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MG Midget and Sprite Technical - Standard or uprated springs?

My 1500 midget has a Road 83 cam (TT10504N) giving a cam lift of 0.288" (compared with 0.240" on the standard cam).

Can I use standard springs, or should I use use the uprated (TT1307) springs instead?

My preference is to stick with the standard springs to avoid the problems highlighted by Deborah Priest (thanks Deborah) in response to my recent enquiry about valve seals.

Thanks

Michael
M Davies

The TT Road 83 cam is relatively mild in that it has less duration than the cam fitted as stock to the 1300cc Spitfire MkIII, albeit a tad more lift.

In a 1500 it's probably going to make you somewhere in the realm of 80-85 bhp.

Given that the 1500s don't rev anywhere like as well as their smaller brethren, and that cam will have run out of 'puff' by 6500 rpm, I would say that you are unlikely to get valve bounce so the stock springs should be fine.

HOWEVER, you MUST check the installed heights (34mm) and you NEED to check both inner and outer springs for coil binding at full lift (there should be a minimum of 40 thou [1mm] between the centre coils). Additionally the clearance between the valve cap and the valve guide at full lift MUST be checked; a minimum clearance of 60 thou [1.5mm] is required here.
Deborah Evans

Thank you Deborah for your swift and informative response. Much appreciated!

Michael

PS Anyone want a set of slightly used uprated springs?
M Davies

This thread was discussed on 29/06/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.