Refacing rocker arms - false economy?

[JimEB]

Hi,

I suspect my PI's rockers have pitted faces - they're getting noisier and are hard to adjust. I appreciate that the shaft will most likely be worn too...

Is it worth trying to get them refaced or simply buy new ones? I remember reading somewhere that Triumph ones were only face hardened to a miserly depth  ??)

If new, then Chris Witor advertises NOS ones, but are the Rimmer/Moss ones NOS or repros?

[Nick Jones]

Depends how deeply worn...... and how knacked the shaft is.  I tend to use an 0.008" feeler gauge these days!

Genuine NOS - fine (think only one hand still available?) other offerings seem to be rather crap.  I was given sight of a freshly broken new one recently and it was not a high quality item in finish or material.  Suspect a refaced and bushed (if needed) original would last alot longer.

Nick

[Hogie]

I don't know if anybody has tried to re-harden rocker arm contact faces but has one considered applying a coating of hard weld material.
You can get welding stcks of all grades. Specific ones for applying a hardened surface may work.

Easy enough to apply and grind back to shape.
The bush is simple enough.

Would an over hard rocker pad be too unkind on the valve stem.

Roger

[GT6 M]

After ye grind the rockers doon, they will be better than a new,n.
reason is the metal behint the indent, has now been compressed / work hardened.
so is actually stiffer / tuffer than the OE stuff.
the OE case hardening is still there, its just the case hardened bit, has actually pushed / sqasshed the underlying soft metal into its sell, thus forming an indent, and also mek,n the underlying metal much stiffer noo.

that is, IF the rocker face has no disintegrated..

So re face, and they better than OE.

{ there is a stuff oot called Casenite,  but needs to be red hot , then dip,roll the stuff into it
Or, bung all rockers into a sealed container, cover with the stuff, and bake for a few hours
at v v high temp, to get the gasses into the metal pores.  but its hard work.}

Some intresting reading in here.
so read,ndigest. ;)
http://academic.uprm.edu/pcaceres/Courses/MechMet/MET-6A.pdf

M

[Hughbert]

796 wrote:

After ye grind the rockers doon, they will be better than a new,n.
reason is the metal behint the indent, has now been compressed / work hardened.
so is actually stiffer / tuffer than the OE stuff.
the OE case hardening is still there, its just the case hardened bit, has actually pushed / sqasshed the underlying soft metal into its sell, thus forming an indent, and also mek,n the underlying metal much stiffer noo.

that is, IF the rocker face has no disintegrated..

So re face, and they better than OE.

{ there is a stuff oot called Casenite,  but needs to be red hot , then dip,roll the stuff into it
Or, bung all rockers into a sealed container, cover with the stuff, and bake for a few hours
at v v high temp, to get the gasses into the metal pores.  but its hard work.}

Some intresting reading in here.
so read,ndigest. ;)
http://academic.uprm.edu/pcaceres/Courses/MechMet/MET-6A.pdf

M

Other processes to consider
http://www.tstcoatings.com/wear_resistant_coatings.html

http://www.amphardchrome.co.uk/metal-spraying.php

http://www.tstcoatings.com/hard_chrome_replacement.html

http://www.mbicoatings.com/content.cfm/Coatings/THERMAL-SPRAY-COATINGS/category_id/102/page_id/171

[sparky_spit]

I'm with Marcus on this.  I did this once on a 1300FWD engine and it made a big difference to being able to get a more accurate adjustment.

The good bit is that the indentation is highly polished and therefore easy to see and keep an eye on as you grind the whole surface down.  I used a whetstone, as used for sharpening wood plane blades, with a drop of oil. As it is flat, it is easy to follow the curve of the rocker face and you keep going until the shiny bit becomes level with the rest of the face.

[99176]

I've always refaced and then used 'Kasenit'.
May be difficult to locate these days, but I'm still working my way through a large tub bought in the seventies.

[MarkDeTriomphe]

Nick_Jones wrote:

Genuine NOS - fine (think only one hand still available?) other offerings seem to be rather crap.  I was given sight of a freshly broken new one recently and it was not a high quality item in finish or material.  Suspect a refaced and bushed (if needed) original would last alot longer.

Nick

A bit like this one?  :'( .  I was only driving gently at the time, honest!

Mark

[Nick Jones]

MarkDeTriomphe wrote:

A bit like this one?  :'( .  I was only driving gently at the time, honest!

Mark

Indeed...... that actual one in fact!

Nick

[Richard B]

MarkDeTriomphe wrote:

  I was only driving gently at the time, honest!

