Marc, click here. ---->Well, ****, that only shows the intake valve opening.

Watch 1 of the 2 diagrams. Now, just picture the numbers I gave as amounts of time if you will. Watch the correlation of the intake vs. exhaust valve opening and shutting.

IO = intake valve opens
IC = intake valve closes

EO = exhaust opens
EC = exhaust closes

See if that helps.

 

remember the amount of advance ground into the cam is mainly to take into the account of timing chain stretch. that way it keeps the valve events inline with the crankshaft. even a new chain won't keep the cam exactly where it's supposed to be. you can install a new chain, turn the crank and you 'll see it move a couple of degrees until the chain tightens up on the downward side of the chains direction of movement before the cam starts to turn. damn cam manufacturers, they think of everything don't they.

 

Do double rollers stop stretch?

How many degrees worth of stretch does a timing chain usually have in it, by X amount of use?

 

Thats it! All these cams, I think it is time for me to get one. I want one so bad! Well, after I get the trans swap done!

 

no they do not. they just take longer to stretch over time because you have two chains taking the load instead of one. i don't know of any formula, or rule of thumb, concerning how much stretch will happen over a period of time. to many factors involved in that. heat, chain material, valve spring pressures, how you drive the vehicle to name a few. i've seen on one of my own motors where i've pulled the cover to put a cam in and seen my double roller chain move 10* after about 2 years of use. but, i drive the **** out of all my cars. i'm not gentle at all. and that's measuring from rotating the motor on direction until all slack is removed. then rotate opposite direction until all slack is removed.

 

How does Vinci decide on 5*?
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The reason I ask is; If its not known how much stretch the timing chain will have after X (the users amount of wear put on the motor), then why grind in 5 degrees advancement into the camshaft? It would probably be smarter, if your going to play it this way, to ask the driving conditions exc. to figure out how much extra advance to set in the camshaft, so you come out even, later down the road. At least, this would be a more effective guess.

I'd personally, want my camshaft set up to my engine. Just install a double roller and have it coated exc. to protect the chain from stretching.

You said, the cam manufacturers think of everything, but really it sounds more like a guessing game. Like you said, what if you get 10* worth of stretch.

 

you can't go too far in the advancing or the valves might hit the pistons, power loss, and so forth. you can always call and ask them about it.

 

ok, thanks for the help mrr