Author Topic: A 10 Super rocket Head/Valve spring mystery Help and advice needed  (Read 1185 times)

Offline Brianh

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After many virtually trouble free miles I recently needed to replace a loose inlet valve guide in my super rocket.  No problem there  a + 5 thou oversize guide was obtained from SRM  fitted and a local auto engine rebuilder recut valve seat   so far so good .  When ordering the valve guide I also orderd a new set of SR valve springs.  As the head was on the bench I took the time to clean and decoke the combustion chambers etc  Now here is where the mystery begins,   When it came to installing the new valve springs I noted that they are quite a bit longer than the ones I removed, Having looked up the spring spec for SR Alloy head it would appear that the new longer springs are correct.  The springs that were originall fitted ,  it would seam are for an iron head A 10 or A7 SS alloy head.     
    Have I been running on the wrong valve springs for the last 19,000 miles,  if so I have not noticed any problems.   OR  have I got a converted  A7 SS Head in which case do I need to refit the original springs.   The ID number on the head casting is not clear. The inlet tract measures 28mm you can still see the rough casting on the inside and it shows no signs of being opened up.  The inlet valves are 37mm dia  and the exhust valves are 35mm dia, The valve seats appear to close to the edge of the combustion chamber to have been modified.   I have added some photos   ( I hope )  Any help and guidence will be greatly appreciated  Thank you


Offline chaterlea25

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Hi Brian,
Could you post some photos of the valve top cap and collets fitted to a valve?
The SR top caps & collets are different
also the bottom washer under the springs
This would help identify what you have
A photo of the underside of the combustion chamber and its diamater will help id the head

HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Offline Brianh

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Hi  John 
Thanks for the prompt reply.  I thought I had posted all the photos but it looks like only the last one appeared I think I know what i did wrong I will have another go. The combusion chamber measures 70mm .

Regards  Brian

Online Greybeard

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Might this just be the difference between a new and used spring?

Online edboy

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the iron head smaller valve springs i have are always darker than the alloy head ones but your old outer spring is longer as they are 17/8" std so no harm done i would guess.

Online beezermacc

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If the combustion chambers are 70mm then it's a Road Rocket or Super Rocket head. If you can get the magnifying glass out and try to discern the part number that would help. It is likely to be either 67-1126 or 67-1549 or 67-1549 overstamped 67-1571. BSA used the same exhaust valves on all the alloy head A10's which measures 1.382" (just over 35 mm), but there were three different sizes of inlet, 1.415" (36mm), 1.455" (37mm), and 1.5" (38mm) used broadly in line with the development of the cylinder head over time. If you can read the part number on the head you are on the trail of which inlet valves it should have. There were only two types of springs used, one type for the SR and RR, another type for everything else. Your springs, caps and collets look correct as they are different (as with the springs) to all the others. Springs should be 51 / 54 mm, whereas all the others are 39 / 48 mm inner / outer. You need to have the correct valve spring base and top cups as they are also different to all the others. Hope that helps.
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Offline chaterlea25

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Hi Brian,
It looks like you are good to go  *ex*

When you assemble the engine again just check that the valves will lift a bit more than the full open cam position
wind the engine over till each valve is fully open in turn, use a lever to check that each valve can be opened at least 60thou more with the lever, (dont force the lever!!!!)

HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Offline Brianh

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 In reply  to your very helpfull responce . All the original springs i removed were of Identical length so i think it is unlikley that the differance in length is due to wear.   I must have been supplied and fitted the incorrect springs when I rebuilt the engine 19,000 miles ago   Suprisingly as previously stated the engine was running well until the loose valve guide issue.
Unfortunatly  most of the part number on the casting is unclear even with a magnifying glass.   what i can make out is 67 1-2-      this sort of ties up with the information kindly provided by edboy.

Thank you all for your help and advice .  I think there is enough evidence to sugest my head is a road/super rocket and I have previously been running on the incorrect valve springs.   I am going to fit the new ones and check for clearance on full lift as recommended by john I will let you know the outcome.   

Just out of interest can anyone advise what differance if any I am likley to experiance with the new longer springs

Regards   Brian

Offline duTch

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 I think the RR/Sr springs are bigger diameters too(?), so if your old springs are same dia., then they've sagged; I discovered I was using the incorrect springs, so bought correct new ones- then realised I had the wrong caps/collars...then realised the collets/keepers were wrong too  *pull hair out*


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Online Klaus

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Unfortunatly  most of the part number on the casting is unclear even with a magnifying glass.   what i can make out is 67 1-2-      this sort of ties up with the information kindly provided by edboy.


Regards   Brian

If the combastioncamber is 70mm it is 67- 1126 its the head for A10.
67-1122 is for A7 and 66mm in diameter.

cheers Klaus


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Offline Rocket Racer

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My road rocket head started life as an A7SS head, but had been radiused to 70mm and had a mixture of collars etc. caused me no end of problems as I didnt initially realise that I had a mismatch and the wrong collets for the collars (differing tapers). I guess the lesson was 70mm might appear to be A10 but wasnt necessarily if altered and in 50 years a lot of opportunity for mistakes occur.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline Joolstacho

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S'pose if the valve seat was re-cut too deeply it could have the same effect as shorter springs, ie the valvestem would sit higher above the head, so higher above the springtop.

Offline Brianh

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My initial query was regarding the additional length of the new  correct size SR valve springs over the springs that were fitted,  The bike has been running fine for 19,000 miles with no noticable problems until the recent loose valve guide .  All other components are ok.  It was when I contacted SRM to query the new springs that they suggested I may have an A7 head. The part number on the casting is not clear and inconclusive but  Looking and measuring the inlet tract  (28mm)and combustion chambers ( 70mm )they show no obvious signs of previous machining so I beleive I have a road or super rocket head and I had previously fitted the incorrect springs even though they were supplied as SR Springs.  I am going to reassemble the engine with the new springs but as a precaution before start up I will check movement at full lift as suggested

Thanks again for all your input