Timing the cam

I installed the crankshaft, cam followers and cam then installed the gearbox. First snag was that the crank was hitting something, so off came the gearbox! Eventually I found that because the cam was in a random position (no timing gear yet) the crank can hit the lobes, you learn something every day! Next job was timing in the camshaft, I have given some step by steps below because a few people asked how to do that. Once I got the correct offset key I assembled the timing gear. Its not usual with duplex gears but I used a tensioner as all that slop just does not look right, Apparently there is no definitive answer, you can fit it or not, best advice seems to be that if you do use one dont put a huge tension on it, just take up the slack.

The whole idea here is that it is difficult to find the maximum lift point of a piston or a cam lobe because it moves so slowly at that point. A much more accurate way is to measure the piston or lobe as it is on the way up (when its still moving pretty fast) and at EXACTLY the same point when its on the way back down. The maximum lift is in between those two points.

1.First you need to establish TDC so have a wild guess, it doesn't matter if its not accurate, Install your timing disk on the crank and a pointer pointing at TDC and then put a dial gauge on the #1 piston so that it reads about halfway through its range. Now pick a point on the dial a little lower than its current reading (I usually go 10thou lower) and note it or set the little index mark on the outside of the dial gauge, that will be the point where you will take the crank angle readings.

2,back the crankshaft off a little and start back towards tdc again and stop at your chosen dial Gauge reading.

3,Note the reading on the disk. here its 8 degrees btdc

4,Carry on rotating the crank until the dial gauge peaks and starts going down again, stop at exactly the same dial gauge reading

5,Note the reading on the disk. here its 4 deg atdc

6,The point exactly between those two readings (2 deg btdc) is TDC so turn you crank till the disk reads exactly that.

7, Finally turn the disk so that the pointer is pointing to TDC or Zero degrees. (don't disturb the pointer or the crank position!)

Now move your dial gauge to sit on the number 1 inlet pushrod. Now you do the same thing but this time you are finding the peak of the cam lobe.
1,rotate your crank until the dial gauge peaks and set the dial gauge ponter and pick your point on the gauge where you will make the readings.
2,back up the crank and then start towards the peak stopping at your chosen reading to note the disk reading (here its 80 deg atdc)

3,Carry on rotating the crank past the peak then stop as the dial hits the same point again.
4,Note the reading again , here its 124 deg
5,The point exactly between those two is the cam timing figure, in this case 102 deg (44 degress between the two ponts, 1/2 is 22, 80+22=102)
6 Every cam has a specification, mine is 106 degrees, so I installed a 4deg offset key and it was spot on. Dont forget the offset keys can be installed 2 ways, one advances the timing the other retards it
Thats useually enough but if you wanted to you could check any of the lobes in the same way, e.g an exhaust lobe.

Watch out for the camshaft!!

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