Hot 2 liter engines

[TargaFlorio]

I can't fully agree with that, the 2 litre cup cars all rev to 8k, they're not using solid rockers.

I didn't say that you can't rev a non-solid rocker engine past 7300 RPM. You can do all kinds of stuff with a modified 2.0 engine.

This thread was originally about 2.0S vs 906 engine differences. As such, I was referencing what Porsche did / used in period. Porsche's non-racing engines topped out at 7300. Their race engines (with solid rockers) went to 8K.

My comment was about the perceivable difference of driving a 911R/906 engine vs. a 68S engine. As such, the higher revs really made an impression on me.

Ciao,
n.

[Jeff Higgins]

I'm a bit confused - there are obviously no "tappets" per se in these engines, so it looks like somewhat of a terminology issue. Where do the shims go with these solid rocker arm engines? Is there a "bucket" over the valve spring as is commonly used on modern motorcycle engines, with the shim either captured under it or in a recess on top of it? Would such a "bucket" be what we are calling a "tappet"?

I can't find an image that includes a rocker arm, so imagine this setup with the cam moved over and a rocker arm in between. This is what I mean by the "bucket" and the "shim":

[gled49]

The lash caps go over the valve stem, with different thickness shims. Also parkerized shafts for oil retention. A solid rocker is almost 2 oz. lighter than a standard rocker, which assists in raising RPM. Gordon

[Schläfer]

The lash caps go over the valve stem, with different thickness shims. Also parkerized shafts for oil retention. A solid rocker is almost 2 oz. lighter than a standard rocker, which assists in raising RPM. Gordon

Great photo Gordon, may I ask how long it takes to accurately set the valve gaps? I’m guessing it has to be done with the engine out too?

[Jeff Higgins]

Thanks Gordon, that's kind of what I had pictured. It looks like the caps are really just very small "buckets" that fit over the valve stem rather than the whole valve spring. I'm assuming with this design that the stock valve, valve spring, and retainer configurations are still used, albeit with lighter valves, heavier springs, lighter retainers, etc.

Schläfer, it looks to me like they could be adjusted in the car. Just loosen the rocker shafts and slide them out of the way so the rocker arm is free. We replace broken rockers in the car, and this doesn't look any different than doing that.

[gled49]

When building a lash cap engine, valve length is critical. Typically the 2.0L valves are 2mm shorter with lash caps. With those valves NLA, valves need to be shortened. 3.0L valves are usually ok. You can run stock valves, they don’t have to be lighter. Springs and retainers, whatever you want. I use the valve spring replacement tools (with engine assembled), to change lash caps, depress retainer with spring and use magnet to remove cap. It can be done in car. After build and dyno, valves are adjusted, and usually next adjustis done with overhaul. Tools pictured not the bolt stretch w/dial. It takes time to use solid rocker, but having the lash cap selection is the real problem. And Porsche lash caps only fit 9mm valves. Hot rod engine builders want to use TI valves, usually not metric. There are different ways to reduce weight in the valve train, this was the old school way. G

[Jeff Higgins]

Ah, o.k., that looks way easier than how I was thinking it had to be done. I hadn't thought that there would be room to get the cap and shim out just by using the valve spring compressor. But, of course, there has to be room to get the little split collars (I'm not sure what the "real" name is for them - "keepers"?) out when you push the retainer down, so of course there would be room to get the cap and shim out as well. Great info - thanks for sharing.

[TargaFlorio]

While we're on the 906 valves / rockers subject, here are specs that were provided by factory:

- The rockers were steel with hard-chromed surfaces
- Claimed weight for the solid 906 rockers was 65g. Regular 911 rockers with adjustment nut were 125g
- As mentioned above, valve stem diameter was 9mm and the valve head sizes were 45mm (intake) and 39mm (exhaust)
- Valves were sodium filled
- Valve heads (for valve lash adjustment) were available from 1.5mm to 3.2mm with 0.05mm jumps between each size
- Factory recommendation for newly built engines was to use valve heads between 2.0mm and 2.7mm
- Valve lash was to be set at 0.1mm
- Valve tool was P141 (see attached pic, it looks like one of the photos posted previously)



With the solid rockers the factory set the continuous redline at 8000RPM and temporary redline at 8200RPM

Ciao,
n.

[Jeff Higgins]

Good stuff, guys.

On a related note - why no roller rocker tips? They are pretty ubiquitous in the world of hot rod American pushrod V-8's, which are turning at somewhat lower rpm. The idea is to eliminate any side loading on the valve stem. The rocker tip, describing an arc as it pushes the valve down, necessarily applies a bit of a side load to the stem. I assume it's not considered enough of an issue for anyone to feel like they need to deal with it in these motors. Thoughts?

[TargaFlorio]

Good stuff, guys.

On a related note - why no roller rocker tips? They are pretty ubiquitous in the world of hot rod American pushrod V-8's, which are turning at somewhat lower rpm. The idea is to eliminate any side loading on the valve stem. The rocker tip, describing an arc as it pushes the valve down, necessarily applies a bit of a side load to the stem. I assume it's not considered enough of an issue for anyone to feel like they need to deal with it in these motors. Thoughts?

I'm not an engineer but I think roller rockers would add weight at the worst location (the tip). Porsche eliminated the adjusting nut at the tip of the rocker to save weight in that crucial location. The lighter rockers had less reciprocating mass which allowed for higher sustained RPMs.

Perhaps this also had something to do with the availability of the springs at the time. I remember Porsche had a valve spring issue with their 547 engine which was solved with springs that were manufactured in California. At the time, none of the German manufacturers were able to provide a spring that measured up the Porsche's requirements.

I'm sure the engineers and engine builders on this site will be able to give you more info on the intricacies of the valve gear as it pertains to engine performance.

Ciao,
n.