Kent Cams question

[misterdimwiddy]

With an estimated 70mm cam sprocket diameter (have not got one in my hand), this gives 220mm sprocket circumference equating to 1.64°/mm of rotation.

With 0.4mm skimmed off the head, this will retard the cam timing by about 0.65° unless I have got my maths wrong.

[cobbadiggabuddyblooo]

Timing wheel are only a few bob and it's not hard to slot the cam sprockets.
You can just be complacent just like with your ignition timing, or you can get it to perform to the potential it has to offer as those have found who have fitted a prog ignition.
Just that little bit here and that little bit there all start to add up.
This also allows you to time the cams exactly for the output it is designed to produce.
Cam timing just like ignition timing can be manipulated for specific purposes too.

[QuickDraw]

I like the little plug' for the ignition units slipped in there Cobba'
One day mate, for sure.

Thanks for the calculation breakdown mdw. Makes sense to me. Good to get some perspective.

Perfection is the goal for some, and that's cool. But I reckon two thirds of a degree retardation will probably give me back 0.496384 Nm of the torque that I lost below 3875 rpm when I went to the bigger cams and heavier chain-oil.

[dandywarhol]

With an estimated 70mm cam sprocket diameter (have not got one in my hand), this gives 220mm sprocket circumference equating to 1.64°/mm of rotation.

With 0.4mm skimmed off the head, this will retard the cam timing by about 0.65° unless I have got my maths wrong.

You taking into account the 2:1 crank/cam ratio Mister? Cam timing is measured at crank degrees

[misterdimwiddy]

With an estimated 70mm cam sprocket diameter (have not got one in my hand), this gives 220mm sprocket circumference equating to 1.64°/mm of rotation.

With 0.4mm skimmed off the head, this will retard the cam timing by about 0.65° unless I have got my maths wrong.

You taking into account the 2:1 crank/cam ratio Mister? Cam timing is measured at crank degrees

Quite right

Please excuse my oversight.

[Rod.s]

As Phuk pointed out there is so little in it i can't see it's worthwhile, the Kent YAM9 re-profile is so mild that it certainly wouldn't warrant slotting the cam sprockets IMO. Had my head skimmed/flowed some 15 years ago & all is good without altering cam timing/slotting?

You might not see the worth, but I am sure EVERY quality engine builder in the world can It's not only the gain in torque/HP but the engines total balance and a reduction is vibration that is gained. Sonic vibration has been known to atomise fuel in carburettors, starving an engine within a small RPM range.

Horses for courses, if you an't got the right horse you gonna lose, then all you are is a horseless looser

[Rod.s]

I'm talking of skimming a head 0.25/0.40 mm to raise the compression - then you need to slot the sprockets

I hadn't thought of this ...good to know! Head-shave is coming up on my list in the next few weeks. How many cam degrees thereabouts would we be looking at?

Are you looking at skimming the head for the added compression or to true/repair the head?

[phuk72]

You might not see the worth, but I am sure EVERY quality engine builder in the world can It's not only the gain in torque/HP but the engines total balance and a reduction is vibration that is gained. Sonic vibration has been known to atomise fuel in carburettors, starving an engine within a small RPM range.

Horses for courses, if you an't got the right horse you gonna lose, then all you are is a horseless looser

If you are really concerned about that, have your crank balanced. How many people have paid out for that? Or actually bother to set the squish etc etc.

FFS it is a TRX road bike - not a race bike

[dandywarhol]

I'd be happy that Yamaha do a reasonable job on the crank and balancer shaft with stock rods/pistons. I'd say it's essential that the crank is rebalanced if aftermarket pistons/rods are different weights to stock

[phuk72]

I'd be happy that Yamaha do a reasonable job on the crank and balancer shaft with stock rods/pistons. I'd say it's essential that the crank is rebalanced if aftermarket pistons/rods are different weights to stock

I wouldn't be so sure about that .... but I completely agreed that the crank should be balanced if not using stock items (but I'd wager that most who have fitted 'big bore' pistons didn't)

[dandywarhol]

I'd be happy that Yamaha do a reasonable job on the crank and balancer shaft with stock rods/pistons. I'd say it's essential that the crank is rebalanced if aftermarket pistons/rods are different weights to stock

I wouldn't be so sure about that .... but I completely agreed that the crank should be balanced if not using stock items (but I'd wager that most who have fitted 'big bore' pistons didn't)

Do you think the TRX engine has a lot of vibration for a parallel twin?

[NWS870R]

As Phuk pointed out there is so little in it i can't see it's worthwhile, the Kent YAM9 re-profile is so mild that it certainly wouldn't warrant slotting the cam sprockets IMO. Had my head skimmed/flowed some 15 years ago & all is good without altering cam timing/slotting?

You might not see the worth, but I am sure EVERY quality engine builder in the world can It's not only the gain in torque/HP but the engines total balance and a reduction is vibration that is gained. Sonic vibration has been known to atomise fuel in carburettors, starving an engine within a small RPM range.

Horses for courses, if you an't got the right horse you gonna lose, then all you are is a horseless looser

Loser? Was there any need for that Rod? Personally i don't give a toss what you fellas do with your engines TBH. I was just saying that unlike yourself i have met SDN & know what he uses the bike for & it will not require slotting of the sprockets.

Some people shouldn't be allowed near the internet

[dandywarhol]

Whoah - lets calm down here!

NWS - you are an extremely well respected frame/bike builder and I'm in awe of your skills and projects - and have been for years.

I'm also respectful of skilled engine tuners/builders and I know of very few folks who are uber skilled in both disciplines. My interest is both chassis and engines but I only really know about engines - I can set up a chassis ok but would have difficulty building one = I put forward an opinion which I believe to be right.

Let's get this back on track and put forward what we think or believe is for the best and not just slagging off others..........................................

[misterdimwiddy]

I'd be happy that Yamaha do a reasonable job on the crank and balancer shaft with stock rods/pistons. I'd say it's essential that the crank is rebalanced if aftermarket pistons/rods are different weights to stock

I wouldn't be so sure about that .... but I completely agreed that the crank should be balanced if not using stock items (but I'd wager that most who have fitted 'big bore' pistons didn't)

I fear I may have paid the price for not doing this Still pleased the motor stayed together and didn't throw me through Craner curves on my backside.

Hey ho. It did go well while it lasted and my 5 yrs of TRX ownership has been tremendous fun.

Off to see a 2003 Tuono this Friday and taking a pocket full of cash and my trailer with me!

[NWS870R]

Whoah - lets calm down here!

NWS - you are an extremely well respected frame/bike builder and I'm in awe of your skills and projects - and have been for years.

I'm also respectful of skilled engine tuners/builders and I know of very few folks who are uber skilled in both disciplines. My interest is both chassis and engines but I only really know about engines - I can set up a chassis ok but would have difficulty building one = I put forward an opinion which I believe to be right.

Let's get this back on track and put forward what we think or believe is for the best and not just slagging off others..........................................

To be fair Dandy - i didn't call anyone a loser did i?

My head work was done by Rob Mathews - former head development engineer for Micron & founder/owner of RMD Dyno, a very respected man in the tuning world. The same engine has survived 15 years of road & track riding & is still making 95 BHP with TPS still connected.

As you said - i can only put forward an opinion which i believe to be right