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ET: Engine (Twin) Valve guides



SteveO

Active Website User
VOC Member
I recently experienced a "death rattle" from my Rapide while coming home from the club. I cut the engine, pulled over and got home via the AA. I have now stripped the top end of the engine and found the front exhaust guide loose in the head, when I push it in andout it makes the tapping noise that frightened me so much. Enclosed are photos comparing exhaust and inlet guides. There seems to be a locking ring missing off the exhaust, that is in pieces of phospor bronze which fell out when I removed the rocker I think. What is the prognosis? I presume I need an oversize guide and new lock ring and probably a new valve (and a machine shop to fit them), but is the well where the guide fits damaged also, will this need welding up?
IMG_4157.JPG
For comparison, here is the inlet
IMG_4159.JPG
 

timetraveller

Well Known and Active Website User
VOC Member
I had the same thing happen but in my case there was no noise that I was aware of. It was not until I took the bike apart for something else that I found no lower guide and the lock ring in three pieces up with the valve spring. No, I don't know how it did it either. I got an over sized guide made up and reamed the hole. What you do after that is up to you but remember that the big port heads did not use lock rings. At least for the time they expected big port headed engines to run they must have though that it was safe to run without lock rings. If that is not to your liking then there was a lower guide, made in Germany I think, which was made as one piece consisting of the guide, a tube going upwards with a slot in the side to let the rocker enter and the top was a fit against the base of the top guide. This ensured that the guide could never move upwards unless the whole top end disintegrated. I think that the chap who invented and made those is no longer around but once you have understood the idea you can come up with something yourself which would mimic the idea by fitting one on top of the lower guide and being trapped by the upper guide. I designed one for a local chum with the same problem.
 

SteveO

Active Website User
VOC Member
Thanks for that. I see now that the lock ring is threaded to the head rather than the guide and the threads are obviously well gone now! Stevens says the only fix for this is tap the threads out bigger and fit a specially made lock ring but your comments about big port heads are noted.
 

Albervin

Well Known and Active Website User
VOC Member
If you know an expert TIG welder and machinist then that is the route I would go down. Both of the lower exhaust valve guides in my Shadow were seriously compromised by someone who thought he was doing an excellent (?) porting and polishing job. The guides were rotating in the thinnest of bosses and it would only have been a matter of time before an expensive failure. All fixed for not a lot of money and, more importantly, confidence in the engine.
 

SteveO

Active Website User
VOC Member
What are the big unions on the rocker tunnel on the TPV heads? A change to the lubrication system and a more positive location for the rocker spindles?
 

timetraveller

Well Known and Active Website User
VOC Member
The 'fir tree connectors' at each side of the new boss is to help to reduce potential leaks by replacing the A45AS and all the little bits that go with it. The bolt and screw on top require a reply from someone else.
 

vin998

Well Known and Active Website User
VOC Member
I would guess the bolt and screw on top are something to do with locking the rocker and its bearing/bush housing in the rocker tunnel.
 

timetraveller

Well Known and Active Website User
VOC Member
I'm sure you are right but never having worked on a TP head I am not sure what he has opted for. There are several designs intended to improve on the original; screws holding the bearings up and what I was told was a Fritz Egli design where only the upper half of the rocker bearing is used and so on. Several more over the years have been tried but Terry probably had his own ideas as to what would work well.
 

SteveO

Active Website User
VOC Member
Hmm. The TP guides look a lot thicker than standard, well mine anyway. My exhaust guide is so loose I think I could push it out cold if I tried. Someone has also nicely polished my inlet tract too, but not to the detriment of the guide as far as I can tell. Presume the improvements to oiling require hollow rocker shafts?
 

davidd

Well Known and Active Website 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

Website 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
 

vin998

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
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

Well Known and Active Website User
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!
 


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