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MG Midget and Sprite Technical - 1.5 rockers (again - sorry)

Somebody else on this BB recently started a thread discussing the merits of 1.5 ratio rockers. That discussion inspired me to take the opportunity to fit some Minispares cast 1.5 rockers as I had to replace a broken head stud. The result was tremendous with a really evident increase in power throughout the rev range and no evident loss of torque. I think this change was the missing piece in the engine 'jigsaw puzzle' (I have a ported MG Metro head and HIF44 but standard camshaft). The other thing that surprised me was how much wear there was on the old rocker shaft after relatively few miles (not sure how many miles but less than 10K).

My only concern (apart from the addition of yet more noise at full chat) is that tickover has now become 'lumpy' and I can't get a smooth tickover (it's smooth as anything once the revs rise). Is this to be expected since 1.5 rockers mimic a hotter cam or have I got a yet another minor problem to sort out?
Chris H (1970 Midget 1275)

set tappetts to 15 thou, set tickover to 1000, see if it's any better
David Smith

Chris,

IIRC Vizard mentioned the OE shaft as being soft and the aftermarket offerings even softer so did not wear well especially with higher lift cams. The last time I rebuilt the rocker assembly, maybe 20 years ago, I used a gas carbo-nitrided rocker shaft from one of the usual mini suppliers, it along with rebushed and refaced pressed steel rockers has worn extremely well used with a 285 or 286 cam. The benefit IIRC of the gas process over truftriding was that the gas process didn't leave salt residues in the shaft which required cleaning before use.
David Billington

Davis S - Tappets already set at 15 thou and tickover at 1000. Should I go wider on the tappets(16 thou)?

David B - that's way too technical for me!!! Minispares do supply a heavy duty shaft.
Chris H (1970 Midget 1275)

A slight increase in idle roughness is to be expected from higher ratio rockers on any given camshaft - although the valves are not in overlap for any longer, they are open further during that time, increasing the flow-back effect which confuses the idle.

Any move towards a hotter cam profile will have an effect on idle - ranging from minor waffle through to idling on only 2 cylinders, depending on just how much hotter the profile is. Howver, there may be a change in mixture requirements. If you have adjusted the mixture to best already, then you are probably OK.

If you open the tappet clearnace too far, you will end up with the clearance being taken up when the cam lobe is past its opening ramp and accelerating rapidly. This will result in premature wear of everything. For the standard cam the opening ramp finishes at about .015" on 1.5 rockers, so I wouldn't set it much more than that.

We cope with any unhelpfully waffly idle still present after having checked timing mixture etc by increasing to around 1200 RPM or so, which usually cleans it up.

The main thing I see is that you have good torque from the word go despite its idle. That's what is more important for drivability.
Paul Walbran

Paul, thanks for the comments. I did change the needle to a slightly richer one (as suggested by my copy of WinSU software). The idle is not so rough as to be a problem - it's just that when the idle was smooth before you notice these kind of things and wondered if it can be eliminated, I can live with it as it is but I'll try increasing the idle speed slightly as suggested.
Chris H (1970 Midget 1275)

Hi Chris, I started the other thread I will be fitting mine this weekend, I'll report back with my findings.
Looks like they made a nice difference to your car.
J Lodge

Well I can confirm they make quite a bit of difference, really seem to free the old girl up and like Chris I have lost no torque and sounds like it would rev forever!
Sounds better too.

I am a very happy man, money well spent.
J Lodge

Oh damn. How much are these things again? And would they be a good idea on a 1293 with a Piper 270 and a 45DCOE? Mine doesn't do anything much below about 2750rpm, then revs freely right round to 7K making 91bhp at the flywheel. Torque isn't fantastic according to the RR printout (low 70s) but if 1.5s won't necessarily harm it...

I know I should leave well alone but you know how it is :)
Jordan Gibson

Jordan,

What size chokes are in the '45?

How about fitting 1.5 rockers and an HIF44 SU with a K&N filter? My bet is that the torque will be significantly increased, and the ultimate bhp about the same?

Richard
Richard Wale

Have used 1.5 roller (bushed) rockers for years.

First used on Vizardized big valve 1380 making 90HP@6,500RPM at the rear wheels. APT VP3 cam, 45DCOE, 11.0-1CR. 110RON CAM2 gasoline, 28 degrees advance. Went like stock below 3k and went like stink over 3.200rpm. Totally streetable though very lumpy idle @ 1100rpm, not quite so lumpy or fast with original stock
rocker set-up. 1.5's made big difference.

Currently driving Cooper S cammed 1293 @ 10.5-1
with cam advanced 4 degrees for Metro inlet timing. Carbon-fibre belt cam drive, Pierce alum. head, standard valve sizes. 30 degrees of advance on 93PON (USA) unleaded premium.

Stock carb. set-up upgraded to AH2 needles, red springs and Hi-Flo air filter assembly with
K&N elements.

Initially equipped with upgraded 1.3 MiniMania rocker set-up. Converted to 1.5 (bushed) RR
set-up.

The difference in overall torque is extremely
noticeable. Idle is not as smooth at 800rpm
but acceptable non-theless. Tires easily
"chirp" in first gear without even trying and 2nd gear "chirp" as well when pushed. Very torquey set-up.
Robert E. Shlafer

Richard - 36mm chokes. CR is 10.1:1.

I've wondered for a while whether a HIF44 might be a better overall setup, after reading various people's views and experiences on here. It would be a bit of a wrench to move off the Weber though - they are rather sexy wot? :o)

Would fitting 1.5 rockers necessitate a rolling road session to set everything back up? If it's RR territory then changing carb at the same time makes more sense, if not then I'll probably leave that 'til later.

It has to be admitted that IMO there's nothing much wrong with the way it drives at the moment apart from poor fuel consumption compared to the SU boys and a lumpy idle/take-off. So whilst there may be more torque to be had I'd need to balance that with effort/expense to get at it. Easy wins such as 1.5 rockers *seem* to be (until I'm told otherwise) more palatable.
Jordan Gibson

Jordan, I also have a weber and have always struggled with the lack of low down pull compared to the Su but these rockers have made a huge difference. but I'm still going down the Hif44 route as I like to have lots of torque.
J Lodge

You can have lots of torque with a '45 but you need the right exhaust manifold to do so.

Either the Janspeed CV or the more recent Maniflow Stage II will increase the bottom end to *almost* the same as a good HIF44 but with the additonal benefits that a '45 brings to both the feel of the car and top end.

Without wishing to start a 'Bob'-style debate <grins> the best way to make torque is compression. Jordan - I have a 270 on a 1330 which produces well over 100lb.ft across the rev range but I run 11.5:1 with bog standard rockers.

From the work that I have done over a number of years the cost of 1.5 rockers are not really worth it unless you are building from scratch but its not my money ;-)
Toby Anscombe

Interesting Toby. I do have a Maniflow manifold, but I'm not sure of the spec. There's an invoice to the PO here from Maniflow for an 'Isle of Wight Frogeye Sprite Ex Man', £250. The engine was built running at 11.2:1 but the PO dropped it to 10.2:1 (not 10.1 as I said earlier).

Hmm, some say big difference on 1.5s, some say not much...


Jordan Gibson

This thread was discussed between 23/06/2008 and 28/06/2008

MG Midget and Sprite Technical index

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