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Discussion Starter #1
My posting did not make it so I will try again...
I have been trying to calculate the valve overlap on my engine..
Advised by my machine shop . I have to calculate the distance the valve cups move from fully closed to top dead center when the lobs are pointing inward. That is when the intake valve opens and the exhaust valve closes...
I hope this is correct.
It is hard to set up a gage to do so , but after several hours of working on this I was able to get the following readings:
exhaust 058
intake 042
I have no idea how i should interpret this numbers and what is the factory over lap set up? Help needed
I also ran a compression test and got an across the board reading of 150.. what is the factory range?
I also measured the valve gaps and got some unsatisfactory readings according to the factory set up..
#1 exh: 018 / in 011
#2 019 / 0125
#3 020 / 015
#4 020 / 015
#5 020 / 0125
#6 019 /014

I will have to do some shim grinding to get within specs..
Please add your grain of thought to this thread
 

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Herve,

I'm not sure what you or your shop is asking. The term overlap is usually used in context of valve timing, specifically the duration of how long the exhaust and intake valves are open at the same time (when the exhaust stroke turns into the intake stroke). The Alfa Romeo specs (see below) tell you the precise points (in crankshaft degrees, not camshaft degrees, as well as "linear displacement of cup") of when the intake and exhaust valves are supposed to open and close, which implicitly defines overlap.

These specs do not address valve lift and/or the camshaft profile (the slope or rate of change of the rising and falling edges of the cam lobe) because, from a factory perspective, this is a given (different story for tuners or enthusiasts).

I'm not an expert on valve issues. If the information attached below is not sufficient, I suggest you talk with Richard Jemison and Rich Ott (and please let us know what you learned).
 

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I suspect your machine shop is asking for information on timing the cams. They want to know the Maximum Open Position (MOP) of the cams. I don't have the 2600 camshaft info handy but let us suppose you had a Lamborghini Espada (!): I happen to have the numbers for that handy.
The inlet valve opens at 32 deg BTDC and closes at 60 deg ABDC
Add these two values plus 180 deg=272 deg.
Divide by 2=136 deg.
Subtract the 32 deg (the amount it opened before TDC)
You are left with 104 degrees. This is the point at which the valve is fully open after top dead centre and is the number or The Alfa Equivalent Number that your machine shop wants.
You just need to look up the cam timing numbers for the 2600 engine and do the arithmetic as above
 

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Discussion Starter #4
Thanks Ruedi and thanks David..
One more question Ruedi..how accurate is the original marking on the cams? I am not trying to turn my car into a racer just a very fun cruiser...Would you say using this marks will give you a good set up every time? or should i torture myself into finding a better timing set up.. my cams are in excellent condition and originals...
Herve
 

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Richard Jemison
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Cam timing

Just tell the machine shop that the LCs should be 104 intake and 106 exhaust if these are factory Alfa cams. If aftermarket/regrinds etc. they most likely should have similar LCs but lash will be far different.

If stock cams lash should be no less than .016 intake (.016-.018 with .017 best)
Exhaust lash should be .018

If aftermarket cams (no seating ramp) intake lash .010 exhaust .014
 

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Discussion Starter #6
Hi Richard
Thanks for taking the time.. can you enlighten me and tell me what are lash and LC's..(pardon my ignorance.but I am willing to learn..)
Herve
 

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I will jump in before Richard-"LC" is lobe centre--this is the N.American way of saying what I said "MOP" maximum open position. We limeys tend to use more descriptive language ;) (Lash is valve clearance but I will leave that to Richard)
 

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Discussion Starter #8
Hi David HiRichard..
Thanks for your lightning answer.. According to the factory manual..lash on the exhaust should be .021..is .018 a better adjustment? I read somewhere that the
exhaust valve can be a little tighter so they spend a bit more time on the seat and transfer heat to the seat to cool down.. is that the reason for a tighter set up?
Herve
 
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