Rockers

chris_seven · 12-12-2006, 01:33 AM

Reading the posts about 8000rpm + 2.0 litre engines I have a couple of questions about rockers.

We are currently starting to build a Twin Plug 2.0 litre motor which we hope will produce 210+ BHP

I was under the impression that the investment cast rockers were only good for about 7500 rpm on a routine basis.

I am aware that Porsche used a 'solid' rocker that gave no valve adjustment and needed alternative followers and a shim for adjustment.

I can buy 'solid' rockers that have been re-manufactured here in England but thay cost about $3000 per set and need 'Motorsport' rocker shafts that are supposedly still available from Porsche Motorsport. I can easily have the relevant tappets and shims made but the total cost is still very high.

I also think, but can't source, adjustable forged rockers are available.

Any comments about valve trains would be very helpful, and my questions are:

Does anyone know where to source 'solid' rockers complete with shafts, tappets and shims.

Does anyone know where to source adjustable forged rockers and what are their safe limits.

Any other comments welcome.

andrew15 · 12-13-2006, 01:01 PM

Adjustable forged rockers were on the early 65-66 models
The last set I had went for $350 last year - used but in decent shape
Apparently the ratio is slightly improved 1.5:1 vs 1.4:1 for the cast rockers.

You may want to call Henry at Supertec as I think he uses the adjustable forged version in some of his engines and may have a set available for purchase.

Regards,
Andrew M

tom1394racing · 12-13-2006, 01:07 PM

how do you tell the difference between the forged rockers and the cast rockers?

Is the a visual cue like surface finish or stamping?

andrew15 · 12-13-2006, 01:43 PM

Armando has a great side by side comparison on his website:

http://www.pbase.com/9146gt/factory_racing_parts_rockers_adjustable

tom1394racing · 12-13-2006, 02:13 PM

Andrew

Thanks for the reference!!!

tadd · 12-13-2006, 04:18 PM

Chris:
After chewing on this for a bit, it seems that the real 'weak part' is the non pressure fed plain bearings. Do you think it would be as simple as pressing out the bushing, measuing the rocker ID, the shaft OD and then wadding thru a bearing cataloge for one that fits the spacing? If it wasn't such a PITA, you could just buy needles and pack them w/o a cage (maybe if you used the later cam trays with the bolt on shafts?). It just seems impossible to get pressure oil to each shaft, hence using needles. The two-strokes of my youth got on just fine with silver plated cages and the tiniest amount of oil mist for the crank/rod bearings.

tadd

chris_seven · 12-15-2006, 06:02 AM

Tadd,

I have a few sets of used rockers which are in good order but I was looking for a regular supply.

My real concern with the cast rockers is their fatigue life as I had a couple break some years ago and I have assumed that a forged rocker would be better in this respect.

davidppp · 12-16-2006, 10:57 AM

Ah, yes..the Curse of the broken Rocker.

There have been several aftermarket rockers which break....

It is possible to visually ID these fakes..but I do not have pictures..Does anyone have some please?

Kind regards
david

gestalt1 · 12-16-2006, 11:02 AM

arn't the rockers designed to be the weak part? they break so valves don't hit pistons full force etc.. I guess the only reason that would happen is in a timing chain/tensioner failure.

davidppp · 12-16-2006, 11:11 AM

Sure..

And as far as I know, Factory parts do survive with highlifts and revs..how high and how much lift Iam unsure..but these fakes do break,,quite often..under normal use..

Kind regards
david

Walt Fricke · 12-16-2006, 05:31 PM

Well, weren't the factory forged rockers also the ones that had no bushing? Maybe for racing later on Porsche bushed these forged ones? The RSRs had them. Anderson discusses this in his book, as I recall. In any case it is easy to tell them apart. All the cast rockers look about the same, and the forged ones just plain look diffferent.

Before I dynoed my 2.7 race motor I shifted at 8,000 routinely. At first I broke a few rockers without having caused this myself. then this stopped happening. I attribute this to the fact that the weak cast rockers broke.

For all I know one could rev even higher with good cast rockers. Someone sold some for a while that had been carefully polished (some rough grinding used on the stock parts, to remove flash I suppose, and that has to include some stress risers) and X-rayed. But there wasn't enough market for all the trouble he went through to do this.

The forged racing rockers used lash caps to adjust valve clearance. Too tight? Depress the valve, pull off the cap you had installed on the tip of the valve, put on a thinner one, release spring. This seems quite a pain, but with the right valve spring compressor I think maybe it went quickly. Of course, you need several sets of caps.

Tadd - I don't think the factory drip oil system is as bad as you think. I don't think it is the weak link in a 9,000 rpm motor. Sure, maybe you have to rebush sooner, but such a motor is a 40 hour motor anyway, no? So you will have frequent opportunities to check the bushings.

I just got my smaller bore gauge, and found that even my spare batches of rockers with fairly worn bushings (judging by a wiggle the rocker test) were still within the factory wear limit (if only just). As to needle bearings, I always thought those ought to be just the low friction thing until I read something Gene Berg wrote. He claimed needles are made for something that spins, and he pooh-poohed using needles for a rocking motion. Elephant Racing claims the same for their poly-bronze suspension bushings (I have Shine Racing needles up front, and love them, but that doesn't mean Chuck is wrong). But my take is that needle bearings are overkill. And the mind boggles at the thought of hand inserting little needles between the rocker and the shaft, though I suppose using a dummy plug would work. You'd also need a very well made very small washer at each end so the needle ends wouldn't reach out to gouge the cam carrier?

