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MG Midget and Sprite Technical - High lift rockers

Been chewing over the idea of getting 1.5 forged rockers for the A35. Currently 1293 A Plus/10.5/MG Metro cam/HS6/Maniflow twin box.Tailored advance curve gives 80 brake at about 30 degrees. It's runs a 3.55 diff and apart from a conking out session last year has been vice free for the past 5 years. So the question is would hi lift rockers (MED forged type) be a worthwhile addition. Some suggest you lose torque below 3000 rpm and gain the odd BHP only at the top end. Others say 1.5's transform the power delivery with no loss of tractability. But no one seems to have any RR data before and after fitment - so the prospect of spending close to 300 quid (rockers,HG,RR) on the off chance of another 3 or 4 BHP might not be a good return. Any thoughts?
f pollock

You will get more power from an other cam for less.
But if you don’t want that hassle then the rockers will give an increase
O K

When I first went FISC racing, I was already running in the MGOC championship, in which I could only run a standard cam or MG Metro version.

FISC regs were much more liberal, but as I didn't have two engines, I had to keep the Metro cam. I opted for 1.5 rockers when running with FISC and they really worked well with the Metro cam.
Dave O'Neill 2

Definitely worth a try but I'd go for the Minispares ones at £223. Not much more than a cam change (cams are expensive now and add followers etc) and less work. A straight fit with no messing about, I've had them on mine for 10 years now with no problems.
John Payne

We fitted the 1.5:1 aluminium 'roller tipped' rockers 15 years or so ago, and have had no problems with them since. The argument at the time was that it was equivalent to 'going up' a cam (in our case that would have been from a 266 to 276), but retaining the characteristics of the existing cam. The cam at the time was a 266, and after fitting the 1.5 rockers, there was no noticeable change in the shape of the power band, just a bit more of it.

We were also advised to go for roller tips to avoid additional sideways stress on the valve stem at maximum lift - the 'pad' type will increase that bending stress with the increased lift.

The rockers have done around 60,000 miles since fitting them, and even after fitting a 276 cam about 10 years ago, they run very quietly at 0.015" inlet and 0.018" exhaust clearances (+0.003" on the standard rockers), and no wear is apparent in either the rocker shaft bushes or the rollers.

I notice that MED are also offering roller tipped rockers with a larger rocker shaft diameter to avoid breakage (we have had one 'heavy duty' rocker shaft break at No. 1 valve). The MiniSpares webpage for the 1.5 forged rockers says to 'Tighten posts evenly to stop potential fracturing of rocker shaft' TWICE!!

MiniSport are offering the 1.5:1 roller tipped rockers for £165 incl VAT at the moment, which is a very good price.

Richard
Richard Wale

It depends on your cam

The more lift your cam has the less benefit there will be to using hi lift rockers

Once you get around .425 of lift your maxed out, there is no more advantage beyond the .425 of lift

So if your cam is stock and the lift is around .250 to .325 then yes you will see big improvements but if you got a radical cam already lifting to .400, then you wont noticnotice very much if any

If you are going to do high lift rockers and your also going to be elbows deed into the engine, advance your cam timing an extra 3-4 degrees for some extra low end torque for that stop light to stop light suck your ass to the seat sensation

Ideally you want to get to that .425 lift or as close as possiable that vizard talks about without going over it

Can someone back me up or disprove me on the .425 measurement... I'm not 100% confident it could be .475 lift

Prop
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I think the message I'm getting is the distributor advance will need recurving, possibly in conjunction with basic cam timing, as well as a needle change to see the full benefit. So a rolling road session to optimise the advance and fueling relationship would have to be a given. Years ago I used S rockers with offset bushes in a 1000cc FJ engine (+ 649) and I was constantly rebushing them they became so clattery. In the end I threw them away. But the roller tipped one's look altogether better engineered, and I think if the geometry and spring rate are correct, they should prove easier on the shaft and guide. Not sure about sucking your ass to the seat - powerwise the guy at MED said expect 3 to 5.
f pollock

