Confused.com over the 421cc conversion

[marlow]

So I've been getting advice from Steve (TSS) about how to go about this seemingly popular mod but am getting a tad confused (not hard, bear with me).

He says we need to buy the Athena 392 kit, then 4mm stroker crank obviously, then bigger heads to allow the longer stroke, and finally I don't want Wiseco pistons which all the kits seem to come with so then Wossner pistons to be bought also. Only the Athena kit comes with pistons and heads so these would be going to waste, right?

[filbert]

Either to waste or his spare parts shelf, unless you can find someone to sell you only the parts you need rather than a complete kit.

[marlow]

Well, MY shelf, I'm from UK and wouldn't go to Aus direct am just finding here seems to have the most info.

OK so now I'm just finding out about the cheetah kit options which have the powervalve. Have not read much about anybody using this kit so is this a more/less reliable option perhaps?

[JonW]

Ok, bit by bit... The Athena kit comes with a head, it is fine. It does not have Wiseco pistons, they are Athenas own i think. I sold mine on ebay and after fees netted $80back or so against my Wiseco 573s.

+4mm crank can come from anyone. TSS ones are nice as they are balanced, I have one. Lots of other brands offer +4mm cranks and some people are doing longer units that need case trenching but will net you more power, however... beware of the cheapo cranks on ebay, they are generally crap.

Cheapest Athena kit when i last looked was Wicked Motorsport and i picked my kit up from them in LA when i was there, Roger is a great guy to deal with and did some post work for me on my cyls that was well worth the extra money. no one else does that. he was friendly and has given me lost of extra advice both before and after purchase. He loves RZs and that helps.

Wicked also do the Athena cyls on their own, will posrt them too if you want, also different heads (including their own billet RZ style head with removable domes! wish i had one of those, Aaron has one, see his pics) and many other parts, but not sure if they do Wosner, speak to them and tell Roger i sent you, it may help as he will remember me, I rode his bikes and had a ball when i visited him.

[marlow]

See the first line confuses me straight away lol (I pretty much got the rest). You say the head in the Athena 392cc kit is fine for a stroker crank? Why am I being told by TSS it isn't?

[JonW]

it depends on how you want to run the +4mm crank. You can either put a spacer plate under the cylinders and then fit the head as it comes out of the box, or you can run without a spacer plate and then have the Athena removable domes turned down on a lathe so that the pistons can run into the head. Steve @TSS used to offer to cut domes and im 99% sure has done so in the past for people on this or another forum, else Wicked can do that as I had it done by them so i could run without a spacer on my build with Wiseco 573s. If you run standard Athena pistons (without offset wrist pins) instead of the Blaster pistons (Wiseco 573s) then things will be different. But... whatever head you get you would have the same issue as its the length of the rod v's the length of the barrel that's the issue, adding a spacer or recessing the head allows the +4mm extra stroke to be accommodated. Its swings a roundbaouts how yo make it fit, and fitting the barrels up and down relative to the stroke also changes the port timings of course. Decide what you want to do and then make it work is the plan. Personally i wanted low ports, no spacer so used 573s and recessed/reprofiled domes. bolted together easily. My build thread is on Norbos forum in the rebuilds section and ive not held back and shown the good and bad of my build up etc. HTH.

[g0zer]

Only the Athena kit comes with pistons and heads so these would be going to waste, right?

yep thats correct. wasted $400 worth of pistons and wasted $200 worth of head and domes. also you are then up against the added problem of oil pump for the 421 which will take more money to solve. then the 421 is going to use more fuel and the range of the 392 is already pretty appalling.

then you will need to come up with a thermostat housing solution and adapt the temperature sender. then if your motor is making more heat start screwing around with sourcing and adapting bigger radiators. new carbs, tuning new carbs and motor. price list and time required for the job goes up and up.

plus you are likely to have some screwing around dismantling and reassembling with different base gaskets to get the squish dialed in. when slinger on the rz forum machines combustion chambers for people he takes the barrels and head/domes and returns the lot with the base gaskets he used to set the squish. then you will need $1k worth of pipes with spigot adapter since athena barrels dont have the exhaust flange.

imho unless you have good reasons for a 421, leaving it 392 is a far better option both practically and cost. cheapest to build and imho best all round engine is a 350YPVS.

[marlow]

Well I guess I'd better get onto Tony @ Gibsons (UK) and hope he knows wtf he's doing then

I want something that is going to rip snort and cackle like a lunatic and keeps up with Gixer 7's (if possible), pretty sure these bikes can blitz 600's at least? JonW what power is your bike and what sized sports reps will it blow into the weeds? I'll check your thread too thanks.

