Author Topic: cylinder head 67-1126  (Read 2191 times)

Offline 1660bob

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cylinder head 67-1126
« on: 23.10. 2009 20:21 »
Hi All, what cylinder head have I got? cast into the underside of the inflet manifold is the number 67-1126, its an alloy head and is  SUPPOSED to be a super rocket head . I can find no such number in my parts book, nearest being 67-1121 (A7 s/star....) Any ideas on this one appreciated, Bob `C`

Online RichardL

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Re: cylinder head 67-1126
« Reply #1 on: 23.10. 2009 20:38 »
An often recommended site when such questions come up here on the forum:

http://atlanticgreen.com/a10alloyhead.htm

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline 1660bob

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Re: cylinder head 67-1126
« Reply #2 on: 23.10. 2009 22:13 »
Thanks Richard,that 67-1126 on the link you gave is definately the head I have with the large dia. valve seats all but touching in the middle of the combustion chamber. Reason for the enquiry is my cam has scuffed up badly on the lobes and I am told there seems to be a lack of vertical movement in the valves i.e. springs are getting coil bound on full lift. valves and hardware seem to be stock Super-Rocket .It was suggested to me that the head was possibly a re-worked A7 item, but this is obviously not the case. I am beginning to think it is more likely to be something to do with the apparently replaced valve seats -the mystery deepens...........
cheers, Bob `C`

Online RichardL

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Re: cylinder head 67-1126
« Reply #3 on: 23.10. 2009 23:49 »
Bob,

I can't say that I am expert in all the varieties of valve springs and valve collars, but I wonder if the wrong combination, perhaps from an iron head, would reduce the overall valve travel that is available.

My inclination is to think the scuffing is due to something else, not having heard of valves lacking adequate vertical movement (unless, of course, they are hitting the tops of pistons due to a mess up in timing gears, but you would have heard that rather loudly, and probabaly not have been running).

Running out of valve-spring travel would, I think, lead to bent pushrods. How are those looking?

How are the tappets? Are they nice and free to move in their cubbies in the bottom of the barrels? Are their surfaces scuffed and/or deformed?

Another possibility is that the cam was reground without rehardening the surface.

Perhaps the last engine rebuilder forgot to use assembly lube on the camshaft and tappets when the engine was rebuilt and, then it was just too long before the cam lubricating gallery got filled after the engine was first started.

OK, that just about exhausts my ideas and, unfortunately, I can't say with certainty that any one of them is a slam-dunk. I trust some others here will correct me, confirm me, or add to the list.

You might want to post a photo of the cam to give me and others a better idea of the type of damage.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline BSA_54A10

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Re: cylinder head 67-1126
« Reply #4 on: 25.10. 2009 11:41 »
Have a close look at the underside of the head.
It is not uncommon to have a lot of material skimmed off the bottom to increase the compression ratio.
This can cause a very bad contact angle between the rocker and the valve if the pushrods are not shortened by the appropriate amount whit the type of resultant damage that you have to the cam or followers.
Bike Beesa
Trevor

Offline 1660bob

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Re: cylinder head 67-1126
« Reply #5 on: 25.10. 2009 12:57 »
Good point Trev, both the head and barrell have been re-faced, I dont think too much has been skimmed off but food for thought nevertheless. Bob.