Just to throw a little more info in, I prefer bushed rockers rather than needle rollers as the needle rollers have shown rapid wear in hard use as the load is only taken by around three of the needle bearings rather than a broader surface area on a bushed shaft.
On the rolling road we get good results with mild cams, very litle losses at lower rpms then stronger mid range and extended top end. We have had very good results with 266 and Piper 255 cams; 276 and Piper 270 getting a little hairy with more lower rpm losses!
Different case with full race cams and high lift rockers depending on cam profile. With a cam that worked well with std rockers on a 1950 B engine( lots of overlap) the engine, with high lift rockers fitted would only start when igniton cranked up to 60 degrees BTDC then ran like the provernial sack of ****! With a much reduced overlap cam (below 100 degrees) the high lift rockers worked well.

Peter
Peter Burgess Tuning

The MiniSport roller rockers looks very interresting.
When installing those on an engine that has been running, wouldn't it require a grinding at the stem top's, allthough there are no visible signs of wear here?
Second, will the dismantling and retightening of the head nuts in the four rocker post's have any impact in the tension's in the cylinder head, when off?
Jan Kruber

I would assume to lift the head and change the gasket - not to do so would almost certainly risk it blowing prematurely. With the head off the plan would be to lap the valves and replace any stem seals if found work hardened. Never heard about grinding the top of the stem - but I've never seen one suffer from wear.
f pollock

Jan is correct to inspect the valve tips. The ex ones especially can and do tend to suffer.
We have never lost a head gasket yet by removing the four rocker post head nuts then re torquing.
Peter
Peter Burgess Tuning

Peter, your reply makes it even more tempting to order the roller rockers, they are quite a bargain :-)
Hmmmmm......
Jan Kruber

The roller rockers that Mini Sport and other sell are usually 'roller tipped' only. The actual rocker is bushed where it fits on the rocker shaft - as Peter says, using needle rollers here is not recommended.

'advance your cam timing an extra 3-4 degrees for some extra low end torque'

This is an interesting one. The first cam was a Kent 266 and was fitted 4° degrees 'advanced'. I was surprised at the low speed torque, even though it is a 1380.

When looking to go to a '276' a few years ago, Piper were newly offering a billet cam with cross-drilled and lubricated lobes, so that was the choice. On contacting Piper they were insistent that it was timed 'straight up', which it is.

It is noticeably more 'cammy' than the 266, and I do wonder whether it is as much to do with the cam to crank timing, as the additional valve opening? Conversely the idle is smoother, which is a characteristic of retarding the cam timing (in comparison with 4° advance before).

The idle is even better now with the Nodiz 3D ignition mapping system has been fitted - the advance on idle is ~20° BTDC (incl vacuum).

I really MUST get up to Peter B's before long and get the Nodiz ignition map set up 'properly'!

Richard
Richard Wale

It was Peter Burgos that put me onto the ad 4 degredegrees advance when timing the cam within lift rockers and it makes a big difference... as Peter told me you drive alot more at lower rpm on the street then you will top rpm on the track which makes alot allot of scence

I've got the swiftune Sw-05 camshaf with the opular purple high lifter rockers .. and I love the set up

Prop
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i fitted high lift roller rockers because they looked good in purple. . . . .like a magpie i like shiny things.
P Bentley

P bently

Painting the engine bright fire truck red adds 5 easy horse power to the engine... (seriously ;)

Prop
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Prop has it almost right...... you need to paint the car red, not just the engine.

