Measuring Valve Timing - Strada 130TC

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andygriff
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Measuring Valve Timing - Strada 130TC

Post by andygriff »

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)
Guy Croft
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Re: Measuring Valve Timing - Strada 130TC

Post by Guy Croft »

FL posn doesn't require the valve clearances to be set but measuring IVO/IVC does.

If you want to know valve timing - you measure from exact (?) start of lift to end with the running clearance set as per cam mfr recommendation. And - the variation in measurements (1 thou" or more) you get on the dial gauge is quite usual and quite unavoidable due to clearances in valve-guide and follower-bore and the camitself. Digital mapping devices take measurements straight off the cam and are much more accurate in that regard but you still get 'scatter' - in that case from the surface condition of the cam. You can derive the valve lift from the cam lift map by measuring the event from say 0.4mm to 0.4mm at open and close.

However if you want to compare your cam inlet/exhaust valve open/close with 130TC OE data 7/52 inlet 51/8 ex (crank degrees) be aware that is quoted by Fiat with a wide clearance of 0.8mm (referred to in the manuals as 'clearance for timing check) NOT the actual running clearance. The logic for stating that is NOT entirely clear to me I have to say.

What you get with 0.4/0.45mm clearance on the OE cams I really haven't got a clue what the OE valve event is, sorry. FL OE is 112.5 and 111.5 and your figures - in fairness - aren't far off that, 113.5 and 114 (your figure of 66 subtracted from 180).
(I should point out that FL is always quoted as inlet ATDC and ex BTDC)

Hope this helps in the first instance,

G
andygriff
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Re: Measuring Valve Timing - Strada 130TC

Post by andygriff »

Hello Guy,
Thank you very much for your prompt response to my questions !

I was wondering if my engine was incorrectly timed at first - as I was using the OE valve timing data as a reference.

The effect different valve clearances have is quite interesting...

My engine has much tighter clearances than the recommended OE checking clearance, and so it seems logical that the valves will therefore open earlier and close later as a result
( I can see this in the figures which you have stated).
My inlet opens 25deg before OE and closes 28deg later, which allowing for measurement tolerances, seems logical - a variation between respective opening / FL / closing points of only 3 degrees.
The exhaust on the other hand, is not as symmetrical. It opens 15deg before OE, but closes some 28deg later - Variation of 13 degrees on the closing side.
Perhaps this is simply due to component wear - if so, I will attempt to find the offending component(s) during my strip down. I assume that the actual exh profile are not assymetric.

I will now remove the cams and carriers, and attempt to plot the profiles (measure the event as you say) - cams fitted in inverted carriers, and measurement taken from the bucket.
Photos will be taken so that I can document the measurement process.

Guy, when you have some time, I have three more questions if I may:

1. When plotting the valve event, do I assign the zero degree point on the degree disc to the mean full lift point on the camshaft lobe ?
2. What is meant by the term "Lift Integral" and how does it differ from Duration ?
3. Do you know of / have an Excel formula to aid converting the measured data into a diagrammatic form ?

Yours Sincerely,

Andy.
Guy Croft
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Re: Measuring Valve Timing - Strada 130TC

Post by Guy Croft »

Try the attached format. Lifts are with follower ie: flat follower lift.

Degrees are cam not crank.

G
Attachments
77 cam map.xls
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andygriff
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Re: Measuring Valve Timing - Strada 130TC

Post by andygriff »

Firstly, thank you for the Excel sheet Guy.
It will be a very helpful tool when plotting my camshaft "events" and consequentially, helping me to work out weather my cams are std or reground.

I have set up the inverted cam carrier in the vice, and am now ready to begin plotting my camshaft "event".
Using this method I firstly measured the total lobe lift for the intake cam...
Measuring 130TC intake camshft lift via bucket tappet. (Cam carrier inverted).
Measuring 130TC intake camshft lift via bucket tappet. (Cam carrier inverted).
IMG_2087.JPG (94 KiB) Viewed 8235 times
I measured the total lift to be 412 thou (the only long stroke dial DTI I own is imperial) which equates to 10.46mm if my maths is correct.
Subtracting the OEM running clearance of 0.45mm gives me a true lift of 10.01mm - Which I a assume is a slight lift increase over OEM ?

Next I want to begin plotting the intake camshaft lift vs camshaft degrees, but to do this I need a datum point at which to call Zero.

Having found the exact point of full lift (FL) using the normal method employed to find piston TDC (degree measurement taken 50 thou either side of FL /2) ...
Establishing exact full lift point of camshaft using the same method employed to find true piston TDC - This accounts for nose dwell period.
Establishing exact full lift point of camshaft using the same method employed to find true piston TDC - This accounts for nose dwell period.
IMG_2088.JPG (83.57 KiB) Viewed 8235 times
Is it safe so assume that my "zero" point will be 180 degrees opposite ?

Your sincerely,

Andy.
Guy Croft
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Re: Measuring Valve Timing - Strada 130TC

Post by Guy Croft »

Yes, fractionally over OE.the highest lift was the 130TC which had a nominal value of around that ie: about 9.6mm valve lift.

Use FL as the zero point and measure lift from there either direction (ie: on opening and closing flanks) down to zero. As you are measuring flat follower lift (with the bucket in - as you need to) your true valve lift will commence 0.4mm from the zero lift point (however many degrees that is) and the closure will take place 0.45mm before it.

You would multiply those cam degrees, from start of valve lift by 2 to get the extent of lift and closure in crank degrees, then adding the inlet and ex event together will give you the true valve event duration in crank degrees.

G
Robert
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Re: Measuring Valve Timing - Strada 130TC

Post by Robert »

Hello Guy,

Is is possible to get the cam values of the original Strada 130TC as you gave for Pitatore 77 ?
You certainly know that I miss this values (related in another thread in the Q&A forum part).

Thank you for your help if it is possible of course.

Robert
GC_131
Guy Croft
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Re: Measuring Valve Timing - Strada 130TC

Post by Guy Croft »

Sorry Rob,

I don't have any standard cam maps, never needed them really.

G
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