Dougie Posted December 21, 2020 Report Share Posted December 21, 2020 Hi guys (Novice alert..be gentle!) My first outing in my GT6 Vincent Hurricane didn’t end too well! Exhaust Rocker arm broke, seems to have given up under stress? Maybe just one of those things? Anyone else had the same? Where’s the best place for a replacement? and should there be a copper bush or something between the arm and the shaft? cheers Link to comment Share on other sites More sharing options...
Clive Posted December 21, 2020 Report Share Posted December 21, 2020 You need to check why the arm has snapped. Does the valve move easily? (obviously take account of the spring tension) but if that seized the arm would snap. Otherwise the replacement arm will go the same way. All teh main supppliers should have arms? or good used? A complete used shaft should not be expensive, and check the actual shaft for wear as they are not expensive new, and a no-effort job while you are taking it apart anyway. Link to comment Share on other sites More sharing options...
Anglefire Posted December 21, 2020 Report Share Posted December 21, 2020 I doubt its unheard of - but I would say its rare! The only real reason I can think of for a breakage like that is seized on the shaft - lack of lubrication, or everything set too tight - but I can't see how the latter could happen! Link to comment Share on other sites More sharing options...
Pete Lewis Posted December 21, 2020 Report Share Posted December 21, 2020 to snap the bore in half looks more of excess load/impact fracture its not been a progressive failure has this got a high lift cam and needs big tappet clearances to avoid bottoming the valve spring set it to the std 0.010" and kaboom the rocker Pete Link to comment Share on other sites More sharing options...
JohnD Posted December 21, 2020 Report Share Posted December 21, 2020 The picture is not aclose up, but the bearing surface of the broken rocker looks to be excessively worn, with deep scratches along the line of the shadow in the first pic. Such wear would indicate either inadequte lubrication or excessive loading, leading to wear-induced fracturing and failure of the rocker. I would dismantle the rocker assmebly, inspect other rockers, and the shaft, and be very critical of any that showed signs of wear. Shaft replacement is straightforward. JOhn Link to comment Share on other sites More sharing options...
RogerH Posted December 21, 2020 Report Share Posted December 21, 2020 1 hour ago, Dougie said: Hi guys (Novice alert..be gentle!) My first outing in my GT6 Vincent Hurricane didn’t end too well! Exhaust Rocker arm broke, seems to have given up under stress? Maybe just one of those things? Anyone else had the same? Where’s the best place for a replacement? and should there be a copper bush or something between the arm and the shaft? cheers Hi Dougie, can you post a well focused, HD pic direct onto the crack faces. It should/may be possible to tell how it failed. Roger Link to comment Share on other sites More sharing options...
Nigel Clark Posted December 21, 2020 Report Share Posted December 21, 2020 There is a bronze bush inside each rocker. The bush that goes with the broken rocker is almost certainly still on the shaft. As has been said, this is a rare failure on a Triumph but not unheard off. Possible causes are: - Seized valve. Had the engine been standing unused a long time before this happened? - Lack of oil feed to the rocker shaft. Oil is 'metered' up to the rockers through a drilling in the rear corner of the block and cylinder head from the rear camshaft bearing. With the rockers, pushrods and spark plugs removed, spin the engine on the start and once the oil warning light goes out, there should be a pulsing dribble of oil coming from the feed hole below the rearmost rocker pedestal. Both will need to be checked before restarting the engine with a replacement rocker. Also check that the relevant pushrod hasn't been bent by the load needed to break the rocker. Nigel Link to comment Share on other sites More sharing options...
NonMember Posted December 21, 2020 Report Share Posted December 21, 2020 13 minutes ago, Nigel Clark said: There is a bronze bush inside each rocker. Are you sure? I thought that was an after-market "upgrade". Link to comment Share on other sites More sharing options...
Clive Posted December 21, 2020 Report Share Posted December 21, 2020 1 minute ago, NonMember said: Are you sure? I thought that was an after-market "upgrade". I thought it was the reconditioning process. Bore the arm, insert a bush, ream to size. But bras/PB or whatever is probably a good idea. Saying that, the original rockers last really well anyway. Link to comment Share on other sites More sharing options...
RogerH Posted December 21, 2020 Report Share Posted December 21, 2020 The Moss Webcat shows both bushed and non bushed Here Roger Link to comment Share on other sites More sharing options...
Nigel Clark Posted December 21, 2020 Report Share Posted December 21, 2020 1 hour ago, clive said: I thought it was the reconditioning process. Bore the arm, insert a bush, ream to size. But bras/PB or whatever is probably a good idea. Saying that, the original rockers last really well anyway. I've only seen these rockers with bushes but with hindsight, I couldn't be certain if they were original. Nigel Link to comment Share on other sites More sharing options...
JohnD Posted December 21, 2020 Report Share Posted December 21, 2020 Nigel could be right! (no surprise!) This is an unbushed rocker from Rimmers: The wall looks much thicker than the broken one. But look at the bearing face and compare! Link to comment Share on other sites More sharing options...
Clive Posted December 21, 2020 Report Share Posted December 21, 2020 25 minutes ago, Nigel Clark said: I've only seen these rockers with bushes but with hindsight, I couldn't be certain if they were original. Nigel Now I feel unsure! Link to comment Share on other sites More sharing options...
