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#486107 - 04/17/13 4:29 am And another weird observation, Short Rocker arm??  
Joined: Aug 2001
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KC in S.B. Online content
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KC in S.B.  Online Content

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Santa Barbara, California
Looking at the '69 A65 head I had just put on recently, and noticed that the RH exhaust rocker Adj screw was not even CLOSE to hitting the valve stem in the center. It hits the stem near the back edge ! So, measured all the rockers, and the intake arms are visually shorter, and both the exhaust arms are longer,......... but this RH exhaust is shorter than the LH exhaust arm, and the forging is slightly less beefy. Are there different exhaust rocker arms in different years? This can't be right, and I can't believe it had not been noticed before.


Down to 1 BSA, 2 Triumphs, 2 '56 Chevys
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#486113 - 04/17/13 5:58 am Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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run990 Offline
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run990  Offline
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lancashire united kingdom
i had exactly the same issue with my bike,one rocker was shorter & lightly built towards the others.i bought a set of rockers off eBay & sorted the job.my engine is a bit off a bitsa so i assume the rocker arm was off a a50 or a unit single.my pushrods were odd as well so i got new ones.bike was lots quieter afterwards

#486148 - 04/17/13 1:13 pm Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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KC in S.B. Online content
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Santa Barbara, California
"Quieter"........ HMmmmm, that's the reason I started tearing the motor down in the 1st place! Wouldn't it be just Peachy to find the noise was not the drive side Roller bearing after all ! Although come to think about it, I doubt you could feel a banging in the handle bars from a rocker..........!!!
Thanks for the comment. I didn't think A50 valve train parts were any different than A65, although valves are smaller. Maybe so, since the combustion chambers are certainly smaller,..... ALOT smaller! That 1 RH Exhaust rocker is certainly made of a lighter, more delicate forging, and measures shorter, thats for sure. I can't say any of the parts on this motor were on it from the factory either, and for that matter, that is true for most engines after this much time gone by. At least I do have a box of bits I can sort through and see if I have something that looks and measures closer to the length of the LH side exhaust, which looks better on this motor.
I am curious if yours, "exactly that same problem", was also the RH rocker? Certainly is interesting to know someone else has seen this also, Thanks!


Down to 1 BSA, 2 Triumphs, 2 '56 Chevys
#486189 - 04/17/13 4:59 pm Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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run990 Offline
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lancashire united kingdom
my rocker problem was an inlet rocker,it was at such a bad angle that the tappet adjuster was almost missing the valve top.over the years & people building up engines from boxes of bits parts get substituted etc.also these bikes went thru the worthless phase so were bodged just to get running.i also had an exhaust rocker that was narrower across its width causing excessive tappet noise with its endfloat.i assumed the rocker was from an a50 or similar as it fitted in every respect bar valve stem centre

#486258 - 04/18/13 2:42 am Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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Santa Barbara, California
OK, I looked at another motor, and the exhaust rockers on it were hitting at a better spot on the stem, but still not centered. I dragged out a box of valve train stuff, and measured a bunch of exhaust rocker arms, and they are all the same. What changes is the forging, and the size of the forging, but the distance from push rod ball to shaft to adjuster are all the same. My best guess is that one motor has guides placed slightly different than the other motor. Still not great, but nothing I'm going to be able to change. Still weird.........


Down to 1 BSA, 2 Triumphs, 2 '56 Chevys
#486271 - 04/18/13 5:06 am Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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Pete R - R.I.P. Offline
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Pete R - R.I.P.  Offline
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Vic. Australia
You should be able to measure the distance from the rocker spindle to the valve stem.You'd soon know if one guide was out of place.
It would probably show inside the head too;one valve at an angle to the hemi,instead of radial.

