37 replies to this topic

[kaney]

when fitting these higher lift cams and greater ratio rockers ....

how much is engine wear increased? and on what parts?

is the performance increase enough to justify this greater wear?

Kane

[Bluemini]

The idea of roller rockers is to reduce the wear on the valves, the rolling action over the top of the valve stem reduces the side load on the valve and guide. Normal rockers tend to push the valve onto the guide, causing more wear.

Reading an artical in the tech section of Mini Mag (the one with the 8 port cluby on the front) it says that small bore engines dont benefit from roller rockers and that a cam on its own is enough, any more lift and it starts to loose power.

[Dan]

Small bore motors do see the benefit of full roller rockers 'because they reduce internal friction losses quite considerably and make the mill even more rev-happy. But they really don't like hi-lift rockers. You should never go above the 1.3:1 rocker with the small bore block, and that's why they make the 1.3 roller sets.

[miniman5]

so how do roller rockers work then? i know ho wnormal ones work does it have cams at the top as well?

[lewis]

thanks for telling me that because i was told by someone that i now realize was talking a load of cubbled custard told me to get it at 4:5:1, :nugget:

[dklawson]

Miniman5, how do they work? Take a look first at a normal rocker. They have a center pivot bushing as a fulcrum. At one end (rear) is the hole for the adjusting screw. At the other (front) end is a hardened contact pad that pushes against the tip of the exhaust or inlet valve. Roller rockers come in two basic types, bushed and ones with bearings.

Both bushed and arms with bearings have the same adjusting screw at the rear. At the front the hardened contact pad is replaced with a ball bearing or annular ring. As the arm actuates the valve the bearing/roller ring rolls across the top of the valve stem. This rolling action prevents the side loads mentioned earlier which accelerate valve guide wear. The cheaper arms use bushings for the fulcrum just like standard rocker arms. The more expensive arms replace the bushes with needle bearings.

High-lift arms move the position of the fulcrum back towards the adjusting screw and must be used with compatible rocker shaft pillars which move the whole rocker shaft to the rear.

[miniman5]

ahhh! i think i under stand there!

[lewis]

could anyone advise a place with decent prices on peformance parts i:e jack night developments

[TimS]

higher ratio rockers also open the valve a little earlier and closes it a little later .

not quite, it moves the valve further in the same amount of time, the duration does not change, only the lift and velocity/acceleration of the valve

[TimS]

when fitting these higher lift cams and greater ratio rockers ....

how much is engine wear increased? and on what parts?

is the performance increase enough to justify this greater wear?

Kane

It is worth it, there is not much more added wear espeically with roller tip rockers there is even less as mentioned in previous posts.
Performance increase is good and even beetr with other modifications as flowed head and stg1 kit. These work together to give even more power. As long as the engine is looked after then wear isnt much quicker although it would be advised on a full rebuild while the engine is out and the cam is going in!

Something else too to think about is cam timing! verneir gears are needed for accurate timing set up especailly on modified cams! so add that onto the cost. Personally i think it is worth it, to feel the power kick in feels great though over do it on the duration and u will be pulling away from the lights at 3k rpm just so that u dont stall it

[kaney]

may have to look into it sometime...like when i get a job

[lewis]

exactly why im getting a job that pays more than 5 pound an hour (being 16 money does become small)

[Ben H]

I have had modded 998 minis for some time now and have run kent 276 cams and 1.5 rockers in loads of then including my current engine. The head is off an MG metro (block pocketed) and it has been known to give about 60bhp on the rollers, at the wheels. My girlfriend uses it for sprinting and hillclimbing and on the hills it could do with a bit more grunt.

As far as ware goes on these engines I have never got much more than 25000 miles from one without a total rebuild. It depends how you drive. With the 276 cam in a 998 it will not pull until about 3000rpm, and when i say not pull I mean no power at all. Then after 3000 rpm it will go very nicely upto about 7000rpm if the head is upto it. If you are the sort of driver (as I am) that loves to rev it between each gear then don't expect it to last long. Revs kill engines, but to get power from a small cc engine you have to rev it......

[TimS]

exactly why im getting a job that pays more than 5 pound an hour (being 16 money does become small)

im on less than that working at halfords and 18 and a uni student now

[lewis]

whats halfords like?

As far as ware goes on these engines I have never got much more than 25000 miles from one without a total rebuild. It depends how you drive. With the 276 cam in a 998 it will not pull until about 3000rpm, and when i say not pull I mean no power at all. Then after 3000 rpm it will go very nicely upto about 7000rpm if the head is upto it. If you are the sort of driver (as I am) that loves to rev it between each gear then don't expect it to last long. Revs kill engines, but to get power from a small cc engine you have to rev it......

i will definitley bear that in mind, thanks ben h