878 ARIAS 12:1 SLIPPER SKIRT PISTONS on offer

[Kenny]

They certainly look the part but I'd be a little bit worried about the extra 30 grammes at 9,000 rpm I don't suppose you could use the stock gudgeon pins?

They are lighter than the originals by 30 grammes not heavier

[cobbadiggabuddyblooo]

The std Yamaha pins longer by 2.5mm so won't fit.
The weight saving on the pin is due to being shorter and chamfered on each end with the thickest part being where the con rod runs and upon the inside edge of the pin boss.
Close up shots will show the weight saving on the pin boss which also has been tapered with the thickest part on the inside by the Conrod .
I'll post some close up hi def photos shortly showing the beautiful engineering of these pistons.
They are balanced too ( notice the underneath shot and the small divet machined to balance against the extra valve relief for the inlet) and all edges have been rounded .
Just look at the exhaust valve reliefs and the rounded finish between the cut outs to aid flow .
The close up photos I took today of the valve reliefs will show the finished edges.

[dandywarhol]

They certainly look the part but I'd be a little bit worried about the extra 30 grammes at 9,000 rpm I don't suppose you could use the stock gudgeon pins?

They are lighter than the originals by 30 grammes not heavier

Still best to lighten the crank webs to compensate for the lighter pistons Kenny

[cobbadiggabuddyblooo]

It's worth the money to balance any performance motor.
Spend an extra $500 and balance the crank and ceramic coat internals , win win, especially in longevity and wear., Heat dissipation and power loss.
2%-5% gains in horsepower over the rev range and 5% + gains in torque are well documented purely from ceramic coating engine parts with no other modifications like lighter weight oils or remapping.

[cobbadiggabuddyblooo]

Here you can see where material has been machined off the pin boss to support the use of a shorter pin. Notice how close to the conrod extra material has been left for strength and support.


By the oil ring land you can see how it has been machined to capture the oil from the bore to feed it under the piston for cooling.



Oil it fed to the pin from the oil scaper rings and has a groove machined around inside the pin boss for distribution all around the pin.


The I.D. of the pin is tapered for weight loss but strength is still retained close to the inside edge of the pin boss and small end on the con rod. This compliments the extra material left on the inside of the pin boss seen on the 1st photo.



You can see where the exhaust underside of the skirt has been machined and material removed in the small divot to counteract and balance the piston with the extra valve pocket for the inlet side.

[cobbadiggabuddyblooo]

You can see the shaping on the valve relief to aid in flow by soft contouring the valve relief.All the edges after machining have been de-burred and the flat top nature of the piston.

[cobbadiggabuddyblooo]

Price is $700 due to added expense of having them lightened , compared to the advertised price for a pair of JE878 pistons here in Australia (approx $660 after delivery and fees )
$700 includes free delivery in Australia or an extra $50 will be needed for overseas shipping.
Contact me to discuss customs valuation and import tax/duties if in the UK.

[cobbadiggabuddyblooo]

only 1 set of pistons left,
Aust dollar has fallen over 2c since the first order was paid for 2mths ago so the next order will be around $15 more if the $ stays at 0.85c US
Hopefully I can get at least 1 more order in before they just get too damned expensive.

[mik_b]

Hi Cobba,
Curios about these. What Diameter are they? Also, last time I read about your build The Ross pistons were the hot item apparently, what happened?
I ask because I emailed them for a quote, came back at 330 usd for the pair inc. rings & pins.

[cobbadiggabuddyblooo]

The extra milling is $18 US on each piston x that by 3 to get 1 Trx piston to a functioning state and I paid for extra again to have further machining done to get the weight down even further.
Don't forget these prices here are per piston so add another $100 odd per piston to your base price.

The Ross with it's slipper skirt and flat top is a better option I feel than the JE 878 full skirt and domed design, but if you want to pay more you can have even better again.
The minimum they will do is 4 piston too.
All these factors add up and bring the price over $1000 Aust .
Plus I might add $145 US shipping ..
After paypal exchange the Aust$ is presently worth 81c US .
They are a personal order and not an off the shelf item too and I increased their size to 1.5mm (878cc) compared to the 1mm pair of Ross (868cc) pistons I picked up on gumtree with the Carrillo rods over 12 mths ago. I wasn't the one who placed the original Ross order.

[cobbadiggabuddyblooo]

Due to the ever decreasing Aust $ .. I will no longer be importing any pistons.

[cobbadiggabuddyblooo]

Dry run completed today with a pair of Arias piston using my head with the 1mm oversize valves.
Using a 0.9mm copper head gasket, I feel confident enough I'll have the clearance to run this 1mm oversize set up with no extra fly cuts to the valve reliefs.

Squish was 1.5mm well above the minimum set at 1mm by Arias.







The photo below shows an Arias piston with a 2mm oversize valve sitting central to the valve relief with approx.1mm clearance.

[dandywarhol]

Are these the 2mm oversize from Sanddune Cobba?

Would I be right in saying stock Yamaha pistons would need to be flycut to accept the 2mm overs?

[cobbadiggabuddyblooo]

The std valves have enough clearance .
You need around (1.5mm) inlet and 0.100" (1.5mm) exhaust clearance to the top of the piston.
But depth is not the issue , radial width is if using the 2mm oversize valves is at minimum spec.
But this is something you will need to check yourself.

[Kenny]

So the answer to my PM question is they will be good to go as std with the 1mm over sized valves yes?