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

[onthelam]

Euro has been slipping so thought it might be a good time to buy a Gori Racing kit, thereby at a stroke getting correct exhaust for the port timing and carb., etc. BUT it has a cast iron cylinder.
Any negatives of cast iron vs an alloy kit.

[bristolmod]

I like cast cylinders- you can simply rebore them. Nikaseal obviously needs replating when scored/ worn.

Alloys dissipate heat better though.

I do like steel lined alloy as long as the steel is good and hard.

You pays your money etc.......

Chris

[Monty]

1000 miles running in V twice round the block...

[B-Race Tuning]

Set up correctly, with correct air/fuel mixture of consistent octane rated fuel (ethanol included), I believe they would pan out in the cast iron's favour. pretty much based purely economics overall. An alloy cylinder will go longer between necessary cylinder refurbishment but costs far more. Most alloy cylindered engines, be it scooter/ motorcycle or car, fail before wear is an issue. Manufacture for alloy is more expensive/ or to buy (depending if you're making it yourself or buying in, but either way costs more).
Higher 'power' creates more heat, alloy conducts heat far quicker but has to be thicker to maintain stability as heat is applied so with proper design no advantage heat wise, other than alloy will disperse heat if something alters the correctly set heat setting (air/ fuel ratio being common due to air leak or fuel issues) and therefore less/ no warning before irretrievable damage. Therefore cast iron works in your favour there.
More intricate cylinder design (read 'more powerful') made generally from alloy as is cheaper for the mass casting rather than small batch and is 'in favour'.
I love the performance of RB'S, Super Monza, TS1 but as a local, thrash engine, as a touring/ distance engine I'd opt for Iron. And with the increased fuel usage of a higher performing engine, more fuel stops (Hare v Tortoise scenario), so you still arrive at destination at 'relatively' equal time. Combine that with riding with others that don't have similar (lower) speeds and the gain is....?
Any good Iron Cylinder (Indian 200, ported) will maintain 65+ at a tiny fraction of cost of any engine/ cylinder kit designed/ ported/ built to SUSTAIN 80+ (Iron or alloy), (We still do it, and it's jolly good fun, but must accept it costs a lot more).
If you fancy the Gori kit, do it, don't think that because it's Cast Iron it's in any way inferior to an alloy kit.
Horses for courses, and fashion of course.
S

[mick1]

The alloy kits (due to better heat dissipation) seem more forgiving for a novice to set up. The cast (set up correctly) are probably as reliable as an alloy but they need to be set up more accurately.

A seize on an alloy may require new plating and is probably a terminal brake-down, whereas a seize on a cast may see the scooter driving off again after unfreeing the seize........albeit slowly and nervously.

[barnsleybilly]

How does the gori compare in price against, say a BGM 225 kit from scooter centre?

[ArmandTanzarian]

A seize on an alloy may require new plating and is probably a terminal brake-down, whereas a seize on a cast may see the scooter driving off again after unfreeing the seize........albeit slowly and nervously.

I think that's the crux of it. Properly set up, an alloy kit is better but if it does go wrong.......

[HxPaul]

Nobody has mentioned the absolute ball ache of running in a cast iron cylinder.At least with an alloy cylinder you only need to run the piston rings in.

[B-Race Tuning]

A seize on an alloy may require new plating and is probably a terminal brake-down, whereas a seize on a cast may see the scooter driving off again after unfreeing the seize........albeit slowly and nervously.

I think that's the crux of it. Properly set up, an alloy kit is better but if it does go wrong.......

Armand, what I was getting at, and is a long time argument, is WHAT is BETTER? At what? I do agree that generally alloy kits are better, but only because the designer/ manufacturer chooses that material. I'd rather have a GT kit over a Mugello and performance is VERY comparable. A well set up Iron kit IS equal to the same well set up kit in alloy if set up correctly. It makes a difference when a mechanical failure of a seal or, unwittingly ethanol laden fuel is included into the equation. If it wasn't for these factors (allowing component factors built into the engine, i.e. up to the job asked to do ), we wouldn't have ANY unreliable Lambretta engines. I've had no engine failures since we started (as a business, 15 years) that were related to whether cast iron or alloy, or set up. Component failure because it was sold as up to the job, standard components not meeting OE specification or fuel sold not as it should have been, YES. If set up comparable and well, it makes no difference. A well set up 177 cast iron engine can match and exceed an alloy 225, not set up correctly (but running , in the owners perspective, well), proven and testified. I also don't believe the mantra that any engine cannot be run at full throttle on the road, up hill, down dale on a(for example,)Motorway or dual carriageway. Our engines can and do run for a full tank of fuel at full throttle with no issues, cast iron or alloy, vespa or Lambretta, proven and testified.
I'd be as happy with a cast iron TS1, RB, Super Monza as an alloy version of the same. It's the build and set up, and that accurate set up makes them equal. If it goes wrong, the cast will show signs the rider can understand earlier to the inception of a fault to salvage the engine. The Alloy kit by it's nature will not show those signs until it's terminal.
S

[goldeneye]

Nobody has mentioned the absolute ball ache of running in a cast iron cylinder.At least with an alloy cylinder you only need to run the piston rings in.

ive never seen the logic in that "1000 miles" thing. if the bore clearance is right , and its set up properly, I usually leave them on high tickover for as long as I can , then take it easy round the streets for a bit to check the jetting , don't do any motorway riding for the first couple of hundred ,then just ride it as normal. I always use/recommend mineral oil for running in. alloy barrels I just leave on high tickover for an hour and ride as normal, but as people say when they go bang, they cost a lot more to fettle. I run a cast barrel on the lammy , and a alloy on the vespa , but the current engine on the bench for my next project is a cast iron barrelled vespa engine (Polini Suzuki T5) both have their pros and cons, so I like both. maybe the question should be WHICH cast iron barrel and WHICH alloy barrel, as there are good and bad of both materials.