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Timing mark on crankshaft pulley; Why is it NOT aligned with the keyway?
Topic Started: Aug 1 2012, 05:52 PM (4,598 Views)
jaevans
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Quick question that will hopefully help me understand timing better. The crankshaft pulley has a keyway that matches the timing mark on the engine block but the groove/timing mark on the pulley is offset from this. Why is that? It seems to be advanced a certain number of degrees but if we set our timing, say to 8 degrees advanced using this mark, isn't the timing even further advanced? :hmm

John
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Memphis metro


Show me a picture. If indeed it is offset, then the key is sheared or partially sheared and the keyway on the crankshaft is in bad shape.


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t3ragtop
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Turbo3 and Twincam Tweaker

the keyway corresponds to a mark on the block that represents top dead center. the timing marks on the plastic timing cover are in a different location.

the notch on the accessory pulley is offset to match the 0 degree mark on the timing cover when the crankshaft is at tdc.

you have to keep in mind that everything is relative when it comes to timing marks and the actual positions of things. top dead center describes the piston in the #1 cylinder being at the top of it's stroke and it's relationship to crankshaft position.

you can make an arbitrary mark for crank timing anywhere you like as long as it's positional relationship corresponds with the #1 piston being at the top of it's stroke.
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Memphis metro


:smackface I missed the pulley part. As t3 says, the timing indicator on the pulley can be in any 360 position in referance to a fixed timing tab as long as it is timed on top dead center, compression stroke, cylinder number one when the referance marks are made. Imagine if you had it timed on top dead center using the current timing tab and block mark. While you had it lined up on top dead center, You could go anywhere around the crank pulley and scribe a line from the pulley to the block and that would be accurate for top dead center.
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t3ragtop
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Turbo3 and Twincam Tweaker

that's okay, doc. your pic is right on time. you can see the offset of the zero mark on the timing scale from the keyway on the crank gear.
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jaevans
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Yes, the photo clarifies everything for me and is as I suspected, but certainly wasn't positive about. The cutaway timing cover shows the offset on the pulley I was expecting from the key on the sprocket. Thanks all. By the way, Blue, is that your picture of the timing cover? Does anyone run their Metro like this? It sure would make adjustments and assembly a lot simpler, but I realize it puts the timing belt at some risk.

I've got an old timing cover that I replaced because the top was melted/chewed up so I think I will make a cutaway like this while adjusting things. Thanks for the terrific idea.

John
Edited by jaevans, Aug 1 2012, 08:30 PM.
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Johnny Mullet
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Fear the Mullet

I just installed an under drive pulley on my EcoMudder and noticed this also for the first time. The timing light mark is not in line with the notch.
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t3ragtop
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Turbo3 and Twincam Tweaker

johnny, i don't think that the underdrive pulleys were machined with timing notches. you have to file a notch in yourself if you need one and make your own index pointer for the smaller diameter.

i've gotten a few under drive pulleys that had marks on their od that came from the jaws on a lathe that really looked like timing marks, though.

i use a piece of stainless wire twisted up to mount under a bolt. i hammer the pointer end of the wire to a flat.

i also learned a long time ago to use an indexing degree wheel on the crank and a dial indicator on the #1 piston so i could generate a table that described the piston's travel to degrees of crank rotation. i have a little fitting i screw into the spark plug hole that has a marked rod on it for quick checks. i use those things when i set up static timing for cams and ignition.
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jaevans
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On second thought, the location of the existing timing marks on the cover are not the most convenient location since the timing tensioner is behind it. It may be worth make a different guide and marking the pulley a different way so that the degree marks and corresponding pulley mark is at, say, the 2 o'clock position versus the 11:30 position the timing cover uses. All I'd need to be careful about are making sure the degree angles are correct. I could use a portion of an old timing cover and just make sure the distance from the crank sprocket center is the same as the original location. Of course, I am just brainstorming a way to make it all easier so feel free to criticize, one way the other. BadBent's photo may clarify what I am thinking, though I haven't marked the 2 o'clock position.

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Woodie
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Lots of us just throw the entire timing cover into the trash can. Ignition timing is better set by ear ASSUMING YOU KNOW WHAT YOU'RE LISTENING FOR



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jaevans
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Woodie
Aug 2 2012, 05:20 AM
Lots of us just throw the entire timing cover into the trash can. Ignition timing is better set by ear ASSUMING YOU KNOW WHAT YOU'RE LISTENING FOR



Well, with my hearing loss, I wouldn't trust my own ears most of the time.
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