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 Post subject: Cam Install Question
PostPosted: Thu Oct 07, 2010 11:18 am 
Cams + Headers

Joined: Sat Feb 28, 2009 6:55 pm
Posts: 55
I have installed the "D" cam in the block of the B20. The key on the crankshaft sets the orientation of the cam gear (and mark) relative to the crank. The key on the camshaft sets the orientation of the cam gear (and mark) relative to the the cam shaft. The crank was set so that #1 piston was at TDC and the cam was installed so that the orientation mark on its gear lines up with the orientation mark on the crank gear. In my understanding this should set the crank and cam in the proper orientation relative to one another. Is this correct? How does "degreeing in" the cam affect this? Do I need to "degree in" or am I good to go with the setup as is? Thanks for any help.
Bill


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 Post subject: Re: Cam Install Question
PostPosted: Thu Oct 07, 2010 3:43 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
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Location: Calgary, Ab
You are good to go if you line up the timing marks as they should.

You are better to go if you take the time and have the equipment to measure the crank angle that the camshaft achieves peak lift and have the ability to alter that angle if necessary. The difference is probably in the order of 1-2, 5 ft-lbs of torque max, but is more in the way the car runs above or below the peak torque figure.

Generally when the camshaft is advanced from optimal, the torque curve will get meatier before the torque peak (lower RPMs). This happens because the engine builds more compression and traps more intake charge since the intake valve closes sooner and the engine is turning relatively slowly.

Generally when the camshaft is retarded from optimal, the torque curve will get softer before the torque peak but a bit stronger in the top end (high RPMs). This happens because the intake valve closes later and gives more time below TDC with the intake valve open, and the engine is turning fast enough to take advantage of this. Furthermore, the exhaust valve opens later, giving more time for the combusted gasses to exert force on the piston.

The window of opportunity here is maybe +/- 7 or 8 degrees around the optimal, before combustion efficiency goes out the window due to goofy valve timing events.


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 Post subject: Re: Cam Install Question
PostPosted: Thu Oct 07, 2010 6:05 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 3131
Location: Lethbridge, AB
Ugly Duck wrote:
You are good to go if you line up the timing marks as they should.

You are better to go if you take the time and have the equipment to measure the crank angle that the camshaft achieves peak lift and have the ability to alter that angle if necessary. The difference is probably in the order of 1-2, 5 ft-lbs of torque max, but is more in the way the car runs above or below the peak torque figure.

Generally when the camshaft is advanced from optimal, the torque curve will get meatier before the torque peak (lower RPMs). This happens because the engine builds more compression and traps more intake charge since the intake valve closes sooner and the engine is turning relatively slowly.

Generally when the camshaft is retarded from optimal, the torque curve will get softer before the torque peak but a bit stronger in the top end (high RPMs). This happens because the intake valve closes later and gives more time below TDC with the intake valve open, and the engine is turning fast enough to take advantage of this. Furthermore, the exhaust valve opens later, giving more time for the combusted gasses to exert force on the piston.

The window of opportunity here is maybe +/- 7 or 8 degrees around the optimal, before combustion efficiency goes out the window due to goofy valve timing events.


You can't really degree the cam in a pushrod engine as the gear is pretty coarse - you could re-cut the keyway, but that's a lot of effort. My trick to lining up the helix is to use a Sharpie to mark the tooth that is marked one the cam gear and the valley on the crank gear. This makes it easy to line the marks up.

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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 7:07 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
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Location: Calgary, Ab
People with V8s typically have a much looser connection between the crank and camshaft due to it being chain drive, and I know that anyone who calls themselves an engine builder in that world is very careful about setting up the cam. I would be a little disgusted if the Redblock drivetrain can't keep the cam accurate to 1 degree, but I've never pulled one apart before. If the gears are floppier than a timing chain, that's a problem.

Is the key not removable and replaceable with some sort of offset key, for those who crave the last little bit of performance from their engine and have done the testing to know where to set their cam?


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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 7:12 am 
Haha, I just built a W24 Octo-Turbo, now what?!

Joined: Wed Dec 21, 2005 8:03 pm
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Location: T2C
I've seen offset keys on eBay...

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'67 123GT
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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 8:46 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
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Location: Lethbridge, AB
The gear train has very tight tollerences and is nothing like the floppy timing chains in a V8. While the offset key would work, what I was trying to relay was that the crank/cam gear are not exactly what I would call fine toothed. I don't recall the tooth count for either (and if I knew one, I'd know the other) - I was just trying to steer the OP away from the notion that you can just flip things around by a tooth and advance/retard a cam by a degree or two.

**Edit - here's a picture of the gear drive. Crank gear is 28 teeth - cam gear - 56.**
Image

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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 10:13 am 
Cams + Headers

Joined: Sat Feb 28, 2009 6:55 pm
Posts: 55
Thanks for the information. I'm not up for recutting keyways. I will assume that if the marks line up at TDC then that is as good as I'm going to get and "degreeing in" is for cam setups other than mine. Thanks again for the education. This is fun, worrisome at times given the investment, but still fun. Thanks. Bill


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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 11:16 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 3131
Location: Lethbridge, AB
I've only installed a couple of cams in B18/B20's - I've degree'd them and they have been ground correctly. Dale has seen offset keys on eBay - so if you need to alter the position of the gear train a little there is a solution.

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 Post subject: Re: Cam Install Question
PostPosted: Fri Oct 08, 2010 12:55 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
Posts: 3492
Location: Calgary, Ab
122_Canuck wrote:
I was just trying to steer the OP away from the notion that you can just flip things around by a tooth and advance/retard a cam by a degree or two.


Okay, cool. I didn't pick up on that, but you're absolutely right in that you can't skip a tooth and pretend it'll do your engine any good.

And for the sake of discussion, 28/56 is pretty fine compared to the OHC timing belts, which are 19/38, and the timing chain in (for instance) a Ford 302, which is 22/44. You still wouldn't want 13 degrees of advance/retard, which is what you'd get by skipping a tooth on the Redblock pushrod cam, but I know that the Redblock OHC WILL get you home with the cam 19 degrees out. Just because the engine runs doesn't mean the cam's in right, so double-check your install, Bones! (Visually is fine...)


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 Post subject: Re: Cam Install Question
PostPosted: Sun Oct 10, 2010 8:06 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Location: Lethbridge, AB
Totally agree - check the cam position using whatever method you like. No need for anything fancy just a dial indicator and a degree wheel should be fine (oh and the obligatory coat hanger needle). Check the specs and see where the lobes are located.

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