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Rocker ratio 1:1.13 is not showing in my physical measurements.

Submitted by paul_shore on Fri, 18/11/2022
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Heavy Twins

Hello

I have a problem in that I am seeing the same movement of the valves as the cam lift.

Dial test indicator (dti)  to follow the valve and before assembly the cam lift from base circle to top of nose.

Cam pn22729 should have a lift of 0.330. 

I am getting valve axial movements  of 0.345 0.315 0.309 0.300 and cam                               lobe respective lifts of 0.320  0.322 0.309 0.306.

I have bought this shaft to replace my original (ebay).

Cam lift x rocker ratio = axial valve travel.

My question is were has the rocker ratio gone ? e.g. 0.320 x 1.13 = 0.361

I understand that the ratio for the Atlas is 1.13: 1

Can anybody help please.

I will have buy a new cam and put it down to experience.

Regards Paul.

 

Submitted by jonathan_newton on Fri, 18/11/2022

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…Is your rocker is not working at optimal angle. Your ratio is defined by the length of the rocker from its rotational centre to its points of contact on the devices, (valve and cam).

Optimal angle is when the rocker is 90 degrees to its rotational centre and the cam is at 50% of its travel.

Valve regression common cause for this loss of ratio.

 

cheers

Jon

Hi Jon,

Thanks,

I will check the push rods as I've read norton changed the length by .0100 shorter so this will affect the 90 deg mid point of the rocker.

The engine was in an awful state when I bought it (complete bike matching numbers) .

Anyway thanks.

Regards Paul.

 

Submitted by richard_cornish on Fri, 18/11/2022

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Hi Paul,

   The cam followers have a radiused profile which affects the valve lift as the cam turns. Being 2 different profiles means the the lift will not be linear to the rocker ratio. As Jon says, the only point will be at the maximum lift where the 1 to 1.13 ratio measurement will be accurate.

 

 

 

 

Submitted by ashley_cutler1 on Sat, 19/11/2022

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Measure the total movement of the valve, then set it to mid point of this figure, the valve adjuster must be vertically in line with the valve at this point of travel. Once you have achieved this then the reading you get will be accurate. Make sure the followers are not picking up on any wear ridges in their bores.

Remember old cams made on old knackered machinery will not be as accurate as modern manufacture. 

Thanks Richard and Ashley,

My followers are the perfectly flat type not the radius-ed ones.

I will set the tappets so they are axially in l line with the valve stem at half the entire valve travel, and then check again to see if I am getting the rocker ratio.

Won't be for a while as I having some maintenance myself (new knee).

Regards Paul

Submitted by bill_moline on Thu, 01/12/2022

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To check rocker ratio it is necessary to set the rocker horizontal on a rocker spindle mounted on an angle plate. Then take two dial gauges, one on each end of the rocker, and move the pushrod end exactly one millimeter and take a reading at the rocker end. This will be the rocker ratio, and yes it is 1.13-1. Bit of mucking  about but the only way to be sure.

 



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