1967 Cooper S 1275 ignition timing

[iain1967s]

Hi. I finally finished rebuilding my original thin flange engine, but I need a little advice for dynamic (strobe) timing the ignition accurately.

The BMC manual says 2° static, 4° @ 600 RPM using original 40819 centrifugal-only distributor. But that sounds very retarded to me ?

Anyway I don't actually have a 40819, the nearest equivalent distributor I could buy is the MiniSpares 12G2140, which says 7° static and 22° at 1200 RPM.

I split the difference and set it at 5° static just to get the engine started.

Considering I also have a new camshaft, I really need to fast idle at 2000 RPM or higher to bed the cam lobes in to the tappets for the first 20 minutes or so. I really don't want it running retarded and overheating during that time.

So what I would really need to know is where the ignition timing should be with the centrifugal advance active, say around 2000, 2500 or 3000 RPM.

Can anyone help?

Thanks.

[Spider]

I just had a look in the UK manual and for some reason it again is incomplete.

The Cooper S came out of the factory, ready to run on 100 Octane fuels.

To run on these fuels, the timing figure is 2 deg BTDC @ 600 RPM.

However, an alternative figure is given by the factory of 3 deg ATDC @ 600 RPM, for 97 RON.

These figures are also Camshaft dependent and are based on the AEG510 profile.

For the AEG148 Profile, the figures are not clear but appear to be 3 deg ATDC @ 600 RPM for 97 RON.

I'll add here though, that these figures are different for unleaded fuels of today, they burn quite different.

For 97 RON a figure of of around 3 degrees BTDC @ 600 RPM would be close to the ball park - assuming the engine spec is bone standard and the cam timing is also set properly.

The figures quoted on the Mini Spares site are for when this distributor is used in the Sprite Engines, which run a lower CR and so need a higher initial advance.

Lovely looking car mate

[iain1967s]

Thanks Spider.

I'm in Massachusetts, USA and the choices are Regular, Plus and Super at 87, 89, 93 AKI reapectively. Those are equivalent to 91, 94, 97 RON in the U.K. I'm using Super of course, so 97 RON.

The camshaft is a new ST510 from Mini Sport. That is the same profile as AEG510, the factory standard spec for a Cooper S 1275. Pistons are +20 with new rings correctly gapped, and I gave the bores a light hone.

The cam timing should be good. Although I only set it up 'dot to dot' with a standard woodruff key and new high quality IWIS duplex chain from Keith Calver, there was no perceivable backlash and I did use a dial gauge for verifying midpoint at TDC.

My concern is that I don't want to idle the engine at 600 RPM to set the ignition timing, until after the cam has bedded in to the new tappets.

Would I just need to add 3° to the centrifugal advance per the MiniSpares graph? Is it that simple?

[LMM76C]

Not really much help but when I put together a new engine in period with originally std 510 cam but CR of something over 11, HS4s and LCB, I had terrible problems with timing - overheating and running on. Only trial and error sorted it.
Are the original figures for the original S cam rather than the 510?

[Spider]

Iain, as you won't be doing much wide open throttle 'stuff' for a while, set the timing to a static 5 - 6 degrees BTDC. Not an ideal way to do it, but will be close enough to get some miles up to then set it dynamically. Avoiding WOT and having it out a few degrees isn't going to hurt anything (as far as the timing goes).

LMM76C, there were two different profiles used in the Cooper S. the 148 was used until just before they changed over to the 12G940 Head Casting, then they went to the 510.The difference between these was the 510 has a longer exhaust duration to coff coff 'compensate' for the smaller exhaust valves. There were a few cars however that were fitted the the 163 head and the 510 cam.

[iain1967s]

Thanks Spider. Will try that.

My S engine has a rebuilt 163 head and I’m using the 510 cam profile.