Measuring Valve Timing - Strada 130TC
Posted: January 14th, 2010, 12:24 am
Dear Guy and fellow forum members,
Quite some time ago, I acquired an engine which had been removed from a Strada 130TC rally car in the early to mid 90's.
The engine has been modified, but the spec is basically unknown to me - I would therefore like to strip the engine to determine exactly what I have.
To begin with, I thought it might be a good idea to measure the current cam timing, as currently assembled, before removing and evaluating the camshafts.
I accurately found TDC with the head still in place using a piston stop (inserted in No 4 cylinder), zero'd my timing disc at TDC accordingly.
I then attempted to measure the points at which the intake and exhaust valves start to open / finish closing - using a pre loaded dial gauge acting on the tappet shims of No 1 cylinder.
From my initial measurements, the figures recorded where not quite what I expected.
I therefore have a couple of questions…
1. Firstly, when measuring the valve opening / closing points... At what point in the initial valve movement should I consider the valve to be opening ?
I have seen 0.005” lift mentioned as a rule of thumb, but have read that this should be done with zero clearance on Fiat SOHC engines - What is correct for the TC ?
It appears to me, that any variation in the determined "initial" point of valve movement, can affect the reading on the timing disc by as much as 1 degree per 0.001" valve lift !
I found it quite difficult to establish the exact point at which the valve first starts to move off its seat (due to DTI fluctuations while turning the engine over), so I used 0.001" of valve lift to take my opening figs, and the same before valve closure, for my closing figs.
NB: My dial gauge didn't always return exactly to zero during the closing measurements, which made this measurement particularly difficult to pin point accurately.
I had to continue turning the engine over in it's normal direction of rotation and recheck this point a few times - and then stop 1 thou before fully closed to get my measured fig (1 thou before). Using this method I obtained the following timing figures:
Intake opens 32 BTDC - Closes 80 ABDC / Exhaust opens 66 BBDC - Closes 36 ATDC
Full lift Intake 113.5 ATDC / Exhaust 66 ABDC. (Full lift calculated by finding lobe centre via measurements 0.040" before / after full lift)
2. Secondly, I realise that valve clearance will have an effect on the above measurement, so should I correctly shim up the valve clearances when carrying out these checks, or is there a calculation I can use to correct this relationship with cam timing ? My current valve clearances on No 1 Cyl are 0.13mm Intake and 0.10mm Exh.
Thanks in advance !
Best regards,
Andy Griffiths - Jersey (Channel Islands)
Quite some time ago, I acquired an engine which had been removed from a Strada 130TC rally car in the early to mid 90's.
The engine has been modified, but the spec is basically unknown to me - I would therefore like to strip the engine to determine exactly what I have.
To begin with, I thought it might be a good idea to measure the current cam timing, as currently assembled, before removing and evaluating the camshafts.
I accurately found TDC with the head still in place using a piston stop (inserted in No 4 cylinder), zero'd my timing disc at TDC accordingly.
I then attempted to measure the points at which the intake and exhaust valves start to open / finish closing - using a pre loaded dial gauge acting on the tappet shims of No 1 cylinder.
From my initial measurements, the figures recorded where not quite what I expected.
I therefore have a couple of questions…
1. Firstly, when measuring the valve opening / closing points... At what point in the initial valve movement should I consider the valve to be opening ?
I have seen 0.005” lift mentioned as a rule of thumb, but have read that this should be done with zero clearance on Fiat SOHC engines - What is correct for the TC ?
It appears to me, that any variation in the determined "initial" point of valve movement, can affect the reading on the timing disc by as much as 1 degree per 0.001" valve lift !
I found it quite difficult to establish the exact point at which the valve first starts to move off its seat (due to DTI fluctuations while turning the engine over), so I used 0.001" of valve lift to take my opening figs, and the same before valve closure, for my closing figs.
NB: My dial gauge didn't always return exactly to zero during the closing measurements, which made this measurement particularly difficult to pin point accurately.
I had to continue turning the engine over in it's normal direction of rotation and recheck this point a few times - and then stop 1 thou before fully closed to get my measured fig (1 thou before). Using this method I obtained the following timing figures:
Intake opens 32 BTDC - Closes 80 ABDC / Exhaust opens 66 BBDC - Closes 36 ATDC
Full lift Intake 113.5 ATDC / Exhaust 66 ABDC. (Full lift calculated by finding lobe centre via measurements 0.040" before / after full lift)
2. Secondly, I realise that valve clearance will have an effect on the above measurement, so should I correctly shim up the valve clearances when carrying out these checks, or is there a calculation I can use to correct this relationship with cam timing ? My current valve clearances on No 1 Cyl are 0.13mm Intake and 0.10mm Exh.
Thanks in advance !
Best regards,
Andy Griffiths - Jersey (Channel Islands)