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Cam Identification For Setting Timing


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#1 malc_west

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Posted 22 November 2020 - 06:45 PM

As the title mentions basically I'm mid process in swapping to a duplex timining chain and want to do the timing myself. Is there any way to correctly identify which cams been fitted by the past owner with out removing it and if yes how?
Thanks for any help it's always much appreciated

#2 nicklouse

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Posted 22 November 2020 - 06:49 PM

It depends on what it is. 
 

some are marked on the drive end.

 

many have rings or groves on the shaft to show what they are.

 

you can also measure the lift and max lift position which helps ID the spec.



#3 malc_west

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Posted 22 November 2020 - 07:16 PM

Il inspect the end and see if there's anything to go on, I suspect it's probably just a standard cam that you get in a 1275 metro but thought it'd be worth confirming. To measure the lift could that be done by working out the rise and fall of a push rod? Thanks

#4 Cooperman

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Posted 22 November 2020 - 10:56 PM

Unless the engine is for a competition car and if you cannot identify the cam, set to 108 degrees ATDC and you'll be fine.

A Kent cam has a nominal 106 degs whilst all BMC/ROVER cams have 110 degs (except for a couple of old race cams).



#5 Spider

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Posted 23 November 2020 - 12:10 AM

I'd suggest measuring each lobe of the cam first, to check it for wear and at the same time, you'll soon see it's 'grind' profile as well as identifying features like the Clearance Ramps, which will be somewhat essential for setting the Tappet Clearances.

You can then use the figures you've measured and compare them to some of the other published grinds to get a feel for it's characteristics and approximate timing to the Crank.

 

To measure the Cam, you only need the same gear as you do for Timing it in, a note pad and pencil. When I map out unknown Cams I generally get lift figures every 50, except around the Base Circle, and then also jot down in a finer way around the Base Circle to Clearance to Opening Ramps and likewise on the Closing side of things, to get a clear picture of what they look like and that'll also help with working out the Tappet Clearances.



#6 gazza82

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Posted 23 November 2020 - 10:26 AM

Il inspect the end and see if there's anything to go on, I suspect it's probably just a standard cam that you get in a 1275 metro but thought it'd be worth confirming. To measure the lift could that be done by working out the rise and fall of a push rod? Thanks

Markings are usually on the pump end where there is more "flat" areas .. 



#7 malc_west

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Posted 23 November 2020 - 07:00 PM

Unless the engine is for a competition car and if you cannot identify the cam, set to 108 degrees ATDC and you'll be fine.
A Kent cam has a nominal 106 degs whilst all BMC/ROVER cams have 110 degs (except for a couple of old race cams).

Cheers, I'm going to do this as the cam has no marks I can see. I intend to get a full engine rebuild when funds are more available so 108 degrees should see me till that point. Is there any reason I can't put a little grease on the timing sprockets just to make them easier to slide about whilst trying to do the timing? Cheers

#8 Cooperman

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Posted 23 November 2020 - 11:20 PM

Polish the inside diameters of the sprockets with emory cloth so that they slide on and off easily. Then add a small amount of grease and the job is easy.

If you set to 108 degrees, it'll be more accurate than a lot of cams set on the 'dot-to-dot' basis which is how the vast majority of cams are timed in. I've seen standard cams and sprockets give as much as 8 degrees of error when set dot-t0-dot.

At 108 it will work very well. Then, when you do a full engine build and fit a brand new cam, you can set it to suit whichever one you have bought.



#9 malc_west

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Posted 24 November 2020 - 07:31 PM

Cheers mate il get on to it this week end hopefully




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