Rotax 300 builld

Anything related to Lambretta or Vespa Scooters fitted with LC, Motorcycle and/or Auto engines!
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RManson
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Sun Dec 30, 2012 3:52 am

First off, a big shout out to Rich_T and Rocho68 for their motivation on this project, whether they know it or not. Of course, my old buddy Hotrodlambretta was a huge influence and motivator as well!

Here's what I'm starting with. Jet 200 purchased locally in Los Angeles...

ImageRotax Lamby build-023 by PotvinV8, on Flickr

I was going to wait to post until I had a bit of significant progress, but I've some hit a few bumps in the road so i figured I'd work through them via the forum. Anyhow, the gist of the build is a Rotax water cooled barrel, using a 64mm stroke Lambretta crank mated to a 125mm rod. Bottom end Lambretta, top end Rotax. Here's the barrel:
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This one's fun. A comparison to a stock 200 barrel.
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And the obligatory 'gasket on the crank case' shot...
Image
Last edited by RManson on Wed Aug 30, 2017 9:32 pm, edited 2 times in total.

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RManson
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Sun Dec 30, 2012 4:00 am

Machining the crankcase down was the first order of business
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Then it was a matter of hogging out a piece of 25mm aluminum to match the barrel. This will get welded to the Lamby crankcase.
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Next, the cases are machined to match the bore of the Rotax barrel.
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An aluminum slug fits inside the adapter plate and ensures that the barrel bolts up centered.
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Last edited by RManson on Wed Aug 30, 2017 7:52 pm, edited 1 time in total.

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RManson
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Sun Dec 30, 2012 4:15 am

At this point, the adapter plate is tack welded to the cases until everything is 'dry fit'. I'm still sorting out the crank and until I know if I can install it without modifying the cases, it will remain as such. With the 64mm stroke and 125mm rod, I'm not sure if it will slide in like a standard Lamby crank, hence the hesitation to weld everything up. In the meantime, I'll move on to the water pump assembly and the crank case inlet.

Image
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Gonna weld some support tabs under the barrel that tie it to the crank case as well as machining the crankcase inlet. Not quite sure how to go about that though....

Here's a shot of the area with the barrel bolted up.
Image
Last edited by RManson on Wed Aug 30, 2017 9:07 pm, edited 1 time in total.

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paulnobodyimportant
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Sun Dec 30, 2012 10:24 am

Phew, I thought that cleaning an inlet manifold with a dremmel was bad enough, but your project takes the biscuit. Extremely interesting and have a lot of time for people like you who have the skill and patience to carry our mods to both lambrettas and vespas. Will follow this thread to see how it all works out, so good luck.

grimspeed
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Sun Dec 30, 2012 12:25 pm

64mm and a Kawasaki rod will need the crankcase banding and a groove inside and also a small piece
filing off the mag side to alow the crank to enter the case !
i have a horrible feeling.things are going to go bang

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RICSPEED
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Sun Dec 30, 2012 1:44 pm

i would also say the lc inlet will need to come from the base
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Adam_Winstone
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Sun Dec 30, 2012 2:44 pm

^^^... as Grimspeed said, you will need to address the stroke increase. This should be done by having someone who knows what they are doing or you may find that your casing distorts out of alignment. Also, make sure that the cylinder is not going to foul the frame tube. You can address this by tilting the casing mouth and cylinder down so that it increases clearance (have a look on line for photos of the DAK, DAC, DAX, whatever (lol) conversions).

Adam

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RICSPEED
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Sun Dec 30, 2012 2:49 pm

Adam_Winstone wrote:DAC
;)
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Adam_Winstone
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Sun Dec 30, 2012 2:57 pm

^... thanks. I should know that as I really respect the work that they do!!!

Adam

Edit: Not meant to sound sarcastic, their work is excellent.

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Rich_T
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Sun Dec 30, 2012 4:16 pm

Great stuff but a couple of things. I hope you've done some homework on the crank side of things. If you haven't done a dimesnioned schematic of the crank/piston/cylinder arrangements at TDC and BDC you really need to do one. You mention a 125mm rod, the most common one available is CR250 but this has a larger pin. This, coupled with the much heavier piston, and a vey substantial increae in power will mean you really MUST aim for a solidly constructed crank (CR250 style) for everything to stay together.

The other thing I think you have done is build the centre line of the Rotax cylinder on the centreline of the original cylinder. This is going to seriously hamper your crank design in that you have limited width for the crank webs between the drive side bearing/seal and the centre line of the bore. It looks like your crank is going to be stock width (40-41mm wide or thee abouts).

You've got to weld in the crank case reed at some point. I would suggest that you look at putting enough weld or fabrication around the case to accommodate webs or big end throw of 108mm diametre. There is also the issue of crank balance, with a piston of this size and long rod on a 64mm stroke the little Lambretta webs would be massively out of balance. I think you are certainy looking at a one off crank which is going to be heavily loaded with tungsten to try and recover some of the balance.

I have all of these cranks and rods drawn on CAD, if you send me an Email I can help you out with the crank design. At the very least I can give you a drawing of the modified crank and what weights need to be put in and where. I can send you some screen shots of the schematics too.

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