Picture above shows contents of TSS/Athena
421cc kit as described in the panel opposite

TSS/Athena 421cc Kit Contains:

Athena cylinder and head kit
(68mm bore) with head studs and acorn nuts, washers and O-rings/gaskets: $750

58mm stroke crankshaft (+4mm)
with 115mm con-rods and silver-plated small ends: $485

Wossner forged piston kits
A pair of piston kits which = 2 pistons, 4 rings, 4 circlips, 2 piston pins: $290 (Piston pin is 6mm higher than stock Athena piston)

New CNC machined head domes
Pair: $85

Total:  $1610

(If you already have an Athena cylinder/head kit, and a +4mm stroker crank, you only need to pick up the stroker pistons and head domes, as pictured at left. In this case the total cost is $375.)

 

 

 

 

 

 

 

 

Note from the pic at left that the new TSS 421 head insert (dome) allows for the higher piston protrusion of the 58mm stroke crankshaft.

Also the squish band has been modified to suit the new engine configuration, and the cubic capacity of the combustion chamber has been increased to allow for the higher compression ratio.

All this means that you can simply fit these stroker head inserts to your Athena cylinder head, and together with the stroker pistons, the engine is assembled as simply as the stock Athena 392cc kit.

We have selected Wossner forged pistons for this conversion because of their high durability, especially at very high revs.

Pic 1: Standard Banshee top case


Pic 2: Top case marked out for machining


Pic 3: Finished top case


Pic 4: CNC machined top case

Tech Notes

The Athena cylinders can be simply bolted onto your stock YPVS or Banshee engine cases but to get the best out of this conversion, the top case needs to be machined out to match the larger transfer port pattern of the Athena cylinders.

Pic 1 at top shows a brand new Yamaha YFZ350 top engine case that is completely stock.











Pic 2 at centre shows the top case marked out for machining; which can be done manually with a die grinder (the rough work) followed by progressively finer finishing with rotary sanding wheels, cotton-impregnated porting mops and finally polished with cottom mops and metal polish.

 

 

 

 

 

Pic 3 at left shows the finished job.


























Pic 4 shows a top case that has been CNC machined to match the transfer porting of the Athena cylinders.

This is something that we can get done in batches of engine cases, to minimise the per-unit cost.

The easiest way for us to achieve this is to use batches of new Banshee cases, which are then sent out to customers worldwide from the CNC shop.

Note also the top case gasket cavities have been filled in with Devcon; this is an optional step which is done to give more base gasket area - but is more typically done to bigger bore versions of this engine, which need the top case to be bored out to accept the larger cylinder spigots.

This Devcon infilling process is not necessary for the TSS/Athena 421cc engine.




(Note though that when using Yamaha RD/RZ (YPVS) engine cases, which have a shallower front gasket face than Banshee cases (as shown in the pic below), the sealing plugs for the Athena cylinder need to be stabilised by sealing off the coolant plug holes, typically with Devcon on top of the cut-down sealing plugs.