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MG Midget and Sprite Technical - Roller rockers

Christmas is coming and Santa has asked me what I would desire... Why say folks to MiniSpares Purple 1.5:1 rockers?

I assume a bolt on job...? What difference in performance?

Cheers

Mark
Mark O

Be prepared for significant increase in noise.
Guy W

Guy

In a good way?

Cheers

Mark
Mark O

I bought a set for my 1275 A series but it didn't suit my particular engine. - Metro big valve head, 12:1 compression and 276 cam. They were very noisy and seemed to considerably reduce the torque response at lower revs. In retrospect I probably didn't give them enough of a chance to get them set up properly, but I returned them, swapping them for a complete 1098 engine for my Frog, which was a better deal at the time. :-)
Guy W

They should be a simple bolt on job but just watch out for things like the washers on the head bolts catching on the arms. I seem to think they are very close and that I needed to file one or two down.
They seemed to be better from a geometry point of view, my cyl head is quite a lot thinner but I could still use standard length push rods.

I don't find them patticularly noisy but then they were replacing a very worn set and my engine is very noisy anyway!

Power wise they seem to suit my engine set up perfectly. Mine is 1310cc, 10.8:1, 37x29 head, 286 cam and Aldon dizzy. It's still drivable below 2000 rpm but only at light throttle. Power really starts at 3k and then properly comes on song about 5k. It revs right round to 7.5k no bother.

Basically I would say that fitting them will be like moving to a slightly wilder cam. It will move the power band up slightly but should give you more power when you get there.
john payne

Interesting comments - thank you. My engine is probably closer to Guy's, 1275, same Metro head, HIF44, Kent "sports" cam, 123, 5 speed box....I noted some RR curves on the web and observed basically as John says - power/torque increase coming in higher up the rev range. I quite enjoy the low down torque however, and always baulk somewhat at revving the proverbials off an old engine...The thinking is also based on the somewhat worn originals, but that said, performance seems unaffected by same.

Hmmmm...may ask Santa for an RC40 back from the manifold instead - but then again I do have a nice SS in place at present and it does look rather fine from the rear.....

Mark O

Hi
I have run roller rockers on my engine for eleven years. Guy raises a good point that of noise. They might be annoying to some over long distances.
Alan
Alan Anstead

Hi Mark, careful the 1.5s don't give you coil binding. We use Mini Spares C-AEA526 valve springs for lifts over 400 thou". We also tend to advance the cam up to 4 degrees as the overlap is worse with the higher lift rockers.

Peter
Peter Burgess Tuning

I have the purple rollers your wanting... I like them, yes noisey but I want people to hear me comming before im there

A couple of thoughts for justified performance...

1st you have to have a PORTED head with good quality oversized RACING valves

Next is your cam choice... ideally my thought is a high duration low lift cam is what benifits 1.5roller rockers

If your cam is a high lift, then your going to over shot that spot where the valves opening is no longer producing any positive benifits (.495+)

So if your cam has a lift of .400 and a long duration it wont do much ...in fact you could lose performance

But if your cam has a .275 lift and pointy duration plus the cam timing advanced a few extra degrees ... then yes its going to go like snot.... but your cam is going to wearout alot faster also

You may want to also seriously consider some harsher stiffer valve springs to avoid valve bounce... and if your running a lightened or aluminum flywheel, then your going to be at risk of alot of extra valve spring bounce


A couple of side notes... I had to grind out the inside of my valve cover to avoid rubbing and you will need to trim down a set of feeler gauges as you will need to approch the valve lash from the side... never the front, as the roller will absorb any feeler gauge thickness and give false readings

Also with a 1.5 ratio... the .12 clearance is no longer sutiable and you will need to recalculate your set up for the new rocker... im running .16

And yes, this will effect what net sizesyour SU carbs are running and weather or not you may need to upgrade to duel SU HS4 carbs

Ect ect ect

Or just rebuild the engine pure stock but perfectly balanced and lightened and strap on a
Small bwm supercharger like what moss sells for the midget... that would get your goose popping


To much info ? Haha


Really the more worn out, and the less modified the engine the less my above notes become vital... you wont see the big benifits of a well thought out and designed engine, but it will be easier to tune and less of a learning curve to devolope

For me,once you go down this path, its hard not to see how one part effects every other modification and the over all engine and it becomes a 5 year build with no front door to walk away from

Look at danial stepaltons books and of course the 1275 yellow bible written by god himslf, david vizard. Another good insight is kieth culver... he has an online section of the web called "culvers courner"

And you thought you were just going to bolt this new toy in and drive eh.... haha

Prop

Prop

vizard
Prop and the Blackhole Midget

If only I had posted 10 minutes sooner I could have been the cool kid on the block... id looked like id really knew what is was talking about... peter steals the show, but then peter is the real deal... haha

Prop



Prop and the Blackhole Midget

RC40 from Magic Midget - magic! Love the deep bassy resonance even on a completely standard engine.
Jeremy Tickle

Basically Prop is spot on. They aren't really a bolt on mod, more something to incorporate into an engine build.

Mine were OK from a spring binding point of view but did need quite a bit removing from the inside of the alloy rocker cover. I think I advanced the timing as recommended by Peter.
john payne

Maybe Santa should be delivering Peter Burgess ?
Andy Phillips (frankenfrog)

Remember a Peter Burgess is for life, not just Christmas. Mind you, I am cheap to run, a few Old Speckled Hens, some Bacon and egg cobs/baps/rolls from Carol's Cafe, child size clothes and shoes so cheap to dress, could use cast off Ken or Action Man (with moving eyes/hair) clothes :)

Peter
Peter Burgess Tuning

I rang Kim at Magic Midget who offered a Maniflow LS031 as a viable and indeed better alternative to an RC40. Very helpful chap, and I am seriously tempted. Like Jeremy, I do enjoy a bass exhaust note...even better when hood down, reverberating off the stone walls of the glens on a still winter's day.
Mark O

This thread was discussed between 01/12/2015 and 02/12/2015

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