Lagondaforum

Subject: Rocker pin survival rate!

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I have had my 14/60 for several years with no significant problems. More recently I had the engine professionally rebuilt since when (and I don't imply any connection) I have had two rocker pins fail about 50 miles apart. Whilst the rockers were replaced during the rebuild, the pins are original.

In my understanding, pin failures are rare (more so than rocker failures which themselves are uncommon) and I think that these failures cannot be just random and coincidental. Has anyone had a similar experience? All bright ideas will be much appreciated.

John

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Subject: Re: Rocker pin survival rate!

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Hi John, I had a series of pin and rockers fail a few years ago following the fitting of my new semi downdraft head. The problem was finally traced to a valve guide not fully pressed home. Although when I replaced the broken item I set the correct clearance when the engine heated up the rocker hit the top of the valve guide and then either the pin or rocker broke! As I was on a rally in France at the time I did not fully investigate until I came home. Is it the same rocker/pin failing? Have you had the valve guides changed? I would suggest you check the clearence between the top of the guide and rocker.When I finally found the cause of the problem I took about 20th from the top of each guide.

Subject: Re: Rocker pin survival rate!

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Thanks very much for this Mike. Yes, the guides have been replaced and also the camshafts are high lift which would compound the sort of problem you describe. I hear no sound of touching when the engine is spun on the starter but of course a hot engine and high revs are a very different scenario. I'll investigate as you suggest.

Different pins failed - first #4 exhaust and then #1 exhaust.

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Subject: Re: Rocker pin survival rate!

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When I had the problem it ran for some time between breakages If only I had found the cause on the Rally running with larger tappet clearances would have got me home! I guess with the new cams you are already running with at least 10thou clearance.

Subject: Re: Rocker pin survival rate!

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I would suggest that you have at least .050"/.060" between
the top of the guide, and the top cap bottom/split collet
bottoms at full lift. The reason for the gap is to stop oil
being forced down the guide. Make sure the top of the guide
isn`t flat, it needs to tapper downwards and outwards from
the valve bore.

Ray Sherratt.

Subject: Re: Rocker pin survival rate!

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Mike, Ray,

I've now had a look at one of the valve assemblies and am a bit wiser. The guide is certainly OK - fully seated and a standard 2 litre guide. But I think you are right that there is inadequate clearance between the valve cap and the guide though it's difficult to measure through the springs on full lift as the pockets are quite deeply recessed. I think I'll try the plasticene pad ploy.

Many thanks for the help, much appreciated,

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Subject: Re: Rocker pin survival rate!

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Put the valve at full lift, and arrange a suitable leaver to
open the valve further. If you have a dial gauge and a base
to mount it with, set the gauge on the top cap, set to zero
and lever the valve open, take a reading. You need at least
.050" more. If you have a high lift cam allso check for valve
spring coil bind.

Ray Sherratt

Subject: Re: Rocker pin survival rate!

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Ray,
No dial gauge but plasticene suggests the clearance is much less than 50 thou. At least I now understand the pin failures.

Thanks for the help, much appreciated.

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Subject: Re: Rocker pin survival rate!

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Thanks John just trying to help

Ray.