E: Engine Setting MkII Cams With No Timing Marks...Equal Setting?

[Jez Nemeth]

Got some reground re-stellited Gary Robinson cams for Comet, believed to be MK2's -seem to fit from profile.
Indicator marks are all out...so what's the best, easiest way of setting up to check equal lift? There was an old thread from 2012 with much of this detailed, but wondered if there were other methods folx use around finding equal lift to determine and set a cam with no orientation marks accurately?

 

[fogrider]

Simplest way is to set the inlet cam at full lift with the crank at 97 deg ATDC . (for Mk2's).

Ignore nay-sayers, read the Burton Performance website, they build high performance rally engines and their official method is inlet at full lift.
I have to say though, their description is way over-written, they did'nt learn how to apply precis at school !
It's actually very simple and with careful use of the dial gauge, you can be to 1 degree.
97 is the calculated full lift, but my first twin went best at 101 ATDC on Mk2's, so many other factors influence performance.
Give it a go !

 

[Robert Watson]

Or

equal lift of valves (adjusted at zero clearance) at 4 deg BTDC give or take a degree or two. Built about 8 engines that way, all strong runners.

 

[vibrac]

Haven't looked at a timing mark on a cam in many a long year after I set it at equal opening at 4deg BTDC I may mark them up if they are in immediate risk of coming apart again, if thats not the case then I am not sure why I bother because if a year or so passes I will probably ignore them and (read start of text)

 

[Jez Nemeth]

Haven't looked at a timing mark on a cam in many a long year after I set it at equal opening at 4deg BTDC I may mark them up if they are in immediate risk of coming apart again, if thats not the case then I am not sure why I bother because if a year or so passes I will probably ignore them and (read start of text)

Thank you mr Vibrac and happy new year sir! Read your old thread from a time ago, one I mentioned -excellently explained the process indeed. Just setting up the BIG comet single again and swopping out the 105's for these MK2's -all help is gratefully received!!

Pressed the cams in myself, so I pretty much know 99% the marks are out of kilter...be surprised if they line up on the large Idler, be to total chance if they did...

They'll be more questions to come as I'm rebuilding the bike, many bespoke parts compared to my standard Comet which is part of the fun -so may set up a post on the project page -have q's around sag, and setting up for performance and events...anyway down the line, it's still early in the year, just a heads up.

 

[Cyborg]

If you use fogrider’s method, then just for fun check how close it come to equal lift at 4 deg BTDC.
Terry Prince recommend I use a different method yet ( using a specified amount of lift on the intake at a certain point before TDC. Don’t recall the numbers. I used that method and then checked to see how it compared to 4 deg BTDC. It was right on the money.

 

[chankly bore]

Yeah, and I know this is Colonial and slack, but if the cam profiles have been ground using the original slot on the outer end of the shaft, then pointing that slot exactly between the pushrods at 4° BTDC will give you timing very close. Worked on the "Comet on Steroids", anyhow.

 

[bmetcalf]

That is how I decide where to put the cams. I have checked it for the 4 deg BTDC.

 

[Jez Nemeth]

Yeah, and I know this is Colonial and slack, but if the cam profiles have been ground using the original slot on the outer end of the shaft, the pointing that slot exactly between the pushrods at 4° BTDC will give you timing very close. Worked on the "Comet on Steroids", anyhow.

Being colonial myself, do really like the sound of the 'slack method' easiest point between A & B and all that... will defo try that one - thx

 

[vibrac]

At the risk of repeating briefly for a Comet omitting 'minor' points
rotate the engine until the valves are equally open
immobilise the cam with a screw in an adjacent cover screw hole
remove the half time pinion
rotate the crank to 4degrees to tdc hold it there
find the best fit keyway on the pinion