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MG TD TF 1500 - Valve spring questions

Hi all,

When disassembling a spare head recently, I found a washer(30mm dia x 1.5mm thick) sandwiched under each valve spring bottom washer and the head. I'm assuming they are there to increase spring pressure. The head has been shaven and was previously used with a high-lift cam. Any thoughts?

Also, does anyone know what the spec is for coil clearance under maximum lift conditions for XPAG springs? My measurements seem to indicate that the industry accepted figure of 0.06" is difficult to achieve.

cheers,
David
David Padgett

What is your installed height? With a stock cam you should be nowhere near coil bind
W. A. Chasser

The installed height measures approx 44.5mm which is about 2.5mm below the spec height (which I believe is 1.874" or 46.9mm for the large coil). Previous owner tells me the cam produced a lift of 10.7mm at the valve.
David Padgett

It is normal machine shop practice to shim valve springs to the recommended installed height, which results  in the proper closed valve spring pressure.
1.865" has been used as OEM installed height, close enough to 1.874". Yes, .060" is recommended minimum clearance of the outer spring @ full lift. Is the 10.7 MM lift @ the valve gross, (no valve lash) or net using the recommended valve lash? If you can identify the camshaft get the manufacturers recommendations on seat pressure, & valve lash, as well as timing specifications.
BTW rocker arm ratio is a nominal 1.5: 1
Stock valve lift is a nominal 8 MM
Len Fanelli
Abingdon Performance LLC.
Len Fanelli

Im only guessing but perhaps the machine shop shimmed an early set of springs ( in error to get recommended seat pressure as spec'd for late the MK II /TF performance springs @ 150# closed. Do you know what seat pressure you have? Do the springs have any color markings left on them?

Bill Chasser

TD-4834
W. A. Chasser

After my fast road cam was installed coil binding led to a couple of rockers breaking on the track. I now run a single spring. It is called an RR220 - doubt if it is Rolls Royce - but other than that I don't know its origin. Works well - floats at about 6300, if I'm silly enough to get that high.

David
D A Provan

Thank you all for your contributions.

Len, unfortunately the PO of the head no longer has the cam or any other details (apart from the lift value which for some reason has stuck in his head)!

Bill, there are no markings on the springs, nor do I have seat pressure details. Maybe I could try measuring this.

BTW, this head was given to me some time ago but I'm not proposing to swap it out with the one in my car - I was just interested in the way it was set up.
Your responses however, have inspired me to check the condition and parameters of the springs of my in-service head - something perhaps I should have done ages ago, especially as my cam is not stock.

cheers,
David
David Padgett

This thread was discussed on 18/03/2017

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