GT240 Build

Anything related to Lambretta scooters....ask technical questions, post helpful information, or just read and learn.
GeorgeS
registered user
Posts: 142
Joined: Fri Feb 27, 2015 1:58 pm
Main scooter: 1961 Series II Granturismo 240
x 9
Contact:

GT240 Build

Postby GeorgeS » Mon Apr 18, 2016 8:44 pm

I mentioned in the 'GT Big Block' thread about having one of the 62/110 cranks so here's some pictures of the crank & the work so far. This thread also gives me a place to cry for help when I run in to problems, despite having some excellent advice right on my doorstep in the form of 'James round the corner', as I think at some point I will become a nuisance with my questions and constant requests to borrow his tools. James, I promise to look after your tools & feed you San Miguel as needed.

I have a standard Li150 Series 2 which is far too slow for todays roads & I started to look at what I could do to make it more fun to ride. One thing that really swayed me to Gran Turismo was watching Edens YouTube clips and thinking to myself that's pretty much exactly what I want. Also, I see frequent references to Rich's great customer care.

After speaking to @Rich_T I put my name down for a 62/110 crank and the 70mm bore kits he's still working on. What I'm looking for is a motor with plenty of pull and is good for touring. I'm not particularly precious about protecting the history of my S2, but I can see from the engine & frame numbers that my engine is original to the scooter (1961) and rather mess about with it I'll stick it on the shelf it it's original running form & have picked up some SIL large block cases for this project:

Image

These cases are very rough & I'm still trying to flatten out some of the more nasty casting marks. Perhaps I should also add that this is my first delve in to a Lambretta engine to this degree, having only taken care of more basic maintenance in the past, but have plenty of experience with smallframe vespas.

The work on the transfer ports is nearly done, here's an earlier picture before starting work on the drive-side (using the packer for the GR kit as a guide):

Image

Image

My old man is a whizz in the shed & has a passion for making working model steam engines. In his garage he's built himself a CNC mill & all sorts of other fancy stuff, so last weekend I paid him a visit and we had a go to get the trench machined in the cases that's required for the 62/110 crank. First step was to make up some dummy bearings out of a lump of nylon rod that I got from RS Components (cheapest I could find, white is cheaper but was out of stock).

Cutting the rod:
Image

A bit of turning:
Image

Image

Drive side done:
Image

Mag side done:
Image

Now I could finally unwrap the crank and fit it in to the dummy bearings & get a feel for how much machining was needed. It would actually turn with no material removed but it was just grazing the surface.

Next step was to mount the casing on the CNC Mill and find the centre of the aperture:
Image

This device is a centering probe, the mill software moves left until it contacts the surface, returns to the start point and moves right, then forward and back, so you have a centre point reference. We had a problem here in that something went wrong & we had to repeat this a few times, with one time instead of the probe returning to centre it done the opposite and wrecked the probe end & put a small score on the gasket face. Dad had another probe tip & the score isn't too bad, I'll look at that later.

We then put the tool diameter in the software & the size of the cut required and ran it though a few times without lowering the tool in to the case. Getting this bit wrong is not a nice thought so we were very careful & cautious and eventually went for it.

Here's the big keyway cutter in position:
Image

And making the cut:
Image

Using a tool with such a big cutting surface was pretty much hitting the limit of what the mill could do. First run wasn't deep enough, probably because we'd under-measured the size of the aperture, so we added another 1mm and went for it again. The large cutting surface causes a lot of vibration & we went for a further pass at the same depth to clean it up some, the noise sounded like something being tortured.

If you're still reading, well done, I've really rabbitted on here.

Could you achieve the same by using a dremel to cut a trench? Of course, but I love this kind of stuff and it's always good to spend some time with the old man in his shed.

I'll take some picture of the crank & the cut channel & post up later.

