MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

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 - Roller rockers 1.5

Hi all!

So, last week I sorted out all of Nick's engine parts and went home with an estate car full of gear boxes and crates. It was a lot to go through and we're still finding stuff! I left the two spare engines UK side, we decided to rebuild them at my dads.

One bit of interesting kit was a brand new set of 1.5 roller rockers.
I know Nick already fitted a hot cam, but I have no idea which type.
From the book "tuning BL's a-series engine" I gather that these rockers go well with hot cams as they give the extra lift that these cam's usually don't provide.

Can I fit these rockers without getting worried about valves hitting pistons? Is there anything more to it than just fit them (i.e. timing etc.)?

Cheers,

Eddy
Eddy Veuger

I always thought that 1.5 rockers were an alternative to a hot cam. If you have a hot cam maybe you don't need the rockers (others may correct me on this). Chris

Chris H (1970 Midget 1275)

Hi Chris,

Hot cam's give more lift, but mainly more duration and different timing. If they would give the desired lift then the "nose" of the cam would get too pointy.

Cheers,

Eddy
Eddy Veuger

Opinion varies on 1.5 rockers (see the archives for a few happy hours). Some of the mini forums split on almost religous grounds.

1 argument is that you should get all your lift from the cam of your choice and go with the orig rockers. 1.5 rockers will kill the valve train in a matter of hours. due to the increased side loading.

The other side goes that the roller tips actually reduce the side loading. If you dont go mad on the springs you should get perfectly acceptable life out of the valve train. And "you cant have too much lift" (until a valve hits a piston of course!).

Vizard quotes that his megadyne cams (266/276/286) were designed to be used with 1:1.5 rockers - especially on the larger bores.

They dont give the cam any more absolute duration..but if you count effectice duration (say the period the valve is >20 thou open) they do increase that as the valve will have opened to that point earlier and closed later. So they can have the effect of making the cam feel more than it is. They are certainly quicker and easier to fit than a camshaft (unless the engine is already out) so are attractive for that reason to some.

I have a set on my 1275 with kent 266 - and will be moving them over to my 1380 with Morspeed PH3 cam. That cam already has significant lift so I will be checking for any piston problems during the build (but dont expect any)

Because you need to undo half the head studs to fit - its best to change the head gasket at the same time. I didn't when I first fitted mine...and had to a few weeks later...

Dean
Dean Smith ('73 RWA)

If you want a pointy nose cam ....I'll take some pictures of the Morspeed PH3. I am worried how long that will stay its original profile.
Dean Smith ('73 RWA)

Correct me if I'm wrong, but its all about getting more fuel/air into the combustion camber for a bigger bang and more power.
So to achieve this, bigger valves = more space to let fuel/air in
different cam = holds valve open longer = more fuel/air
High lift rockers = opens valve further = again more space.

I have 1.5 lift rockers on a mild road cam with no problems.
you could always fit them and turn the engine over by hand before you fire the engine up and bend valves, but I really don't think it will be a problem.
One thing though when setting the tappets Vizzard recommends an extra few thousands of an inch maybe 14tho instead of 12.

A Lomas

Eddy.

I know the engine that Nick fitted to the car and I would be hesitant to fit 1.5:1 rockes just yet. I will find out which cam was fitted and also if the head will suit.

Maybe best to chat about this off board......

Mark.
Mark T. Boldry

Eddy,
Are those the purple ones? I tried that set on my car with a Megadine 276 cam, but found that in my case they didn't work as I wanted, so Nick took them back.

Nothing wrong with them as such. When I first fitted them they were very noisy, but once I realised that they needed shim pedestals to get them to work at the right angles, they were much better. In my case the problem was that alythough they gave quite a noticeable increase in power this was accompanied by moving the power band up the rev range too much for my liking. Great for sprinting, but not so good for my type of driving around twisty, hilly, Lake District roads.

Guy
Guy Weller

Eddy what cam is in that big engine of yours?

I am a true 1.5 adept they work perfectly!

All of the talk about valve train wear is a left over from the time 1.5 rockers were not roler tiped.
But with roler tiped rockers and a harder shaft there should be no problem

I know several people whom have used them for manny miles without problems

Dean please show!
it is one of the manny cams on the wishlist (together with the re13 and vp range)

Onno Könemann

Hi Guy,

Yes, they are purple, so it's very likely we're talking about the same set.
Did Nick try them on his engine? Have you any idea of the cam nick used? He only told me it was a hot cam, but I never imagined that there might be so much choice. According to Vizzard they seem to work well on the bigger displacement engines like my 1430.

For all I know Nick already fitted different rockers, I will take the top off one of these days and investigate.

I must say the learning curve on this car is getting quite steep indeed! And like Nick I find myself getting in deeper and deeper!

Cheers,

Eddy
Eddy Veuger

Nick, I don't think Nick ever used them, or intended to use them on his car. They came his way at a specially good price, so he bought them anyway. Then sold them to me and then took them back again when I found they didn't really suit my type of driving around here. Car went well with them, but was always screaming in a low gear to get the power!

