Posted by: nwracing | August 28, 2012

Camshaft timing – or how to drive yourself loopy!

One of the jobs I detest more than anything is checking the camshaft timing against manufacturers specifications. For some reason I seem to tie myself in knots and usually have to go and have a lie down. However, I am sure I’m not on my own so I’ve put together a description of how I go about it. I intend to do this in a couple of blogs to keep it simple, for me!!

First things first; to do this properly you need the right kit. Degree wheel, (the bigger the better), piston stop and dial gauge with stand. Most of this is now relatively cheap and a quick search on ebay should see you alright. Now there are a number of steps to doing this and I hope to show on Andromeda’s engine what we did.

Step 1: establishing Top Dead Centre (TDC).  Make sure you have the cam and timing chain or gears installed. Then mount your degree wheel to the crank.

Degree wheel mounted on crank.

Tighten the crank nut enough so that the wheel does not move when you turn the crank in either direction. Next mount a piece of wire, (mine was part of an old coat hanger!) somewhere convenient and bend it so that you can read the degrees on the degree wheel.

Then fit a piston stop. Mine is a fancy shop bought item but you don’t need this, a piece of angle iron will do with a bolt in it. Wind the bolt a short way down so that the piston will stop before it reaches TDC. Turn the crank until it meets the bolt, it should be touching, don’t force it or you could hole the piston. Read off the number of degrees shown by the pointer on the wheel, in our case 38 degrees. The rotate the other way and read off again, in our case 34 degrees.  TDC lies between these two readings. So as there is 4 degrees we halve this and this gives us 2 degrees to be added to the smaller of the two. Now bend the wire to read 36 degrees. If you’ve got it right you should be able to rotate the crank either way and it should show 36 degrees. If you take a look at the picture you will see that I have miraculously got it at 0 degrees.  As I’m a simple soul I like to work from zero so install another pointer below the one I used and zero this one. Now if you think you’ve made a mistake get your other bit of kit, the dial gauge and stand out and mount on the engine.

You can see how I’ve done mine. Set the dial gauge on top of the piston and then rotate clockwise until the gauge tells you that you have moved the piston down the bore by about 4mm, the read the degrees on the degree wheel. If you keep turning in the same direction until the piston comes up again and the dial gauge reads 4mm. Read off the degree wheel and you should have the same reading both sides.

All this to find Top Dead Centre, but it is massively important and trust me, don’t make the mistake I did once and rely on the timing mark and the pointer fitted to the engine. I was only fortunate that I caught it before real damage was done.

Next time cam timing; Cam overlap and cam centreline and all the other weird terms I will try to explain.


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