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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Mini Spares Purple Roller Rockers test

Hi All

I tried to post this twice yesterday but it never seems to have made it!

I attach a pic of a before (last year) and after(yesterday) test of the MiniSpares Purple 1.5:1 rockers. I like these as they are bushed not needle rollers where the the rocker arm rubs the rocker shaft.

The engine is 1275 +30, Piper BP255, 1.401" inlet valve Fast Road head, twin 1 1/4" SUs and lcb manifold and freeflow system. The dizzy curve is a little long, with the timing correct for +3500 rpm we lost a few bhp below 3500 due to a couple of degrees too retarded. I was hoping for more bhp but such is life. Will be interesting to see how other setups work. With A series we are building up a slow picture as we do not have enough in with known tuning packages.

I forgot to say....bhp 70 at wheels with 17 bhp losses gives 87 bhp at engine, very smooth running. 255 was chosen to pull high geared 5 speed box.

Peter


Peter Burgess Tuning

Happy new year Peter.

Last year did it have std rockers?

If so that's a good bolt on mod. I agree about the needle rollers on reciprocating parts..

Great to have the comparison facility
Dan Cusworth

Hi Danny

Happy New Year to you too.

Last year standard rockers so it is a bolt on mod. It is a shame I couldnt quite get the low rpm bhp too. Maybe next years present will be a 123Tune, the owner has a good car and adds on each year :)

Peter

Peter Burgess Tuning

Hi Peter,I have had these in for about 7 years now with no problems.For interest,what valve clearance did you set?
steve cowling

Hi Steve

Standard was 12 thou so I set em to 15 thou with the higher ratio rockers.

Peter
Peter Burgess Tuning

are these the £180 or £500 set? If the cheaper, this is useful info as I'm planning to use the same on my overbored 1275 with Piper magnum 270 cam and LCB / janspeed exhaust.
What needles are you using / do you recommend for the twin SUs?

Graeme
graeme jackson

Peter, I guess low end won't be much different, as the "seat to seat" timing has not changed?
Dan Cusworth

Hi Graeme

These are the 180 purple ones.

The sus are on M needles with K&N filters (midget one with stub stacks built in). Don't forget you will need different valve springs to accomodate the extra lift we use the Mini Spares c-aea526 ones.

Peter
Peter Burgess Tuning

Thanks peter.
graeme jackson

I put some of these on my Sprite a few years ago after my RR tuner was taking the mickey out of my very worn original ones! Remember them Peter?!

Anyway, I've found the Minispares ones excellent, easy to fit and with good geometry, never need adjusting and look very well made. Spec is 1310cc, 37x29 head tweeked by Peter, 1.5 Rockers (.016"), 10.8:1 CR, Aldon dizzy with pertronix, Kent 286 and a HIF44 with BDL needle filed almost to a point by Peter! Last time it was on your road Peter (your old one) you told me it was 100 - 105bhp at the wheels. It's really nice to drive with loads of power above 2500 and even more above 4500. It revs to about 7k normally with occasional forays over 7500.

I'll be interested to see what it gives on your new road when I get round to booking it in again.


John Payne

Hi Peter,

Do you know how hard it would be to re-space these roller rockers for a 1098? I have asked minispares directly and they don't do a 1098 kit.
M Leask

I have them...I broke in my.cam with the factory then installed these

major.night and day differance...I I dont have numbers...just seat of.the pants

just remember to slide the feeler gauge in from the side..NOT the front

prop
Prop and the Blackhole Midget

Do the Minispares cast rockers fit a 1098? I have never had to fit the ally purple rockers on a small bore A series. They are handed, 4 left and 4 right. I will see if I get time today to see if it looks like they will fit a small bore head and post a pic and info.

Peter
Peter Burgess Tuning

Hi Peter,

This is the answer I got from minispares when I asked them through their website.

"Hi Mitch, we don't do a specific kit but you can use the 1275 version I believe, you will just need to adjust the spacing of the rockers to suit the valves."

Now since I am still learning an awful lot about everything spridget related, I'm going to say that spacing a set of rockers to suit is beyond my skill level. It seems that this hasn't really been tried before with the minispares rockers. I am more than happy to be wrong on that last point though :-).

Mitch
M Leask

Hi Mitch

It looks like you need to shim the rocker arms away from the rocker pedestals by 1 to 1.5 mm. Not too hard a job. You will notice that most a series shafts are already shimmed if done properly. I attach a pic of the rockers loosely fitted to a 1098 head.

Peter


Peter Burgess Tuning

Hi Peter,

Thanks for the pic. It is much closer than I expected. It seems that it is doable after all. I was under the impression that the spacing difference was bigger than that.

Mitch
M Leask

im not sure about this for a 1098

I recall that the valve to piston clerance was okay on mine (1275) but on a 1098 ????

remember, these are high lift ratios (1 to1.5 ratio).

its only cash and hard steel,

prop
Prop and the Blackhole Midget

In standard form the 1098 head is deeper than the 1275, so valve to piston clearance shouldn't be a problem.
Paul Walbran

Most cams do not lift over say 3 or 4 mm at TDC so valve to piston is unlikely unless valve bounce obtains.

Peter
Peter Burgess Tuning

thats good to know...if that works...its going to make that Iittle engine turn Into a serious pocket rocket

esp if the combustion pocket is deeper then the 1319 head....

im curious ....if there is nothing to be gained beyound the valve being opened 1/2 inch on the 1319 (1275 head)

will.the same apply on the small bore head...or would + 1/2 inch be more advantagous

prop
Prop and the Blackhole Midget

Hi Peter

All the best for the New Year

Just looking at your pic. of the rockers,
You mention that they are handed - If the only difference in them is that offset roller, from here it looks as though they would line up better if they were all swapped over to the other sides of the posts.
Worth a try maybee
Cheers Willy
William Revit

Hi Prop

Rule of thumb is flow doesnt usually increase dramatically above 0.25 D, which is 0.350" for a 1.401" inlet valve. Life doesn't work as simply as this so most cams will lift much higher, all this increases the valve/time area and gives loads of lovely power(sometimes).

Willy, this makes them even worse, you can shim them the way they are, not if they are too far over the other way.

Peter
Peter Burgess Tuning

Hi all

A little seat of the pants response from the owner.....says it goes like ****!

The extra 5 bhp at the wheels has transformed the performance. I suppose it is like taking the handbrake off.

Peter
Peter Burgess Tuning

This thread was discussed between 17/01/2013 and 23/01/2013

MG Midget and Sprite Technical index

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