Timing/idler gear/adjuster follow up

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.

How do you alter in any way the length of the chain between two fixed sprockets without destroying the relative valve timing when the slop is removed by adjusting the tension and coning back to the exact same number of links as before on the top run of chain?

I’m not as much interested in being right as I am in stimulating a conversation that solves a challenging problem. This is the current one. The solution is always helped along by an understanding of the physics. Is this one solved in your estimation? Or are you playing devil’s advocate?

How many degrees of rotation are allowed by the retainers? Time the cams with #6 TDC. Tap the cam sprockets onto the cam flanges at the same time maximising tension on the outside run. Both sides. Get as much of the length of the chain between the cam sprockets as you tap them onto the camshaft flanges.

Open to discussion.

Edit: but not now. Time for Netflix and tea with the missus. Carry on, J-Lers. Solve the mystery and let me know in the morning.

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Pete,
I’ve always set the intake cam a little retarded, about .030 on the gauge and when the chain is adjusted it pulls it, usually, right into time.

I like problem solving as brain exercise, not blood sport. But I lose interest and/or patience when/if it turns out that normal assumptions cannot be used when assessing the possible solutions - often due to different meanings given to words or expressions by different parties including me.

So in my mind - and I don’t think I was alone - the OP was describing something almost impossible, where ‘turning’ the crank failed to rotate the fully-assembled cam sprockets so he could fit their second bolts.

Consequently, we went down several rabbit holes (I think) where slipping or lengthening chains didn’t (or did) mean moving over the teeth instead of with them, or making the chain longer rather than looser etc.

Now I’m guessing that possibly the degree of crank rotation was so small that normal chain slack accounts for not an assumed and very strange failure to rotate’ but merely a small lag before cam movement that we’ve all encountered.

Meanwhile, the initial attraction of an unusual problem has faded and the likelihood of learning something novel has probably disappeared altogether. It would be nice if the OP came back eventually with the answer as to what he did differently from when he took the engine apart, but I’m not going to lose any sleep over it.

Not so much blood as frustration.

The OP initiated a thread here, then a second thread, then a third, followed by a fourth, fifth and a sixth, this one - all in pursuit of solving the same issue.

The basic question “is there slop in the outer run of the chain” is still unanswered. If there’s slop, then the probability is good that high mileage chain lash is the culprit - merely delaying movement of the cam sprockets rather than there being no movement at all. This has already been suggested. If the outside runs of the chain are snug then lash is ruled out and it must be that either the (one piece) intermediate gear is not in fact turning OR the upper chain is not engaged in the smaller sprocket of the intermediate.

I’m done too.

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For my forth attempt, chain lash would be confirmed or denied with a 20 dollar camera to verify that the chain is moving on the intermediary sprocket. Likely even by feel by grasping the outer exhaust segment and holding it tight. It seems like OP has either given up or figured it out and moved on.

Phillip, any updates?
Tom

I think most (But not all) are over complicating the issue. Again when trying to rotate top sprockets to add second bolt to the adjusting plate, the top chain does not rotate when I turn the crank. And to add extra info:

  • I have turned the crank enough to take up any slack in the chain.
  • I can’t see but assume the upper chain is not engaging the intermediate sprocket. I don’t think I can get spy camera inside to prove this but may be wrong.
  • I can clearly see the lower chain rotating the intermediate gear ( forward part) and assume the back part of the intermediate gear is rotating also as two gears are one piece.
  • I have tried about five times to get first bolt in adjusting plate with varying amounts of chain slack in different places
  • I have carefully studied all of your posts but none answer my question of why isn’t top chain rotating

Your best guess is that top chain is old and worn and way too much slack exists. So I have totally dismantled the chain system. All gears look good and top chain superficially looks ok but I am waiting for new top chain I ordered to compare the old and new
Will let you know what I.find. Incidentally, I am not a pro category mechanic butt havie been working on old jags for about 20 years, including total restoration of a junk XK120

Apologies for being defensive when it is clear I am doing something wrong. Just wish I knew my error.

I‘m at my wits and and yes, we’re all overcomplicating. Everyone wants to see and look in person I bet. Good luck and I hope you find the answer soon! I think there’s not much more we can possibly provide.
Looking forward for results.

I really dont see that members are over complicaded things…so far you have about 5 other threads on this issue…im still waiting for an answer on the thread where you insisted that the adjuster was seized…good luck with your rebuild…Steve

Phillip,
Sorry to hear you have not found the solution.
At this point, you seem to believe the chain is too long and thus slack.

Several have suggested reaching down below the sprocket with a hook to see if the chain is slack. Just curious, when you did this, was the chain extremely slack?

No need, I do not see you as being defensive, I see you as being frustrated, as I would be also.
Tom

Been following and thinking about this one…
I don’t recall but has anyone suggested removing the cams and, with an extra set of hands to hold the chain under tension, try to rotate the crank ? This would eliminate any chances of bending valves.

Marco

Marco

Phillip, still curious what you found?
Tom

One month after my first post, I have finally solved my mystery. To reiterate, I reinstalled a rebuilt head. Then I inserted one bolt on each of the top chain sprocket plates connected to the cam shaft. But when I rotate the crank shaft to get at the second bolt hole, the top chain did not rotate And the forum had many questions and comments, none of which helped.
I then spent weeks opening the timing chain section and replacing the top chain in a guess that the chain was too loose. No help.
Today a new theory; the shop rebuilding the head tightened the cam shaft bearing caps too much so it was too hard rotating the cam…
And yes, when I losened the caps the top chain and sprockets rotated when I turned the crank. Before the cams were not turning but the sprocket plate was rotating on the single bolt. I never turned the crank before more than about 20 degrees to avoid damaging the valves A long story: apologies.
Do I feel stupid for not figuring this out sooner Yes. But the problem is solved

Sorry, but this makes no sense to me. First, yes you can over tighten the cam bearings. It’s one of the few cases where the manual specifies actual torque values (15 ft-lbs IIRC). So that is the test, not is it easy to rotate the cams. Generally if they’re over tightened, the studs simply strip out. They’re only 1/4" fasteners and won’t take much abuse.

Second, even if it were possible to over tighten to the point where the cams struggle to turn, it wouldn’t manifest as the upper cam chain slipping. Under no circumstance should that be possible. If it was possible then the first time you planted your foot in the pedal the chain would slip and you’d be dropping the engine for rebuild.

Third, if you randomly loosened the cam bearing caps to make it easier to turn, you’re going to end up with other issues.

You need to go back to the well and figure out this problem.

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Philip
The bearing caps can only be tightened a certain amount. Even if you over torqued them, it shouldn’t cause the cams to bind. It sounds as if the bearings are not the correct size for the current diameter of the cams. I would plastigauge them and see what clearance exists.

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is it possible that the serrated plates do not grip because they are not locked in, so the cogs turn as well as the chain, but neither the bolt nor the cams?
that would be a crass error though, and the upper chain would have moved.

20 crank degrees is not much and it is a good idea to investigate in case something feels wrong. but if the upper chains moved and not the cams something was not explained correctly.

If the cams were that stuck I third that you should inspect EVERYTHING.

You

I’ve never knowingly insulted anyone on J-L in nearly 20 yrs but you have a bloody cheek IMO Philip. The questions were necessary to clarify the seemingly impossible scenario you misdescribed and actions and outcomes that never took place as described.

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Just my two cents. If the cams bind when the caps are tightened, generally it means the head is warped or, far less likely, a cam is bent. Cams usually break before they bend. Milling the head on an OHC engine makes it flat, but does not take the warp out.

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