Author Topic: Roller Rockers for a 998  (Read 821 times)

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Terry

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Roller Rockers for a 998
« on: July 05, 2012, 03:30:00 AM »
Hi,

Found myself looking at roller rockers this morning and came across an option I was not aware of before, just buying the rockers and fitting them to the standard shaft and posts. Also fell into a site that has a couple of good articles on setting up Roller Rockers, albeit for MG's, properly.

These seem to to be a known brand from the US,
http://www.harlandsharp.com/948_1275_mgb.htm

While here is an article the explains the general principles of Roller Rocker Installation,
http://www.flowspeed.com/rocker-tech.htm

And for some specific instructions on the above Harland Sharp variety,
http://www.flowspeed.com/harland-sharp.htm

All seemed to make reasonable sense to me, but I am sure everyone has their own ideas on what is best and how to do it best.

Terry
13: "I am the scariest number."
666: "No, I am the scariest number."
2020: "Hold my beer and watch this."

Cujo. 1999 - 2016

Terry

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Re: Roller Rockers for a 998
« Reply #1 on: July 20, 2012, 07:49:40 PM »
Hi,

A little bit of an update on this highly engaging thread. :)

The general wisdom that I have come across is that if engine not likely to exceed 8000rpm very often that Roller Rockers are generally not worth the effort.

I mentioned my research to Lindsay at www.minis.com.au about what I had read about adjusting the height of the rockers to get close to an ideal lift and found he has shims for doing just that and agrees it is important, even on standard rocker set ups. So I will be giving them a go when i put the head back on.

Terry
13: "I am the scariest number."
666: "No, I am the scariest number."
2020: "Hold my beer and watch this."

Cujo. 1999 - 2016

spider

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Re: Roller Rockers for a 998
« Reply #2 on: July 20, 2012, 08:07:20 PM »
Roller Rockers can be worth the effort / money, but increasing the Rocker Ratio is not always beneficial and can even be a backward step, until you start doing some serious RPMs.

Roller Tip Rockers will greatly increase the valve guide life, but only if they are set up correctly.

I run them in the 1.3:1 Ratio of some of our road goers, but for off roading, I prefer the ugly pressed ones. These I've found highly reliable.

That book I mentioned in another thread a while ago, written by Des Hamil, covers in some considerable detail on how to set up and get the best from any rocker set.
Old Moker's never die - they just smell that way

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Drakman

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Re: Roller Rockers for a 998
« Reply #3 on: October 18, 2020, 08:35:09 PM »
Hello Everyone,

An old thread I know but I figure if anyone searches roller rockers this might be the place they will end up.

I have been playing (read that as spending way too much money) on roller rockers recently so I thought I would note down my observations/feelings on the subject.   Hopefully this might help someone else looking at roller rockers.

I started out with a set of Harlan Sharp roller rockers for my rebuilt 1275 engine fitted with a Kent 276 cam.

The Harlan Sharp rockers are extremely well made, an excellent rocker arm.  Rocker arms is all you get though
, you have to make them up and that is a pain as the rollers in the arms aren't offset.  To line them up correctly over the valves the pushrods will hit the pushrod tunnels in the head casting, I haven't tried them on a small bore yet, I am hoping they might fit better.  I did get to use them and they were fine but I didn't like the crazy angle the pushrods were on.

The next set I tried were MiniSport 1.3:1 blue roller rockers that come completely assembled.  I had these fitted for a bit under 8000 Klm,s and they were really good, noise and power wise.  I had an issue with these with the pin that holds the roller tip.

The next and current set are from MiniSpares and I went for the 1.5:1 purple rockers that come with  just the arms, posts and heavy duty shaft.  These are well made with a pressed in roller tip pin, they fit really well BUT on driving the car, it has definitely lost torque down low.  Where the cam would pull from 1500 rpm with the 1.3:1 rockers it now needs to be at 2500 rpm to pull away in top.  I think in a Mini or a more race oriented vehicle they would be good as it does have more go once I get it up to 3000 rpm.  I find I have to change gears more often than with the 1.3:1 rockers.

In conclusion when I sort the issue with the 1.3:1 rocker arms I will go back to those.

Cheers
Dave

Terry

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Re: Roller Rockers for a 998
« Reply #4 on: October 19, 2020, 08:22:38 AM »
Hi,

not that I know lot about this stuff, but with the bigger lift you would be getting more demand for air per cycle so are you making adjustments to the carby to increase the fuel mix to compensate for the changes down low?

Terry
13: "I am the scariest number."
666: "No, I am the scariest number."
2020: "Hold my beer and watch this."

Cujo. 1999 - 2016

Drakman

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Re: Roller Rockers for a 998
« Reply #5 on: October 19, 2020, 09:29:10 AM »
Hi Terry,

The theory is that the 1.5:1 ratio opens the valve about 20 percent more.  The opening and closing timing stays the same as does the duration.  I did alter the carburetion and the ignition timing, I gave it 5 degrees more advance without any ping and enrichened the mixtures till it was turning the plugs black. Then I tried one heat range hotter on the plugs, it made a slight difference but not enough for me to want to keep the 1.5:1 rockers.  I am sure on a dyno I would see a marked increase in HP figures with the 1.5:1 ratio rockers but for on the road drivability, the 1.3:1 rockers would be my first choice. 

The 1.5:1 rockers seemed to "move" the cam starting effect up the rev range by about 1000 rpm.  On a track or perhaps for a more spirited driver? the 1.5 set would be an excellent choice.  The car is much more street friendly with the 1.3 rockers fitted.

Cheers
Dave

 

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