Too many red MGs......
Dominic Clancy

Not to metion there is always knife blading the butter fly valves in the carbs and adding lead balls into the gas tank to add more residual lead to the fuel

Prop
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My 1275 from 1971 is stock, I believe. How high is the lift on a stock cam ?
Are the 1,5 lift rollers a quick fit, when having a stock cam? By quick I mean: no advancing or retarding of the cam?
Normal street use.
Jan Kruber

For your ride the rockers are the sheet metal rockers and they are 1:1.25 ratio

Yes very simple modification 1/2 Saturday if your reasonable competent and have a decent set of tools and you postphone afternoon tea

You wouldn't have to adjust the cam, as is is fine, not to mention adjusting the cam setting is a 3 day job

Even tho your removing the head studs along one side I'd stager there removal

Also slide the feeler gauge in and out from the side NOT the front (roller tipped rockers) or else it will give a false reading due to the roller action... if it's not roller tipped then slide the feeler from the front

You may have to trim down a set of feelers to fit in from the side

Depending on which set you get you may need to get an aftermarket valve cover to fit and even then you may need to grind off a few spots inside due to clearance

And plan on a quick check and retune... nothing big it may need a minor adjustment here and there

When you disturb the head studs, give it a quick positive turn 1st (just a hit) to tighten the head studs then release the head stud tension but in 10 to 15 inch pounds at a time across all the studs... not ine stud at a time

The purpose of slight tighten 1st is it breaks the tread seal and removes any binding of the thread studs

There are 2 popular rockers sets, set's the purple and the gold, the purple are more then enough to handle the job, I would avoid the build it your self kit... I am aware of only one person that did the individual build it your self kit on eBay and it didn't go to well

The good set is nice but I fear it's over built and those the super high cost

Also you will need a wider valve lash of around .015 to .018 ... look up Keith culver he has a good article's floating around on how to determine what the new valve lash will need to be.

Anyway it's a few tips to help out...nothing to serious

But yeah I think it's a great idea to gain a little extra butt suck in the seat... esp for a stock cam
1 Paper

The good set is nice but I fear it's over built and those the super high cost

Should read...
The gold set is nice but I fear it's over built and thus the super high cost ... but the purple kit is more then enough to do the job for a street car
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Do you speak specific about the purple mentioned in earlier replies above, at £16,18 from Mini Sport?
And no shimming of the rocker posts?
Just fit and maybe a new rocker cover?
Jan Kruber

That's correct... the purple set is really popular

Shimming, it depends on how many times your head has been resurfaced or rather the amount removed


But I think you need a lot removed before you need to shim it... and aluminum heads need to be shined I think

The after market valve cover is the common boxy shaped with the rib vents on top


Here is a tip for the valve cover and gasket use 100% silicon the cork gasket to the valve cover and let it cure so the cork gasket is permantly bonded to the valve cover

On the mating surface of the cork to cly head put a smear of white lithium grease then attach the cover to the cly head the heat from the engine will melt the white litiume grease and make a tight seal

When you need to take the valve cover back off just bump it with a rubber mallet to break the seal then just add another smear of white lithium grease and repeat... you can use the cork gasket over and over
I
Then
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So I went and bought the Minispares 1.5s and they are on the car. Taking them apart to oil them up before installation it's clear the bush to shaft tolerancing varies a bit and is far bigger than even the 5 year old ones I've just taken off, which are a far tighter fit on the shaft. Bit of a surprise, but the expansions may be different to the OE item so it may be OK. Anyway the motor fired right up and although more busy sounding it's definitely not a clatter which was a slight concern.
I'll have to spend an hour grinding out the alloy rocker cover as the arms are touching here and there - got a feeling a steel one might fit straight on.
f pollock

I'm interested in Peter Burgess's suggestion that it is OK to remove the rockers without removing the head. What's the procedure if doing that? Drain coolant and release all head nuts (to avoid warping the head) or just the four head nuts holding the rocker pedestals and leave the others alone)?
Chris Hasluck

I'll bet on just the ones holding the rocker pedestals...
David Smith

If it was me, I would be tempted to release the pressure on all of them, in reverse order.