All the best,
George.
0 x

User avatar
Doom Patrol
registered user
Posts: 2057
Joined: Wed Jan 07, 2009 5:03 pm
Main scooter: Lambretta GP 150 going on 200
Location: Darkest Gloucestershire
x 5
Contact:

Re: GT240 Build

Postby Doom Patrol » Mon Apr 18, 2016 8:55 pm

I've only a vague idea of what you're doing, but it's very impressive. :D
0 x

Spanish Fly
registered user
Posts: 240
Joined: Tue Nov 30, 2010 1:23 pm
Main scooter: P200e
Contact:

Re: GT240 Build

Postby Spanish Fly » Mon Apr 18, 2016 9:00 pm

Proper job! Interesting stuff. Keep up the good work.
:D

SF
0 x

holty
registered user
Posts: 558
Joined: Wed Jul 15, 2015 11:52 pm
ebay user ID: amholt123
Main scooter: lambretta gp
Location: east yorkshire
x 16
Contact:

Re: GT240 Build

Postby holty » Mon Apr 18, 2016 9:18 pm

nice work, i will need to trench my case when i put my 64mm crank into my rotax 290 buid, i intent to use my boring head in my lathe to cut the trench, as i dont have a milling machine, keep the pics coming
0 x

Adam_Winstone
registered user
Posts: 1538
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP
x 10
Contact:

Re: GT240 Build

Postby Adam_Winstone » Mon Apr 18, 2016 9:46 pm

Doom Patrol wrote:I've only a vague idea of what you're doing, but it's very impressive. :D


... basically, it is a big tool spraying fluid everywhere!
0 x

User avatar
Doom Patrol
registered user
Posts: 2057
Joined: Wed Jan 07, 2009 5:03 pm
Main scooter: Lambretta GP 150 going on 200
Location: Darkest Gloucestershire
x 5
Contact:

Re: GT240 Build

Postby Doom Patrol » Mon Apr 18, 2016 9:49 pm

Oh err...
0 x

User avatar
eden
Dealer
Posts: 1165
Joined: Thu Feb 27, 2014 8:44 pm
Location: ILCLAND
x 18
Contact:

Re: GT240 Build

Postby eden » Mon Apr 18, 2016 10:12 pm

Great post :) Doing this s**t is what its all about for me :)

Rabbit on some more :)
0 x

Chris in Margate
registered user
Posts: 350
Joined: Thu Sep 03, 2009 7:53 pm
Main scooter: Lambretta 1964 225 Special
Contact:

Re: GT240 Build

Postby Chris in Margate » Tue Apr 19, 2016 8:41 am

So very impressive. I could never tire of looking at this engineering expertise and "exploration". More please !
0 x

User avatar
jonzo172
registered user
Posts: 114
Joined: Tue Feb 16, 2010 9:35 am
x 3
Contact:

Re: GT240 Build

Postby jonzo172 » Tue Apr 19, 2016 8:47 am

Nice work George... keep it coming!
0 x

GeorgeS
registered user
Posts: 142
Joined: Fri Feb 27, 2015 1:58 pm
Main scooter: 1961 Series II Granturismo 240
x 9
Contact:

Re: GT240 Build

Postby GeorgeS » Tue Apr 19, 2016 1:50 pm

Thanks for the replies. I absolutely love the spannering aspect to scooters but I have to keep reminding myself that not everyone does as I can frequently bore people stupid with my ramblings (including my wife). It's also why I prefer the older stuff to the newer stuff, it's more of a challenge for me personally, but ultimately if its got 2 wheels and puts a smile on your face, who cares.

Here's a few pictures of the crank. It's really not possible to capture the quality of the machining & finish of this, it has to be seen first hand, it's almost a shame it won't be seen.

Image

Image

Image

You can see the eccentric crank pin in the pictures. At the risk of getting very nerdy, I have to mention the gaskets that come with it, they're a thing of beauty!

Here's the cut trench, cleaned up with some wet&dry + WD40. You can see the markings at the edges left by tool vibration:

Image

You'll also notice a few casting holes, but I don't think that's anything too serious.

We also drilled and tapped the chaincase to accept the Li ramp, which I'll probably pinch off the series 2 along with the rest of the mechanism, as this seems to be a common thing to do. Any comments on this anyone?

Next step for me is to get a better finish on the drive-side port, sort out the remaining casting marks and then have a good clean-up before putting it together. I'm still short of a clutch, chain and front sprocket, electrics and exhaust, so got a while to go yet. I'll post up more as I go along.

All the best,
George.
0 x


Return to “Lambretta Tech”

Who is online

Users browsing this forum: Bilko, immylam and 12 guests