Cam timing ~ stock 325i cam ~ proceedure?

[Chuckcruzin1986]

Hi,
I milled my head .050" and bought an adjustable cam gear. I want to set the cam to the "Stock" 325i setting.

Help please

Chuck

[e30trooper]

install a stock cam then........... and put on TDC...

[E30_fiend]

Just align the adjustable cam gear to zero so there is no advance or retard then torque that down. Install the cam while the motor is at TDC, set cam to TDC and done. As long as the cam gear is centered on the cam, it will be just like the stock gear except later you can adjust it.


Taylor

[Chuckcruzin1986]

I am using a stock cam. The head is milled .050"

install a stock cam then........... and put on TDC...

Sorry I was not clear about my situation.
Chuck

[Chuckcruzin1986]

My head is milled .050"

Just align the adjustable cam gear to zero so there is no advance or retard then torque that down. Install the cam while the motor is at TDC, set cam to TDC and done. As long as the cam gear is centered on the cam, it will be just like the stock gear except later you can adjust it.


Taylor

Are you saying the .050" will not change my cam setting?
Chuck

[slippery]

If you want it dead on you need to stick a degree wheel on the crank and a dial indicator on the cam itself, are you willing to buy those pieces? Otherwise you will need to take it somewhere.

J

[jlevie]

If you move the head 0.010" closer to the crank center line the load side of the belt needs to be 0.010" less to retain correct cam timing. Which means the cam needs to be advanced so that the load side of the belt distance is correct.

The cam sprocket is darn close to 4.875, which means it's circumference is 15.31". Advancing the cam to make the load path 0.010" longer is .00644 of the circumference. Multiply that by 360deg and you get 2.32deg for ever ten thou of decking.

I don't trust adjustable cam sprockets. I've seen a couple of cases where they have shifted and the results aren't pretty, but they are expensive.

I deck the head on a Spec E30's engine to max (the bottom of the limit dimples). To correct cam timing the index hole in the sprocket is drilled out to 1/2" and a bushing with an index hole offset by 3/16" is used to reposition the cam relative to the sprocket. Once assembled the bushing is trapped and can't come out. So there is no possibility of cam timing changing.

The sanity check on cam timing is that both the intake and exhaust valves should be open the same amount at valve overlap. Which occurs when the piston is at TDC between the exhaust and intake strokes.

[Chuckcruzin1986]

Thanks Slippery

If you want it dead on you need to stick a degree wheel on the crank and a dial indicator on the cam itself, are you willing to buy those pieces? Otherwise you will need to take it somewhere.

J

Yes, I want to do the indicator thing. I am a machinist and do not see a problem with doing it. I see the next post has more detail and will respond to him. Thanks for you thoughts and since I am not home free, more ideas would help.

Thanks,
Chuck

[Chuckcruzin1986]

Now we are making progress

If you move the head 0.010" closer to the crank center line the load side of the belt needs to be 0.010" less to retain correct cam timing. Which means the cam needs to be advanced so that the load side of the belt distance is correct.

The cam sprocket is darn close to 4.875, which means it's circumference is 15.31". Advancing the cam to make the load path 0.010" longer is .00644 of the circumference. Multiply that by 360deg and you get 2.32deg for ever ten thou of decking.

I don't trust adjustable cam sprockets. I've seen a couple of cases where they have shifted and the results aren't pretty, but they are expensive.

I deck the head on a Spec E30's engine to max (the bottom of the limit dimples). To correct cam timing the index hole in the sprocket is drilled out to 1/2" and a bushing with an index hole offset by 3/16" is used to reposition the cam relative to the sprocket. Once assembled the bushing is trapped and can't come out. So there is no possibility of cam timing changing.

The sanity check on cam timing is that both the intake and exhaust valves should be open the same amount at valve overlap. Which occurs when the piston is at TDC between the exhaust and intake strokes.

Thanks Jlevie

I would like to use an indicator on the lobes and get it right.

So if I understand you correctly, I will bring the engine to TDC and using an indicator turn the cam until I split the difference exactly..............

I hear people saying that a card comes with a performance cam so I am guessing you can do your way only with a stock cam?

Thanks again
Chuck

[jlevie]

You will have to have the lobe curves as a function of crank angle for anything other than a stock cam. With a stock cam, both valves will have the same opening at valve overlap. Some other cam may be different.

[Chuckcruzin1986]

Thank you again. I am off and running with this

You will have to have the lobe curves as a function of crank angle for anything other than a stock cam. With a stock cam, both valves will have the same opening at valve overlap. Some other cam may be different.

:p