Vernier Cam Sprocket.

[BillyWhizzz2002]

Hi all,

Just wanted to find out what is the benefit of a vernier cam sprocket.

I have one fitted to the kent cam on my engine, I checked the static timing on engine with crank at TDC on no1 the cam timing is not at TDC but out half a tooth. I know that the idea is so you can then adjust the cam timing a little but advancing or retarding the cam timing will do what ?

[Hammy]

The object is to allow you to get the cam timing spot on. Manufacturing tolerances can lead to the cam timing being a bit out from the manufacturers optimum. The vernier pulley allows you to get the timing spot.

note that having the marks aligned on your crank/cam pullley may not therefore mean its timed spot on

And/or  - for some configurations a bit of playing with the timing either side of  the manufacturers setting can alter power delivery and give benefits, this is for the advanced experimenter tho, mere mortals sohuld use it to get timing spot on using a dial gauge to determine TDC a vernier pulley to work out the angles and the dial guage again to measure/determine max lift.

[Neil Purdie]

On a standard OHC or DOHC engine, if you skim the block or head or replace the camshaft(s), the timing marks on the standard fixed sprockets are unlikely to leave the cam(s) at their recomended timing positions.  When the cams are set to their correct timing position, this usualy leaves the timing belt teeth sat ontop of the teeth of the sprockets rather than inter-meshing

You then have 3 choices,

half a tooth advanced

half a tooth retarded

buy a vernier and set it correctly

Moving 1/2 a tooth will probably lead to a slight loss in power and potentialy give valve to piston contact if your unlucky.....

  Likewise dont forget to check the bolts on the vernier because this can be expensive if the timing slips  

[DIY Si]

Also, if using an after market cam, moving it forward by a degree or two can often bring the cam in earlier, thus making the engine a bit less cammy, and often giving a little extra top end.

[CedricTheBrave]

non standard Cams will have different optimum open and closed positions and therefore you will need to adjust the position of the cam to benefit from these optimum positions.

The aftermarket cams should come with this information to allow you to set the cam timing at tdc correctly

[nikpro]

mere mortals sohuld use it to get timing spot on using a dial gauge to determine TDC a vernier pulley to work out the angles and the dial guage again to measure/determine max lift.

Its better to actually measure the valve lift at TDC as it's more accurate than maximum lift.

[stu999]

QUOTE

Its better to actually measure the valve lift at TDC as it's more accurate than maximum lift.

Assuming, of course, that the manufacturers quoted part lift figure is correct, and that other parts of the valve train geometry will not affect the lift measured...

[nikpro]

Its better to actually measure the valve lift at TDC as it's more accurate than maximum lift.

Assuming, of course, that the manufacturers quoted part lift figure is correct, and that other parts of the valve train geometry will not affect the lift measured...

I agree Stu but even if the figures are not pinpoint accurate you are still only measuring one dwell angle (crank) compared to two and there is no need to measure degrees of crank rotation - the manufacturers figures are probably more accurate than the MK1 eyeball in respect to measuring the previously mentioned angles?

[stu999]

Weeeelll, I make my comments after pi55ing about with a fellow members Pinto powered car early last year. I used the 'part lift' method first, but 'mark one eyeball' wasn't at all happy. Even after checking, and rechecking my work, and trying the method on different lobes, it was obvious that the cam timing was *way* out - when at TDC, the cam lobes was noticably offset, rather than being approximately open by the same amount.

Reset using max lift at crank degrees, and all was well

[pistonbroke]

More Bling !