Ah don't think it's finished yet for u to know that

[JonW]

g0zer, $400 worth of Athena pistons? i sold mine too cheap, but they looked pretty cheap units to be honest and Athena sell them cheaper than 400 dont they? and the Athena head was easily used in the build so dunno why you say he needs to sell it off? not being funny but you seem pretty down on the 421? whats the beef?

Im using premix in mine, TSS is sorting a solution to the oil pump but i just thought id use premix and be done. sure it isnt as simple and pump, but its not rocket science to carry a small bottle of oil on the bike. I may also keep my oil tank and put a tap on it or something. we'll see. I am used to riding enduro KTMs on the road and for events so i guess i dont mind adding oil to my fuel as much as most people.

Thermostat housing is sorted, i found a kart place in Sydney that will sell one for 69.95 with a nice stat etc.

Rad, carbs and pipes, yep you will need those of course... but youd want to upgrade those i would think anyway. you can run the OEM carbs and still make ok power and in the uk you might get away with the OEM LC rad as its 750ml, but not the YPVS units of course as its tiny. i bought my pipes from Wicked, they were designed for the 421cc and were good value. Gibsons will do what you want tho i expect.

LOL Marlow, yeah its not finished... sorry m8. Here g0zer has built an Athena i think and so did Twinrock (in a Mito) as did Brian (in an LC). Plenty of Banshees with the Athena kit of course.

[g0zer]

g0zer, $400 worth of Athena pistons?

how much is the set of wossners/blasters/wisecos he will need to replace them with? if he needs to replace the pistons its cos he is being talked into a 115mm rod.

other option for a 421 is to use 110mm rod length with athena pistons +4mm stroke so barrels come up 1mm and the combustion chamber needs to be relieved 1mm to re-center the port timing.

[JonW]

I think i paid 180 for my 573s, got about a clear 80 back on the Athenas, even if i paid 180x2 for them its not 400...

[g0zer]

your ebay fu must be good, i paid over $400 for the proX in my ypvs. i havent built one, i started to but ended up with a 90 degree 115mm rods +4mm crank, an unbalanced flywheel, a stator with proxies that wont fit under the crank cover and no ignition system or correct pistons or head. by the time i managed to figure out what i needed to do to make it all work everything i was sitting on except the athena kit was basically anchor weights.

[JonW]

Got them from Wicked Motorsport with the rest of my Athena setup. Like i said it could have been 180x2, but i did sell off the Athena units for just over $100 on good ole ebay so got some money back.

[JonW]

Just seen your edit g0zer, I thought you were one of those who had done an Athena, my apologies. Sounds like the stuff you had was the old TSS stuff that Steve was talking about sending out replacements for, might be worth an email in that direction.

[marlow]

Must admit this forum is alot easier to read the the one your project is in, colours do my eyes in lol.

Yeh so it seems there are plenty of complications that arise with the build such as the heat problems and other nit picky things, but you would think that if the conversion has been done enough there would be standard parts and methods a given tuning company would use therefore minimising labour costs. I'm not sure if the Gibson farm has any experience with this particular upgrade but I know Stan Stephens has delved into 611cc Cub stuff, he is probably the next one nearest to me albeit a 2 hour drive or so.

I am wanting to get hold of whoever this is yamaha rd350lc rd 421 banshee - YouTube Just listen to the rasp from those pipes as he floats by, a rarity I find hard to come across even on plenty of tuned banshee videos. This is obviously in the UK and finding people closer to me who have done this mod is probably essential.

[JonW]

There are too many permutations to have many standard parts for builds like this i think, but talk to Wicked, thats what i did and he supplied most of my kit as a package hence why i went that way.

Stan was brunt by the cheetah guys i think and was down on them in a mag article i read, what he thinks of 421s i dont know. Check the uk forums as many guys have some kind of issue with him. ive not used him so cannot comment.

That bike you show on youtube is Chris' bike, its on the same forum as mine, further down the page, he is christyres on there. Him and smads have built some rockets but i dont think Chris' bike is an Athena, its a resleeved basnhee. Hes a good lad tho and will help you if he can.

[JonW]

Chris' bike = sex on wheels imho: 2 strokes and i'm done - Login

[marlow]

Oh brilliant so he is around then! I'm almost banking the noise of the bike is down to those tiny end cans, love them pipes need to find out where he got those! Cheers for that

[JonW]

i think he says in his or smads build threads where the pipes come from...

[marlow]

This dream is becoming really drab now. I'm not getting a good response from Gibson who says he has little experience with Athena kits but has tested a few customer's bikes and hasn't been impressed with any of them. So I've now asked his opinion on the best way of getting 90hp from a YPVS lump and see what he says.