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Mar 03, 2016 9:37 pm
Mar 03, 2016 9:37 pm
Subject: Re: Tappet clearances - why the variation?
I have been helping Tim Gresty reset the camshaft timing on his 2 litre and I now realise that some of the section I wrote in the revised handbook is misleading. 4 thou tappet clearance is right for the standard 14/60 and speed model cams which have duration of 225 and 236 degrees respectively and should be timed to open at Top dead centre. However the Leonard Reece cams and Newman cams are designed to have a duration of 256 degrees with 8 thou tappet clearance . If 4 thou clearance is used with these later cams the duration goes up to approx 270 degrees .
It is also very important to have the inlet valve open position well before top dead centre at say 15-18 degrees and then double check that it closes 58-60 degrees after bottom dead centre. Any later closing will result in blow back through the carburettor at lower revs. This was what Tim had with his engine because I had timed it to open too close to top dead centre and the performance was very poor.
I have been helping Tim Gresty reset the camshaft timing on his 2 litre and I now realise that some of the section I wrote in the revised handbook is misleading. 4 thou tappet clearance is right for the standard 14/60 and speed model cams which have duration of 225 and 236 degrees respectively and should be timed to open at Top dead centre. However the Leonard Reece cams and Newman cams are designed to have a duration of 256 degrees with 8 thou tappet clearance . If 4 thou clearance is used with these later cams the duration goes up to approx 270 degrees .
It is also very important to have the inlet valve open position well before top dead centre at say 15-18 degrees and then double check that it closes 58-60 degrees after bottom dead centre. Any later closing will result in blow back through the carburettor at lower revs. This was what Tim had with his engine because I had timed it to open too close to top dead centre and the performance was very poor.