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MG MGB Technical - Rocker Arm Spacer Set?

Just curious what the opinion is of these. Worthwhile for street performance?

1971 MGB. Street car. 10:1 compression. Head ported and polished. Slightly hotter cam.

Rocker Arm Spacer Set

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=66136

TIA
Max71

How do the original springs "rob performance ". More importantly will you feel the difference? IMO - no!
Michael Beswick

Oh yes, the pressure of those springs on the pedestals is going to 'rob' a huge amount!

Old MacDonald getting to you again, Michael? :o)
paulh4

Thanks. They always have the magic marketing words like "rob performance".

Just to fully understand - with the OE springs at higher RPM do they move? Thus making less positive action from the tappet face to the valve?

While we're here: Any thoughts on roller rockers? Its winter. Time to dream a little about spring (no pun).
Max71

"Any thoughts on roller rockers?"

Yes, they're expensive.

Roller tipped, or full roller?
Dave O'Neill 2

Next to negligible increase in performance. I've got a Moss supercharger system on my uprated engine that is pretty much the same as yours. The biggest improvement was a properly setup distributor. Worlds of improvement in performance. RAY
small

The springs work fine for me on my supercharged engine
and fit without filing. Any slight drag could be a good thing helping to control valve bounce. Cant see spacers doing any harm though. Denis
Denis4

Hmmm good question on rollers. These?

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=63984

Or Harland?

I always felt the dizzy held back the engine performance. I did a DIY electronic version and noticed smoother running at higher RPMs. It wasn't reliable and went back to points. Jeff did my dizzy.

After lots of hand wringing I guess the 123 is the way to go as its full electronic and curves can be tweaked with a phone. Downside, really an investment.
Max71

"with the OE springs at higher RPM do they move"

These are the springs between the rocker and the pedestals. I assume you mean "do they allow the valve to move sideways at high RPM"? They may, but since there is a far greater force from the valve springs attempting to resist the force from the push-rod that will open the valve I can't see any effect on valve opening/closing at all, even if the pads are slightly dished. I would expect that to cause the rocker to move into their 'normal' position if anything.

Ideally knock-sensing retard ignition is the way to go, but I've not come across that for the MGB. Short of that programmable, where you can individually set a given number of discrete steps to give minimal pinking anywhere in the throttle/rev/load range. The 123 is an expensive way of achieving that, personally I'd rather use an add-on module, so it can be bypassed into 'limp' mode if it should fail. There are a couple of these in the UK, one of them at 1/3rd the price of the 123. A pal has one, and while it has allowed him to derive his own curve (very different from the factory curve) he's not been able to say with any degree of confidence that it has improved performance.

Remember, a good standard points system will beat a knackered one any day of the week, and for much less cost than any electronic system. It's not generally realised that an electronic trigger actually results in _less_ HT spark energy than points with a given coil, as the electronics include more series resistance than points do. That's one of the reasons why North American spec cars with factory electronic ignition got a 'sportier' coil - to compensate. And with the 45DM4 variable dwell system it was sportier still, more so than aftermarket ones which are designed for points and other fixed dwell systems.
paulh4

Thanka Paul. My dizzy (25D) was recurved and rebuilt. Running Lucas Sport coil. Its sad the points I really like are NLA. The only advantage of that DIY electronic was that smoother feel at higher RPMs. At lower I didn't notice a big change.

The 123 looks nice except the price is pretty dissuading.
Max71

my real gripe with price of 123 is the feeble warranty.
if it came with say 5 years, or even a reasonably priced maintenance contract then there would be peace of mind against it failing on day 366 - and having to return to NL....
G
Graham Moore

Max-
Tubular steel rocker arm spacers were used by the MG factory race team in order to positively locate the rocker arms and thus preclude the rocker arms from longitudinal 'walking' at the very high engine speeds that their race engines attained. Such tubular steel rocker arm spacers were made available to the public as special-order competition equipment (Long, Special Tuning Part # AEH 764; Short, Special Tuning Part # AEH 765). However, the Original Equipment rocker arm spacer springs (BMC Part # 6K 871, Moss Motors Part # 329-220) are quite adequate for this task at engine speeds below 6,500 RPM, and also have the additional advantage of less friction as well as damping valve train vibration and its resultant noise, plus allowing oil flow to wash away abrasive contaminants from the rocker shaft. In short, on a street engine, there is no point in installing them, and some disadvantages if you do.
Stephen Strange

Thanks Stephen! and Graham (wish both aspects would change: price/warranty)
Max71

This thread was discussed between 12/02/2017 and 19/02/2017

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