What did you do today? Cobba's rebuild

[Trixed]

[sanddune51]

Great work Mate

Keep the posts coming, I want to know all there is to about your little beauty .

Significant that you should have lightweight wheels, I resisted a very strong urge to buy Phil's slipper clutch, that I could put the money towards carbon fibre wheels (well, a man can dream )



Mark.

[QuickDraw]

Great to see it all together Cobba'!

[cobbadiggabuddyblooo]

Cheers Brett,
Be an interesting A-B comparission with your bike too both having the same forks and Ohlins rear .
The forks are full racetec modified with .9 springs, reworked cartridges to suit the Trx and gold valves on both rebound and compression plus the same offset and stepped billet trees to get me the same length and offset as the std Trx.
I'll head up your way sometime over the next few weeks as there's some great roads around you in the hills behind the Sunshine Coast.

[QuickDraw]

Sounds great Cobba'! I'm still flat out with work until the end on the school hols (13th). Then I've booked myself some time to fit the FCRs & rear kit. Tooooo busy I've been!!

[cobbadiggabuddyblooo]

A little more feedback after travelling 350 km since back together.
Stability, rock solid and no head shakes out of corners when hard on the gas.
I'm used to the light and nimble feel of the wheels now and have found no issues at high speed even on windy days. No issues I can feel of under steer out of corners with the 180 rear tyre too.
I will now push the forks 10mm up through the trees to see how it performs to just quicken the steering a little. In it's current position with the stepped top yoke, I'm actually at the same height as a std Trx .
So this 10mm should negate the extra 12mm or so because of the 70 series tyre on the front.
I already have 5mm shorter dogbones on which I found to be a happy medium between the std length and 10mm shorter yzf750 dogbones.
Before the rebuild I found the bike a little flighty at high speeds on sweeping bends with the yzf dogbones Inplace .

1 thing I can feel now especially with solid pegs is a tapping sensation from the rear end.
I'll bet my bottom dollar this is coming from the loose fit of the suspension mounting bolt and bushes.
Even though all new bearings,bushes and bolts where used, the tollerence between mounting bolts and bushes was pretty sad and sloppy from std
Others from suspension specialist have said the same about Yamaha in general with loose fit tollerence on shock/relay arm /dogbone mount bushes and bolts.
Although its not really enough to effect day to day handling, I can see this being a good starting point to introduce rear wheel chatter if pushed really hard.
Just a real annoying feel through your feet tho.

Wavy discs certainly have some extra bite and grabbed a handful when a car popped out in front of me and locked the front wheel for a second to a hollowing screech.

[cobbadiggabuddyblooo]

Rebound tuned in, forks up through the top yoke 14mm and time for a ride up over Mt Glorious ad down the other side. Compression tuned in on the ride up the mountain to the cafe,quick Latte and then down the other side.
Those who have ridden over the mountain will know it offers everything from tight hairpins, hard braking and some good sweeping corners down the other side till you reach the Wivenhoe Dam/Summerset Dam Tee intersection.
Then turn around and do it all again going up hill and the only fault I found was as per the photo.



While on the downhill ride, I caught up to a couple of other bikes and through one of the flip flop sections which dips in the middle, I though it may have been the sidestand scraping but here's the culprit.
The Akrapovic pipes sit off centre and a little to the left hand side under the bike and the O2 sensor bung for the L/H exhaust found the ground first.
So next time the pipes are off, I'll grind the bung on an angle to give me the clearance I'll need.
It was a fast flip flop and a good low spot between them and full credit to the suspension soaked it up beautifully and kept a nice line all the way through even with the scrape.
There was a couple of corners I came in a little deep and even under brakes with those pesky hollows working the suspension into the corner and trying to stand the bike upright, again I could feel the wall of the tyre soaking most of this up and still keeping the line I needed and if I had the std rims, I d have a bit of a fight on my hands.
It's these times you can really notice the difference with the lighter weight wheel as well as the drive out of the corners. Plus building suspension specific for the bike, rider and task at hand.
This also is when the Akrapovic system is working to it's full potentual with over 5HP gains at 4000rpm on a stock motor in the twisties it is in it's element. I'm looking forward to the added 15 odd HP ontop of the 85HP already on tap when the new motor is inplace.
A tip to all..
Go out and pick up a R6 throttle tube with the handlebar body from a wreckers as they have a 60 degree action compared to 78 degrees on the std TRX.
Riding in traffic is a breeze and no stress and any feedback you may have read about this making it harder to ride in traffic and when on off throttle is needed , I actually found it a lot more comfortable and easier with the wrist action and fits using the std cables .
So do yourself a favour and track one down, you won't regret it..
So overall suspension and wheel modifications , I can not be happier and look forward to the next track day.

[Mincehead]

Well Brian, you might not be the Messiah but you`ve grown some in technical knowledge that`s for sure.
Oh and Rod, yes, I think it might have been me that mentioned 25mm as rake and somewhere in my addled grey mass a figure of 23.5mm comes up for those beautiful NWS alloy frames.
VERY well put together thread, muchly enjoyable to read too.

[cobbadiggabuddyblooo]

Thanks Mince,
Yes I used that info from NWS frames thread, spandontrx and your input on the stepped yoke for the r1 forks , input from Kaylas threads and so many others and compiled that wealth of information to engineer a really nice Trx and hopefully make others aware of the potential of these old dogs.
Credit goes to Tony Foyle and Graham Bell as I leant so much on the principals of frame and motor design .
I don't sit behind that mixing console any more but engineering is engineering , just instead of attacking a graphic or cross over , compressors or gates, its now flow rates, pulses , timing and harmonics in just another format. But the principals are the same.
And yes , I am still a naughty boy..

