Author Topic: Poor Super Rocket Camshafts?  (Read 564 times)

Offline Clive

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Poor Super Rocket Camshafts?
« on: 05.11. 2015 15:10 »
I have been aware that my 1962 Rocket does not produce the power I would expect - even after a total rebuild. I suspected the cam timing may not be spot on so I ran a check and discovered that 3 of the valves were opening and closing within reasonable limits of the specified values (In 42' BTDC, 62'ABDC, Ex 67' BBDC, 37'ATDC) but one of the exhaust valves opens 11' early and closes - nearly 30' late! This must mean that the profile and rotational position of this lobe on the cam shaft are both wildly inaccurate. The massive 'overlap' would account for the loss of power, I reckon.

The camshaft I used was the one fitted to the engine when I acquired the bike some years ago and the machine had been dormant for some 30 years before that so no certainty of its origin. Has anyone else experienced a similar problem? Does anyone know anything about the manufacture of poor quality camshafts?

Thanks - Clive

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Re: Poor Super Rocket Camshafts?
« Reply #1 on: 05.11. 2015 16:12 »
Hello Clive and  *welcome* to this mad world of Bsa and this wonderful  forum ,which isn't mad , well only some posts , but where you will find an answer, the members are great friendly and knowledgeable . re your question I've never had an issue with cams and am not aware of any real problems, for instance ,my present bike was revamped about 14 yrs ago and I changed the cam but only because I upgraded to bigger valves and sportscam/followers but  the original cam which had been in the engine sine I acquired it 25 yrs prev was still usable. I've keep it for that reason ,some scuffs and marks but serviceable .
I'm sure someone will be able to confirm if there ever was a production or batch problem with cams. I'd suggest that a look at the cam was required and comparing to another cam would show any wear ,incorrect engineering that there is . Not being an expert I'd wait for confirmation from more knowledgeable guys who will be around very shortly I'm sure .
How about an into in bikes pictures members to let us know a little about you your bikes etc enjoy Bob.
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Re: Poor Super Rocket Camshafts?
« Reply #2 on: 05.11. 2015 19:18 »
G'day Clive, welcome.
The only cam I've had that was out was one that was reground. 14 degrees out left to right.
One badly worn cam follower could give your symptoms.
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Offline Clive

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Re: Poor Super Rocket Camshafts?
« Reply #3 on: 05.11. 2015 19:25 »
Yes, that's true but I checked the whole valve train when I built the engine. I suppose, though, it is possible for a failure to have occurred since. Thanks - Clive

Offline Clive

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Re: Poor Super Rocket Camshafts?
« Reply #4 on: 05.11. 2015 19:27 »
Regarding previous, but one, contributor's suggestion. It would be difficult to make a comparison of my camshaft with another without building it into the engine. This is because it is almost impossible to determine when the follower begins to lift off the base circle, know the duration and match each lobe's operation with crankshaft position otherwise. I know this as I have, oddly, suffered a similar problem with a Norton Dommie. Am I jinxed?
Clive

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Re: Poor Super Rocket Camshafts?
« Reply #5 on: 06.11. 2015 19:20 »
G'day Clive.
Had you noticed if you needed to adjust the tappet on the bad one more than the others?
You can map a cam (out of a motor) with a lathe, degree disc and dial gauge.
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Offline Clive

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Re: Poor Super Rocket Camshafts?
« Reply #6 on: 07.11. 2015 08:29 »
Thanks. I agree this could be done but the curve resulting from a dial test indicator probe will not be representative of the true valve opening & closing periods as this will be determined by the followers and the rocker arm ratios. The whole valve train needs to be assembled to get the true result. In addition, and crucially, it would be difficult to determine whether each lobe is correctly located relative to the all important key-way.

I know that a damaged/incorrect follower would affect the valve opening & closing periods but I know these were fine when I built the engine. Damage to the follower is unlikely to increase the valve open period anyway; it would more likely diminish it. I am thinking that a poorly ground camshaft could have 3 lobes with correct  profiles and one incorrect and this 'rouge' lobe also inaccurately located, relative to the other 3. I am struggling to come to any other conclusion!