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MG Midget and Sprite Technical - Valve clearances

Hi, I spoke to Piper today regarding the timing in of my cam (HR270) as I could only find information online regarding the BP270 and wasnt sure if they were the same.

As I've got the engine out I thought I would double check the P.O installation.

As it turns out it is timed in a 107* ATDC (the same as the BP270)

What came as a surprise was that the valve clearances for the inlet and exhaust rockers was different; 0.014 for the inlet and 0.016 for the exhaust.

I will set it up as they advised but I was just curious as to why it needs a different setting as I've always set both inlet and exhaust the same.

Thanks
Mark
Mark Whitmore

Mark,

Most A series settings use the same for inlet and exhaust. The slight difference on the clearances recommended to you is probably because exhaust valves run hotter than inlet, so are liable to expand a bit more.

Guy
Guy

Since when using an aftermarket cam, you must follow the manufacturer's instruction, as only they know what their cam was designed for the gap to be for that particular cam, I expect that Guy is right, but only Piper can tell you for sure.

Same thing goes for "hot" or "cold" gapping, the factory called for cold with the stock cam, but some cam manufacturers call out their specs for when hot.

Norm
Norm Kerr

Its out in one piece then Mark !!
Did everything go o.k.
Rob Newt

The rocker clearances are governed by the clearance ramps on the lobes, which are between the base-circle and the opening and closing ramps.

If the clearances aren't correct, the valves will not begin to open, or return to their seats at the right time, so the duration will be either too short or too great.

You should always check the clearances given by the cam manufacturer in order to get the best from your camshaft. Also, when using higher lift rockers, the clearances need to be increased by the appropriate amount.
Dave O'Neill 2

Hi, thanks for all your comments. It was just curiosity regarding the gaps, I would always follow the manufacturers guidelines.

Rob: all came out nice and easy, gearbox should be coming back from Klassik Transmissions around next Tues/Wed so if itall goes back in as easily I should have your hoist back to you on the 19th or 20th.

Thanks
Mark
Mark Whitmore

This thread was discussed on 09/03/2011

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