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domV8

Original Poster:

932 posts

68 months

[news] 
Friday 26th November 2010 quote quote all
Was wondering -

What are the differences of "roller rockers" to the standard OE items - and what makes them better for hig-speed rpms..?

I often hear of "alloy roller rockers" - alloy I could see being lighter, and therefore might accelerate/deaccelerate quicker, making them more suitable for high revving, but what is the "roller rockers" part..?

Essentially - how are OE and roller rockers different..?

Many thanks,


Dom

blitzracing

4,079 posts

107 months

[news] 
Friday 26th November 2010 quote quote all
I thought these where for use on overhead cam engines, where the roller runs against the cam lobe more closly, not push rod engines

Magic919

9,519 posts

88 months

[news] 
Friday 26th November 2010 quote quote all

Transmitter Man

3,180 posts

111 months

[news] 
Friday 26th November 2010 quote quote all
and available for the RV8: http://www.v8buick.com/showthread.php?t=212223

Phil

spend

12,476 posts

138 months

[news] 
Friday 26th November 2010 quote quote all
blitzracing said:
I thought these where for use on overhead cam engines, where the roller runs against the cam lobe more closly, not push rod engines
That would be a roller cam where the followers have a roller, also available for push rod engines wink
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Brummmie

4,751 posts

108 months

[news] 
Friday 26th November 2010 quote quote all
I tried roller rockers on my LS motor, it gave it valve float as the weight of the bearing is over the tip and it accentuates the extra weight.

domV8

Original Poster:

932 posts

68 months

[news] 
Saturday 27th November 2010 quote quote all
Brummmie said:
I tried roller rockers on my LS motor, it gave it valve float as the weight of the bearing is over the tip and it accentuates the extra weight.
Is there any advantage to roller rockers for running higher rpms then? From the "HiFlow" page it looks like the rollers are there for minimising friction between the rocker and the valve stem..?

I see the effects that lightweight rockers have in terms of lowering reciprocating mass, and adjustment to rocker ratio could also have beneficial effects - but from Brummies post it would appear that he saw adverse effects from the offset weight, and valve float is exactly what you are trying to avoid when running higher RPMs...

So if looking to run higher rpms - would one choose simply a lightweight rocker, or a lightweight roller rocker..?

Many thanks,



Dom



spend

12,476 posts

138 months

[news] 
Saturday 27th November 2010 quote quote all
All the roller rockers I've seen for RV8 are lightweight... but beware many don't have the correct offsets like the KB's (TA's look like a fine reproduction BTW) & YT's - thats in the horizontal plane between the pushrod tip and valve stem. You also typically get valve clearance adjusters, avoiding silly geo changing shims on hydraulic installs or ideally allowing solid cams and pushrod oiling + more substantial pushrods. If you want a valve train that can rev you are going to have to get suitable springs, if getting valve float something would likely have been specced incorrectly (probably springs?).

eff eff

474 posts

91 months

[news] 
Saturday 27th November 2010 quote quote all
Saw a US website that suggested different pushrods (longer I think) and stonger beehive style valve springs to control float

Guillotine

5,357 posts

151 months

[news] 
Saturday 27th November 2010 quote quote all
roller rockers are much better for high lift and high revs.

the rocker tip (that sits on the valve stem tip) travels up and down in an arc from the centre point of the shaft. Think of the shaft and rockers viewed from the end) The higher the cam, the further it travels and the greater the arc.
This arc generates a side load on the valve. Particularly as higher cam and valve travel means greater spring rates to keep the tip of the rocker on the tip of the valve and prevent bounce.
Now increase the revs by a thound rpm (+20%? my eales engine revved to 7800rpm) and you have a massive increase in the valve side loads.

Roller rockers, are bigger (reducing shaft loads) and have a roller at the tip allowing it to roll across the tip of the valve and massively increase valve life, valve guide life and rocker/shaft life.

Probably b0ll0cks but it's how I see it, as a layman.

Andy

Geoff Ashcroft

304 posts

93 months

[news] 
Saturday 27th November 2010 quote quote all
You're about right Andy IMO, as it takes a fair bit of horsepower to open valves. So the use of rollers (roller followers in pushrod and roller rockers in OHC motors) help to reduce friction, easing the load on working faces and improving valve-train durability. Simples.

Transmitter Man

3,180 posts

111 months

[news] 
Sunday 28th November 2010 quote quote all
Andy,

I wonder if you looked into also adding roller lifters which I have with a roller cam in my other engine:

http://www.compcams.com/Products/CC-'Hydraulic%20R...

Phil
420 SEAC

Guillotine

5,357 posts

151 months

[news] 
Sunday 28th November 2010 quote quote all
yes I would, gotta be better than flat.

How do they keep them lined up? ie the bearing at 90 to the cam?

A

Slow M

2,036 posts

93 months

[news] 
Monday 29th November 2010 quote quote all
Guillotine said:
yes I would, gotta be better than flat.

How do they keep them lined up? ie the bearing at 90 to the cam?

A
dog bonz, OK, dog bones, they look like a childish version of a combination wrench. There's also a hinged type, where a bar is hinged to a pair of lifters, keeping them parallel.

Slow M

2,036 posts

93 months

[news] 
Monday 29th November 2010 quote quote all
Brummmie said:
I tried roller rockers on my LS motor, it gave it valve float as the weight of the bearing is over the tip and it accentuates the extra weight.
Would you be so kind as to mention the make and model of the rockers in question. Also, at what RPM did you see float, and with what lift, lobe, and springs? I'd love to see the mass comparison between the roller and the one you're comparing to as well. Was it a stock unit?
Thx,
B.


GAjon

1,935 posts

100 months

[news] 
Monday 29th November 2010 quote quote all
Not the best of pictures (mobile phone) but here's some I made earlier on the V6 pushrod.


Brummmie

4,751 posts

108 months

[news] 
Tuesday 30th November 2010 quote quote all
Slow M said:
Brummmie said:
I tried roller rockers on my LS motor, it gave it valve float as the weight of the bearing is over the tip and it accentuates the extra weight.
Would you be so kind as to mention the make and model of the rockers in question. Also, at what RPM did you see float, and with what lift, lobe, and springs? I'd love to see the mass comparison between the roller and the one you're comparing to as well. Was it a stock unit?
Thx,
B.
Comp Cam R roller rockers, that engine was a 383ci, with forged internals, valve float set in at around 5800rpm, it then hit a wall at 6200rpm (182mph).
Dont remember the cam spec, was around a 233 .580ish lift.
I have standard rockers back in it aswell as a bored ls3 block and ITBs, and it revs clean through to 7k now.

Slow M

2,036 posts

93 months

[news] 
Thursday 2nd December 2010 quote quote all
Brummie,
THX,
B.
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