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MG Midget and Sprite Technical - Rocker (the valve type) interchangeability

Took the Frog on a 200 mile round trip to Wales to put some mileage on the new engine and I find the tappet noise is quite load.

The night before I re-torqued the head and adjusted the tappet clearances to 15 thou' (higher than standard lift on cam but not sure what cam) and before doing that the tappets had been noisy from first start up.

The rockers are the pressed steel type and when adjusting the clearances last night they reminded me of my front teeth. All there but not neccessarily in the right place.

Now, as it happens I have a low mileage Mini 998 automatic engine (30,000 ish miles) and the rockers on that are the later wide cast? type. So would they fit a 1275 engine and are they any better or worse than the pressed steel type?

The 1275 head is a Metro unleaded type so presumably should have had the wide cast rockers anyway so I know nothing about the parentage of the ones currently fitted.

Spent an enjoyable? hour looking through the archives wondering why the threads were mostly about fitting sills? No useful insights were read.

Rob

Rob aka MG Moneypit

The problem with not knowing the parentage of your pressed rockers is that they could be from a small-bore engine 850/998/1098 and not a 1275.

While you can fit 1275 pressed rockers to a small-bore engine without adverse effects, the same is not true of the reverse scenario.

As for the wider sintered rockers, they ARE interchangeable between engines.
D O'Neill

Sintered rockers are the way to go.They are quiet,never need adjusting and rarely wear out.Put them on a new shaft and you should be fine.
Fergus Pollock

Thanks all. I'll go with the later A+ rockers as I want the car to be reliable without needing valve clearance adjustment every 6 months. I have ordered a solid spacer kit from mini spares so will fit the rockers later this week.

Anyone used solid spacers? Pro's and cons, if any?

Rob
Rob aka MG Moneypit

What stops the fabricated rockers from a smaller sized engine fitting a 1275? Is it to do with the position of the valves relative to the push rods?
G Williams

Have you ordered the spacer kit that includes shims? as you will probably need them to get proper alignment.
http://www.minispares.com/product/Classic/C-AEG392.aspx
Also, check the faces of your rockers before fitting. Now is the time to reface them if they are worn.
j hall

I wouldn't bother with solid spacers. I had them on the FJ engine and although you can shim them up cold, as soon as the engine warms they'll expand and nip the rockers. So you end up dismantling the valve gear several times adding clearance till they just have an interferance fit when hot. And because they'll all end up different lengths you'll need to number them so they don't get mixed up. You're better off staying with springs really.
Fergus Pollock

Graeme

The valves were repositioned on the 12G940 head, due to the larger diameter.

The small-bore pressed steel rockers have a circular pad which does not fully cover the tip of the valve stem. The 1275 rockers had a wider, oval pad which does cover the valve stem. They also changed the profile of the pad by moving the centreline of the radius outwards, effectively increasing the rocker ratio.
D O'Neill

Yes, C-AEG392 are the ones I have ordered from Mini Spares complete with shims but as Fergus has pointed out if they expand so much you have to leave a lot of clearance maybe I will stay with the springs.

I've taken the rocker assembly off the low mileage Mini engine and they look really clean with almost identical wear marks on all of them. I may fit them tomorrow and forget about the solid spacers.

Can't remember what the shape of the pads on the pressed rockers were but I do remember it was difficult to set the gaps correctly.

Rob



Rob aka MG Moneypit

This thread was discussed between 01/06/2014 and 03/06/2014

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