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John L

Camshaft timing

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Further to my recent question about cam chains, I'm trying to get my head around cam timing.  There are some items I need to fully understand, learn. Please correct if I'm wrong.

Cam lift, is measured with a DTI on the push rod and records the moment the cam lobe starts to lift the cam follower.

Valve lift, is when the rocker arm touches the valve stem taking out the set valve tappet clearance and the push rod is just tight to turn.

The original PI valve timing is listed as 35 65 65 35.  Are these the actual points that the valve starts to open and close as in valve lift above?

I'm battling to get a new camshaft timed to the spec sheet that I have been given for the cam, I'm beginning to think that the 2 are not matched to each other, or I'm not fully understanding the sheet given.

The cam sheet gives a figure of 0.032" inlet valve lift, crank to TDC, then fit chain, but it doesn't  then correspond to the valve opening figures listed, turning the crankshaft to the points required is missing  by up to 5 degrees for opening and closing figures,  

The new HD chain is very tight to slip over the protruding knob on the cam, and so very little slack either side, not like before, so not sure if this is correct, new parts again...….?

John

 

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I use the Fulllift method...which is at 105°.... try that....

The timing numbers are always considering VC. This actually means, reducing VC you can change your timing.

Jochem

 

Edited by JochemsTR

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Jochem,

So the timing sheet I have quotes 0.250" cam lift, inlet and exhaust,  It quotes 110 degrees cam peak difference, and a cam duration of 276 for inlet and exhaust.

So how do I set the cam and crank with these figures please, or do you need some other numbers?

The other numbers quote are  68 degrees exhaust valve opens BBDC

28 degrees exhaust closes ATDC

28 degrees inlet valve opens BTDC

68 degrees inlet valve closes ABDC 

John

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Hi John, 

from Kent Website: use your 110 degrees in following example: 

“What is 'Full lift' cam timing method?

For many years the most commonly used method has involved establishing top dead center (TDC) as a datum (zero degrees) and positioning your camshaft with its inlet valve at maximum lift at a given position relative to this datum.

For example take our Ford x/flow camshaft number 234 which has a quoted figure of inlet timing @ full lift = 103 degrees. This means that the inlet valve should be set to be fully open at 103 degrees after top dead center. Therefore using a protractor or timing disc you can establish 103 degrees after TDC and it is at this point that your inlet valve should be fully open. Minor adjustments from the standard timing point can be made with the aid of adjustable timing kits or an offset dowel.

I hope this helps, if not let me know.
Jochem

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You can type your cam timing data into this and then print out a timing disc that will glue to an old cd.

https://www.blocklayer.com/degree-wheel.aspx

 

cheers

Peter W

PS  is the head fitted?  If so remove the rocker gear so the valves cannot be pushed into the pistons due to incorrect timing.

PPS. installation figure is 110 degrees after tdc on the crank from the info you provided.   The inlet cam lobe must be fully open on cylinder no1(2nd pushrod from front).  When the crank is set to 110 degrees atdc.
So...
remove rocker gear.

Find tdc of crank and fit timing disc.

Set crank to 110 atdc.  

Using dial indicator- Set cam so inlet valve cam lobe of no 1 cylinder is at maximum lift ie fully open. 

Now without disturbing your cam or crank.   Loop chain on sprockets and fit.  ....Adjust cam sprocket alignment by turning to alternative holes.

Here is a nice instruction for 4 cyl TR but basic principle works for 6 cyl

https://www.macysgarage.com/cam degree.htm

Edited by BlueTR3A-5EKT

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I fitted the last two cams with the rocker shaft installed and #1 inlet valve adjusted.. The cam was a 41/71/71/41 and I locked the sprocket onto the cam where the #1 inlet valve pushrod just wouldn't spin with my fingers at 44 degrees BTDC as I wanted it 3 degrees advanced to compensate for wear ( which will reach 6 degrees eventually ).

That was easier than the " rock " method in the Bentley manual I'd done previously which gives the same result for symmetrical cams like yours appears to be.

 

Cheers, 

Tom

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There is something very strange going on here, if time up the cam with 0.032" lift on #1 inlet valve and set the crank to TDC fit the chain, if I then turn the cam to full lift and check the position of the crank its 10 degrees out.

If I check then the opening of the #1 inlet valve with the 0.014" tappet clearance,  as stated in the timing sheet, with the push rod just tight,  it is at least 10 degrees retarded, and not opening at 28 degrees as detailed.

If I also set the cam to full lift and check the crank position its 10 degrees retarded

Am I doing something wrong, or I'm beginning to think that the spec sheet is not what the cam is ground too perhaps?

Any suggestions as to what I'm doing wrong, I would be very great full, I'm beginning to think there must be something adrift or I'm bats!!  

John

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John, I can only speak for the Fulllift Method. How did you locate the cam in its Fulllift position? You need a dial gauge on the cam follower, timing disc and approach the cam from both lobe sides. Are you sure you have Fulllift position? After Fulllift you turn your crank to 110 degrees. Now hang up the chain und turn around 2 times. Measure Fulllift again and check whether you are within the 110 degrees with a maximum offset of 2 degrees.

If you have done all this, and there is still a retard.....your cam may not be to spec....is it a used cam? new from known suppliers?

Jochem

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