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Cam Timing


Anglefire
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I decided to check my cam timing this afternoon - just as another theory check for my fast idle issue.

And I do think it is slightly out - but before I pull off the pulley and cam timing cover thought I would get some words from the wise. Then thought I would ask the question on here :lol:

What I've done is this:

Pulled the rockers off the engine, found the point at which no1 inlet is rocking and with my stuck on timing disk on the pulley, have zero'd my dial gauge with the cam at its highest point.

Then turned the engine one way until I read 5thou and then the other way until it again reads 5thou. At each point the gauge reads 5thou make a note of the angle - the mid point of the two angles being top of cam lobe I believe.

It looks to be about 2degrees out. 

I've then counted the number of teeth on the large pulley (from a picture off James Paddocks website) and I count 42 teeth. That gives an angle of 8.5deg per tooth - which is twice engine rotation so I guess actually 4.25 crank degrees. 

So given that, I can't improve on the timing? Or can I? I can't reverse the pulley as its the Canley duplex one and has an offset unlike the simplex.

So, its going back together for now. 

And I await the wise comments!

 

 

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Anglefire,

Surely we've had this conversation before?    Rather than fiddling with valves on No.1, look at those on No.6, and the "Equal Lift on Overlap" method.  You have a dial gauge, should be straight forward, although a second gauge makes is simples!

For a description of the ELoO method, see: http://sideways-technologies.co.uk/forums/index.php?/topic/7770-equal-lift-on-overlap-the-other-cam-timing-method/&tab=comments#comment-102167

John

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oyure checking the degrees at a known drop from lobe  max height   and halving  the marks  .,,,,should be fine  

i just measure off the rockers or use the feeleres big gap and check for equal rocker clearances , ive got a good few dti but the mag   base never fits anything flat 

ones a loose neck but that can move is not firm when the knuckles are all pulled tight 

so yes rockers off gives a good flat to lock the base on 

pete

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I've spoken to Newmans Cams today and the conclusion is, essentially, that as it's not a race engine to leave well alone. Being 112 ATDC rather than 110 means its advanced a bit so it will have the torque curve a bit lower down the rev range.

http://auskellian.com/paul/links_files/spitfire_cam_specs.htm

I might change my mind later on - but for now, I'm not going to worry about it and concentrate on getting the idle sorted.

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55 minutes ago, Anglefire said:

I've spoken to Newmans Cams today and the conclusion is, essentially, that as it's not a race engine to leave well alone. Being 112 ATDC rather than 110 means its advanced a bit so it will have the torque curve a bit lower down the rev range.

http://auskellian.com/paul/links_files/spitfire_cam_specs.htm

I might change my mind later on - but for now, I'm not going to worry about it and concentrate on getting the idle sorted.

Hello   Mark

                     112 is about right in my book as when the chain wears in (they do not stretch!) It will be as near as dam it 110 degs 

I read somewhere this what race engine builders do and I did that on Spitty and will do the same on the new engine!

Roger 

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Hi Angelfire,

i am new on this forum but I have recently done the Cam timing on my Spitfire mk4 with a standard stock cam, I keep seeing the confusing information which is very complicated and it relly does not have to be, if you have the standard stock cam (ONLY STOCK STANDARD) the following procedure will check if your timing is out.

You can does this with only the rocker cover removed however it will be difficult to rotate the crank nut but not impossible.

Step 1 - Rotate the cam until valve 8 (one nearest to the car windscreen) is fully open (other terms like as reached its highest point have been used). I carefully watched the valve stem (long rod) at the back of the valve goes no higher, take your time with this and make sure you have it right. Valve 1 is now closed to test this if you can slide the valve from side to side easily and rotate the valve stem the valve is closed. Now adjust the gap or valve clearance to 0.40.

Step 2 - Now do the same with valve 7 and adjust valve 2 to 0.40.

Step 3 - Now from there you should not have to turn the cam far to get the point of balance, with your feeler gauge you are now going to time the cam and get valve 1 & 2 clearance exactly equal. To begin with I closely look at the gaps between 1 & 2 valve to see if there were similar I used a magnifying glass to get a close up view, I had to move the cam (very slowly) clockwise & anti clockwise to get the gap somewhere near. With my feeler gauge I think I used 0.10 thickness (I am sure the thickness is not critical, the idea is to find the point of balance) to get the gap exactly equal. This took me quite a while although the gap was similar the drag on the feeler gauge was not quite the same, don’t be happy with just being close get it perfect. Once perfect I used my feeler gauge with a 0.09 thickness to check the point of balance for both valves 1 & 2 with this thickness you should be able to place in the clearance with very little drag and it should feel the same for both valves. Now with a 0.11 thickness feeler gauge you should not be able to insert between both valves. This is a good way of checking the valve clearance is the same. 

Step 4 - Now look at the timing marks on your crank the mark on the pulley wheel should be exactly at TDC

Another way of checking without doing the above is to place the crank at TDC and valves 7 & 8 should be exactly the same one about to close & one about to open they should look equal and you should not be able to rotate the valve stem, if either is not right timing is out.

Let me know if you need the full steps to replace chain and gears.

Hope this helps 

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On 26/02/2018 at 9:41 PM, Anglefire said:

John, I've just read your write-up - makes a fair bit of sense though I'm not sure how its better than using the cam lift method I've used (except I got it wrong of course!) - don't get me wrong, I'm not saying its not, I'm just curious!

It's not better, it's another method.     The advantages are that you do not need to have been told the Magic Angle by the cam grinder, and as PJ has just described (his method is another implementation of ELoO) you can check the cam timing just by removeing the rocker cover.    No need to get into the front of the engine, removing the chain cover etc.

John

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