Mini Engine Question

[qwerty]

Can somebody please explain what a roller tip rocker is in a mini engine. Apparently it's like uprating the cam?? Is this true? Is the cam in the cylinder head of a mini?? Sorry for being a simpleton

[iRocco]

It replaces the standard rockers - the bit which pushes the valves up / down.

The cam is located in the block towards the back.

Roller Rockers aren't really ne cessary on std Mini (A / A + Series) engines as you won't see a lot of gain - but are worth it if you're thinking of upgrading the std cam / sylinder head. They're an expensive mod tbh - better save you're money for a bigger bored engine.

Sorry about the big pic:



Rockers are the parts numbered 41 - and fit to the other parts around that area in the pic to the shaft numbered 28.

The cam is numbered 106 and fits in the block behind the access panels (more or less) on the back of the block.

Hope this helps.

[qwerty]

Cool. So does it have the same affect/effect as replacing a cam in a normal car? How difficult is it to replace the cam?

[iRocco]

Kinda - they provide more movement on the valves than std rockers.

Cam replacement is relatively easy - but best done with the engine out. You can do it with the engine in, but by the time you've taken all the bits off needed to gain access to it, you might as well have taken the engine out!

[Deleted]

It can do, a roller rocker has a little roller at the end that pushes the valve open instead of a flat pad like on the standard rocker gear. It only really comes into its own at very high revs with high lift because it reduces friction. On a non race cam the benefit is debatable, plus ona road engine the valve clearances go out much faster than with normal rocker gear, or so I've been told.

[Mr K]

its a cam in block type engine, it is offset from the crank and bores, for obvious reasons, then the roackers are operated through pushrods.

a roller rocker has a small wheel on the tip to push against the valve, this in its self wont free up tomany horses, however it will smooothen things up abit, and generally work better, not to mention look good atop your engine and be a nice thing to stare at when you remove the rocker cover.

the way that they can give more power is through changing there ratio, the distance from pivet to the top of the valve, and the distance from pivet to the top of the push rod, by varying this you can chance the mechanical advantage that the pushrod has, there for giving higher levels off lift to the standard setup, obviously durations, overlap, etc etc will all be controlled by your cam, as is lift, but this is just a way to get even more lift.

i don't know how the rocker mounting studs (if they are on studs - i am not an A-series man) are held into the head, but if they are just pushed in like an essex v6 you should definatly tap the hole and screw in the securing studs!

Now the experts will come and correct me!!!

[Mr K]

damn, beaten too it!!

[iRocco]

nickyboi said:

damn, beaten too it!!

You should type fatser

Rocker studs screw in to the head - so no probs there.

As said above really, don't consider investing in rollers for a std engine / cam setup.

[qwerty]

So thats what the 1.5 and 1.7 that they're advertised with means. The lenght from the pivot to the top of the push rod??

[Seth]

Roller tip rockers will not on their own make any significant improvement unless they are of a different ratio to the standard rockers.
Starting form the beginning, the cam in the block pushes upwards against the followers (or lifters) which in turn push the pushrods. The pushrods locate in a ball and cup kind of way against one end of the rocker arms. The other end of the rocker arms then push down against the valves opening them. The valves are closed by springs which force everything back the other way.
The rockers don't locate in any way on the top of the valve so there is actually a rubbing action as the valves go up and down. Roller tip rockers remove this rubbing action by having a roller at the valve end so all they really do is reduce a small mount of friction within the valve train.
It might be that some roller rockers have slightly different length ends when compared to standard rockers and so the leverage ratio between the pushrod and the valve is changed. This means that the valve will open slightly further for the same amount of pushrod (ie cam) movment. The cam timin wouldn't be altered in any way though and it is often this that can have a much greater affect on performance.
Basically in my opinion they're only something worth investing in if the rest of the engine is already highly tuned.
Hope this hasn't confused too much.

[iRocco]

The 1.5 and 1.7 relates to the theoretical ratio of the rockers.

I believe the standard rockers are 1.5........?

I put 1.7 rollers in my 1380 and only saw a 2bhp increase........and for £190 it's a curse word bhp gain / sendage tbh.

For that money you could get a better cam and get the car set up on an RR.

[Davenger]

ordinary roller tip rockers only reduce friction between the rocker tip and the top of the valve.
You can get roller tip rockers that are offset to give more leverage and push the valve down further effectively increasing the time they are open in the same way an uprated camshaft would, but like iRocco said, they're only worth fitting if you've already got an uprated cam in there.

I think that's right anyway

[qwerty]

I thnk standar are 1.2 or 1.3

[Davenger]

Something like that, you can get 1.5 and 1.7 but they're not worth the bother unless you've got a really high spec engine

[iRocco]

qwerty said:

I thnk standar are 1.2 or 1.3

I think you're right 1.3:1

[slater]

okokok! hold on here. Ignore the ratio for a second.

There are 2 types of roller rockers.

Full roller rockers: these have both roller tips and roller bearings insted of brass bushes on the pivot.

Roller tip rockers: These only have the roller on the tip and retain the standard brass bush on the pivot hole.

Full roller rockers are very expencive, double what roller tips cost but make sure you know what you are getting as roller tip rockers were basicly a way to try and scam people into thinking they were getting a cheap set of full roller rockers!
If you ignore the differance in ratio then they have the advantage of reducing valve train friction and this helps the engine rev higher. Obviously full roller rockers are better than roller tips at this.

They are only relly nessicary and cost effective for a race engine!

Now onto ratios.

Standard ratio veries depending on what type of rockers the engine has as standard (eg. pressed steel, forged, sintered a+) but its between 1.1 and 1.3.

Roller rockers are avalible in 1.3, 1.5 and 1.7 but remeber you can get the higher ratio for much less money if you offsett bush the existing rockers or buy some non-roller high ratio ones!

They will give a simlar effect to fitting a longer duration cam but it is much better to fit the a cam and leave the rockers standard. If you relly feel the need to fit higher ratios then for a small bore up to 1098cc you should use 1.3 ratio for a road engine and 1.5 for race. If your fitting to a 1275 or bigger then you can get away with using a 1.5 ratio on the road but 1.3s may be a better bet. (1.7s are for extreme race use only!)

In summery roller rockers have there advantages but they are best left for race cars where you can afford to spend alot for very little gain. if you fell the need for more ratio in your engine then ofsett bush a set of standard rockers (Hot tip: pressed steel are cheap as chips and very strong with slight modifications!)

[Autofive]

i ve got a copy of david vizards book ' how to modify the mini' for sale - this will explain everything

pm me if want postage quote