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MG Midget and Sprite Technical - Vernier Cam Gear

I've just bought a vernier cam gear to use on my 1500 midget (which was nearly 6 degrees out on the standard duplex) but it came with no fitting instructions...

Does anyone have any instructions or advice to offer - either specific (torque settings etc.) or general?

Thanks

Michael
M Davies

Further ... I dismantled my engine to find that the duplex timing chain was set at 108.5 degrees rather than the specified 103 for my 'Road 83' cam.

I've bought the very expensive vernier gear just in case I should need it when I reassemble it, though I realise it may be a bit over the top on such a mild cam.

How accurate do I need to be with this cam, as I may be able to get close with the standard gear... Or is it better to aim for 'perfect' now I have the engine in bits?

Thanks

Michael
M Davies

As stated the TT Road 83 cam is relatively mild at 266 degrees duration and really requires to be timed 'Straight Up' at 103 degrees ATDC.

Retarding it by that much will just kill the top end to the point where you might as well have a stock 1500 cam!

I'm pleased to hear you have a duplex set up - the simplex chain is one of the bugbears on these motors. Why BL didn't fit a duplex as stock is beyond me given that it is exactly the same component as used on the TR5 and 6.

If you have a vernier then fit it - at least that way you can get your cam timing right!



Cam sprocket to cam - 24 ft.lbs

I'm betting the vernier is a 'Kent Cams' one. The vernier lock bolts (allen bolts) should be done up to 20 ft.lbs

You will need to check the alignment of the cam sprocket and crank sprocket with a straight edge. If this is out then it can be corrected by adding or removing shims behind the crank sprocket.

Additionally when you fit the oil thrower you will have to reverse it (ie concave surface towards crank sprocket) because it will not fit in the normal orientation with a duplex sprocket.
Deborah Evans

Thanks Deborah. That's exactly what I wanted - needed - to know! Now I'm looking forward to putting it all back together...

(PS It's a 'Powertune TMC1225' vernier cam gear from Moss - which is identical to the one that Cambridge Motorsport sell - only more expensive. Doh!)

Michael
M Davies

Hi Deborah

I thought retarding the cam loses bottom end hand over fist and makes things happen later at high rpms?

Michael

Any cam must be timed in correctly to get the best from it, if your cam should be 103 degrees I would aim at 101-103 as a good setting. The vernier is a good idea with 1500 engines.

Peter
P Burgess


Peter, you are of course correct I should have said bottom end.

Senior moment in all this heat I'm afraid.
Deborah Evans

I have heard that anything more than 2 degrees out is too much.

--Jack
JM Morris

Are the duplex ones different from the simplex? Can't remember. Simplex can be set anywhere you like just by flipping the sprocket and/or using different pairs of bolt holes.

FRM
Fletcher R Millmore

Hi Jack

The timing will depend on the application. Usually 1-2 advanced will work fine. On a full race cam retard can seriously upset power delivery. However say you are stuck with a standard cam in a race series where you really need as much top end as possible, I have seen 9 degrees of retard produce best results ( that was on a championship winning 1500 Midget engine). If you fit high lift rockers it is good practice to advance the can around 3-4 degrees to keep the bhp lower down, standard timing with hich lift rockers gets very hairy...remeber things are opeing and shutting ealier and later with higher lift rockers and makes the cam act more wildly.

Confusing isn't it? That is why it is good to take cam advice from one source say Piper/kent/Crane etc and not take a guess from the figures published, those who have experience are worth asking too.

With the B we still get people buying 714 cams which do not work well for normal road use, they were developed for shale rally where one needs revs but no sudden input of torque....henece engine flat below 3000 then just revs to 7000 and usually gives less bhp than standard cam :(

Peter
P Burgess

Hi, Peter. Thanks for that. But I'm confused (as usual!): Deborah says retarding the cam kills the top end but you state that retarding the cam gives more top end.

Or am I taking it too far out of context?

Thanks!
JM Morris

Hi Jack

As Deborah said above, she had a bit of a brainfade on a hot day as we all do now and again and that retarding the cam kills the bottom end.

Peter
P Burgess

Thank you to everyone for your comments and advice, and especially to Deborah and Peter. I just want it all back in one piece! Michael
M Davies

This thread was discussed between 29/06/2010 and 07/07/2010

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