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Camshaft timing


phil866

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Two options come to mind.

1) Buy a Haynes book and follow the instructions (don't remember it being too tricky).

2) Buy a dial gauge, set #1 to TDC then use the gauge to find the point #4 cylinders inlet and exhaust valves are equally open.  That's the point you want the cam with the crank at TDC.

Note: #2 is from memory and should be checked! :)

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Trouble is there are no timing marks on either of the new Cam or crank sprockets. I think I will drill through the old timing mark on the old cam sprocket, bolt the old and new to the old cam and punch duplicate markings via the drill hole.  As for the crank sprocket I can see no timing mark on the old or the new so I'm a bit stuck there!    Never mind, I'm a 'Sunday Driver' now!!

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Yes, using the flywheel is more accurate than using a degree wheel - but it's nothing like as accurate or as easy as using a dial gauge on the 7/8 rocker arms!

Again from memory but I believe it's...

1) If it's a running engine, skip to step 2, otherwise set the cam up as the Haynes book.
2) Find TDC and set up an accurate mark.
3) Set up dial gauge on #7 rocker arm and zero it.
4) Rock engine back from TDC until #7 is off-cam.
5) Read off the dial gauge to see how far open #7 is actually at TDC.
6) Repeat 1-4 on #8.
7) Change the cam timing based on the dial gauge number (i.e. if #8 is more open than #7 at TDC, turn cam to correct and either flip cam toothed-wheel or fiddle with your vernier wheel for the best match to that position).
8) Repeat 1-5 to check you've got it right/gone the right way.

There you have it - a perfectly (standard) times cam, regardless of overlap/duration, symmetrical/asymmetrical profiles, etc.  If you want to tweak the cam timing for performance then you'll need a lot of money or a rolling road in your garage!  (even then you use the same logic to adjust the timing by the desired amount, just aiming for a specific difference between the opening of #7 and #8 valves rather than an identical one).

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It's very simple assuming you don't have the gearbox attached.

Attach a stiff piece of wire to something at the back of the engine - make a loop and bolt it to the block.

Use a dial gauge on piston no.1 and find TDC.

Bend the piece of wire to point at a flywheel tooth - try and get it to the centre of the tooth.

You might want to rotate the crank backwards and forwards to make sure you get it correct.

There are 116 teeth on a Spitfire flywheel (there were on mine anyway) - which works out to 3.1 degrees per tooth. If you work out the half teeth then that's 1.55 degrees.

Now work out where your cam is meant to be timed - mine was 108 degrees - so that works out at just under 35 teeth. (34.8 to be more precise)

Then just rotate the crank and count the teeth.

Couldn't be simpler.

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Make sure you take your time - you can get it as spot on as you want. Make sure you double check everything - the only real thing that gets in your way is the chain and the slop - everything else is perfectly "mechanical"

Make sure you rotate the engine the right way... if you turn it backwards you will get slight errors (due to the chain)

When you've done everything up check it again.

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  • 4 years later...

In reply 6 - 13, point 2 is find & mark an accurate TDC.

Is this on both gear wheels or just the crankshaft gear wheel, also is it a good starting point to transfer the timing mark from the old cam gear wheel, by means of drilling a hole through it ?

Cheers,

Sam.

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