Here are at least four varieties of cast rockers. Note how some have a cast groove at the adjuster end, and some are straight sided. Some have no cast identification, some have the Porsche part delta (one has a delta plus a dot), and some have a B. I don't know what to make of this, though I think the B rockers are elderly (as, say, from either the 2.0 era or the 2.2 era - these are from a motor Grady Clay built and it was an amalgam of those parts plus some 88mm cast iron Japanese cylinders). I don't know what any of these external differences mean, but these are all seasoned veterans.

Walt Fricke

chris_seven · 12-17-2006, 03:15 AM

I have heard the story that the cast rockers are designed to break if the valves hit the pistons and it may be information that was given at the time especially as it seems early engines did suffer tensioner problems.

I would have thought that the force needed to break a cast rocker and a forged rocker would be very similar in a single impact condition and even if the force was 20-30% lower it is still sufficient to do significant damage.

I have also been told that it is better to have cast rockers when you 'buzz' the engine and just kiss the pistons with the valves as again rocker failure would 'save' the engine. I would have thought in this scenario the valve stem wouldn't be in contact with the rocker as it would float to remove the valve to piston clearance and the type of rocker is irrelevant.

I just don't buy in to 'sacrificial' rockers. I think it is much better to have a bomb proof valve train that operates properly and fit chain savers etc.

I agree with Walt that polishing or peening cast rockers to improve fatigue performance is a good idea and if they then take the revs without failure would be more cost effective than 'solid' rockers.

Shim adjustment of rockers is quite easy and used on many engines such as Ford BDA, XK Jags, Lotus Twin Cam etc, etc so I am not to worried about this procedure.

I do agree about needles not being ideal for essentially a 'static' application and as there wouldn't be any procession of the needles I wouldn't be surprised to find some fretting after relatively short times.

Bushing forged rockers would be quite straightforward even if the supply of these parts was still to an older design.

I am therefore still interested to find a supply of new parts

Walt Fricke · 12-17-2006, 09:54 PM

Anyone who doesn't think that the ability of the cast rockers to break more readily upon overstressing than the forged ones do has some practical value should try having the aluminum IS gear strip sometime. That will make a believer of you.

I had all 12 break in maybe 5 seconds at Hallett. No wonder the engine quit. But I'm still running the pistons, and as I recall most of the valves were still OK.

Walt Fricke

(now using straight cut steel IS gears)

Jeff Alton · 12-18-2006, 05:23 PM

The overrevved 3.6 I bought had 12 bent valves, and 12 bent adjustment screws, and 12 perfectly good (crack tested) rockers........

This was just a "kiss" of the valves to pistons but no broken rockers...

Cheers

MBruns · 12-18-2006, 05:56 PM

The bottom line is if the valve train is setup proper with all the critical clearences set, proper valve springs the rockers are not an issue, we have 2.0 race engines turning 8500- 9000 all day, we use stock adjustable rockers for most all of our engines with great sucess, the exceptions are the RSR's and 935 type that are designed to run the solid non adjustable rockers. and they are expensive !

Mike Bruns JBRacing.com

Walt Fricke · 12-18-2006, 07:34 PM

Mike

With the factory 2.8 RSR's HP peak at 8,000, I'd expect you'd shift at about 8,500 or so. If the stock cast adjustable rockers can live with those revs and more in a 2.0, why would the forged non-adjustable (except by the lash caps) rockers be required for the 2.8? Is it because the valve is a little larger and thus heavier?

Walt Fricke

(935 stuff is beyond my horizon)

MBruns · 12-19-2006, 04:34 AM

Porsche designed the center oiling cams to be run with the forged non adj. rockers in the early race engines thru the 962 and late air cooled 3.8 RSR, I would imagine that they didnt want to have the weak link in the system for a race engine, so if they did hit a piston they could keep going. the solid rockers have a different ratio than the adj. type and the factory cams were ground for that. The non adj. rockers are upwards of 300.00 each and take a special coated shaft, The current race cams available from Elgin and Web-Cam are designed to run the adj. style, so with the proper springs they work fine, and it does not take all day to set up the valve lash.

Mike Bruns JBRacing.com

tadd · 12-19-2006, 06:10 AM

Smacks head...

Like duh!

I totally forgort that the center lube cams have holes in the base circles! For some reason I was thinking there was oiling holes only in the bearing journals.

tadd

304065 · 04-03-2007, 02:53 PM

Hmm. . . 930 105 043 00 is bushed and has no groove.

901 105 043 00 is a supercede to the above

I think there are at least six types of adjustable rockers

Early forged with silver-solder tip
Cast, no bushing
Cast, bushing, grooved no marking
Cast, bushing, grooved, triangle marking
Cast, bushing, no groove, "B"
Cast, bushing, no groove, triangle marking

"930" is below (thanks PP!)

304065 · 04-13-2007, 10:46 AM

Update: I have the type with the groove and no triangle, identified third from the right in Walt's excellent photo. These weigh approximately 120.3g without the adjuster and nut and 137g with adjuster and nut.