Author Topic: Cylinder head (1965 B40)  (Read 294 times)

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Phil C

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Cylinder head (1965 B40)
« on: 06 February, 2018, 19:30:33 »
I'm concerned about the cylinder head fixings on my "new" bike. Photos attached show:
LH side (nearside)of bike:  at the front is a stud with a nyloc nut at the top, nothing at the bottom except the bottom of the stud just sticking out below the casting (might not show on photo); at the rear is a nyloc nut at the top of a stud, and a nut of some kind on the bottom.
RH side (off-side) of bike: at the front is a stud and a nyloc nut on top; at the rear is what appears to be a bolt.
Any thoughts please?  Should I be concerned?    Phil (novice)

PS will need to put second photo on a new message - can't send both on the same message.


AWJDThumper

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Re: Cylinder head (1965 B40)
« Reply #1 on: 07 February, 2018, 09:11:20 »
The rocker box is normally held down via 9 x studs with nyloc nuts on top. The studs screw into the cylinder head and sometimes the bottom of the stud can be seen poking through. Sometimes people use bolts instead of the studs but this is not a good idea because it's very easy to wear out the thread in the soft alloy cylinder head.

Phil C

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Re: Cylinder head (1965 B40)
« Reply #2 on: 07 February, 2018, 09:44:08 »
Thanks AWJDThumper, that's reassured me a bit (although I can only see eight on mine.) Also I don't know why one of the studs has a nut at both top and bottom - I just hope it's not because the thread inside the hole has been stripped or badly worn.   Phil (novice)

AWJDThumper

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Re: Cylinder head (1965 B40)
« Reply #3 on: 07 February, 2018, 17:02:30 »
There should be 9 studs, two of which mount the head steady bracket with another one behind it which you might not have seen. Unfortunately, the nut underneath the stud is probably due to the thread in the head having been stripped which is not an unusable occurrence. Normally, they are easily repaired with a Helicoil.

Phil C

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Re: Cylinder head (1965 B40)
« Reply #4 on: 07 February, 2018, 18:17:45 »
As I feared. I haven't fitted a helicoil for many years, and have forgotten the finer details of their use. Would it mean the same size stud as original could then be used again?   Phil.

Phil C

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Re: Cylinder head (1965 B40)
« Reply #5 on: 07 February, 2018, 18:47:18 »
In fact my memory is of fitting helicoils in blind holes. Can they be used on a through hole?   Phil.

Phil C

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Re: Cylinder head (1965 B40)
« Reply #6 on: 07 February, 2018, 18:50:19 »
I think it's coming back to me now. You drill out to a certain depth, not all the way through, and then fit the helicoil which will bottom in the new enlarged hole, before you snap off the tang?  Phil.

AWJDThumper

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Re: Cylinder head (1965 B40)
« Reply #7 on: 07 February, 2018, 18:52:33 »
es to the previous question. The Helicoil kit includes a drill, a tap and a set of spring inserts which enables you to use the same bolt/stud thread size as before. For the cylinder head, the safest approach is to use a pillar drill to both drill the enlarged hole and to tap the hole afterwards before inserting the Helicoil spring. That way, you make sure everything is machined vertically. That said, I normally do it by hand but you have to be very careful because some of the tapped holes in the head are not very deep and it's easy to end up trying to machine it off axis.

Yes to the second question - it makes no real difference to the process whether the hole is blind or not. However, you need to choose the correct length of Helicoil expressed as multiple and fraction of its diameter, D.