If the bottom chain does not turn then it’s a Woodruff key issue, can’t be anything else !
Or the intermediate sprocket has sheared ! this will be a first for the book !
Yeah… but it turns. 15/16 is the intermediate
How many degrees did you turn it again? Is it not even moving the upper chain in the least?
Sorry for making this so muddy. The chain can hang below the teeth someone said (on 3.8 and 3.4) and you said the chain was slack so off with the head and have a very good look at the chain.
I’m still wishing for a wand camera view, 20 bucks on Amazon. We’d have the solved by now with a view of the underside of the chain.
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I suspect this is the issue. What the OP means by ‘turning’ or ‘moving’ is very short movements at the crank which are half that angle at the cam.
So his definition of moving/not moving may be what one would get from a gear train, not a chain drive where perhaps chain tensioners (plural) and the lower chain guide above the lower tensioner, are badly positioned, leading to excess slack which gives the appearance of something detached because he stops turning for fear of damage?
Why not remove both camshafts, then there will be no damage to valves, then rotate crank a full 360. Upper chain should still rotate although loosely. If the upper chain and sprockets do not then the front timing cover has to come off.
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Two sprockets only in older engines. The intermediate gear in this engine should be one piece, #14 in the schematic below, and there is no way in the world it would shear in two.
It would take less torque to shear the woodruff key in the crank bit it would still be considerable, something you’d definitely notice.
He is implying in the post David quoted that he can see the intermediary gear turning. I hope that is true. If so then if he’s taken up the slack in the outer segments of the upper chain while mounting the cam gears and gotten one bolt threaded in each cam, and the tensioner is tight, they should start moving very quickly after the intermediate gear starts.
I can’t replicate the geometry of the four gear arrangement on my desktop but can determine the difference in the overall length of the upper chain when fully engaged in the intermediate sprocket v. when it is fully disengaged. It’s 1/8". Here’s a video:
throwing this out for discussion/debunking.
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I think Nick has nailed it. When I assembled my engine, I remember now that I had the same problem. I had to fiddle the chain to get it to land properly on the bottom sprocket.
I think you got it. It’s probably worn enough that it allows a bit of sideways movement which has allowed it to fall onto the bare middle section and also still bolt up to the cam gears. On a brand new chain it only wants to be moved around in a single plane.
The distance between teeth in the sprockets is 3/8”. That’s also the span of a link in the chain. I expect if the OP added a single link’s length of chain between the cam sprockets there would still be sufficient throw in the idler eccentric to snug up the chain.
You can’t add/subtract a single tooth/link without a cranked link. I don’t think that’s possible on duplex chain. Remember too that whatever change you measure on a loop of chain is double that length on the same unfolded piece of chain.
I’m not suggesting physically adding or subtracting a link to the chain, only increasing the number of links between the two cam sprockets by one, thereby requiring the idler to take up more slack between the cam sprockets, ie more toward the greater extent of its range, and shortening the outside run.
One eighth doubled is one quarter, and the spacing between links/sprocket teeth is 3/8”.
Here’s another video.
So how did his chain get so long? He said he could rotate the adjuster 360 degrees and the chain was still not engaging. I do not know the answer, but the chain seeming too long is why at one point I wonder if the cam sprockets are not correctly in position, dropping down slightly. One reason photos may help.
Tom
You’ve lost me 
You cannot alter the distance between centres except by using the existing eccentric, which has a fixed ‘stroke’ that cannot be changed.
You cannot alter the chain length by 3/8. The minimum is 3/4”.
Adding or subtracting 3/4” will likely throw the eccentric out of range.
Now you’ve lost me. Are you saying you can’t physically shift the chain over a single link?
I’m processing, still not getting.
Edit: the cam sprockets are disconnected. You achieve as snug a fit between the intermediate gear and the sprockets as you tap them onto the cams. That is to say the outside run of the chain. Get these snug and the rest gets taken up by the idler eccentric. I’ve asked before, is either side of the outside run sloppy?
If, as suggested, the chain and sprockets are meshed as they should be and the OP can still turn the eccentric 360 degrees then I’m out of ideas.
When you take a pin out you are left with male and female chain ends. The only way you can change by one tooth is using a cranked (gender change) link. These have a female end and a make end. The bent side plates are a weak link (no pun) in tension, so they are avoided except in low power drives. I have never seen a cranked duplex link but maybe they exist.
What you do instead is you remove two pins either riveted or paired on a spring link, leaving two male chain ends, capiche? The minimum you remove is two more pins to take out one link and a pair of side plates (2 pitches-3/4”) and leave the newly-expose male end to be joined to the other male end with a spring link or soft rivet link.
Wrapping chain snug round sprockets and getting two male ends to be snug is unlikely to happen if you’ve shortened the chain by 3/4”
Alright. We’re not talking about the same thing. I don’t mean physically adding or subtracting a link to the chain. I mean maximising the length of the existing chain between the cam sprockets to minimise slack on the outside runs.