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Rocker Arm broken


Dougie
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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

 

5C89C5D9-0AA2-43A3-96DD-5BC1D3DC1871.jpeg

5ECD5BEF-2E4E-4127-B5D1-3C4B956C975F.jpeg

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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.

 

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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

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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

 

5C89C5D9-0AA2-43A3-96DD-5BC1D3DC1871.jpeg

5ECD5BEF-2E4E-4127-B5D1-3C4B956C975F.jpeg

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

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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

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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.

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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

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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!).

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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. 
 

AE8A085B-A19C-4419-8B5F-B0E2538B1FAD.jpeg

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

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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

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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. 
 

AE8A085B-A19C-4419-8B5F-B0E2538B1FAD.jpeg

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

 

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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 

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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

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