speed motorway miles, cht gauge, check, check check. Unfortunately it hole'd at 65mph doing 5,900 revs (I've done over a dozen runs of 10 miles at 7,000 revs, 77mph with no problems what so ever)
Ah well, new piston and barrel re-line then I can start again.

Mark what exhaust are you using?

Franspeed race. It is (was) absolutely brilliant. Rides lovely through the gears, will pull from 3,000 revs in fourth and when you want to spank it, it goes like a scalded cat. Hit 4,500 revs and it just takes off.

[Blaginit]

Hi Mark1 what timing btdc were u set at when you holed piston or are you variatronic cheers for any help

[mark1]

Hi Mark1 what timing btdc were u set at when you holed piston or are you variatronic cheers for any help

I've got an mtech ignition advance / retard fitted. Set at 22 degrees at tick over. I was only doing about 60/65mph.

I've spoken to ron about jetting advice, guess I'll just have to have a play and see what happens. I'm going to do plenty of plug chops to see where it's at.

[Blaginit]

Hi mark maybe I've miss read but I thought timing for these kits is 17 degrees btdc that's it or they just run to hot and you loose your 30% heat reduction ?im not sure as anyone got any paperwork I'm still waiting for my kit.

[MickYork]

I've had a M-Tech fitted on my Avanti for over 2 years with no issues. It's set at 24/23 and retards to 16...ish.

[Scooterlam]

Hi mark maybe I've miss read but I thought timing for these kits is 17 degrees static that's it or they just run to hot and you loose your 30% heat reduction ?im not sure as anyone got any paperwork I'm still waiting for my kit.

I run static 17 btdc, this is just a safety measures because of ethenol in fuel.
with a cht gauge I rode at around 70 mph for 50+ miles at a time and the head never got hot.
I feel it could run 19 degrees easy but fit as Ron advises and get used to it before changing anything.

[mark1]

I fitted the Mtech to try and help with the mid range boggyness.
I took it to scootererotica for a dyno session and Dan recommended the ignition be set to 22 deg retarding to 16.

you won't be disappointed with the kit, it's truly amazing. Out of the box with the right gearing and set up it'll beat a std TS1, there is a lot of talk about these being a touring kit. With a franspeed race fitted it is every bit a tarmac tearing racer. When i hit 4,500 revs it takes off. On the flat I've pulled 7,400 revs on 4.7 gears which gives 81.4 mph.

[Captain Pugwash]

A little more done today.

Barrel held in a rotating jig, it's easier to port.


Diamond coated burr 600 grit, starting on the first transfer port.




First transfer. Cut



Second transfer. Cut



Putting a chamfer back on on all the cut edges.

[Captain Pugwash]

I can't reassemble the barrel yet, because I don't have long enough barrel studs, the original studs were only just long enough as I had threaded them as deep into th case as I could get them after tapping the holes the full depth. But now with around 4mm added to the barrel height, there's no longer enough thread to torque the head nuts onto.

I think I will try some Vespa Barrel studs as they are a few mm longer also they have rolled threads.

[MickYork]

Did you have the Avanti fitted to a standard crank before fitting the 60mm ? If so did you have it dyno'd ? It would be interesting to see the differences between the standard and the 60mm.

interesting thread

[Captain Pugwash]

After fitting a longer 110 rodded 60mm stroke HB crank I now needed to set the transfer heights as these are now raised a couple of degrees over standard.

New longer barrel studs fitted 170mm, and several differing thickness base packers and head gaskets.



Changing the entry angles of the transfers has increased their duration, fitting a 110 rod and the 60mm stroke helps lower the raised and re-angled transfers.



Choosing a packer to set the transfer timings while using a degree disc.



This is the Exhaust port timing with the packer setting the transfers.



Which seems a low exhaust port height relative to the transfer port timings, but there's more port time area on the wide bridged exhaust port.

Next I needed to set the squish clearance and after trying a couple of different thicknesses I had a set of base and head gasket/packers. 2mm and 2.5mm



Next I needed to dowell the cylinder-head to the barrel, this is because the thick head packer/gasket now prevents the cylinder head sitting into the bore.

Once the head is dowelled and Centralised the squish can be checked more accurately.





Measuring at four points near centre of squish band.



And measuring the same four points at the edge of the squish band.




The difference can be seen in the impression made in the solder as the solder has been squeezed between the piston and the head, it shows that the profile of the head doesn't completely match the piston, I already knew this from my first dry build. It might look like its a massive difference but it's only a few thou of an inch.

I was trying for close to 1.5mm squish as the extra length on the stroke will raise the compression ratio, where the increased squish clearance will lower the compression ratio.

In all, the barrel assembly is now just over 4mm longer than it should be.

Will post some more as and when it happens.

[Jamjo]

Another great thread to follow , keep up the good work Mark

[Captain Pugwash]

Another great thread to follow , keep up the good work Mark

Hi James,
I was hoping I would have had the engine in the scooter by now but other stuff keeps getting in the way.

Can't get time to do much scootering over the next three weeks so hopefully pressure test and check the volume above the piston at TDC.
Then when I get time put the engine in set the timing and see how she goes.
Will be fitting a taffspeed copy pipe first then later try a Franspeed on it.

anyone that's ridden an Avanti knows how good they can be, I just hope my "Home Brew Bodging" isn't going to cause me too many issues.

[Wack]

Doesn't look like bodging to me

[Eden]

tinkering is the law!


Looking good Mark

[Captain Pugwash]

Had a couple of hours in the Garage after getting home from work today, I took this picture before I took the engine apart after the dry build stage.



It shows the head packer/gasket aligned using the head dowels.

It really needs to be done if the cylinder runs a negative deck height as the piston will most likely hit the edge of the gasket if it isn't central to the bore.
A standard Avanti would never need this but mine is stroked out to 60mm with the cylinder lowered this means I have a couple of mm extra piston travel at the top of the barrel.

All parts were cleaned up and checked prior to re-assembly, it was pressure tested at 6psi, it did slowly loose pressure over a One hour time period, dropping to 5 psi.

I hope to find time to Burette the cylinder head tomorrow which will check the trapped volume above the piston, looking for close to 10-1 geometric compression ratio.