12 replies to this topic

[Purple Tom]

Hi,

I've always wondered about full roller rockers and roller tip rockers. Firstly, what is the difference between them? Secondly, what do they do? Am I right in thinking that they just increase the amount the valve opens?

I have a 266 cam fitted at the moment, so what are the implications of fitting full roller rockers or roller tip rockers? Is there any difference in noise or reliability between the two? Will fitting them make a difference in terms of power/torque, and are they worth the money?

Also, I notice there are several different ratios to choose from. Which is best for a lightly modified 1275 engine, with a 266 cam, stage 1 kit, HIF44 carb, slightly ported head but nothing major?

Sorry about all the questions, its just they've always puzzled me!!

Tom

[Pickup76]

Roller tip rockers are just to reduce the lateral load on the valves i think, and the different ratios are the amount more valve lift you get with them i think. Im not really an expert though, maybe the mini docs can correct me.

[philster]

roller rockers do not increase valve lift this is down to the ratio of the rocker. Roller rockers are mostly available in either 1.3 ratio or 1.5 .
1.3 i think is the standard ratio (someone correct me if i'm wrong)
This then leaves 1.5 which is a higher ratio so you get more valve lift.

Below is a simple (ish) diagram to show the difference (not exact only an example) between a standard and a high lift rocker.

On the second diagram you get more valve lift because of the change of pivot point which causes the rocker arm to move further with the same input from the push rod (which goes to the cam)

phew!

[Guess-Works.com]

They say a picture is worth a 1000 words... I think you have an essay's worth there.... great post philster...

and yes 1.3 is standard...

PS. What ever rocker you use they will not change the duration or timing of the lift, only the speed and amount... ie open and close faster and further with 1.5's (infact approx 15% faster and further )

[dklawson]

Excellent picture post!

1.3:1 may be standard on later engines but for early 1275s like mine the Cooper-S forged rockers were 1.22:1 (nominal).

I have stock rockers for the moment but someday will install high-lift rockers. A friend of mine with a Spitfire installed the equivalent of 1.5:1 rockers on his 1300 engine. He did some un-scientific time/distance sprints on a local road before and after the installation. He claims to have shaved a couple of seconds off of his 1/4 mile times. Again, it was un-scientific but did show an easily measurable improvement on an engine comparable in size to that of the Mini.

[Woody]

I have fitted 1.5 ratio roller rockers on my 1275cc engine and the differance is definatly noticable out on the road , the acceleration is better and i have a few mph more on top end .

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[Dan]

The Cooper S forged rocker was the first one to be built to 1.3. All the others (the pressed steel ones, standard forged ones and even the very late nasty sintered ones) were 1.22ish as you say. I run Cooper S forged rockers in my 998 and they are great. They have a nicely profiled nose which does a lot to reduce side loading, but not as much as the roller sets obviously. Roller sets reduce internal friction losses greatly which is why you will see a performance increase even with a near standard ratio. They are also very light in weight and so reduce the inertia of the valve train meaning the engine can theoretically accelerate faster, although this is usually hindered by other components.

[philster]

Although i know how roller rockers work i have never actually fitted any, does anyone know if there are any downsides to fitting them or is it all good! Also i'm assuming they could be fitted to a standard 1275 setup without problems.

I'm now a firm fan of bolt on power after spending a fortune on my old 998 lump for around 60horses and ending up with a very unreliable engine.

I was also thinking of purchasing a spare head for the mg lump and having it ported, putting better guides in and converting to unleaded. Would a machine shop do this obvoiusly i won't need bigger valves because the mg head is about as big as you'd want to go on a road car anyway so would it be cheaper than buying say a stage 3 head off the shelf?

[Bluemini]

One thing you need to watch out for when fitting larger ratio rockers is the amount of coils the valve springs. I had a set of 1.5's on one head and they were fine, I put them on another head and the valve spring was pressed down that far on full lift that all the coils touched, ending in bent valves!! There are a couple of ways round this, either buy uprated springs with less coils or get the spring seats machined out a bit.

[minimadjonesy]

also, a minor thing that I have foundon the various cars in the club with these fitted is that they do tend to knock the rocker cover! One of the lads had them fitted by vmaxscart and even they said that this was a problem!

[TimS]

the difference i found is the at power band moved further up the rev range

[Bluemini]

The rocker cover needs modding, if you fit the flat top alloy type, you need to grind out an area at the back of it on the inside to give the adjuster screw area some clearance. I have managed to get a metro sloping type one to fit on mine without having to grind it.

[Woody]

had to take the metro lid off mine as it sounded like a machine gun
plenty of room under the steel lid .