[cobbadiggabuddyblooo]

Another400km ride done yesterday heading out along the Woodford/ Beerwah road with some good fast sweeping corners through the countryside and down the Peachester range to Beerwah where I caught up with Brett on his TRX also set up with an early R1 front end.
Back up over the Peachester range and throught to Melaney and onto Kennellworth to the cafe for a chinwag and coffee.
From there over the Obi Obi range and down to Palmwoods to Bretts place.
He gave me a heads up on a good twisty road to get from his place to Landsborough then up the range to Melaney again.
From there along the top of the range with those fast sweeping corners again till we get get to another few KM's of range riding up and down again and on to Woodford once again. I couldn't help myself and from there I chose to head back via Mt Mee and Dayboro range all the way to Clear mountain and finally for the last 30 minutes of traffic till home once again.

A lot of those Km,s are 2nd/3rd gear twisty s mixed with flip flops and tight 50-60kmh corners and a few hairpins thrown into the mix. After our coffee break, Brett and I swapped bikes and the first thing apparent was our different riding styles and set ups accordingly on the bikes. Brett has a similar riding style like I used to use for a number of years until not long before my rebuild which I used to discribe.. Ride the TRX like a chook chaser back in the saddle and use your hips/legs and just give the bike it's own head .
Bretts bike easily reflects this with it's fast steering and it felt like everytime I blinked this movement was passed through to the bars.. But lately I've found myself riding a bit more aggresively, a bit more like Dovizioso with later braking at the sacrifice of a little slower corner speed. I even adopted more of a Ben Spies style grip which is can be discribed like a screwdriver grip on the bars with elbows out and body up against the tank instead of laying ontop.
I found this to be excellent if braking in through the corner especially if bumpy or the road is a little corrigated or grooves trying to track the wheel. This needs a bit more heavier damping set up but with Bretts bike with the damping set a little softer on the front I found myself slowly sliding back into the saddle and adopting a bit more of my older style of riding.

So what I learnt or moreso reminded myself from the day was what may suit one rider my not suit another on set up as is all comes down to the style of riding and how you approach it.
No 1 style is right or wrong as a number of world champion racers all, have their own approach to riding.
My first mistake tho was once the motor was in the frame and mobile I just rode the bike and didn't set up the sag so I've gone with a little more spring preload set up on the front and to chase my tail, I've came to a really good set up if heavy on the front end is what I'm after but at the sacrifice of that damping of the softer smaller bumps.
So it may be a good set up to just jot down for my trackdays but for street/road use I have to as I should have known..
Set up my sag to start..
Thanks to Brett for allowing me to ride his bike and the food for thought from the days experience on riding style and again reminded me on how I should approach what I want out of the new front USD R1 front/ Ohlins rear set up compared to the std RSU forks and R6 shock rear from before.
So back to the drawing board , set up a starting point with sag and feel what is the most comfortable riding style I want to adopt and set up the suspension accordingly..

[QuickDraw]

Brilliant ride alright. Thanks Cobba'!
I was amazed too, at how two bikes of the same type with fairly similar hardware (apart from your wheels of course!) could feel so different. One of the things I've always loved about the TRX is how well it is suited to making the bike "your own" in terms of setup, for sure.

Jumping from yours back on to mine, I'm keen as mustard now to even-up my springing front to rear (after I've fitted Kev's Ohlins rear-shock unit). And to junk those CVs and get his old FCR's bolted on!!! I knew my girl was gasping for a drink, but I didn't know how much!

[Tarwetijger]

So QuickDraw, tell me, does he talk that much in real life too?

[QuickDraw]

Nah. He barely says "Boo!"

[mik_b]

Hi Cobba (&others reading),
Mik_b here. It's been a while since I visited the site & am now very impressed at your engine build, a very good read and also very inspiring. So much so that I"ve finally dropped the engine out yesterday and have it up on the bench ready to whip off the head and see about a skim and a squish band measurement. What is the consensus nowadays as to the appropriate measurement? A few months ago some people advocated 30 thou and some disagreed saying it was too tight. I happened to be passing by a performance engine building shop (auto) the other day and asked them the question, they said 30 thou is ok for a performance motor that comes apart regularly but otherwise 40 for street use. I'll go for 30 if thats what people are using without incident. What did you use Cobba? I liked the look of your pistons, where can I get some & what price? I'm torn as to how far to develop the motor as its only done 65k. If I end up taking the barrels off (in order to achieve optimum squish) I just might send the pistons off for the ceramic / friction treatments. Also very interested in a set of the bigger valves if there are any still around (??) as you never know, I do love my classic racing and never miss the Barry Sheene Memorial event at Eastern Creek and now that the rex is eligible I just might get out there ! Cheers Mik.

[cobbadiggabuddyblooo]

Hi Mik,
The squish band is something I'll be discussing with the mechanic who again has the head, barrels and pistons to finish installing the valves- spring -cams and to cc it all.
I'm also looking into maybe having copper head gaskets made .
The motor currently in the bike is a spare I purchased to get me mobile so once I start assembly I'll have some further information on this.
Piston and Carrillo rods where sitting in a blokes cupboard for nearly 15 yrs and his mate at the time was racing TRX's . He was to put them in his own Trx but the 900 TDM came out so he chose to get 900 barrels and rods and they had been collecting dust in his cupboard ever since.
QuickDraw and sandunes both have raised compression with std pistons to around 11.5:1 and you can see how they approached this on their own threads on their own motor rebuilds.
So I'll have some more info on this subject soon.

But soeme light reading as a reminder in the mean time
http://www.motorcycleproject.com/motorc ... crets.html