649 cam timing

[swifty]

Hi . I'm having brain fade at the moment so bear with me . When timing the cam in with the timing gear facing me I have turned the engine clockwise . I have used the round protractor on the front pulley and a dial gauge on the inlet push rod . I've turned the engine and done the sum of 10 degree before and after full lift on the dial gauge . I've noted the measurment on the protractor and added the two sums up and divided by two and with a bit of adjustment on the vernier timing gear reached 100 degrees . The timing needs to be set at 100 degrees after tdc .... I'm a bit confused that I may have set it 100 degrees before tdc ... How will I know ? .... Or does this all seem ok ? ....... Ken

[Vegard]

Are the dots on the timing gear correct?

[smithyrc30]

Go back to TDC and then rotate the engine clockwise (looking at the front) The inlet should be lifting as you rotate the engine and the piston should be falling. If you have it before TDC then the piston will be rising from BDC when you get full lift on the cam.

[swifty]

Hi . Vegard the timing gear is a brand new vernier duplex set up from minispares , so the dots should be correct .... Smith, the piston is on it's way down as the inlet valve is opening . ... I have checked it today over and over and still get the same figure of 100 degrees , but at least I've put my mind at rest that it is correct as can be . ... I must have OCD or something ! ..... The figures I got were at 10 degrees before full valve lift =82 degrees on the protractor and 10 degrees after full valve lift = 118 on the protractor ... =200 divided by 2 = 100 ... As the piston is on it's way down before full lift I would assume this means it's set at 100 degrees after TDC .... Thanks ... Ken

[vulcanbb18]

100 ATDC is dead on for a 649 (assuming this is a BMC spec 649)

Timing is 50-70-75-45, inlet lCA 100 deg, exhaust 105 LCA, for a camshaft LCA of 103 degrees.

Sounds perfect to me by what you've said - I sent myself nuts putting in an offset key wondering if I had put it in the wrong way, measured that a few times to be sure!

cheers,

Jacob

[swifty]

Hi Jacob. Yes it's a genuine S/T camshaft that I found on eBay a few years ago , unused and wrapped up in grease proof paper in a cardboard tube . It's actually the spider drive version ie 529/ 530 . I always find with these cams that the ignition timing needs to be just right to get the best out of them . Going to be using a new swiftune csi dizzy ...... Ken

[Spider]

I'm pretty sure these were originally spec'd to be timed at 110 degrees (I don't have all my notes with me). I'd suggest checking valve to piston clearance if you do want to time it to 100 degrees.

[swifty]

I'm pretty sure these were originally spec'd to be timed at 110 degrees (I don't have all my notes with me). I'd suggest checking valve to piston clearance if you do want to time it to 100 degrees.

Spider I just checked the timing figure I a few books I have and there all saying 100 degrees . Valves can't be hitting the pistons . ( must admit I didn't check ) cos it all running up all ok . ... Ken

[ianh1968]

The only thing that I do different here is to close up the
degree amounts when working out where TDC for the crank
is and also where the high lift point on the cam lobe is.

For the cam in particular, I go for splitting the angle of only
3 degrees either side of full lift to get my figure...

The reason is that many cams have asymetric lobe shapes
which are obviously different on the opening ramp side to
the closing side. 10 degrees in this respect is a LOT.

It might not make the slightest difference, but this is the
way I do things...

And I always wind the engine over in the correct direction
ONLY, never going backwards. With a chain with a nominal
amount of "slop", this could give wildly different results.

Ian