60 or 57mm Crank?

[scuffa]

I have a 56 plate PX125E that is due a rebuild. I’m going to put either a cast or alloy VMC 177 kit on it, probably. Would it be better to stick with the 57 that’s in it, a new ‘race’ 57 or go with a 60mm, assuming the kit is compatible with a 60mm. Thanks

[ironsloth]

Do you plan to do any other modifications to it? If not, stick with the standard 57mm cast crank, I kept the standard one in mine, and I ran a Malossi and a Polini kit in the same lump. If you are doing other tuning parts too, then go for the 60mm, and pack it out. Still not worth the extra wedge for the race crank personally.

[adrian]

I have a motor with vmc 177 kit and long stroke crank, taking it to 187 cc , couldn't say if it makes much difference, but had 78mph on the gps, not quite as fast as my bgm187, but far cheaper

[gpowell]

Some good advice already and i would personally stick with the standard crank Genuine Piaggio cranks are very good.

The difference on "race" cranks is in large only increased inlet timing.

You can do this by cutting the web to allow a longer duration of inlet which will yeild slight gain in the overall process.

A good rebuild should always include matching parts that the factory cannot do in mass production.

Match the carb and box to the casing and make sure no gasket overlap.
Match the cylinder, casing and gaskets.
Chamfer the edges of the cylinder ports.
I aways open up the fuel banjo and fit fast flow tap.

[scuffa]

Thanks for the advice so far. I should have mentioned that I intend to put on a 24/24 carb and a SIP exhaust, or similar, box exhaust. Not got a huge budget to play with, hence the original question. I don’t trust myself to cut the crank correctly to gain extra inlet, so that’s why I was considering buying a better one. Also, am I right in thinking that a 56 PX125 will have a reduced inlet port that could/should be carefully enlarged?

[gpowell]

If you on a budget you are heading in the right direction.

If it were me.... Ive done this for a few people :

Cylinder kit with casings and gaskets matched.
Get the squish clearance right
SIP R2 a good choice
Keep the 20/20 carb, drill the filter and upjet on the pilot to next richer and main (start 122)
Match the carb, box, casing and gaskets.
Fast flow tap.
Enlarge the fuel banjo by drilling it through. Enlarge the inlet in the carb top. Check the top seats correctly as well.
Put new clutch plates and springs in (plus a thrust washer)
Hotter plug.
Check the primary drive plates are secure.
Gaz

[ironsloth]

You forgot one thing… Go on slight diet… 😁 On a serious note, I would fit a fibreglass mudguard too. Whether it’s a full one or a hugger, the weight (and rust!) saving is pretty good, and they are cheap.

[gpowell]

Ha ha... My last lambretta built was full fibreglass; Leggies, panels, mudguard, bridge, glove box ...

[scuffa]

Hi,
I've gone for a 57mm Maz race crank and cast VMC 177 kit. I intend to run it with either a 24/24 or 26/26 carb and SIP 3 exhaust. I understand the inlet port is quite restrictive due to emissions. Can anyone tell me if I will need to enlarge/lengthen the inlet to get the most from the crank and kit and by how much?

[adrian]

Yes lengthen the inlet, will find the measurements tomorrow evening, I have same kit, with 60 crank and 28 carb, cases and barrel ported, and 79 mph on gps , so very happy with that, only slightly slower than my bgm187, just doesn't accelerate as fast

[scuffa]

Thanks Adrian. I've got the engine out now, so when you have the inlet measurements that would be great!

[adrian]

If you can message me your email or WhatsApp, I can then send you the information you need to start opening up the inlet, and pictures, as I can't add them on this site 😒