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Its been done before but this is the first time I've been presented with such a beast.

My pal has an import Italian 150 GP which the engine was clapped out. We were just going to do the usual and bore it to 175.

But then a mate of his who had scooters BITD presented us with a 200 cylinder he had modified to fit into a standard 150 engine case. The spigot has been turned down and the stud holes slotted to accept the 150 stud pattern. I built it up and modified the jetting in the carb to 200 spec and had her running for a bit. Road testing starts tomorrow then he can run it in.

What are the short comings of this method of making a small block into 200?

So far it seems a cheap and effective way to have a standard 200cc Lambretta.

I made enquiries about this a while ago as it's something I was considering for my chop. Dean Orton ran one in Italy and it was described as being very reliable.

There are a couple of drawbacks - one is the lack of 200 barrels that are not stage 4 tuned. As you have to open out the stud holes it's very close to the larger ports, and there is a chance it can break through.
Also, similarly, the barrel can't really be tuned any further. Often a 186 kit will make significantly more power than a standard 200 kit, so it's a fair bit effort for not much gain.

If you have a standard 200 cc barrel, I'd be interested to see how you get on.

Hi

I built an engine with a cylinder similar to yours a few years ago & like you say it's a nice cheap conversion. We did thousands of miles with ours,including wining the bsm championship but they do have some issues.... Cheifly, being that the cylinder head need very regular re-torquing as it'll come loose,run weak/hole a piston etc.. Because the cylinder studs are slightly spragged to fit around the barrel the nuts securing the head don't sit flat. The best cure I found is use quality cylinder studs/gaskets & silicone sealant plus re-torque regularly. Another issue that you've noticed is how thin the spigot is, this set up is really a bit of a one hit wonder, if you sieze it badly, it's scrap. No chance of a rebore, just a hone if you're lucky, best to keep it relatively tame perhaps just a clubman exhaust IMO... Oh & they tend to run a bit hot so don't scrimp on the oil quality or quantity percentage wise.... Did I mention they vibrate a bit as well? If you haven't already, fit some wide engine mounts to fix. We only changed ours because the maintenance got a bit of a chore if you do high mileage & case conversion's to a proper 200 are quite cheap, as are Indian stage four 200 barrels

Good luck with yours, Mark.

Yeah, my mates only new to this so didn't want to spunk 500 - 600 quid on a kit if he didn't enjoy riding the Lambretta.


We were told the engine had been rebuilt before we bought the scooter but, as usual, we were lied to. The last time it saw a spanner was 1969 when it left the factory so his budget was already stretched to more than he wanted to spend. We did buy it as a recent import which had been "restored" in Italy.


I used a 150 head modified to suit the larger piston so the studs are reasonably well lined up and just through holes as opposed to slots.

We'll see how it goes. it was raining today so I didn't go out on it. maybe tomorrow after Ive fitted a new clutch kit!

A mate of mine has been running one of these for several years - loads of miles with no problems.

Leotech wrote:Yeah, my mates only new to this so didn't want to spunk 500 - 600 quid on a kit if he didn't enjoy riding the Lambretta.


We were told the engine had been rebuilt before we bought the scooter but, as usual, we were lied to. The last time it saw a spanner was 1969 when it left the factory so his budget was already stretched to more than he wanted to spend. We did buy it as a recent import which had been "restored" in Italy.


I used a 150 head modified to suit the larger piston so the studs are reasonably well lined up and just through holes as opposed to slots.

We'll see how it goes. it was raining today so I didn't go out on it. maybe tomorrow after Ive fitted a new clutch kit!

Kits from Rimini Lambretta aren't as expensive as that.Cast iron Gori 200 kit to fit a smallblock case is £316 + P&P,a Gori 175 kit is £263 + P&P.or theres the Casa 185.P&P is about £20.
https://www.riminilambrettacentre.com/e ... =casa+185+

It's also possible to use a 200 head without the problems of slotted holes or bent cylinder studs. Get the stud holes plugged in the 200 head, and re-drill them in the 150 pattern. I did something similar years ago when fitting an Li head to an LD, absolutely no problems. It's also mentioned in the old 'Lambretta Manual of Performance Tuning and Conversions' - Page 38 for the anoraks amongst us.....

Steve J wrote:It's also possible to use a 200 head without the problems of slotted holes or bent cylinder studs. Get the stud holes plugged in the 200 head, and re-drill them in the 150 pattern. I did something similar years ago when fitting an Li head to an LD, absolutely no problems. It's also mentioned in the old 'Lambretta Manual of Performance Tuning and Conversions' - Page 38 for the anoraks amongst us.....

I can modify the 150 head in my lathe but I can't alloy weld to plug the 200 holes or spot face it etc to suit the 150 studs, I guess we all do whats easier for us.

