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cam timing

A

aghatas

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gday, i've done some work on my vb 253, i replaced the cam and timing gear from the 8-links to a 9-links. does anyone know how to calculate where to set my ignition timing to? it was 18 btdc from spec, but with blue heads on and the new cam and chain what would it be now? the cam specs are:
Valve Lift int .424" ex .448"
Duration @ .050" int 194deg ex 204deg
Lobe Separation 110 deg
Advertised Duration int 260deg ex 271deg (.006"lift)
and i have set it to 0 deg on the timing sprocket.
cheers.
 

Goon

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On the right hand side of you engine bay, there might be a sticker with the details your after.
 
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aghatas

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are you saying that the ignition timing would still be 12 deg btdc?
 

Doctor Bob

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have you actually measured the cam timing in degrees and set it to that or have you just decided to move it 1 link?

The ignition timing will need to be determined by tuning it.

Rob
 
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aghatas

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i set the timing by the timing gear notches when i replaced the standard 8 link timing gear set with the 9 link timing gear set,
 

craigvk

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Ok. Try this for starters.

Set your 1st cylinder on TDC compression stroke and have the 1st cylinder spark plug lead out. Undo the distributor hold down bolt and then turn the ignition on but not the motor. Take the distributor cap off and the rotor should be at or at least close enought to the firing position of the spark plug 1 lead. Put the cap back on and with the ignition still on, get the spark plug 1 lead and pull back the boot on it and have it 3-5mm from the chassis/ground. Rotate the distributor little each way until you see it spark. As soon as you see it spark, do the bolt up. This means it should be damn close to being spot on for ignition timing. Put the spark plug lead back in and turn the motor over. Using a timing light, read the ignition scale to give you the new timing reading to give you an idea.
This method is almost spot on, but it not absolute 100% and may need some slight fiddling.
 
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aghatas

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thanks, i'll give it a go tommorow, just a quick note though, if i have the cylinder at tdc and adjust the dizzy for spark, wouldn't that mean the timing is set at tdc and not 18 deg btdc which is the original spec? it might be like rob said, ignition timing will be set with a tune up, i only have a timing light and dwell meter so i was hoping to work out if the timing changed so i can set it with the light myself. thanks for the suggestion i'll give it a go.
 

craigvk

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AFAIK, if what I said was done, wouldn't that be good timing? Regardless of the chain you installed? After all, don't you want the cylinder to spark at the exact right time? I am no pro. I am sort of new with motors and I am learning all the time. I am curious to why you went for some strange chain that I haven't heard of. I thought there was only the standard chain and sprockets available. Did you line up the chain's shiny links to the marks on the sprockets for correct cam timing?
I am actually going to be doing what you have done with yours. I am going to be soon replacing my noisy lifters as well as a new cam and timing chain, and possibly new performance valve springs and valve collets.

What cam brand did you choose and where did you buy it from? I was probably going to go with a Crow cam part no. 5666.
 

craigvk

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Hmmm. You said timing gear. What do you mean by that?
 
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aghatas

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the timing gear i was talking about is the timing chain that connects the cam to the crank, the stock vb chain was altered for pollution reg and you can get aftermarket chain that has the timing marks for easy allignment, the cam i got was speedpro brand, cheap but made in the usa so at least its not some chinese copy.
 
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