Colin Lindsay Posted December 21, 2020 Report Share Posted December 21, 2020 This was mine back in the day, and it was due to the rocker being incorrectly aligned with the pushrod. However this one broke almost immediately on startup - how far did you get on yours? Link to comment Share on other sites More sharing options...
Nigel Clark Posted December 21, 2020 Report Share Posted December 21, 2020 16 minutes ago, Colin Lindsay said: This was mine back in the day, and it was due to the rocker being incorrectly aligned with the pushrod. However this one broke almost immediately on startup - how far did you get on yours? I can't see a bush in Colin's broken rocker. Nigel Link to comment Share on other sites More sharing options...
Dougie Posted December 21, 2020 Author Report Share Posted December 21, 2020 Thanks for all the replies ! As far as I can see there aren’t any bushes. It had been standing for a while (garage showroom) as far as I know. I got about 15 miles before it went. picture of the break below. Link to comment Share on other sites More sharing options...
Nigel Clark Posted December 21, 2020 Report Share Posted December 21, 2020 Given that history (standing unused then driven 15 miles), I would suspect a stiff, partially stuck valve. I would suggest checking the oil flow while cranking with the rockers removed. Assuming that's okay, I would be looking very closely at the relevant valve, probably removing the head to be certain it's moving freely. Nigel PS: I really like the Hurricane, in fact with the 6 cylinder engine, it's probably the best Triumph-based body conversion in my opinion (that will get the Sammio fanciers exercised!). Link to comment Share on other sites More sharing options...
RogerH Posted December 21, 2020 Report Share Posted December 21, 2020 1 hour ago, Dougie said: Thanks for all the replies ! As far as I can see there aren’t any bushes. It had been standing for a while (garage showroom) as far as I know. I got about 15 miles before it went. picture of the break below. Thanks for that.I can't see anything obvious that may cause the problem. It looks as if it broke suddenly in one go. Is the push rod bent.? Roger Link to comment Share on other sites More sharing options...
Nick Jones Posted December 21, 2020 Report Share Posted December 21, 2020 3 hours ago, Nigel Clark said: There is a bronze bush inside each rocker. Not on OE ones there isn’t. Nor on most replacements. Just the Moss ones that I’m aware of. Something strange in the close up pic next to the oil hole where it looks like a wear “Island” left by the relief on the shaft has suddenly started seeing contact...... Shaft retaining screw come out allowing the shaft to turn? Or cam change increasing movement range? Nick Link to comment Share on other sites More sharing options...
JohnD Posted December 21, 2020 Report Share Posted December 21, 2020 1 hour ago, Dougie said: Thanks for all the replies ! As far as I can see there aren’t any bushes. It had been standing for a while (garage showroom) as far as I know. I got about 15 miles before it went. picture of the break below. That is enormously worn! Pitted, and what appears to be the remains of some melted (?!?!) material next to the oil supply hole. That may be the cause of a seizure, which was the probable precipatating cause, as there are no marks of a propagating crack. Surely the shaft must be similarly worn and marked, indicating a new shaft? Unless the other rockers are a LOT better, new rockers too! I note that both this and the others shown all crack throrugh the oil vent to the top of the rocker, a clear weak point, but not one that anything can be done about. John Link to comment Share on other sites More sharing options...
Dougie Posted December 21, 2020 Author Report Share Posted December 21, 2020 Thanks all (again). I’ll read and re-read all of the comments, lots to digest. Overall, hope it’s just unlucky and won’t happen on the other rockers! Push rod doesn’t seem to be bent .. Link to comment Share on other sites More sharing options...
Iain T Posted December 21, 2020 Report Share Posted December 21, 2020 See 'Tappet Noise' post, mine didn't break but suffered from lack of oil! Just replacing the rocker is probably not the answer, you need to check the rockers, shaft, retaining screw, oil feed etc. Not sure how you would check a sticky valve? Iain Link to comment Share on other sites More sharing options...
RogerH Posted December 21, 2020 Report Share Posted December 21, 2020 4 minutes ago, Iain T said: See 'Tappet Noise' post, mine didn't break but suffered from lack of oil! Just replacing the rocker is probably not the answer, you need to check the rockers, shaft, retaining screw, oil feed etc. Not sure how you would check a sticky valve? Iain Fill the combustion chamber with string. Remove the valve collets and lift off the springs Turn the crank a little and allow the valve to drop a fraction. You can then waggle the valve to see how stiff it is (when cold). Don;t let the valve drop tooooooo far. Roger Link to comment Share on other sites More sharing options...
Anglefire Posted December 21, 2020 Report Share Posted December 21, 2020 5 minutes ago, Iain T said: Not sure how you would check a sticky valve? Iain Take the the rocker shaft out and give the valves a tap with a brummi screwdriver - should sound solid if its stuck - but in my view given it drove ok for 15miles, it is more likely lack of oil. Link to comment Share on other sites More sharing options...
Iain T Posted December 21, 2020 Report Share Posted December 21, 2020 5 minutes ago, Anglefire said: it is more likely lack of oil. I know all about that.......... Link to comment Share on other sites More sharing options...
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