I knew I had read about it somewhere before. I'll have to dig that book out and have a look.

Went out for a spin today and it felt good. Only 5 miles or so but I was happy enough with it.

He can run it in now! if he decides he likes Lambrettas.........

Post by Leotech » Fri Nov 04, 2016 8:16 pm

I can modify the 150 head in my lathe but I can't alloy weld to plug the 200 holes or spot face it etc to suit the 150 studs, I guess we all do whats easier for us.

You don’t have to weld to plug up those holes. In any case, there's so much zinc in the alloy that welding is usually full of blow-holes.

You can plug them in another way, especially if you have a lathe & confidence in your ability...

One method is to make the existing holes over-size but in the position of the new, desired centres & then tap to a convenient size, say M16, but check! Tap from the underside but not all the way through so that you leave some taper to force against. I think you'll understand why.

Then buy, or make some matching bar, preferably in a good aluminium alloy.

Screw/force in the scrupulously clean bar into the equally clean, threaded holes, preferably with a good retainer like Loctite Studlock for a belts & braces approach.

Clean up any excess on the underside in the lathe.

Finally, drill the clearance holes to suit the M8 studs in the new, desired positions.

I was an aerospace toolmaker by trade, To me it was easier to machine the head to suit, sorry.

I have about 20 of them in a box and it took me about 10 minutes to open up the squish a bit and if it was wrong i'd just do another.

I've got a porcupine 186 cylinder head machined out for my Gori 200 if that's any help?

Interesting to bring this conversion back onto people's radar as we were talking about this old school conversion at the weekend; 5-Nations, Caernarfon, as I've been running one since before the Belgian Euro last year. I've been running the bike regularly since, including W-S-M national, Belgium again for Wassland, , faultless again this weekend, with a mix of road class and hundreds of motorway miles.

Ok, this offers no performance gain over the standard iron 200 that the cylinder came from but it has proven its reliability. FYI the bore is currently out at 66.8mm which shows at least 3 rebore oversized possible, with the thin spigot still coping.

Nothing special, no performance gain over plenty of the smallblock kits but an option and I thought I'd add a little feedback to this thread.

Adam_Winstone wrote:Interesting to bring this conversion back onto people's radar as we were talking about this old school conversion at the weekend; 5-Nations, Caernarfon, as I've been running one since before the Belgian Euro last year. I've been running the bike regularly since, including W-S-M national, Belgium again for Wassland, , faultless again this weekend, with a mix of road class and hundreds of motorway miles.

Ok, this offers no performance gain over the standard iron 200 that the cylinder came from but it has proven its reliability. FYI the bore is currently out at 66.8mm which shows at least 3 rebore oversized possible, with the thin spigot still coping.

Nothing special, no performance gain over plenty of the smallblock kits but an option and I thought I'd add a little feedback to this thread.

Interesting Adam, I wondered what the reliability was like on these conversions as I quite fancied one myself at some point. Just need to find a suitable barrel and persuade a friend with a lathe to help with the machining. I have got a old SR185 barrel that I considered boring out to 66.00mm but the quality of those cylinders are so hit and miss. What carb and pipe did you run on your barrel Adam? cheers Paul

Standard GP spec exhaust, 24mm PHBL, with 4.8:1 top ratio.... just tootles along as a standard 200, perhaps with slightly higher rev ceiling as result of carb.

Adam_Winstone wrote:Interesting to bring this conversion back onto people's radar as we were talking about this old school conversion at the weekend; 5-Nations, Caernarfon, as I've been running one since before the Belgian Euro last year. I've been running the bike regularly since, including W-S-M national, Belgium again for Wassland, , faultless again this weekend, with a mix of road class and hundreds of motorway miles.

Ok, this offers no performance gain over the standard iron 200 that the cylinder came from but it has proven its reliability. FYI the bore is currently out at 66.8mm which shows at least 3 rebore oversized possible, with the thin spigot still coping.

Nothing special, no performance gain over plenty of the smallblock kits but an option and I thought I'd add a little feedback to this thread.

The feedback I have is I thought it was a great motor, we put a 30 PHBH carb on it and it stomped along 60mph+ It happily jumped the standard GP150 3rd the 4th gap even with a 16t front sprocket. He had another mate constantly chittering in his ear about the latest stuff he'd read in Scootering magazine etc. and how he needed to spunk £100's on a kit. He decided it wasn't good enough for him and he wanted a GT186 kit. I told him not to bother but despite my 30 years of Lambrettas I knew nothing. I swapped it all over to the GT186 and it was worse, Yes it was more peaky power, not really any faster and it wouldn't jump the 3rd to 4th gap anymore. He swapped the gearbox to a SX200 one and whilst it made the gearing better it was now struggling to pull 4.8 top gear unless he revved the tool off it. He gave up with the Lambretta and sold it.