What did you do today? Cobba's rebuild

[dandywarhol]

So does someone manufacturer pistons with a different gudgeon pin boss position to accommodate the long and short rods?

How about the effect on primary vibration with the longer rod?

[cobbadiggabuddyblooo]

Thank Dandy..
Your all heart mate...
The main aim of this latest research over the past few months is in relation to timing the cams.
The stroke and rod length is something already set by the dynamics of the motor design and understanding there are certain boundries that you need to work within on how to tune the cam timing to optimize the output your looking for.
Do I really want to go into the physics of it all with rod length and stroke... No
Reading about that earlier in the month I had dreams that night about farting and different resonant frequencies with a hard on compared to a soft on...
But I've learnt so much about cam timing I can appreciate the time and effort put in by Ulf and Hubert and the research and development with the profile on the cams I have now specifically for the TRX.
This link will give a basic summary on farting and rod length.

The epi-eng. link under the rod length drawing on the previous page has a couple of good graphs on secondary piston vibration from different rod lengths with acceleration and velocity thrown in for good measure.
http://victorylibrary.com/mopar/crank-bal-c.htm

[dandywarhol]

Ya like this cobba?

http://www.intmath.com/cg3/curve-shape- ... applet.php

[cobbadiggabuddyblooo]

New cams arrived today and this photo will give you an idea on how the 0.5mm of material from the base circle is ground off to give you the extra 0.5mm lift.
Reground cam left, std cam right.
I'll shim them up in the head over the next week but I'm interested in fitting stock cams first and just getting the exact timing points at 1 mm for a little reference data while the head is on the bike with an old used std MLS head gasket.
I can practice my timing skills before fitting the new cams too then place the playdoe on the pistons so I can do a dry run to check my clearances once again.
The other noticeable thing is the new cams are 62 grams lighter. ( total of both ) So about 4% lighter on both inlet and exhaust.

[cobbadiggabuddyblooo]

Photo shows the cams at 3.2mm exhaust and 2.2mm inlet lift which is around where the cams will sit at TDC and the overlap valve to valve clearance.
Peace of mind for all and those with 2mm oversize valves and large duration cams , no need to worry about clearances between the inlet and exhaust valves.
But you should always check your piston/ valve clearance.
Next stage with the cams /valve clearances set is dial in the cams and check piston/valve clearances with the playdoe again.






With the exhaust closing and inlet opening I still had 3mm at the narrowest point after TDC with the 1mm oversize valves so you have a conservative 2mm clearance those ising a 2mm oversize valve.

[dandywarhol]

[cobbadiggabuddyblooo]

Note to self..
Look at resonant frequency on air intake causing dip in power curve around 3500rpm and overlap.
Carby tray to deflect engine heat and help seal under the tank and plate on top of frame by the headstock to feed under the tank.
Look at exhaust pulse with 270* crank causing leaner burn on no.2 cylinder.
Run 1 size larger main on no.2.

[Killerwhale]

Note to self..
Look at resonant frequency on air intake causing dip in power curve around 3500rpm and overlap.
Carby tray to deflect engine heat and help seal under the tank and plate on top of frame by the headstock to feed under the tank.
Look at exhaust pulse with 270* crank causing leaner burn on no.2 cylinder.
Run 1 size larger main on no.2.

Just as Max did back in the day...

[cobbadiggabuddyblooo]

Yes but the reason why is what I'm chasing.
There is a theory that because of the cam chain galley next to No.2 cylinder, the heat may not disperse as fast because of the way the water jacket is formatted on the cylinders.
What I'm looking at is because you have and exhaust pulse from No.1 you have a more efficient burn (more fuel/air= faster burn rate) and with the design of the exhaust, the pulse from cylinder 2 will not be in phase with cylinder no.1.
So more an ignition timing thing.

[Con Rod]

this is interesting cylinder 1 runs slightly hotter on mine as well, in spite of none of the normal variables

i would be inclined to correct it on the fuel screw rather than the main

[cobbadiggabuddyblooo]

Ignition timing may be difficult as you have no idividual map for each cylinder.
You share a common map with only correction for each cylinder but correction may not be needed over the whole map.
Fueling may be the way to go as a happy medium.

[Kenny]

You may also get some crank winding this will throw out the ignition timing too.

[dandywarhol]

You really think you'll get "crank winding" with a short stroke, one piece crank Kenny?

[Mincehead]

Nah, the movement could only be measured with some seriously finite measuring kit.

[Kenny]

just throwing ideas out there really bud