ET: Engine (Twin) Valve Guides

davidd

Well Known and Active Forum User
VOC Member
Steve,

They are not thicker for the entire length. Essentially, you can bore the guide hole, if needed, and then counterbore the larger diameter hole for the lock ring taking the threads off. The guide is made to fit both diameters. It looks thick, but it is just a standard guide with a flange on top.

That flange on top can be widened so it reaches the walls. Then the guide can be machined out of a large round to include the vertical walls on the outer edge of the flange that will run up to the upper guide much like Norman mentioned. The photo below looks to be two parts rather than one. A guide and a wall.
IMG_0605.jpg

I think this is a special application that Terry did, but it will certainly keep the guide in place.

Terry has a seal in the guide in this one.

The rocker feed bolt is just a straight in bolt with screw to block off the oil passageway at the top.
014.JPG


David
 

oilyrag

Active Forum User
VOC Member
Just started my strip down and this has happened to me. Not sure what to do, I can TIG weld but it's a deep hole plus it will be contaminated with oil. Barrels off next to investigate further.
Chris Tilley.
IMG_0703.jpeg

IMG_0703.jpeg
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
I don't know the thread, but on my Rapide in front inlet must have stripped in the past as a previous owner has had the head tapped oversize and a special locking ring made. I changed the guides when I bought the bike (in bits) and 35,000 miles later its still running OK with the oversize locking ring. It did need an oversize guide as well though so be aware of that as the guide could be loose.

Doesn't Know Thy Beast list various thread sizes in a table?

Simon
 

timetraveller

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VOC Member
Chris, before getting too despondent take it all apart and see just what has happened. At the moment the photograph only shows that the lock ring has unscrewed. Whether it has ruined the female thread or not has to be found out. If it has then I have a design for piece that will trap the top of a new lower guide and be held down by the bottom of the top guide and the valve spring. One would have hoped that all cylinder heads would have been the same in this part but my experience is that there are differences so you would have to get the bit made to fit your cylinder head. That is the diameter and length have to fit your bits. However the gadget itself is relatively straight forwards to make and the machinist just has to have access to your cylinder head to ensure that it is all a nice fit. Keep us informed and good luck with it.
 

chankly bore

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Non-VOC Member
Lock ring threads were originally 20 t.p.i. of 3/4" (inlet) and 7/8" (exhaust). Ernst Hegeler cylinder heads have a nifty extended lower guide that also goes up past the rocker arm fork. It can't go anywhere, even if it wants to!
 

timetraveller

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VOC Member
Here are the drawings I supplied to allow these to be made. Note that if you want to do this for yourself you need to check the dimensions as there is no guarantee that all cylinder heads are the same to within thous.
26081

Note that Chris made a particularly nice job by including an oil seal into the base of this design.
 

timetraveller

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VOC Member
I'm a non machinist as well but if I were to have a go then you can use a lathe to turn the four different diameters and then use a mill with a rotary table to remove most of the largest diameter. Leave just enough to act as a locator in the groove in the cylinder head. Lacking a mill one could use a file but it would not be as neat. I particularly like the way that Chris has managed to incorporate the oil seal. Remember, for all those who have got a damaged cylinder head, you need to see just how much is left of the original thread and then design the final details. If I was to get a batch of these made then I would specify 7075 alloy which is supposedly as strong as mild steel. This mod totally stops any possibility of the lower guide going for a walk about and causing more damage.
 
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