Yeah, right  ;)

[69vitesse]

MarkDeTriomphe wrote:

A bit like this one?  :'( .  I was only driving gently at the time, honest!

Mark

Interesting…

[Hogie]

Why!

Roger

[69vitesse]

2601 wrote:

Why!

Roger

There appears to be either a casting flaw or notch in the arm at the point of failure.
Inclusions or nicks/notches in castings or forgings act as stress risers.

[Hogie]

I thought that was what you were getting at. There does indeed appear to be a small indentation in the edge section.
However this is on the compression side of the arm so wouldn't be heavily loaded.
Looking at the surface structure of the crack face it looks as though it was an instantaneous clean break.
The push rod is seriously bent and broken suggesting a siezed valve.

Roger

[MarkDeTriomphe]

2601 wrote:

I thought that was what you were getting at. There does indeed appear to be a small indentation in the edge section.
However this is on the compression side of the arm so wouldn't be heavily loaded.
Looking at the surface structure of the crack face it looks as though it was an instantaneous clean break.
The push rod is seriously bent and broken suggesting a siezed valve.

Roger

Roger - I agree with you regarding the break.  Will get it out again tomorrow to check, but I assumed it was a clean break.
However, the push rod came from the exhaust valve - assumption is that the broken piece of (inlet) rocker flew over to the exhaust side and jammed the pushrod against the side of its channel - causing it to bend until it could go no further and finally snapping!
Engine has been running since - suggesting valves are OK - except that it is now playing up again so further investigation needed.
Mark  

[thescrapman]

2729 wrote:

There appears to be either a casting flaw or notch in the arm at the point of failure.
Inclusions or nicks/notches in castings or forgings act as stress risers.

There also seems to be the same indentation on the rocker 2 along in the first picture.

[69vitesse]

2601 wrote:

I thought that was what you were getting at. There does indeed appear to be a small indentation in the edge section.
However this is on the compression side of the arm so wouldn't be heavily loaded.
Looking at the surface structure of the crack face it looks as though it was an instantaneous clean break.
The push rod is seriously bent and broken suggesting a siezed valve.

Roger

It is however a loaded component and any casting inclusion or nick is bad. We have a failed component, and what appears to be a flaw at a fail point in the component.
Stress cracking can start from any damage and spread. If there was a crack at that point, the strength of the component would  be compromised. There is no such thing as a benign potential point of failure.

[piman]

Hello Mark,

what springs are fitted, they look quite heavy duty? No sign of spring binding?

Personally I would say that nick would not have caused the fracture as it actually fractured ahead of the nick.

Alec

[Hogie]

Hi 69V,
            cracks are not deisrable ; however a 'crack' in a compression mode will not propagate. Even a'relax-compression-relax' mode will not make it propagate.
As Alec states the 'nick' looks like a profile change as shown on the other rockers.

If the rocker broke because of the 'nick' then you would see signs on the fracture face indicating that.
I believe the arm snapped in one sudden event as indicated by the bent/broken push rod.

Roger

[69vitesse]

Cracks very much can start and propagate in a compressive environment.

[Lord Sorbington]

Check the adjuster screws too, I had severely worn, ridged balls on some of mine which combined with knackered rockers arms and very worn shaft meant they could never be adjusted properly.

[Lord Sorbington]

The extra oil drilling in the upper surface of the repro rocker arms I bought was a mixed blessing too.  Good for rocker tip lube but caused extra oil consumption. Apparently the saloon rockers only had an oil way for where the ball acts on the pushrod but the "sports car" rockers had the extra hole on top of the rocker arm too.

I bought a repro rocker shaft too, it was so nice to have a smooth, quiet engine again!

[Hogie]

Cracks very much can start and propagate in a compressive environment.   ;D ;D ;D

Roger

[MarkDeTriomphe]

piman wrote:

Hello Mark,

what springs are fitted, they look quite heavy duty? No sign of spring binding?

Personally I would say that nick would not have caused the fracture as it actually fractured ahead of the nick.

Alec

Hi Alec,

They are XJ40 springs - no sign of binding and I believe not heavy duty / have been used by many others without issue.

And a little more background:

The whole engine assembly had supposedly only done about 3000 miles since a professional rebuild - the shaft and rockers all looked like new (repro) items - except that the faces on at least 4 of the rockers had been eaten away and could not be re-used (hence the older looking rockers in the photo).

And .. I did forget to mention that I was on my way home from this year's CT autosolo - so the engine had been bouncing off the rev limiter all day.  This might not have helped  ;)

Mark

[piman]

Hello Mark,

with valve bounce there's no way of telling what happens but as I'm sure you know not good for the engine?

Alec