Degreeing cam on 277 motor??

[Dannyh82]

Degreeing a rephased adjustable cam is beating me so far... can anyone put in simple terms how this should be done? I'm getting centre line of 84 on the inlet, when it should be 103, so assume my method is wrong as I expected it to be nearer. My TDC is 100% correct just the method of degreeing in the cam I don't get...

TDC is set

Measure degree either side of max lobe lift by 0.040

Add both numbers togeather

Devide what it equaled

= lobe centre line

Is this the wrong way for the xs motor? Maybe I'm reading the degree wheel wrong

 

[jpdevol]

Assuming a HHB rephase of a stock cam, I like to use left intake opening begining @ 36* BTDC. So, set the dial gauge on the spring retainer with some preload and rotate crank from 60* or so to look for movement @ 36* on the crank. On a stock profile an opening of 36* should yield a lobe center @ 106*ATDC. The left side of motor should be stock marks BTW.

If it's Megacycle go with their opening specs (maybe 21* if you're looking for 104* center)- I find it easier than dealing with lobe centers (that should fall in line once opening is set)

 

[Signal]

Dannyh82, I use a different formula for finding the lobe centres.

Try doing this:

Find the opening BTDC number

Find the closing ABDC number (wind the motor the correct way through the cycle)

Make a note of the smaller of the 2 numbers

Add Open and closing numbers, add 180, divide the result by 2

Subtract the smaller of the 2 opening and closing numbers.

The result is the lobe centre.

You can use this method with any or no lash and the valve can even be open a bit just be consistent.

I have done this a few times and to speed things up I wrote a basic spread sheet to crunch the numbers.

To start set the cam in the stock position, them measure and adjust. On the most common rephase the left remains stock and the right is advanced.

When making adjustments loosen the cam chain tensioner and when testing remember to tension it.

 

[Signal]

For the amount of valve movement I use 1mm ie record the degree wheel reading when the valve has opened 1mm and record the closing number when it is 1mm off the seat at closing. Again you can use any number as long as you are consitent.

 

[Dannyh82]

For the amount of valve movement I use 1mm ie record the degree wheel reading when the valve has opened 1mm and record the closing number when it is 1mm off the seat at closing. Again you can use any number as long as you are consitent.

For the amount of valve movement I use 1mm ie record the degree wheel reading when the valve has opened 1mm and record the closing number when it is 1mm off the seat at closing. Again you can use any number as long as you are consitent.

Very useful - my result is 93.75

 

[Signal]

I could be confusing myself (I end up thinking in circles with the 36 tooth cam and 18 tooth crank sprockets) but I think you are 1/2 a cam tooth out.

 

[Dannyh82]

Very useful - my result is 93.75

Does that mean it needs advancing or

I could be confusing myself (I end up thinking in circles with the 36 tooth cam and 18 tooth crank sprockets) but I think you are 1/2 a cam tooth out.

That could make sens as its got the adjustable sprocket on, so will adjust that and see where I end up. You have been very helpful. Thank you

 

[Signal]

Your cam is too advanced, retarding the cam the lobe centre number will increase.
or another way

retarding the cam means moving it so that opening events occur later.

moving the cam against engine rotation means moving the sprocket into engine rotation
So,Retarding BTDC numbers decrease, ATDC numbers increase (later in the stroke)...

These are notes on my spreadsheet that I have cut and pasted so the presentation is a bit rough.

 

[jay760]

https://www.xs650.com/threads/cam-timing-made-simple.56017/
You might want to read this

 

[Signal]

I got my notes on moving the cam sprocket from Grizld1's posts in that thread.

 

[Dannyh82]

I got my notes on moving the cam sprocket from Grizld1's posts in that thread.

Thanks to you I have managed to do it very clear concise instructions that I needed to understand what I was doing. Thank you!

 

[jay760]

Not sure if it says so in that thread but as you have an after market cam it's worth adjusting the tappets, taking the springs out and turning the head upside down with the cam in and rocker cover in place to check valve to valve clearance you need something like .50 thou or 1.25mm there abouts, it's a pain but costly if you don't and they hit, and they won't hit until you give it some revs pulling away one day

 

[Dannyh82]

Not sure if it says so in that thread but as you have an after market cam it's worth adjusting the tappets, taking the springs out and turning the head upside down with the cam in and rocker cover in place to check valve to valve clearance you need something like .50 thou or 1.25mm there abouts, it's a pain but costly if you don't and they hit, and they won't hit until you give it some revs pulling away one day

I managed to check this with a very small mirror, looks to be about 3mm clearance

 

[Dannyh82]

Ah I get you now, yes this has been checked

 

[Dannyh82]

Thanks to you I have managed to do it very clear concise instructions that I needed to understand what I was doing. Thank you!

I have 103 lobe centre for the inlet now so that's spot on, but my exhaust is 123.3? I take it you can only get one side at the specified centre and the rest are what they are, with it being just one cam?

 

[Signal]

Yes, with a single cam the lobe centres of the exhaust and inlet are fixed at manufacture. The advertised lobe centres should be correct for the inlet and exhaust lobes.

If your cam is from a reputable grinder I would suspect the method of calculating the exhaust lobe centre is wrong.

I have read that many regard the inlet timing is the most important event, and not knowing any better have always set the #1 inlet lobe centre and regarded it as job done.
I always do numerous other checks to ensure that there are no catastrophic mistakes.

 

[Dannyh82]

Yes, with a single cam the lobe centres of the exhaust and inlet are fixed at manufacture. The advertised lobe centres should be correct for the inlet and exhaust lobes.

If your cam is from a reputable grinder I would suspect the method of calculating the exhaust lobe centre is wrong.

I have read that many regard the inlet timing is the most important event, and not knowing any better have always set the #1 inlet lobe centre and regarded it as job done.
I always do numerous other checks to ensure that there are no catastrophic mistakes.

I set my left intake lobe centre to 103 as per your guidance and worked out fine at BTDC 49.5 and 23.5 ABDC, so I thought I will just check the exhaust and got - 70deg BBDC and got 3deg ATDC?? Unless like you say my method is wrong on the exhaust side.

 

[Signal]

I highly suspect your method is wrong.

"The method is the same on the exhaust except the opening number will be a value before bottom dead center (BBDC), the closing value will be after top dead center (ATDC) and again, subtract the smaller number."

Do an internet search for an article by Doug Meyer titled Cam Lobe Centres Explained. Origionally published in City Bike.
I have a word document copy of it but it is proving impossible to attach to this forum.
The article explains how to check exhaust lobe centres.

 

[Max Midnight]

I have a word document copy of it but it is proving impossible to attach to this forum.

Try saving it as a PDF and attach that.

 

[Dannyh82]

Well I have just double checked it and have 103 lobe centre intake and 123.5 lobe centre exhaust so I'm not sure if that's right or wrong but I did think they would be the same.