Guy
Guy Weller

From the left...

Morspeed PH3
Original Ital 1275 A+
Piper 270 (I believe)
Original midget 1275 (stored since '91 - Hence the rust)


Dean Smith ('73 RWA)

Close up of the Morspeed.
Dean Smith ('73 RWA)

try again (doh!)


Dean Smith ('73 RWA)

Dean, be careful not to cut yourself on the top of those lobes.
I run 1.5 roller tip rockers and found they suit my engine spec well. Probably the cheapest mod I made in terms of $/hp.
Need to watch piston-valve clearance, top of valve guide clearance, and binding of springs. And be sure to get the geometry right.
Mike Allen

So, I have been told (by Swiftune) to use a steel shim under the pedestals when installing the purple 1.5 roller-tip rockers on my aluminum head. Any opinions on the best thickness?
David "no lead in my head" Lieb
David Lieb

you should calculate the geomitry
the rocker should be lever when the valve is closed
Onno Könemann

The top of the rocker? A line through the center of the roller tip and the center of the main shaft? What is supposed to be level?
David "Persnickety" Lieb
David Lieb

I was hoping someone would answer Dave's question on what the geometry should look like...
I've got a set of non-roller 1.5's ready to bolt the head down..
They're from MiniSpares..with the taller 'posts'..but sounds like there may still be some adjustment to do??

Thanks all
D Rock

David is right, the line through the center of the shaft and the center of the roller is what matters. This line should be level at half lift, not with the valve closed. If you check the stock setup with the valve closed, the rocker is not level, but angles upward a bit.

As the rocker swings through its arc, the contact on the valve stem moves outward until the rocker is level, then moves inward. If the rocker starts off level, the contact may run right off the valve stem. Setting the rocker at half lift with the contact a bit outboard of the center of the valve stem will keep the contact as near to the center of the stem as possible, given the geometry of the rockers.

You should always install the assembly and check that the contact stays as near the center of the stem as possible, and also make sure that the adjusting screw stays somewaht near the middle of the push rod cup all the way through its range of motion.

The push rod will move side to side in the hole through the head, and clearance here should also be checked, although street cams with stock push rods will usually be OK. Some people drill the holes oversize, but this can break into the intake ports, especially if the head has been ported. The holes don't need to be enlarged front to back, so I just open them up side to side, by hand or in a milling machine. This is important with tubular push rods, and crucial with carbon fiber.
Bill Gavin

I was right??? I don't know how you get that idea! I guessed twice and was wrong both times.

Is there anyone who can give me a rough guess as to how thick of a shim I am likely to nee when using an aluminium head with an SW5-07 cam and the purple Mini-Spares 1.5:1 roller-tipped rocker assembly? Stock pushrods, I think... Kinda hard to order the shims in time for the job when you have no idea where to start. Oh well, I guess I should ask Nick at SwifTune.
David "egg? chicken?" Lieb
David Lieb

It's more common to need to reduce the height of the pedestals than to fit shims, unless you've milled the head a good bit, or your valve stem tips are higher than original. If you increase the valve lift with the standard geometry, the contact will run toward, possibly past, the edge of the valve stem - adding shims will make this worse.

If your rockers already have shorter pedestals, it's possible that you may need shims, but still not the most common case.

If you run out of range on the adjustment screw, shims may seem to provide a solution, but you really need shorter push rods. Tubular pushrods usually can be shortened in a lathe; if you want to stay with original style pushrods, the 948/1098 push rod is shorter.

There is really no substitute for assembling the valve gear and verifying the action on the valve stem. You can do a decent approximation on the bench with a spare head and soft valve springs if you can work out some way to step through cam lift.
Bill Gavin

Bill,

When you talk abot drilling the head for bigger push rods...


What is your defination of side to side, and back and forth.


iS side to side = the length of the head??,

and back and forth the direction of driver to passanger side of the car?


great thread
Prop
Prop***The End in 2012

Hi Prop

I guess that is a bit ambiguous...

I used 'side to side' to mean 'from one side of the car to the other', or toward and away from the rocker shaft.

'Front to back' is 'from the front of the car to the back of the car'.

Since the rocker can't twist on the shaft, most of the movement in the passage will be due to the rocker swinging in an arc, moving the push rod closer to the shaft or farther away. Most of the additional clearance required will be on the side of the hole closer to the rocker shaft. More clearance will be needed at the top of the hole due to the increased angle of the push rod at the top and bottom of its motion.

Since the cam lobe spacing is the same for all Spridget cams, but the valve spacing is different between the 948/1098 and the 1275, the rockers are not neccessarily lined up with the cam lobes, and there will be some 'front to back' motion of the push rod in the passage, but this is small relative to the 'side to side' motion. Roller rockers usually have the adjusters offset to reduce this misalignment.

BTW if anyone actually does need to use shims under the rocker pedestals, be sure to drill ALL your shims, including spares, for the oil hole that feeds the rockers; if any are left undrilled, one will eventually find its way under the wrong pedestal :-(
Bill Gavin

This thread was discussed between 09/02/2009 and 16/02/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.