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Piston and barrel compatibility

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Piston and barrel compatibility

Postby Tequipment » Sun Jun 28, 2020 9:48 pm

So after 3 weekends, 3 tins of gas, 2 club hammers and 10 litres of diesel, the piston is refusing to move.
I was hoping to get it free so I could reuse the standard 125 cylinder and crank, but now I've got the crank turning and moving the cylinder away from the block, I was able to remove half a cup of what looks like mud from around the crank.
There's a lot of sideways movement in the con rod and it looks like it's junk. Now I can cut the rod and move forwards.
As 125 cylinder and piston kits for the Li's don't seem to be available, I've decided to go to a 150 kit as I'm not really looking to improve performance and I need to keep costs down.
Scooter Restorations list some SIL GP150 kits. Are these a straight swap for the Li125 bits, because I've read the crankshafts are different, so didn't know if the pistons etc. are different too?

Secondly, there's a choice of Borgo or Mahle piston. Both are the same price, but is one better than the other?

Out of curiosity, any idea what all the 'mud' is doing in the engine? Is that how oil goes if it's left to sit for a couple of decades? I'll try to upload some pics in a minute.
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Re: Piston and barrel compatibility

Postby Tequipment » Sun Jun 28, 2020 10:12 pm

Image

Image

Image
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Re: Piston and barrel compatibility

Postby Knowledge » Sun Jun 28, 2020 10:53 pm

There is a lot of sideways play on Li cranks, as they are centralised by shimming at the small end of the conrod.

If you cut the conrod to allow the removal of the barrel and piston, then you will need a new crank, so don’t worry too much about the GP and the Li having different cranks. The difference between the two is that the GP has a fatter taper beneath the flywheel. However, changing to the crank will also require a change of flywheel to suit the fatter taper. However, if you ever push further for a bit more more power, the GP crank will cope with it.

You might have already opened a can of worms, but don’t worry, the answer is out there somewhere.
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Re: Piston and barrel compatibility

Postby CHRIS in MARGATE » Mon Jun 29, 2020 8:31 am

Shimming at small end on LI cranks?
That was the SX motor.
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Re: Piston and barrel compatibility

Postby lofty » Mon Jun 29, 2020 9:26 am

you could try drilling a ring of holes around the crown of the piston, this will hopefully allow you to get it separated from the crank and break/cut the rest of it up..
then the barrel will be slavagable (maybe with a slight rebore) and if you can find a oversize 125 piston you will be back in business..

howver it may be the crank is irretrievably damaged, although it may be possible to clean up the webs and get a new con-rod and bearings fitted, this will save changing crank/flywheel etc (although you can get LI/TV cranks if preferred, which will be ok on a standard spec 125)..
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Re: Piston and barrel compatibility

Postby daniel whiteley » Mon Jun 29, 2020 11:08 am

I’ve got a 125 special barrel piston head and crank and also the same of a go 150 if interested
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Re: Piston and barrel compatibility

Postby Tequipment » Mon Jun 29, 2020 5:50 pm

I was trying to work out if the drilling option was viable, but I couldn't find a decent enough photo of the back of the piston to work out where to safely drill.

Thanks Daniel.
Is the 125 Special exactly the same as the series 2 Li125 engine wise?
What sort of condition are they? Would I get away without a rebore and how much would you want for them? :)
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Re: Piston and barrel compatibility

Postby Warkton Tornado No.1 » Mon Jun 29, 2020 6:22 pm

(I may be alone, but cannot see the images fully. The way that some image hosting sites operate is ridiculous! Thank Goodness for Dropbox.....)

Perhaps I am misinterpreting everything, but as the piston is wrecked anyhow, I would choose the biggest hole saw to suit (smaller than the piston 'bore') & carefully drill concentrically through the crown so that the piston will then allow the barrel removal & access to the wrist pin & crankshaft.....
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Re: Piston and barrel compatibility

Postby Tequipment » Mon Jun 29, 2020 6:51 pm

Don't get me started on uploading the pictures. :lol:

Presumably I'd need to drill through both sides the wrist pin after going through the crown of the piston, in order to be able to free the barrel?
Forgive me if I'm getting the wrong end of the stick, but I've not seen one of these pistons out of a barrel before.

To make things more interesting, the piston is stuck at BDC.
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Re: Piston and barrel compatibility

Postby MickYork » Mon Jun 29, 2020 8:14 pm

Removing the piston is easy...….

Step 1: give up hope after using heat, oil and force and get the grinder out.
ImageIMG_20180902_102014 by mick leaf, on Flickr

Step 2: keep on going and give up hope of salvaging the crank.....
ImageIMG_20180909_131242 by mick leaf, on Flickr

Step 3: Success !!
ImageIMG_20180909_132553 by mick leaf, on Flickr

Step 4: debate whether a bit emery cloth will be enough to save the piston
ImageIMG_20180909_132557 by mick leaf, on Flickr

Good luck but be prepared for the worst...….as shown above :mrgreen:

PS...….the mag-flange came out in bits as well :roll:
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Re: Piston and barrel compatibility

Postby Tequipment » Mon Jun 29, 2020 8:19 pm

:shock:
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Re: Piston and barrel compatibility

Postby Tequipment » Mon Jun 29, 2020 8:35 pm

My mag flange is also being a nightmare. Guess I have that to look forward to next.
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Re: Piston and barrel compatibility

Postby Warkton Tornado No.1 » Tue Jun 30, 2020 2:34 am

With stuck magneto flanges, the longer they are in soak with penetrating oil/diesel, the better.

If possible, try to remove all of the six M6 fasteners completely, especially studs!

Construct something in steel, using plate or box section/tube that can be used as a lever utilising the two M6 extract holes. The lever should not be used as an attempt for pulling the flange out, but just to free off the thing via rotation, CW & ACW repeatedly.

Any other methods will probably wreck things, but with patience, once it can be freed off a little, it will come out.... ;)
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Re: Piston and barrel compatibility

Postby daniel whiteley » Sat Jul 04, 2020 1:03 pm

Sorry it’s took a while to reply the wife has been cracking the wip on the decorating , they are in good condition as I recall best thing is for you to come look at them if your not to far away I’m in Sheffield
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