#486278 - 04/18/13 6:15 am Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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run990 Offline
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i just dug the old rocker i removed from my box of bits i keep instead of scrapping.upon closer inspection the rocker is bent slightly it is slightly tighten angled that a good arm,hence my need to buy new pushrods as well as changing the arms.i wonder if a previous owner bent the arm because they ran out of tappet adjustment because of the short pushrods.the more you inspect these old engines you understand they must have been built using selected best fit parts .if you have a box of parts you can build a tight engine just by selection of the best fit parts ,or a real rattler by using poor fit but still within tolerance items

#486406 - 04/19/13 3:23 am Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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KC in S.B. Online content
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KC in S.B.  Online Content

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Santa Barbara, California
My 94 year old Brit bike adviser has weighed in on this observation. He said that what I am seeing is USUALLY caused by valves that have sunk in the seats over many vales jobs etc. When the stem moves up, the rocker would hit near the edge, which does make sense. I do know this head is not that bad, so the question is still a puzzle. Anyhow, good info. He mentioned that is why a good shop will take some material off the end of the stem when doing a valve job, for exactly the reason I am concerned about. He even said he has seen valves so sunk in seats, that the rockers hit the cover!! Although I don't know what type of engine, that would be amazing!!


Down to 1 BSA, 2 Triumphs, 2 '56 Chevys
#486474 - 04/19/13 5:24 pm Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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run990 Offline
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run990  Offline
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i have seen tappet adjusters hitting the caps on old abused c15s .one thing it could be is a loose guide .have you removed & stripped the head.i had a b25 & the guide was so loose it was resting on the valve head.the bike rattled but oddly did not smoke any more then usuall.
the more i mess with my old bikes i am glad the modern stuff i work on for wages are a bit closer in the tolerance department.
one thing it could have fitted is the wrong valve,a shorter or longer valve will mean the rocker starts off in the wrong spot.they should be slightly towards the outer edge & work thru the centre to the inner edge as they open.

#486541 - 04/20/13 1:59 am Re: And another weird observation, Short Rocker arm?? [Re: run990]  
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Pete R - R.I.P. Offline
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Posts: 3,549
Vic. Australia
Originally Posted By: run990
a shorter or longer valve will mean the rocker starts off in the wrong spot.they should be slightly towards the outer edge & work thru the centre to the inner edge as they open.

I don't agree with this.If the geometry is right,the adjuster will contact the valve tip on the rocker spindle side,when the valve is closed.
As the valve opens,the adjuster will roll across the centre of the valve tip.
At full lift,the adjuster will be to the outboard side of the valve tip,away from the rocker spindle.

As the adjuster rolls across the valve tip,there is also some slippage (scrubbing and side-thrust).
Zero-scrub occurs at the instant where a line taken from the valve-tip to spindle centre becomes square to the valve stem.This should be at about 1/3 valve-lift.
As the valve opens further,the side-thrust has changed direction and pushes the stem toward the spindle.

#486568 - 04/20/13 5:37 am Re: And another weird observation, Short Rocker arm?? [Re: Pete R - R.I.P.]  
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run990 Offline
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run990  Offline
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yeah i think i got it backwards,the main thing is that the rocker moves across the valve tip.if it starts off at the wrong end it possibly work its way off the tip ,but i thought you would notice that when setting the tappets.check your pushrod lengths if one is off it will give similar results as the rocker angle changes.

#487427 - 04/25/13 6:24 pm Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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Gordo in Comox Offline
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Comox BC Canada
The A65 and A50 rocker set uses two short rockers for the inlet and two longer rockers for the exhaust. In this shot the adjuster screws are resting on the centre of the valve stems (except where I do not have the exhaust spindle in far enough to keep it straight).

There is no interchangeability for any of them.

Gordo



Without frequent roadside repairs there is no fun in riding!
#487563 - 04/26/13 8:22 pm Re: And another weird observation, Short Rocker arm?? [Re: KC in S.B.]  
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KC in S.B. Online content
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Santa Barbara, California
Ok, nice head! But why are yours hitting the stems at center when relaxed, and mine are not? That is the mystery..... not that I let it stop me from starting the motor!


Down to 1 BSA, 2 Triumphs, 2 '56 Chevys

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