What did you do today? Cobba's rebuild

[dandywarhol]

That makes sense Rod.s, it also shows the importance of a properly designed exhaust system to help get the gas out as effectively as possible.

It's my understanding that the total exhaust volume should ideally be a multiple of the total volume of the cylinder capacities. That way, on the TRX engine a "plug" of 424cc of gas make its way down the exhaust system and that same "plug" of gas leaves the tail pipe, causing a vacuum behind it; effectively helping to draw the next "plug" behind it to the exit.

As I said earlier - I'm enjoying this thread

[cobbadiggabuddyblooo]

Thanks for the technical input both from Alan and Rod, this is what I was hoping this thread will draw.
With my layman understanding that things are done a certain way for a purpose, I feel we may be able to turn this thread into an online PHD in trx850 engine dynamics..

I feel I need to modify the timing wheel set up though and find a longer bolt so i can fit it with the engine case on and drill a hole in the wheel so I can view TDC ..

[Trixed]

That makes sense Rod.s, it also shows the importance of a properly designed exhaust system to help get the gas out as effectively as possible.

It's my understanding that the total exhaust volume should ideally be a multiple of the total volume of the cylinder capacities. That way, on the TRX engine a "plug" of 424cc of gas make its way down the exhaust system and that same "plug" of gas leaves the tail pipe, causing a vacuum behind it; effectively helping to draw the next "plug" behind it to the exit.

As I said earlier - I'm enjoying this thread

I suspect this (vacuum) is the reason the Nojima exhaust is a two into one into two. The middle one being a cross where the gases are crossing each other at high speed. As a result the right cylinder gases end up leaving through the left can and vice versa. Also the the system is 18 kg lighter than stock.

[cobbadiggabuddyblooo]

Brakes on hold due to being too muggy so back into the air conditioning.


I found a bolt long enough to screw into the crank through the I.O. in the centre of the Alternator engine case.
I drilled a hole through the disc so I could view where the TDC mark on the rotor lines up with the mark on the case and remounted the disc with an old wheel spacer.
The spacer was long enough to sit on the crank and protrude out of the large central I.O. by 20mm, just enough to mount the disc and have clearance away from the case.



Now I just need to mount my pointer for the wheel and make up a mount for the magnetic base for the dial indicator...

[Rod.s]

Bravo

[phil108]

[dandywarhol]

That makes sense Rod.s, it also shows the importance of a properly designed exhaust system to help get the gas out as effectively as possible.

It's my understanding that the total exhaust volume should ideally be a multiple of the total volume of the cylinder capacities. That way, on the TRX engine a "plug" of 424cc of gas make its way down the exhaust system and that same "plug" of gas leaves the tail pipe, causing a vacuum behind it; effectively helping to draw the next "plug" behind it to the exit.

As I said earlier - I'm enjoying this thread

I suspect this (vacuum) is the reason the Nojima exhaust is a two into one into two. The middle one being a cross where the gases are crossing each other at high speed. As a result the right cylinder gases end up leaving through the left can and vice versa. Also the the system is 18 kg lighter than stock.

It shouldn't matter if its a 2:1 or 2:1:2, as long as the tuned length/volume is correct

[cobbadiggabuddyblooo]

Brakes on hold due to being too muggy so back into the air conditioning.


I found a bolt long enough to screw into the crank through the I.O. in the centre of the Alternator engine case.
I drilled a hole through the disc so I could view where the TDC mark on the rotor lines up with the mark on the case and remounted the disc with an old wheel spacer.
The spacer was long enough to sit on the crank and protrude out of the large central I.O. by 20mm, just enough to mount the disc and have clearance away from the case.



Now I just need to mount my pointer for the wheel and make up a mount for the magnetic base for the dial indicator...

Bit of research...Thanks to Mark's post on Kent cams
The guy who set up the head lost the book from Kent that came with the cams so I downloaded the info from the Kent Cams site and shuffled through a few of Sanddunes51 posts on his rebuild.
So I've compiled this info and scribbled it down as a reference..


