Fitting RSR o-rings with rocker shafts

[AndrewSlater]

I bought a set of RSR O-rings to fit to my rocker shafts as part of my engine build.

On fitting the number 1 and 4 inlet valves to perform my cam timing, I noticed that each of the O-rings suffered an annular tear, and a slither of a ring of the rubber detached from the o-ring.

Is this normal or is there a method of fitting them to prevent the tearing?
I expect there is enough rubber left to create a seal - but it would seal better if the whole of the o-ring could be fitted.
I have considered cooling/freezing the rocker shafts and rings prior to fitting - whether that would help or not.


As always any advice much appreciated.

Andrew

[johnM]

Hi

Trying to think, as I fitted mine a good few years ago, but I was under the impression that the O ring was actually a rubber washer rather than a typical O ring.... is that what you have??

[AndrewSlater]

Yes John, I think they are called O-rings but are more like a flat rubber washer ( an expensive one at that! ).
When you fit them they seem to have a habit of turning inside out - but I did fit them back to there supplied flat state ( if that makes sense ).

I fitted mine with the rocker apertures lubricated - but I have heard of people fitting them dry. I would expect fitting dry would exaggerate the problem I have seen.
Regards
Andrew

[johnM]

In that case I wouldn't worry too much. As you tighten up the shaft it squeezes the rubber washer which will aid sealing anyway.

Kind Regards

[Gary71]

I'm about to do the same so it's good Andrew keeps asking for advice just ahead of me finding the same problems!

[AndrewSlater]

Thanks John I hadn't considered that - but I still might try freezing the next one to see if the circumference reduces much.

Gary - feel free to jump ahead and then I can pick up some pointers from you
I seem to spend more time asking questions than time on the engine

[fetuhoe]

In that case I wouldn't worry too much. As you tighten up the shaft it squeezes the rubber washer which will aid sealing anyway.

Kind Regards

I don't think this happens as the geometry is all wrong - although it is a common explanation which has been accepted for years.

I am not convinced that they do a great job and are worthwhile.

The end of the shaft really doesn't move a great deal as even at maximum and minimum sizes the radial clearance between the shaft and the housing is only 0.013mm although this increases to 0.0175mm at a typical running temperature.

This would potentially close the top of the slot by around 0.006mm.

This would force the seal outwards by 0.01mm at the very most.

If you examine the end profile of the shaft in detail. I would doubt that the elastic hinge point that allows the clamping load generated by the M7 Bolt to transfer to the cam carrier has much to do with the slot.



As we have a 3-D model and a STP file we carried out some grubby FEA work to confirm that the slot isn't active.

We have just re-designed a Rocker Shaft to use an entirely different sealing arrangement that meets the design criteria recommended by Parker Hannefin and although the drawing does show a slot (drawn before the FEA work) we have decided to make a few prototype without any slots and make some measurements of the force needed to push the shaft out of the carrier.

The 'new' design uses a TiC coated Grade 5 Titanium Shaft which should be more efficient at transferring load than the steel part due to the lower Young's Modulus.

We have re-deigned the nut and the bush to allow the use of a custom sized Viton O Ring which will be used to seal the ends of the shaft.

The cause of leaks in this area is normally due to poor disassembly/assembly which has scored the cam carrier bores.

Rectifying this damage by sleeving carriers or by using oversized shafts would be eye wateringly expensive and tricky.

We believe that by using a correctly configured O ring we will get a decent result in a fairly convenient way.

[Gary71]

Gary - feel free to jump ahead and then I can pick up some pointers from you

No, just behind is fine

I'm currently assembling cylinder heads so will be a while!

Fetuhoe:

Nice solution

Although I think titanium rocker shafts maybe a little OTT for my engine!

[fetuhoe]

I do agree that it sounds a bit 'exotic' but to make the shaft shorter and allow the nut ann bush to fit inside the cam carrier along with a correctly configured O Ring we had to shorten the length of the 'expanding' part of the shaft.

The only way we could think of to still obtain enough clamping was to take advantage of Titanium's lower Modulus so that for a given force it will 'expand' more and therefore transfer load more effectively.

If we can eliminate the grooves we can shorten the shaft without resorting to this technique and go back to using steel.

Having said that the cost difference may be quite small and we think that the complete arrangement will be around £32.50 a set.

This is the shaft, 1 x Nut, 1 x Bush 2 x Viton O rings and a Custom Length M7 Bolt.

If it solves the issue for badly damaged carriers that leak it isn't too bad.

We now have Ti valve Spring Retainers, Adjustable Forged Rocker Arms and Lightend Swivel Foot Tappet Adjusters.

W already have Surface Treated Rocker Shafts which are similar to the 'Motorsport' Shafts used on the RSR so the Ti shafts will replace these parts.

We are working on Beehive Valve Springs and Hollow Valves.

We have Colsibro Valve Guides in production now - they will be manufactured to a 0.025mm TIR concentricity and available in three sizes.

We also have Vernier Adjustable Cam Sprockets and we have drawn but not made tensioner and intermediate shaft sprockets in 7075-T6 Aluminium.

We also plan to make Straight Cut Intermediate Shaft Gears in TiC Coated Titanium.