V8 rocker shaft bronze bushes

[freddynav]

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 forum but the thread 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.

[GDCobra]

I'll be watching this with intereset, I remember the first time I took a rocker shaft apart on mine, couldn't believe the wear on the shaft as well as the rockers. Just a thought, would it not be possible to bore out he rockers to accept a sleeve and keep the shaft OD as per standard? I expect you are only talking about a small reduciton in diameter but I'd have thought keeping the bearing surface as large as possible would be beneficial.

[freddynav]

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.

[freddynav]

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.

[freddynav]

Next job is to ream all the rockers. Currently half way through so pictures to come.

[GDCobra]

Interesting work. Guess I'd miss-remembered how much material there is in the rockers so take your point on reducing shaft size, 20mm doesn't seem too bad, had visions of you going down to 16 which as you say is a bit spindly. What is the standard size by the way?

[ChrisJC]

Interesting idea. Looks good.

I'm curious to know what advantages this will bring?

Chris.

[DaveEFI]

Do RV8 rockers wear out quickly if the engine is properly maintained? Mine seemed pretty good when I changed a worn cam at about 110000 miles, so I just re-used them. And it still seems quiet after a lot more miles.

[freddynav]

From my experience and research it seems very variable as to how long the rockers last. Some of the original items, with good servicing seem to last a long time. However, replacement items seem to be unreliable in quality and when anything is worn in this department a lot of oil is sent to the top end due to the bad tolerances and the valve stems can become swamped with oil. It also leads to reduced oil flow to the rest of the engine. I know there are a lot of varying opinions here and I’m not going to stand here stubbornly saying this solution is absolutely required on all occasions. It’s just a fun technical experiment which I hope might garner some interest.

Continue following if you are interested. We are however in real time now so have to wait until other jobs are cleared to allow me to carry on. Won’t be long,.

[DaveEFI]

Did wonder if it was some replacements being of poor quality. As with so much else. But even a decent design can be improved on, so didn't intend to criticise your project.

[SuperV8]

Did wonder if it was some replacements being of poor quality. As with so much else. But even a decent design can be improved on, so didn't intend to criticise your project.

For my first set of rockers from a well known LR parts place I trial fitted them on the new shafts but the fit seemed rather loose and wobbly! Got the vernier out and the ID of the new rockers was larger than the worn dimension of the original's which were worn well oval! Returned them and the same company sent out a different branded set of rockers which actually looked like the originals and had a much better fit on the shafts. I do wonder how many have just been fitted and then wonder why the oil pressure isn't great!

Interesting project.
Thinking out loud - Is a ball bearing fitment possible? probably need too small a shaft or too much meat taken out a rocker.

[freddynav]

Did wonder if it was some replacements being of poor quality. As with so much else. But even a decent design can be improved on, so didn't intend to criticise your project.

No no I did not think you were criticising. Don’t worry,

[minorv8]

Also the rocker shafts may be of bad quality. I still have a pair of unused aftermarket shafts that were smaller diameter that the worn part of factory shaft. Oversize rocker and undersize shaft = almost perfect

Ball bearings are impossible, needle bearings could be possible but apart from strength may create another issue if the bearing lets go and needles are all over the engine. Some rocker companies in USA nowadays use bushes instead of needle bearings.

[Mc Tool]

I have new shafts and FM steel rockers that are pretty wobbly . The shafts must be ok as they are a firm fit in the rocker posts . I havnt used them yet , thinkin I might just get some roller rocker /shaft/post assy , not that the engine really needs them , bucket list thing, and they cant hurt. I have a few engines in bits and rocker shaft/rocker wear is not consistant. I think ally being soft any grit in the oil becomes embedded in the surface of the ally and its this abrasive that chews into the shafts. If the shafts are chewed but the rockers dont appear worn ( I have some here like that ) they should be binned as fitting said rockers to a new shaft may feel fine(wobble wise ,and they do ) they will chew out a new shaft ( they did ) quickly. Seems crazy to me ......all ya gotta do is change the friggin oil and filter , but some people just dont . The most rooted rv8 engine I stripped had only 88000kms under its belt and the sump oil had to be seen to be believed

[freddynav]

I have new shafts and FM steel rockers that are pretty wobbly . The shafts must be ok as they are a firm fit in the rocker posts . I havnt used them yet , thinkin I might just get some roller rocker /shaft/post assy , not that the engine really needs them , bucket list thing, and they cant hurt. I have a few engines in bits and rocker shaft/rocker wear is not consistant. I think ally being soft any grit in the oil becomes embedded in the surface of the ally and its this abrasive that chews into the shafts. If the shafts are chewed but the rockers dont appear worn ( I have some here like that ) they should be binned as fitting said rockers to a new shaft may feel fine(wobble wise ,and they do ) they will chew out a new shaft ( they did ) quickly. Seems crazy to me ......all ya gotta do is change the friggin oil and filter , but some people just dont . The most rooted rv8 engine I stripped had only 88000kms under its belt and the sump oil had to be seen to be believed

The shaft I am working on shows signs of wear to itself and the rockers themselves have also become ovoid. Quite agree with the statement about changing oil and filters. It’s the seeming lack of tolerances on the new parts in this department that annoys me.