So what does all this scribble mean it doesn't say what's printed on the timing wheel... Then it struck me The timing wheel has been marked to suit a CLOCKWISE rotating crank and the TRX CRANK ROTATES ANTI CLOCKWISE

Next step was to mark my INLET valve opening at 1mm..... inlet Centreline.... and inlet closing at 1mm on the timing wheel.
I used ORANGE play doh to mark the 240 degrees of rotation from 15* Before TDC to 45*After BDC.
That equates to the 240mm duration with the valve 1mm from the valve seat.
Lobe centre angle was marked at 105*After TDC

I then marked the EXHAUST with BLUE play doh which was 49* Before BDC and 11* After TDC.
Centre angle 109* After BDC which again gives me 240* duration at 1mm lift


You can see the valve overlap either side of TDC where both valves... inlet 15* before TDC and opening plus the exhaust 11* after TDC and closing are open 1mm. WHEN ROTATING ANTI CLOCKWISE



Now my brain hurts so back to Holy Flying Circus on the tele...

[cobbadiggabuddyblooo]

Now I can get a visual perception on how the inlet and exhaust valve work in relation with each other..
Just follow the orange brick road
What I can see now too is where the factory timing marks are positioned is right where both valves are closed on compression stroke.
This is why the inlet and exhaust cams on No.1 are set up 180* and centre of the base circles facing each other.




So now I plan to remove the head from the motor and mount the head solidly on the bench so I can use a dial indicator and place my own timing mark on the cam to line up with the cam journal cap. I'll mark this at 1mm lift...
I plan to use the dial indicator on the valve head itself from inside the chamber and once i get 1mm lift, place a mark on the cam itself. ( These will be a number of degrees from the Yamaha punch mark)

So i now have a TDC mark to work from. Set the cams up as per factory spec using the factory punch marks and when I rotate the crank to my Kent spec lobe centre angles of 105 inlet and 109 exhaust, I should be able to rotate the cam within the slotted cam gear to meet my new 1mm duration marks.

When back at TDC on compression stroke, the factory punch marks may end up a couple of degrees from their original position

To give myself a ballpark mark, I checked where the lobe centre marks would be and,,,,and guess what, they are already indicated by the large hole on the end of the cam itself where the cam sprocket bolts on. But I still need to mark this point on top of the cam with the dial indicator method.

[cobbadiggabuddyblooo]

The only problem may be access to mark the cam beside the wheel so I wonder if it be easier to mark the cam and cap at the other end ????

[cobbadiggabuddyblooo]

Note to self..
GeofF Chesterton and head flow info.

http://www.tlzone.net/forums/performanc ... heads.html

[dandywarhol]

There's the assumption here that the Yamaha crankshaft TDC marks are accurate.

The only true way to determine TDC is with a dial gauge down the spark plug hole and even then there an be a couple of degrees of hit or miss due to the short stroke nature of the engine. As you know, a couple of degrees on the crank equate to 4 on the cams....................................

Great thread though - inspirational!

[cobbadiggabuddyblooo]

There's the assumption here that the Yamaha crankshaft TDC marks are accurate.

Yes that's true, I am and I feel confident for good reason.
Just checked how much from the factory TDC mark 1degree is and it's a noticeable amount when viewed. 1.5mm to be exact.
The rotor has a circumference of 540mm and divide that by 360 (being degrees) = 1.5mm. I don't think Yamaha could be that far out.

But I'll still do the piston stop method just to see if this differs and if I have enough extension on the gauge, I'll shoot for a piston crown reading too. This will only bolster what others have told me on the inaccuracies of the piston stop method.
It's nice to be advised but when you put it in practice it will dispel any concerns I may have.

It's like the Ralph and Herbie things from Cheech and Chong.
Looks like dog shit, Smells like dog shit, tastes like dog shit..mmm lucky I didn't step on it..

[dandywarhol]

The only way I've accurately (as possible) determined piston tdc is the dial gauge on the piston crown method - and carefully moving the crank through the "dead spot" until the gauge moves in both direction and effectively halfing the rotational distance on the degree disc. We can get a bit anal about it until we realise that extra bit of plum pudding at xmas will make more difference than the mass production inaccuracies of mass production

[Stankflapper]

Play Doe... Love it! bwhahahaha