OHC experts. caddy northstar

joe_mnAugust 28, 2007

i am setting the timing on a caddy northstar motor. i know the cams turn at 1/2 the speed of the crank. crank turns 360, cam turns 180. there is also an intermediate sprocket that is larger than the crank sprocket. i know why the crank timing mark has to be at 12 oclock. that indicates TDC for #1 cyl. than the cam dots are lined up at 12 oclock to the head surface. why does the manual even mention that the inter sprocket needs to be at 6 oclock? it could actually be pointing anywhere as long as the crank is at 12oclock.

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mikie_gw

I have no idea but Im curious now.
Maybe a sensor on that sprocket. Or that sprocket is actually a balance shaft. There's a reason for sure.

    Bookmark   August 28, 2007 at 9:47PM
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chad_said

That extra sprocket is a balance shaft. It must be aligned correctly or the engine will not run smoothly.

    Bookmark   August 29, 2007 at 1:58AM
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joe_mn

the inter sprocket is where a cam would be on a chevy small block. the FSM shows it as just a pivot point. there is no balance shaft at least on this generation northstar. its a 96 but i am pretty sure northstars never used balance shafts. the assy is actually 3 sprockets stacked on each other like records. the drive sprocket is larger than the crank sprocket and the cam sprockets seem to be the same size as the crank sprocket. i have heard the different sizes are to combat harmonics in the engine rotation. but that does not explain why the dot is required to be aligned?

    Bookmark   August 29, 2007 at 7:30AM
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john_g

Set it the way the manual says too. Otherwise at the very least, any service in the future where only one head and it's associated timing chain would be disturbed could be a trap for the next service technician.

From there I have not pulled information on this engine to be certain of the markings and directions or if Chad is correct and this uses a balance shaft (I would expect that it does, but won't rely on my intuition, I would look it up to be sure). I don't have time to right now. But you are working on an engine that is very critical to get the marks correct, and the chains properlly installed. One mistake, and you will have 1000lbs of scrap.

    Bookmark   August 29, 2007 at 9:12AM
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joe_mn

yes, i aligned all the marks. gotta do what the manual says. i was just wondering why? i did not touch the shortblock or take the cam sprockets off the cams so all i need to worry about is making sure the dots line up. fairly easy job.

    Bookmark   August 29, 2007 at 11:18AM
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