lambretta 290 rotax

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RManson
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Holty,

Where'd you source the mag spacer and are they available in various sizes? I had to knock out a crude one for my Rotax engine but still need to stack a couple gaskets to get the clearances right. Would be nice to have the right combo. Thanks!
holty
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hi ryan, its from martin at chiselspeed
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Rich_T
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Will this arrangement also pack out the primary drive by 5mm too? Would this push the chain out by 5mm and require modification to the clutch crown wheel? If it does you can shorten the drive spline by a few mm to increase the pre-load on the primary drive spring, this will keep it inside the side-case limits but the clutch requires some thought.

For the GT prototype I opted for an LTH/Harry Barlow plus crank with 101mm webs which covers the issue in the short term (as the webs are standard width) but long term I'll have to deal with the same issue at some point.
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RManson
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Would make a good excuse to convert the chain drive to a Gilbert-style belt setup. ;)

Also worth a thought how such a wide crank will be to rotate into the crankcase. I know with mine, I had to machine a recess in the case because the rod is so long. It simply wouldn't fit between that and the offset big end hanging out the crank. With the wider webs it would be even more difficult if not impossible on my setup to get the crank in the case as the rod would probably hit the mag flange base while going in.
holty
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Rich_T wrote:Will this arrangement also pack out the primary drive by 5mm too? Would this push the chain out by 5mm and require modification to the clutch crown wheel? If it does you can shorten the drive spline by a few mm to increase the pre-load on the primary drive spring, this will keep it inside the side-case limits but the clutch requires some thought.

For the GT prototype I opted for an LTH/Harry Barlow plus crank with 101mm webs which covers the issue in the short term (as the webs are standard width) but long term I'll have to deal with the same issue at some point.
hi rich,
by my calculations the drive end of the crank will protrude through the drive side bearing by 5mm extra, the oil slinger will go on as usual and then the sleeve im hoping the sleeve will slide right upto the oil slinger as the splines inside dont have a stop on the inside, at the worst i might have to machine back the splines inside the sleeve if it bottoms out before it touches the slinger, you have sure been thinking about this, im impressed, have you made any more progress with your rotax project? i saw the facebook pics a few days ago, your inlet looks nice, do you intend to cut the base of the cylinder skirt, ive seen this done using an oconner racing template for skidoo racing, heres a pic
Image583 intake cut by stephen holt, on Flickr
Last edited by holty on Sat Jul 29, 2017 6:37 pm, edited 1 time in total.
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Rich_T
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OK, so effectively your drive bearing and seal arrangement is 5mm thinner than stock? Ohh gotta go Captain Phillips is starting..gotta go.
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Rich_T
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I understand your set up better now, and you should be able to grind the splines back if they bottom on the crank. Assuming the drive bearing and seal arrangement is 5mm thinner than standard it sounds like it will go together nicely. Interesting how different people come at it from different angles to achieve the same thing. I don't know how Ryan did his drive side arrangement in the end.

I'm using a 125mm rod so the piston or barrel skirt lengths don't need to be altered. The plan was to make the boost port same as a stock cylinder first off so that it is a straight bolt on. However, this might change when I dyno the first motors. After initial runs I'll start to modify, the plan was to have at least one or two motors running in BSSO for 2017 and see how they hold up.

The exhaust system is finished (it was remarkably easy in the end) I opted for a modified Fran Race, it was the quickest thing to do to get a first dyno benchmark. It connects to the cylinder with CNC machined stub, it was really easy to make from one piece.

The inlet system is designed but not completed, I have to get some corrective welding done to the cases, then machine the mating faces. The critical parts of the manifold are machined and the welder will fabricate the interface between the two. The electric pumps, plumbing and rads are in (I'll run with RS125 rad first). I'll be using my RS125 ignition conversion so there is enough power for the pumps and lights.
holty
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i dont know how ryan did his, but im sure he will tell us, im pretty sure he used a wider crank as he is using a mag side packing plate,you have made some great progress, sounds good, are you mounting the rad under the floor, im going down the electric pump route as well, ive been doing some work on my exhaust, its from a 300 trials bike,ive cut it into sections along th original welds so i can just twist them and reweld, ive got my stub nearly finished off, im just welding a bit at a time to try not to distort it, just slow progress realy but realy enjoying it.
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RManson
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Martin at Chiselspeed did my crank as well but it was built using off the shelf items at the time, so it's a standard web crank.

After welding up the cases, i decided to deck the mag surface. I found that I needed 3 gaskets to get the clearances that I thought it needed, hence the spacer. It's really more a shim than anything.

I must say I'm a bit jealous watching all the innovations coming on at the moment. Wider cranks, new cases, would have made my job a lot easier and loads faster to finish in the end! Could have saved my self a lot of fun!

Excited to see how you guys get on with your projects so keep the posts coming!
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Rich_T
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I'm going for the rad behind the leg-shields (much like Ryans). Have you had yours on the dyno yet Ryan? I also used the Maico 250cc con rod which is 125mm long 22mm big end and 18mm small end.

If the engine performs well, I'll make a production version of the kit which will make it as near out of the box as you can get.

Ryan, you're using an electric pump too with RS125 ignition (I know you ditched the ECU but you kept the generator right?). Is the generator keeping up with the electric requirements ie not running out of juice at night with the lights on?
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