What did you do today? Cobba's rebuild

[cobbadiggabuddyblooo]

Yes I used the dial gauge to get the valve lift at TDC on overlap to start>
As above I worked out I needed to remove aproximately 2.2mm to retard the timing on the inlet so removed the sprocket and elongated the hole by 2.2mm
I then used the dial guage once again to check.
The cams themselves have 3* less duration on inlet and exhaust than the V2 but they have an extra 0.2mm valve lift (8.5mm) with an assymetric grind.
Pretty well much the same as a V2 with same lobe centres just the 3* less duration is offset by the extra 0.2mm lift.

[cobbadiggabuddyblooo]

Looking at the overlap and valve lift at TDC and the flow charts things start to make a little more sense too.
Valves set at TDC on overlap are 2.3mm INLET and 3.2mm Exhaust. (around 40* overlap)

The inlet around TDC has a good healthy 15% increase in flow and not far of the potentual flow but then you look at the exhaust and you can see the exhaust valve at 3.2mm has around 20% better flow and right on potentual flow.
This potentual exhaust flow continues from 5mm down to 3.2mm which during overlap is right where the inlet valve is opening.

The exhuast is goin to be sucking as hard as it possibly can matched with the equally excellent intake flow figures this allows for 100%+ volumetric efficiency equally matched with the Akra system to promote the tuned midrage nature of the exhaust and choice of cam timing.
As mentioned I'm sitting basiclly at the same specs as the V2 opening and closing values in overlap.

If I then look at the dyno chart, I could see around the 5000-6000rpm mark I need to retard the timing here and flatten it out at 7500rpm.
Right where the tuning for the exhaust is.
This may have been the culprit with the sealing issue with the copper head gasket from too much cylinder pressure from the slightly advanced ignition timing at these points.







The dyno result shows the green line with the map below, but I increased the timing by 1 degree 8000(33*), up to 2 degrees at 10,000.(34*)
The red line shows the whole map at -3 except I left the map flat from 7000rpm .(32)
You can clearly see the advantages of retarding around 5000 and flattening it at 32* from 7000
I'll move the timing points around to give me extra so I can soften the curve from 5,000(27* to 32*)-8000

[cobbadiggabuddyblooo]

So here is the map I've settled on as my starting point.
The tps map I've retarded values here too with 36-37* peaks

[Mincehead]

Looking good mate, looking good.

[cobbadiggabuddyblooo]

Thanks Mince..
In hignsight I should have ran the bike with the TPS turned off while sorting the air/fuel and done my dyno runs with it off first. Advance curve was too advanced above 7500rpm, and this is what I feel was causing the excess cylinder pressure and the copper head gasket to break its seal.
It wasn't until I began to ride it long and hard then it would leak.

Wouldn't be surprised if the excess heat from advanced timing and tight piston/bore tollerence took the ceramic coating from the skirt.
Good testimony to the strength of the Arias forged Pistons and the sacrificial lamb being the ceramic coat on the skirt.
New rings, plateau hone and skirts recoated so I'm thinking I might try the copper head gasket once again. In theory the copper head gasket will cope with the higher compression..

[cobbadiggabuddyblooo]

http://www.enginebuildermag.com/2001/08 ... -problems/

Confirms my prognosis with the piston skirt scuffing.

[Mincehead]

Yep, interesting read that mate.

[cobbadiggabuddyblooo]

I could feel the motor above 7500rpm begin to pull back so dere I say the increase from 32-33* was leading me into the start of detonation.
This point is a harmonic to the tuning with the Akra system and the dyno results show a 2* retarded spark is needed around 4000 - 5000rpm, due to the scavanging cramming in more Fuel/air mix and a denser mix burns faster.
You could see the slight gains in torque too from 7500 on the dyno on the -3 degrees run.
So I can see I hit a brick wall with maximum advance at 32degrees.
With more duration and more lift with the new cams I feel this maximum advance will be lower again so I've settled on this as my starting reference on the next dyno run modelled around the Akra system.



So I'll store this program plus the previous revised map posted into the Ignitech and an A-B dyno run between the 2 maps will give me something to compare against.
The last 2 maps are very similar just I've dropped the max advace to 30* and a touch more retard in the midrange on this last Akra model map.
The Over systems really start to scavange from 7,000 rpm so you can really see how ignition tuning to the exhaust and not only your cam tuning can rob you of valuable torque and horsepower.
Another reason why you really should try to match your cam tuning to the exhaust too.

[Mincehead]

A level of tuning science most of us never get into mate, fair play to you for your continued expansion of your mind. You should think of going into business with a dyno you know.

[cobbadiggabuddyblooo]

Next quest on the learning curve is about the TPS values.
The advance curve once set is at wide open throttle ( WOT ) but when using 10-20-30% throttle the charge is less dense and burns slower hence the TPS signal to advance the timing to deal with the change in charge density.
So I studied the snap shots that where taken on the dyno run too which are taken at 60, 80, 100 and 120KPH.
You can see the snap shots are taken in seconds and your RPM values, speed, HP, torque, air/fuel and lambda readings.
Here your influenced by your main jet/needle settings so once an optimum needle position is chosen, snapshots taken with TPS OFF then TPS ON should guide me on how far is too far on TPS advance values.

Your advance map on the Ignitech at the bottom shows your RPM and TPS valves. Now if I can find a way to take the TPS signal from the Ignitech and incorperate this with the dyno software it would make life just that little bit easier than reading from the computer screen when setting snapshots.




Handy link if interested Mince..
http://www.dyno.com.au/index.php/dynote ... rosoftware

[Mincehead]

Cheers mate always interested in such stuff.

[cobbadiggabuddyblooo]

Today I decided to spend a couple of hrs tidying up the tail end of the bike.Ive chosen to keep the std trx cosmetics but just refine the lines a little. Finally got around to fitting the carbon hugger and tail tidy and tomorrow I'll recess the tail light further in under the dove tail.

[cobbadiggabuddyblooo]

Tucked in nicely to give me the finish I was after.
Next Ill fold up a alloy plate to fit under the guard and Ill incorperate the tail tidy/ number plate mount to seal the tail from moisture.

[Mincehead]

I know R6, R1, GSX, even MV tail ends are `fashionable` on TRX`s but like you I really like the look of the original.

[cobbadiggabuddyblooo]

Can't agree more mince.
I thought about bastardizing it with a R6 front fairing but I still have all the original tank and cosmetics in excellent condition and it will be a nice feeling giving litre+ bikes a good run for their money on an old dog TRX...

Marko has offereed to take the bike down to Dave Kellett Motorcycle Engineering and I'll double check all is in alignment and remove a tiny flat spot I put in the front rim on my last trackday, so this will motivate me to fit the engine back in the frame this week.

I'm thinking I might fit all the engine cases and waterpump I have from a black import motor.
Keeping the bottom sump, crank cases, barrels and head silver with a black top sump and cam cover to match the external gloss black engine cases. Just to be different.