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MG Midget and Sprite Technical - Camshaft timing

Just building up a 1275 engine and I have fitted a MG Metro cam as it was something I had around and on paper looks better than a standard 1275 cam. Been told that by advancing the cam timing by a few degrees is will give more torque,
Is this true, does this apply to all cams? Or would I be better timing to factory specs?
R Mcknight

The MG Metro cam is very good and will be an improvement over the standard cam. I found it worked very well with 1.5 rockers.

Advancing it a couple of degrees will improve the bottom-end torque, but you may lose a little top-end power. Having said that, how often will you be running at 6000 RPM?
Dave O'Neill 2

In principle, earlier inlet valve closing (cam advanced) favours torque, whereas later inlet valve closing (cam retarded) favours top-end. This approximates real life but not always.
Generally BMC cams were timed to 110 deg ATDC full lift. Most aftermarket cams now (though not all) have full lift in the 103 to 106 degree range - so are a bit more advanced than the original BMG ones. This points to likely gains from advancing a standard BMC cam from its original timing by 4-7 degrees. And in respect of the engines I have built I have found that to be the case.
Paul Walbran

If you haven't got an adjustable sprocket, how do you advance the cam timing? Surely the keys on cam and crank tie you to a standard timing - unless you want to go a whole tooth!
Nick and Cherry Scoop

Offset keys Nick

Peter
Peter Burgess Tuning

or ajustable vernier timing gears?? Bit more expensive though.
Bob Beaumont

That's clever. I suppose even 7 degrees isn't a huge offset at that shaft diameter. About a sixteenth?
Nick and Cherry Scoop

For the majority of us where a) we're unlikely to spend hours on a rolling road trying different cam timing and b) the build time for the engine isn't critical then offset keys are the cheaper/eaeier way.

Dry build and measure the timing. Compare to factory. order relevant key. Wait 24 hours to arrive. stick key in and finish build.

Now of course...if you could see the fancy vernier timing gears there would be more reasons to buy them ! ;-)

http://www.minispares.com/search/classic/offset%20woodruff%20key.aspx
Dean Smith ('73 RWA)

The offset is 4 thou per crank degree. You can either buy a ready-made offset key (easier but longer if you suddenly find you need one) or make one up if you are against a deadline by carefully filing a step on one side of the key and sacrificing a sliver from a feer gauge blade to pack the other. (Works, reliable, gets the job done on the spot, perhaps cheaper but definitely fiddly to do properly).
Paul Walbran

we had to use the 'Walbran' technique on an MGC as we couldn't obtain offset keys and vernier gears were silly money.

To be honest the offset keys are safer to use as they will not come loose which verniers could, however, we put vernier gears in the race engines as it is maybe more 'proper' for the type of build expected of a race engine, easier to set too :)

Peter
Peter Burgess Tuning

Having the venire sprocket is nice, im glad I had it for my build, and id spend the extra to have it agian if I ever did another engine...im a card carring fan

To really make the venier sproket come into its own and something I wish I had done during my build ... use a 6 inch hole saw and cut a hole on the timing cover over the top of the cam shaft sprocket then cut an 8 inch round cover and secure over the hole with some rtv silicone and some short self tapers...that way you can always access the timing chain sproket without a major engine tear down of the front end to remove the timming cover..

Just saying

Prop
Prop and the Blackhole Midget

Thanks for the info Lads. It will be advanced by about 4dgs and see what happens with 1.5 roller rockers
R Mcknight

I think your going to like it, peter B. Suggested it to me, and it does make a differance at stop lights, just give yourself a few extra feet in front of the car... otherwise its easy to run up on there tail pipe

Prop
Prop and the Blackhole Midget

This thread was discussed on 28/07/2014

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