What are the pros and cons of cast iron vs. aluminium barrel

[ducksta]

[quote="eden"]
People moved away from cast iron with the inception of the TS1 barrel which came out at a time when 95% of the people riding and working on lambrettas didn't have much of a clue about setting up any kind of barrel, due to this cast iron got the reputation for being unreliable. Most people who turned to TS have never gone back to cast iron so they have an 80's skewed memory of cast barrels.

Totaly agree with the above statement, we grew up on shite rebores crap cranks etc, then as eden says people started buying better bits and the ali kits came along at the same time taking people away from the cast barrals, ive just gone back to a dr kit on one of my vespas yes tight bore took some running in but price/power ime happy

[Rich_T]

Alloy barrels are much cheaper to make than iron principally because melting 100kg of aluminium is much cheaper than melting 100kg of iron and 100kg or aluminium makes a lot more cylinders than 100kg of iron. This is the principle reason for the move to alloy barrels. Naturally, they've been making alloy barrels for decades with iron liners but the real cost advantages came when you could ditch the expensive machined liner and replace the process with a plated liner.

As Eden mentions, alloy barrels distort with the asymmetric cooling and the other odd thing which supports the cost saving of alloy over iron is that many LC kits are alloy where the difference in performance between alloy and iron is less critical (example, Gilera runner 180's are iron and performed just as well as alloy versions).

I think the coincidental advantage that the TS1 had was that it came along with controlled components (ie, it came with it's own piston matched to the bore). This fact removed the principle variables that cause a lot of problems. At the time most people were buying different pistons of varying quality and fitting them to cylinders of varying quality. Quality control and consistency was dubious at best and doubtless the reliability of these combinations were compared directly with the, then new, TS1 with dedicated parts. I think is is fair to say that when you apply the same quality controls and consistency to an iron kit you achieve the same reliability.

Additionally, when you put similar features into an iron cylinder they perform just as well as alloy kits and I think that is pretty well documented now as is their reliability but at the end of the day it is the consumers choice.

[B-Race Tuning]

Thanks Rich, I stand corrected on costs of manufacture. So is it fashion/ demand rather than real cost that makes an alloy Polini 210 kit cost half as much again as an Iron 208, likewise a Pinasco 177Iron kit v alloy kit (50%). And is Alloy then passed over to us at higher profit margin because it's 'Gucci', must have? I was under the impression the plating etc made it more expensive? I can easily see the economics of the casting though.
Simon.

[Rich_T]

My comment would be that it would depend on what production line the company operates and the margins they are prepared to accept. Vespa is a much more competitive market with some big players. If the casting line is automated or semi automated and they are also involved with producing similar products they may take a view (it may even be that the who job is subbed to Far East).

Plating in the UK is astronomically priced however, if you are a serious producer such as Athena, Airsal or Gilardoni then you would have a plating plant in house. Once you are geared for that process in production volumes (which means multiple 1000 off batch qty)then the process is incredibly cheap compared to iron liners for example.

The fact is, from Lambretta production point of view, the quantities are too low and the tooling massively expensive to hit automated processes. Even with traditional hand processes the core boxes and patterns for iron are more expensive because the sand packing process is more aggressive on the tooling.

[Rich_T]

Or a more comparative representation closer to home, is the comparison of casting the GT cylinder V the GT cylinder head. The head is less than 20% of the cost of the cylinder but is is not 20% of the volume. From packing the sand patterns to knocking out cylinder head is about 30 minutes, cylinder is at least 2 days (consequently you can get a lot more production through an aluminium foundry floor than an iron foundry and when you use die tooling instead of sand patterns it is even better.

[onthelam]

OT a bit and not related to my Lambretta kit question, but if we are talking mass production, the air cooled step-through "scooters" made in Asia by the millions have as a rule iron cylinders, almost exclusively. One would think that is aluminium is cheaper they would be aluminium. In contrast most big bikes made here have aluminium cylinders, but they are predominantly now water cooler. Not sure if that makes a difference?

[LI150]

Both my lammies are cast. Stage 4 200 and gt186. My Vespa is Ali mallosi 210. I don't have a preference or favour one over the other my choices are what suits me at the time of building the engine.

[Pepot]

I had the same doubts at the time of choosing a 186cc kit. I finally bought a GT186. Most of the alloy kits I saw didn't even have oversized pistons available...and in a 2st, seizure is allways possible.

[Pepot]

OT a bit and not related to my Lambretta kit question, but if we are talking mass production, the air cooled step-through "scooters" made in Asia by the millions have as a rule iron cylinders, almost exclusively. One would think that is aluminium is cheaper they would be aluminium. In contrast most big bikes made here have aluminium cylinders, but they are predominantly now water cooler. Not sure if that makes a difference?

But those modern engine are 4st. Less prone to seizure.

[Strummer10]

I have a Dave Webster stage 4 tuned cast iron barrel on the GP 200. I was gonna get a TS1, but have to say this baby keep right up with them but has the advantage of a quicker off the throttle response to power.....................