Whether that is the correct procedure, or not, I couldn't say.
Dave O'Neill 2

'it is OK to remove the rockers without removing the head'

We had to do it as an emergency in a car park in the centre of Bordeaux when the rocker shaft snapped inside the front pillar! Why did BMC put the oil feed hole in the front pillar, so that the rocker shaft is weakened when only in a one-sided support? Feeding the oil through either of the middle pillars would leave the weakened shaft supported on both sides.

I drained the water to below the top of the block (a good estimate of!), and released all the studs in reverse order of the tightening sequence.

Swapped over the rockers to the new shaft and reassembled in the normal way, including torqueing up all the nuts properly (borrowed a torque wrench from the BritAssist support on the Euroclassic).

Checked the oil level to make sure that there was no unexpected increase, i.e. water, but everything was fine. We did get just a bit of 'mayonnaise' in the rocker cover for a few miles, until the oil ran hot enough, and for long enough to boil off the suspended water.

Checked the head nut torques again after the first heat cycle, and fairly sure I changed the oil when we got back home, as a precaution.

Can be done, with no long-term effects.

Richard
Richard Wale

"Why did BMC put the oil feed hole in the front pillar...?"

The front pillar is probably the easiest route to get oil to the rocker shaft.

The early A-series engines also had the rocker shaft locating screw in the front pillar, but this was later moved to the second pillar, possibly because they had suffered failures of the shaft due to it having two drillings at that point.

You do need to be careful, when replacing the rocker shaft, to make sure that the new shaft has all the holes in the right places. I have seen a couple of rocker assemblies built with the first pillar in the second position, resulting in no oil to the rockers.

Some replacement rocker shafts appear to be 'dual-purpose' with both locating holes present. even when used with the later second pillar with locating screw, you still have two drillings at position one.
Dave O'Neill 2

Chris
We have had no problems with leaving water in and slackening the 4 rocker post 3/8ths nuts and the 4 5/16th nuts. We retighten the shaft steadily so as not to put undue strain on the shaft. We have encountered no problems , no water seepage, no subsequent hgf. Sometimes we have had to strip off and sort rocker shafts whilst on the rolling road it is quite common to see wrongly assembled shafts which do not feed oil to rockers as the hole is in the wrong post!!!!!

We like the purple C-AHT446A rockers for road use.

Peter
Peter Burgess Tuning

I have to admit... if for no other reason, the purple set is just sexy to look at, I hated to have to cover them up, inside the engine

Prop
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It is a sad point of life to inhabit when we both find purple rockers sexy Prop!
Peter
Peter Burgess Tuning

Haha.... it dosnt take much to make us happy that's for sure
1 Paper

maybe we are getting ready for old age Prop, do ladies of a certain age have blue rinses Stateside?
https://en.wikipedia.org/wiki/Blue_rinse
Peter
Peter Burgess Tuning

For you Prop.... (if the URL works).

https://youtu.be/hnW27pqaKlY
Greybeard

This thread has got me thinking. The Frogeye has a 270 cam and 1.5 roller tip rockers, for general bumbling about it's too wild, the Mk IV is pretty much standard and could be wilder.
I wonder if I should just swap the rocker gear, does that sound too obvious?
Paul MkIMkIV

Paul,

Is the Frogeye a 948 engine? That with a 270 (Piper?) alone will be quite/very 'cammy'.


The rocker spacings on a 1275 are different to the 958/1098 I think? Swapping the 1.5:1 rockers seems a good way forward, but don't know about the spacings?

Richard
Richard Wale

They're both 1275s, the cam is a Piper 270, or I'm pretty sure it is, over the years I've rather lost track of which engine has ended up in which of several Spridgets I've owned. Any how it is definitely 'cammy'.
Paul MkIMkIV

Sounds like a good plan Paul.
Peter
Peter Burgess Tuning

Tomorrow's job then...
Paul MkIMkIV

This thread was discussed between 09/02/2018 and 21/02/2018

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