1600 cam timing reality check

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Habitat.pat
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1600 cam timing reality check

Post by Habitat.pat »

I’m assembling my engine with new everything internal, including cam & crank & want to verify the cam timing.

I have new Japanese metric sprockets with a chain with the colored links 8.5 links apart & the engine @ TDC on #1. The sprocket timing marks line up with the centerline between the crank & cam. The cam lobes are down, away from the lifters. As I understand it, that should be correct.

Just for grins I measured the distance from the cam lobes to a straight edge across the bottom of the block expecting the distance to be the same on both lobes, even though the measurements were not to the top of the lobe, rather to the closest point to the bottom of the engine. They aren’t. The intake measures 124.8mm & the exhaust measured 127.6mm. I am now questioning my understanding that the measurements should be the same.

Feedback please?

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Gregs672000
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Re: 1600 cam timing reality check

Post by Gregs672000 »

Well... having never made or heard of this measurement being an actual reference point for cam position, I can't really say. However, as I sit and think about it, the only thing that matters is the relationship between the cam and the crank as it relates to piston position... that's what you're doing... timing the valve opening with piston position. If the sprockets line up with the expected timing marks all should be fine. The cam's lobe separation certainly hasn't changed (assuming stock cam lobe separation). For fun, you could try moving a gear one tooth forward or backward, but I bet you'll see significant deviation from the timing marks.
My experience is with U20 motors only.
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Re: 1600 cam timing reality check

Post by Habitat.pat »

Thanks, Greg.

I assumed that the cam separation angle was centered on TDC, but after checking some on line cam docs I found that that isn’t the case.

Have a great evening.
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Pat
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RustBucket
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Re: 1600 cam timing reality check

Post by RustBucket »

Just align the crank and cam sprocket dots and you're good to go. Worked for me anyway.
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keith0alan
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Re: 1600 cam timing reality check

Post by keith0alan »

When the number one cylinder is at TDC on compression the number 4 cylinder valves will be exactly on the overlap between exhaust and intake. As you rock the crank back and forth the intake and exhaust valves on four will be just opening and closing. Rotate the crank 360 degrees and the number one valves will be on the overlap. Always worked for me.
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Re: 1600 cam timing reality check

Post by Habitat.pat »

Thanks, Keith, I am probably overthinking this…as usual!

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Pat
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Gregs672000
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Re: 1600 cam timing reality check

Post by Gregs672000 »

NEVER anything wrong with asking questions!
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Re: 1600 cam timing reality check

Post by Habitat.pat »

👍
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