The Helios Project (Aprilia RS 125 Rotax 122 Biaggi Race Replica)
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So this arrived this morning.
It's the Italkit Gilardoni 140cc cylinder kit for the Rotax 122 engine.
I feel like a bit of history is needed to really appreciate this cylinder.
Gilardoni is the original designer of the Rotax 122 cylinder way back when.
Original Barrel for reference
A few years ago he revises the cylinder in the form of this cylinder. This cylinder reflects lessons learnt over all of the years people have been racing these engines. All of this is reflected in the barrels design.
Now I was tossing and turning trying to decide what route to take with this engine. Initially, sticking with the Gilardoni Rotax 122 original cylinder, opting to have it ported to reflect my systems designed.
But no matter what engine I bought, the cylinders were all scrap,and it was going to cost £300 to remanufacture the cylinder to usable condition.
I have ridden Aprilia RS 125's since I was 16, that's a little under a decade of riding experience on these engines alone. I have ridden bad ones and I've ridden good ones. I've ridden bog standard ones, and highly tuned ones.
The thing that stuck in my mind the most is how the original engine revs to 14K, and I always appreciated that out of the original cylinder.
When riding Polini's 160cc kit, you lose around 2K over rev. This isn't the case with this barrel. It'll continue to pull hard to 14k, granted it's not the extra CC's that give you the bang.
The porting work on this engine is superfluous, it's extremely well done for a casted material.
Sure there are further refinements that could be done here, a few edges taken off and some minor flaws altered, but on the whole, it's a very well designed cylinder.
Combine this with PJME's Reworked VHM billet head, and you have yourself a very capable top end.
The cylinder is running a relatively high 12.1:1 compression ratio, less than ideal for reliable road use. The fueling on this cylinder needs to be finely tuned to avoid running the risk of detonation. This engine must be run on Shell Super Unleaded, else it's just going to detonate.
All this power is no good if you can't stop for the corners.
I've ran these on my DT, with the older style Aprilia braking system. So running this on the radials will surely surprise me.
These Brembo Sintered brakes are £40 a pop, if you can find a set. Were sold out everyone I looked.
I refurbished the brakes themselves back in Christmas time, and I've just ordered titanium retainer pins and titanium bolts to fix it to the forks.
So far so good.
I need to calculate the squish on the engine I'm building to ensure I get the right compression ratio, then drop the engine into the frame.
I need to order some titanium head bolts, V-Force3 Reed cage and 34mm inlet. The dellorto racing carburettor has been ordered. Some £1000 spent this month already, with more to follow...
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@declan Yeah I'll get a video up when that happens don't you worry
I'm still probably another payday off yet.
Needs CDI (Zeeltronic), indicators, wing mirrors and a good number of other electronics.
I've got the radiator now and hoses.
I expect there is going to be the odd bit here and there left to do.
Fairings have been ordered. They are made to order so they take ten days plus shipping.
And then there are the custom fabriacted bits, plus a little more painting that needs doing.
Should have it dyno'd towards the later end of the summer, see what she's making.
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The compassion ratio on my Athena is supposedly 13:1. And yours 12:1:1? What's the difference? Cool stuff you got there!
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@irongamer727 That's savagely highly.
The stock DT is 8:1 lol.
The higher the CR, in general, the more extremely the powerband and the less torque.
I'd be very surprised if the somewhat powerless Athena kit is 13:1. You can have too much which has adverse affects.
I'd be more inclined to say the Athena is a lot lower, as it's generally a more torquey setup.
The higher the CR the more...unreliable an engine becomes. A lot of stresses on the bottom end and components you see.
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http://www.athenaparts.com/eng/kits/view/7483/cylinder-kit-with-head-170-cc
The data sheet says 13:2:1. No clue if that's the same as 13:1
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@irongamer727 I don't know. But 13:1 is very high
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Generally, higher CR gives more torque, and a better powerband, not the other way around. Otherwise they would surely reduce the CR on endurobikes compared to their MX rivals, to give them broader powerband, but they dont...
"A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency"
This pic from the book "basic 2 stroke tuning":
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Forged Piston Fitted.
Fitted it all nice and snug.
Put the engine away, amazingly (luckily) found one of the circlips had fallen out onto the bench.
Thankfully I found that, not sure how that happened. But that's back in now!
Of course I have bought titanium head bolts for this engine. But I was too eager to bolt all the pieces together and they haven't arrived yet.
But I will fit them when they arrive.
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@calum Oh my thats beautiful!
Do you know how big the difference between the piston diameter and the cylinder diameter is? Or did the piston arrive with the cylinder perhaps? I've always been uncertain how big the difference should be when fitting a new piston. -
@irongamer727 Yeah it probably says in the spec sheet it comes with. I didn't read it. You can tell the piston to cylinder clearances in this engine are large. However I woupd expect that from forged components due to their thermal expansion coefficient.
For reliability I have knocked the compression back, this piston only utilises a single ring. Less frictional losses and bore wear
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@irongamer727 exactly that.
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I guess you purchased the cylinderkit on PJME. I mean that was a pretty good price for it!
I know you have bought the special cylinderhead and got it ported but still, I thought the cylinder would be like £600 or something.
The polini big bore was a bit more. I guess you reckon you can get more power from your kit, but how?
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@irongamer727 So I didn't get this barrel ported. I just said that the porting work is damn good, albeit some minro flaws.
The last RS in my garage used the Polini big bore, before the 140 kit was released.
https://www.youtube.com/watch?v=GobIl4e-mU8&t=2s&list=PL66C1264C7D6205BB&index=3
Very quick bike, but the Polini eventually seized after very little miles and most of it was being ridden softly.
It was my brothers bike, but mi casa, su casa as the Spanish say.
Big bores are hard on engines. It's not the first time I've said it, and it won't be the last, in my experience the Athena was pretty poor for performance. Reliable mind you.
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@calum so the polini isn't very reliable then?
I've heared the same. I'm happy with the Athena though. Strong, not very fast but comfortable. -
@irongamer727 Good torque gains from the Athena, if that what you're after. And, unlike the Polini, doesn't affect reliability.
I can only comment on my own experiences, and that may have been down to incorrect jetting. As this wasn't my bike I wasn't at liberty to jet it as I saw fit.
The reason I went with the 140 kit, is that I am not interested in more CC's, I want it to rev to the moon and the fact that the person who designed this designed the original. It was also (as you say) cheap. Just £40 more than having my old barrel replated and ported with a new piston. Something different as well, I've not experienced this cylinder before.
I'm excited
Still £2k of bits left to buy for this bike yet.
