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GP150 lockdown project

PostPosted: Wed Aug 26, 2020 5:45 pm
by Storkfoot
I have a couple of projects on the go, a Vega and an SX150. I had also acquired a few reasonably priced GP150 parts and already had an engine to go in it.

So, I had a lockdown project but, first of all, I face a couple of challenges related to the leggies and forks.

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Re: GP150 lockdown project

PostPosted: Thu Aug 27, 2020 6:09 am
by Toddy
That will keep you busy Paul ;)

Re: GP150 lockdown project

PostPosted: Thu Aug 27, 2020 6:12 am
by dickie
At the risk of looking stupid, what's wrong with the forks?

Re: GP150 lockdown project

PostPosted: Thu Aug 27, 2020 8:21 am
by Storkfoot
dickie wrote:At the risk of looking stupid, what's wrong with the forks?

The witness marks on the stem are indicative of them being bent. Placing a set square against them quickly confirmed that.

They have been straightened now.

Re: GP150 lockdown project

PostPosted: Thu Aug 27, 2020 8:27 am
by Storkfoot
Toddy wrote:That will keep you busy Paul ;)


Thankfully, the frame is in better condition than the legshields (they came from separate scooters). Also thankfully, I know a good fabricator and welder (Just as well, you think :D ) but he is dead busy with other work at the moment.

Re: GP150 lockdown project

PostPosted: Fri Aug 28, 2020 7:51 am
by jonw
Storkfoot wrote:
dickie wrote:At the risk of looking stupid, what's wrong with the forks?

The witness marks on the stem are indicative of them being bent. Placing a set square against them quickly confirmed that.

They have been straightened now.


I've often wondered how safe this is?
The forks have been bent one way and then bent back, hasn't their integrity been compromised and weakened?

Re: GP150 lockdown project

PostPosted: Fri Aug 28, 2020 8:28 am
by Storkfoot
I see where you are coming from, same principle as bending a fork to and fro. Hopefully, it’d have to be bent a long way and multiple times before it got into the realms of fracturing. But, I am no expert.

Re: GP150 lockdown project

PostPosted: Fri Aug 28, 2020 10:11 am
by dickie
Storkfoot wrote:I see where you are coming from, same principle as bending a fork to and fro. Hopefully, it’d have to be bent a long way and multiple times before it got into the realms of fracturing. But, I am no expert.


You're right. It isn't a big deal. Especially if heat is used in the straightening process. That said, you'd be hard pushed to straighten them without heat.

Re: GP150 lockdown project

PostPosted: Sun Aug 30, 2020 11:50 am
by Warkton Tornado No.1
Steel is a very good durable material & the forks are flexing all the time throughout their life. They won't work harden & crack in even extreme use.

They are normally straightened via the use of an hydraulic press, though a fly press can be used. With respect, heat is not required via the process that I am aware of. But that could just be 'me!' :D

Yet to use heat with engine mounts, either, & I've done a few! It's all about overcoming friction & if you use deep groove ball bearings in a number of sizes (preferably thrust or taper bearings, but I don't have any!) they go in & out a treat....Oooer! I have oxy-acetylene but avoid heat getting near rubber mounts like the plague. Or Covid 19....

Re: GP150 lockdown project

PostPosted: Mon Aug 31, 2020 2:40 pm
by coaster
I worked for a while in a large motorcycle dealership when I left school and straightening fork legs was a regular job for one of the mechanics as he was a big lad. He used a scaffold pole and bench vice to do the straigtening and a surface plate, V blocks and a dial gague , no heat.......that said, Lambretta forks went straight in the scrap bin as did frames and even slightly damaged panel work :shock:

Re: GP150 lockdown project

PostPosted: Tue Sep 01, 2020 8:54 am
by dickie
Gents, you're correct. For the small amount of bending needed there, heat isn't required.

Unless it's been bent a long way or a short amount, many times bending cold is fine.

I should add that although I work in heavy engineering, I'm a control and electrical engineer so I'm around this kind of thing but it isn't actually my area of expertise. So I can't really comment with complete authority.

Re: GP150 lockdown project

PostPosted: Tue Sep 01, 2020 1:30 pm
by Warkton Tornado No.1
dickie wrote:Gents, you're correct. For the small amount of bending needed there, heat isn't required.

Unless it's been bent a long way or a short amount, many times bending cold is fine.

I should add that although I work in heavy engineering, I'm a control and electrical engineer so I'm around this kind of thing but it isn't actually my area of expertise. So I can't really comment with complete authority.


As an engineer, although I am mechanically biased & in general a designer, no doubt our outlooks are very similar. I don't think we ever stop learning in our thirst for knowledge, whilst trying not to forget first principles :D

Not wishing to get too far off topic, mechanical advantage, & how best to achieve it, is probably the main essence of our continued passion for Lambrettas & our enthusiasm for this Forum.

The example of extracting engine mounts, & the massive improvement in method by utilising bearings in the process to overcome thread friction needs to be tried to be believed. I must acknowledge Dave Webster (RIP) for advising me of that.

Similarly, the clutch mechanism has been shown to be improved by modification to rack & pinion. No doubt the Chiselspeed conversion is great & VFM, but my finances won't currently allow indulgence. However, I do have a motorcycle mechanism that I aim to adapt ;)

(I reiterate & apologise to Storkfoot & anybody else if I have hijacked this Post :oops: )

Re: GP150 lockdown project

PostPosted: Tue Sep 01, 2020 2:55 pm
by Storkfoot
No problem at all. I put threads up on this forum for discussion and to try to keep it alive, given that it appears significantly quieter than it used to be.

Re: GP150 lockdown project

PostPosted: Thu Oct 01, 2020 4:47 pm
by Storkfoot
A productive day straightening up a few dings, crossmembers and stabilising the rust inside the frame.
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Re: GP150 lockdown project

PostPosted: Fri Oct 02, 2020 7:57 pm
by Jeff t
Just started a refurb on an Li special what did you use to stabilise the frame?

Re: GP150 lockdown project

PostPosted: Fri Oct 02, 2020 11:40 pm
by Storkfoot
Jeff t wrote:Just started a refurb on an Li special what did you use to stabilise the frame?


Diluted Rust Remover from Machine Mart. I just blocked the two drain holes under the frame, pumped it in and left it overnight. Ideally, you should pump in Waxoyl after blasting and painting, I suppose, but what I have done so far will not do any harm.

Heat and a ball pein hammer, followed by a little bit of welding to sort out the tears:

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Re: GP150 lockdown project

PostPosted: Fri Oct 09, 2020 2:02 pm
by Storkfoot
Welding back so dry build next

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Re: GP150 lockdown project

PostPosted: Fri Oct 09, 2020 7:34 pm
by gaz_powell
Another nice project on the go, Paul.

Re: GP150 lockdown project

PostPosted: Fri Oct 09, 2020 9:40 pm
by Storkfoot
gaz_powell wrote:Another nice project on the go, Paul.


Gaz, My mate who saved the legshields with his welding abilities never wants to see Lambretta legshields again. I tried to reassure him that he had saved a bit of history. He wasn’t convinced :shock:

Re: GP150 lockdown project

PostPosted: Sat Oct 10, 2020 1:44 pm
by bike grim
Looks a good job. I’ve just bought a new welder and want to have a go at some legshields so if anyone has an old set they want to donate to practice on let me know (and panels)