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What causes this symptom? #402951
11/10/11 1:12 am
11/10/11 1:12 am
Joined: Oct 2005
Posts: 208
North Carolina
D
DKA Offline OP
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DKA  Offline OP
BritBike Forum member
D
Joined: Oct 2005
Posts: 208
North Carolina
Here's an email from a friend. Anybody have any suggestions. I'm assuming the bike in question is an A 65.

David,

I helped a friend pull the head off his '69 BSA this week. I was
inspecting the rocker arms and noticed
some blue scorch on the arm that rides the valve (opposite the push
rod) I've never seen what looked like xcessive heat coloration on a
rocker before and... you're a BSA man, any thoughts or can this be
normal. Other clues are:
one piston had suffered a broken ring, causing trmendous suffering on
the cylinder wall.

Bill

Thanks for any thoughts.

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Re: What causes this symptom? [Re: DKA] #402961
11/10/11 2:51 am
11/10/11 2:51 am
Joined: Aug 2001
Posts: 4,260
Owego, NY, USA
Mark Z Online content
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Mark Z  Online Content
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Joined: Aug 2001
Posts: 4,260
Owego, NY, USA
I haven't seen this before, but I would check the rocker oiling. Another thought, a burnt exhaust valve will cause extreme heat in the exhaust port and to the valve - is it an exhaust valve?

Is the scorched rocker on the same side as the broken piston ring? I'm not a forensic expert, but I can't picture the heat caused by the broken ring emanating all the way up to the rocker.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: What causes this symptom? [Re: DKA] #402966
11/10/11 2:02 am
11/10/11 2:02 am
Joined: Jan 2006
Posts: 1,841
Maryland
JD Online happy

Moto-Amish
JD  Online Happy

Moto-Amish
Joined: Jan 2006
Posts: 1,841
Maryland
Man, that's weird. I agree with Mark that I can't see a broken piston ring causing that much heat. If it's an exhaust valve, is the valve loose in the guide?


Josh
Re: What causes this symptom? [Re: DKA] #403034
11/10/11 2:03 pm
11/10/11 2:03 pm
Joined: Sep 2002
Posts: 7,812
Seattle
Alex Offline

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Alex  Offline

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Joined: Sep 2002
Posts: 7,812
Seattle
Since it has to come apart anyway, the head needs to be disassembled and gone through. There's not enough contact between valve and the rocker to transfer enough heat from the valve unless the valve was positively red hot. It's possible that the rocker maybe seized on the rocker shaft, but I'd consider that very unlikely. That's a very low-speed bearing surface and it would be hard for it to generate that kind of heat...I'd think it would be more likely to bend a pushrod.

So, it needs to be pulled apart.


A smattering:
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'67 Royal Star
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'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: What causes this symptom? [Re: DKA] #403110
11/10/11 8:07 pm
11/10/11 8:07 pm
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Ignoramus Online content
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Ignoramus  Online Content
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Posts: 1,516
Auckland NZ
Real hard to see how that much heat could hit the rocker arm no matter what, never say never , but I sure cant think of what it could be.

I would be staring to look for things like has the rocker ever been bent and had a gas torch/welder on it to straightem (but like Alex says more likley to bend push rod than rocker arm) or repair and what you are seeing is left over blueing from heat doing that? Might also be someone has had a gas torch on that end to try to lossen a sezied up tappet adjuster??

Also could be that marking blue dye for reasons best known to who put it there?

strange to just be on one rocker.

I think we need more info or it will just be guess work...any way you can get some pics up?

Last edited by Ignoramus; 11/10/11 8:21 pm.

"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: What causes this symptom? [Re: DKA] #403157
11/10/11 11:41 pm
11/10/11 11:41 pm
Joined: Oct 2009
Posts: 441
new jersey usa
P
pushrod tom Online content
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pushrod tom  Online Content
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Joined: Oct 2009
Posts: 441
new jersey usa
I have noticed the same thing on some of my rockers and just assumed, (ahem) that it was a manufacturing issue. They are in there doing their thing and I never think about it. PRT

Re: What causes this symptom? [Re: DKA] #403877
11/15/11 11:15 am
11/15/11 11:15 am
Joined: Jul 2006
Posts: 466
just a guy from Jersey [Hopewe...
N
nert Offline
BritBike Forum member
nert  Offline
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N
Joined: Jul 2006
Posts: 466
just a guy from Jersey [Hopewe...
I too have seen this regularly. I believed it to be heat treating (hardness) and part of manufacturing.


keep your "oddies" lubricated, and carry a dime
Re: What causes this symptom? [Re: nert] #403985
11/16/11 12:35 am
11/16/11 12:35 am
Joined: Oct 2005
Posts: 208
North Carolina
D
DKA Offline OP
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DKA  Offline OP
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D
Joined: Oct 2005
Posts: 208
North Carolina
Thanks for all the input. I'll pass this along to Bill.

David

Re: What causes this symptom? [Re: DKA] #404053
11/16/11 2:26 pm
11/16/11 2:26 pm
Joined: Feb 2007
Posts: 2,202
Atlanta, GA USA
S
Semper Gumby Offline
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Semper Gumby  Offline
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S
Joined: Feb 2007
Posts: 2,202
Atlanta, GA USA
On my BMW the rocker ends are heat treated and have a blue color. I don't recall seeing this on the BSA rockers but perhaps in its past some one tried to harded the end.

Was it a race bike at one time?


Gaggle of BSAs
a Honda
an old BMW
and a Montesa
Parking lot Elf in training

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