125 TZR Athena big bore kit on RD500 (684cc)

Message

solex27 · #1 Post by **solex27** » Sun Apr 06, 2008 6:39 am

Hi,

I'm studying a 2nd conversion possibility (instead of 3MA cylinder conversion) by using 4 athena DTR/TZR/TDR 125 big bore kit.
The manufacture is really good, reliable.
The piston is made by Wossner (Germany) and forged.
diameter is 65mm (165cc) with Nickasil bore.
So it give's same result as Gus conversion with the original troke 50mm stroke (684cc).
I need to find all information about the barrel dimensions (holes, distance between gasket plans....)
The main problem is the price, near 400 euros, so 1600 for a 500RD !!!

http://cgi.ebay.fr/DT125R-DT-125-TZR-TD ... dZViewItem

I'm waiting your ideas about.

Franck

BroLy · #2 Post by **BroLy** » Sun Apr 06, 2008 7:10 am

Hi solex,

I can give you my opinion, since here in PORTUGAL the Yamaha DTR 125 was the most sold bike for over 10 years, even against the 600 and 1000 bike market.

So, the young people here wanted to tune their DTR's 125 etc to be the best on their neighbour etc, the normal things.

A few years ago, stores started to sell the ATHENA kit, but the result was a disaster.
People assembled that kit, but there were no decent pipes for it, they fit DEP/RINO/FIREBOX pipes, but the performance wasn't good.

The reason is simple, the ATHENA kit PORTMAP is equal to the stock one, the only difference is the bore from 56 to 65, so obviously, the timings and port areas are complete shit.

It's the same for the Cagiva Mito 125 POLINI 64mm kit, portmap sucks.

The only chance to have a good ATHENA is, to reshape completely the portmap of the cylinder, but then you think:

"After investing 400

gus · #3 Post by **gus** » Sun Apr 06, 2008 3:28 pm

Solex, after traveling both roads I have 2 motors of big size (Mark at GP Customs has 1 of those) and yes they can be done but from my experience cyl. changes are not the way to travel unless you have a bunch of resources and machine shop equipment at the ready, I had numerous cyl. avail. and Rick Mammel machining anything I needed, and it was still a major undertaking with the layout of the 500 engine, that is when I decided to use what Yamaha gave us and just go bigger and alter the port timing and use whats available that will bolt on, stk cylinders, stk spacing, stock ex. location, stk carb location and so far it has been very easy, I have new billit heads being quoted that will work for 56-58mm domes or a change to 64-66mm bores along with the correct dome angles, new hi-flo reeds with intakes to accept 34mm carbs all to fit on the cylinders Yamaha put on the bike, and working with Bill Wilson on some pipes, I figure when I'm done I will have 130 RWHP and that may be a bit much for a stock framed RZ/RD anyway, myself I'm making bolt on stuff for the 500 or 643 I don't know just my 2 cents

Jordi YZR500 · #4 Post by **Jordi YZR500** » Sun Apr 06, 2008 7:18 pm

BroLy wrote: The reason is simple, the ATHENA kit PORTMAP is equal to the stock one, the only difference is the bore from 56 to 65, so obviously, the timings and port areas are complete shit.

It's the same for the Cagiva Mito 125 POLINI 64mm kit, portmap sucks.

Agree, I think this is a common problem with stock design rebored kits, any of the avaliable aftermarket pipes suits them neither the performance expected is the properly one from that displacement...

BroLy wrote: The only chance to have a good ATHENA is, to reshape completely the portmap of the cylinder, but then you think:

"After investing 400

Cut sentence BroLy...?

efgal2k · #5 Post by **efgal2k** » Sun Apr 06, 2008 8:21 pm

Hey guys
I'm rebuilding an RZ500 motor for my Spondon frame (I may have the last produced RZ Spondon),
Did anyone get a good result with a minimum mods. using a replacement cylinders or heads?
BTW since I race an Aprilia I know allot of you from the AF1 RS250 forum, It's good to see you here too.

Ofir

BroLy · #6 Post by **BroLy** » Mon Apr 07, 2008 8:02 am

Jordi I don't know what happened, lately my messages aren't posted 100%.

The problem with these 2-Stroke big-bore kits are:

- New sleeves with the bigger bore, but SAME PORTMAP AS STOCK.

In a 4-Stroke, you can install a big-bore kit, then you can guarantee an improve on performance, since the only things that could be dismatched are the valve diameter and exhaust/intake ports, but modern 4-Strokes have already good diameters for both valves and exhaust/intake ports.

Since they don't have portmaps, the problem is solved, more power guaranteed.

For 2-Strokes, most of the times, big-bores are synonym of decrease of power/performance due to bad portmaps, bad correction of head volume/squish, bad exhausts etc...

2-Stroke are very simple engines, but they are very difficult to obtain great performance from them, tuned that is.

For example, my KTM 520 EXC 4-Stroke, if I just simply put a big bore 610cc kit (bore and stroke increase), with my custom dual pipe, with a HotCams (even for stock engine), I would get around 70 - 75hp, even without other valves diameter, springs etc etc etc..

Jordi YZR500 · #7 Post by **Jordi YZR500** » Sat Apr 19, 2008 6:04 pm

BroLy wrote:Jordi I don't know what happened, lately my messages aren't posted 100%.

If I'm not wrong, as I had a similar mistakes time ago, I think is when using uncommon sign as inverted "!" "?" "/" or apostrophes or accents...

Jordi YZR500 · #8 Post by **Jordi YZR500** » Sat Apr 19, 2008 6:09 pm

efgal2k wrote:Hey guys
I'm rebuilding an RZ500 motor for my Spondon frame (I may have the last produced RZ Spondon),
Did anyone get a good result with a minimum mods. using a replacement cylinders or heads?
BTW since I race an Aprilia I know allot of you from the AF1 RS250 forum, It's good to see you here too.

Ofir

Hi and welcome efgal2k, also you can start a new thread introducing yourself and your projects/bikes.