V8 rocker shaft bronze bushes

#1
Hi all,

Having been pretty unimpressed with the quality of replacement standard rocker shafts and rockers I have decided to modify the existing arrangement to include bronze bushes on a narrower shaft. I’ve seen it done before in another but the thread on this forum died a death with no conclusion. My intention is to document the process, explain all the materials used and hopefully offer the service to others who might be interested.

I know there are lots of opinions about steel vs aluminium rockers and from where to get them etc etc. Could I ask this thread does not become another place for such chat. The idea here is for those who are interested to see the technical side of the project and it’s success or otherwise.

I’ll include pictures and measurements plus material specifications. Any useful comments most welcome.
 

jp928

Well-Known Member
#5
Me too! Many years ago when I used to visit our nearest rubbish dump I saw an engine that has some familiar parts on it. Turned out to be a Buick300 - iron block, alloy heads, with a 4 barrel inlet manifold. In those days the supervision was very slack, and I managed to get the manifold and heads away to play with. The heads were beyond saving, but I made a few $ selling the manifold. Dismantled the rockers off the heads, and one of the shafts showed that it had been broken and welded back together....
Mind you, regular oil changes on the larger oil pump might be cheaper?
 
#6
Me too! Many years ago when I used to visit our nearest rubbish dump I saw an engine that has some familiar parts on it. Turned out to be a Buick300 - iron block, alloy heads, with a 4 barrel inlet manifold. In those days the supervision was very slack, and I managed to get the manifold and heads away to play with. The heads were beyond saving, but I made a few $ selling the manifold. Dismantled the rockers off the heads, and one of the shafts showed that it had been broken and welded back together....
Mind you, regular oil changes on the larger oil pump might be cheaper?
In theory I entirely agree you are right, there should be cheaper options. I’ve come round to this for 2 reasons: 1, I love messing around and doing things properly, and 2, through experience and research there just isn’t a guarantee of quality when it come to rockers and shafts. The consensus seems to be good quality and unworn original items and an approach as you suggest is the way forward. Unfortunately, it’s hard to reliably find good used parts for this department, and as I said before the replacement parts in this area seem woefully variable.

Either way, for right or wrong, I’ve started this project so stay tuned. First photos from this weekends work will be posted this evening and then it’ll be real-time.
 

jp928

Well-Known Member
#7
I once suggested to mates in the game that P4 throwout bearings would last longer if they were angular contact types, rather than plain deep groove bearings - reponse was 'then they will last forever!'.
I would be right with you if I didnt have more pressing issues to chase, and recent installation of Island4x4 rockers and shafts. I already found some 13/16 OD x 11/16 ID x 1" long bronze bushings that would seem suitable, if you found 11/16 shafts.
C93200 Bronze Bushing - 11/16''ID x 13/16''OD x 1''Long
 
#8
I once suggested to mates in the game that P4 throwout bearings would last longer if they were angular contact types, rather than plain deep groove bearings - reponse was 'then they will last forever!'.
I would be right with you if I didnt have more pressing issues to chase, and recent installation of Island4x4 rockers and shafts. I already found some 13/16 OD x 11/16 ID x 1" long bronze bushings that would seem suitable, if you found 11/16 shafts.
C93200 Bronze Bushing - 11/16''ID x 13/16''OD x 1''Long
Hi, thanks for the info. I too ordered some shafts from Island 4x4 but I wasn’t impressed by the quality of the Britpart item that arrived. It went back I’m afraid. Your suggestion of an 11/16 shaft is a little smaller that I have gone for. For right or wrong i’ve gone with a 20mm shaft.
 
#9
I made the decision to base the project around a 20mm shaft for the following reasons:

1. The original size shaft is not a standard industrial size that is easily sourced.
2. Keeping the standard diameter shaft would require too much material to be removed from the rocker to leave sufficient strength in the casting for insertion of a bronze bush. A 20mm shaft is a happy medium in these respects.
3. The next standard size down is 16mm (at least from the source I am using) which is rather narrow and could suffer from more flex.

I chose a quenched and tempered precision hollow shaft with minimum surface hardness of 60 HRC and drilled it to original specifications.
 

Attachments

#10
Next was to machine a mount into which the rockers can be placed securely so they can be first drilled to 22.5mm and then reamed to 22.98mm. I also machined a simple alignment tool so when the rocker is clamped the bed of the mill can be aligned with the spindle before machining the rocker. I utilised Land Rover flywheel dowel pins as locators to ensure I can repeatedly position the clamps accurately. Maybe overkill but it was fun.
 

Attachments

jp928

Well-Known Member
#12
I wasnt sure how much material could be safely removed from rocker bore before they were weakened badly. Hence idea of going to a smaller dia shaft. Sounds like you are well along. Are your shafts much harder than the std parts? Fitting sleeves in the std pedestals?
 
#14
I wasnt sure how much material could be safely removed from rocker bore before they were weakened badly. Hence idea of going to a smaller dia shaft. Sounds like you are well along. Are your shafts much harder than the std parts? Fitting sleeves in the std pedestals?
Hopefully I have compromised at 20mm appropriately but we’ll see in the long run. I do not know the specific hardness of the standard shafts but inspection and some very basic testing points to them being surprisingly soft. Indeed the amount of wear on 2 sets I have is alarming considering the rockers in my case are aluminium. I did consider sleeving the pedestals but tbh with C&C machines now it’s quicker to make new pedestals.
 
#15
This does not look like the tooling for a single set ;)
HEHEHE, being a serious ‘hobbiest’ I tend to overdo most things so part of it is due to that. However, optimistically I’d like to be able to do a few sets for people but like most things like this I think the cost of materials may make it a non starter. We’ll see.
 

mrtask

Well-Known Member
#19
From the link you posted, Ron:
"8620 solid steel shafts incorporate a special heat treatment and copper plating method that also incorporates exact tolerance bolt holes which results in the strongest shaft on the market."
Also watching your progress with great interest, Freddurrant. Keep us posted!
 
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