ET: Engine (Twin) Valve Guides

SteveO

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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

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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

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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

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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

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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

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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.
 

Simon Dinsdale

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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

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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

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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?
 
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