Yamaha TRX850 Enthusiasts Forum

For those that have had there head or barrels skimmed what did you do about setting the cam timing?

I'm getting 0.6mm skimmed off my barrel to bring the squish in line with what I want which will throw the cam timing out by about 1.2 degrees.

I was thinking of elongating the holes in the cam wheels so I could set the cams and then lock them up.
Has anyone done this before?

Or are they vernier cam wheels available?
If so where from?

To my knowledge there are no vernier drilled / slotted cam sprockets available `off the shelf` for the TRX (if anyone knows of some please update the thread and correct me ) but yes, having the bolt holes milled (slotted) so that the cams can be dialled in is definately the way to go for accuracy.
I`m certain others have already done this as there are a few camshaft profile varients around and available but I`m fecked if I can find any threads that milling / slotting appears on!
This thread might be of interest to you though:

http://www.trx850.com/phpBB_forum/viewt ... aft+timing

Mincehead wrote:To my knowledge there are no vernier drilled / slotted cam sprockets available `off the shelf` for the TRX (if anyone knows of some please update the thread and correct me ) but yes, having the bolt holes milled (slotted) so that the cams can be dialled in is definately the way to go for accuracy.
I`m certain others have already done this as there are a few camshaft profile varients around and available but I`m fecked if I can find any threads that milling / slotting appears on!
This thread might be of interest to you though:

http://www.trx850.com/phpBB_forum/viewt ... aft+timing

Nobody does slotted cams but it's not difficult to have them engineered. i didn't need any additional adjustment when I did mine

You WILL need adjustment if you drop the barrels that much.

I slotted cam sprox on a yoshi engined Suzuki I raced yonks ago - even went to the extent of making lil slivers of crescent shaped fillers in case the timing slipped but that was probably overkill - shakeproof washers and loctite did just fine

dandywarhol wrote:You WILL need adjustment if you drop the barrels that much.

Oops - didn't read teh inital post properly. he's right, you will

That's a lot BTW

But he's doing a 900 conversion from memory (what's left of it!)

People have been slotting cam sprockets since they were invented and I have never seen a properly slotted and secured cam sprocket move yet. Use a good quality rat tail file just slightly smaller than the hole diameter. Make sure the bolt, camwheel and cam threads are totally oil free and fit with locktite with some locktite under the head of the bolt also. Torque to specs only, do not overtighten. NEVER use any type of lockwasher under the bolt, introducing a soft metal interface between the bolt head and camwheel is asking for trouble. If your slot is going to end up longer than about 1/16 inch mark the cam sprocket with two lines from the original position so your slot follows the correct curve. Work carefully and remove the minimum amount of material so the bolt is a good fit in the hole radially. Check against the cam often.

dandywarhol wrote:But he's doing a 900 conversion from memory (what's left of it!)

OIC - thanks

Thanks for all the replies it's going to give me something to go at!!
I'm going to see how far out the timing is first before I go and do any slotting of the wheels. I do like the sound of the crescent moons for security though!!
The cam chain was new when I built the engine originally 2 seasons ago so it should not have stretched much, thanks for the link Mince.
The barrels have been machined now, my dad is going to drop them off with me tomorrow.
I may even go to the extent of getting the dial gauge out to check Yamaha's markings on the cams.
Will post back with the results.
Off to the shop for some thread lock!!

The machining is now done and I have bolted the motor back together.
The carbs and wiring are not done yet so no test run.
Checked the cam timing on the timing marks and it's so close I'm going to leave it for the moment and see what the dyno says.

can you put a picture of the modified camshaft ?

some say the modification should be about 3° +/- 1mm is that correct ?