List:
As you will recall, turning the crankshaft on the XJ6 did not result in the rotation of the camshafts,
which caused the bent valves. Can someone speculate on what caused the camshafts to stop rotating and what the fix is?
Thanks
Lou
Lou:
Not at all. You said that you turned the crankshaft, but both the camshafts did not turn at all (after they did move correctly before)?
Now that you have to tear it all down again you might want to run a few experiments - is the chain tight on one or both sides on the corresponding sprockets and what does move, what doesnât? The result certainly isnât what we intended or expected. Then when you remove the head things might get clearer - if you are luckyâŚ
David
Hi LouâŚthe camshaft sprocket is in two partâŚthe outer that the chain runs on but the inner that bolts to the end of the camshaft has tiny teath that mesh into teath on the outer sprocketâŚlook close see if they have shearedâŚwere they assembled correctlyâŚSteve
It could be a few things but it would be helpful if you specify what MY (model year) you have.
I had an insident several years ago with my 94VDP where my chain got loose (long story) and sheared the teeth of the small sprocket that bolts to the cam. Here are some photos of the camshaft sprocket assy. and sheared teeth on sprocket that bolts to cam.
Good teeth
Sheared teeth
JM
Sorry, the car is an 1971 XJ6. I did not realize that the sprocket and cam are two separate pieces.
Could the cause of the failure to rotate be that the setscrews were not tight enough, which allowed the sprocket to rotate while the cam stayed in place?
Lou
Just spit balling here but it would have to shear all four bolts, not setscrews, that hold the cam gear adjusting plate to the cams (on my 94 there are 8 bolts). I doubt that happened. Another possibility is that one of the chains broke.
How do you know you have bent valves? Have you pulled the valve covers off to see whatâs going on?
Loose bolts could allow the sprocket to be rotated by the chain WITHOUT turning the camâŚthe bolts would not necessarily have to be sheared off. Looks like that is what happened in the photosâŚloose bolts allowed the sprocket to slightly âsawâ back and forth due to alternating, counter-acting spring forces on the cam until the serrations were destroyed, finally allowing sprocket rotation without cam rotation.
Donât you need a lot of force to shear off the teeth? Itâs been a while and I canât clearly remember, but Iâm sure it is not that easy to turn the crank a few times without the cams moving, which is what happened. It might help to include a short list of what happened exactly to look it up in this thread.
I would imagine it would take lotsa force, acting over a long period of time, to wear down those teeth. My original cam drive set-up was/is very tight with NO slop so I donât see how ANY movement could occur with my parts, thank goodness.
**
Only a closer inspection would reveal the cause, LouâŚ
âŚand it is absolutely vital that it is clarified. Anything from a disconnected lower chain, to excessive upper chain slack, sprockets not connected to the cams or the serrated plate not engaged will prevent the cams following the crankshaftâŚ
While some crankshaft wriggling is required to fit bolts; wholesale turning of the engine with no cam motion is an absolute no-no - no ifs or butsâŚ
Frank
xj6 85 Sov Europe (UK/NZ)
**
1 Like
Shearing the sprocket bolts is impossible by hand. If the cam chain did turn but the cams did not after a turn or two, then the vernier sprockets were probably just clamped by friction without teeth engaged. The photos are not of Louâs parts. IMO chain snapping or loose enough to slip is also as good as impossible in a non-running engine but forgetting a crank sprocket Woodruff key would be easy if not working from experience.
Good, but:
David
⌠20
GroanâŚyouâre right. What the heck can Lou have done? Thing is, unless someone here strips it I assume weâll never know because he must be at the end of his rope by nowâŚ
Is it possible that the crankshaft nut breaks loose?
If not the driving, intermediate sprocket or lower chain might have failed, or the upper chain hangs way loose because it is not tight? That would add the idler to the list.
I would appreciate a writeup. How it felt and what turns.
The lower chain turned. It must be a failure in the transition between the lower and upper chain.
Gentlemen: I offer the following in an effort to determine what happened.
Before this accident happened, I had previously turned the crankshaft and the camshafts did turn in unison.
At that time, I recall seeing what appeared to be a substantial amount of movement in the recess where the chains are located, although I did not pay much attention to them.
However, the last time, when I was in the process of turning the crankshaft that caused the accident, there did not seem to be as much activity in the recess where the chains are located; as though something that was previously moving, what not moving at that time.
Regards
Lou
Lou,
can you pinpoint where?
I guess it is unusual. Iâd offer 11 or 8 as failure points or the chain slack below any of them. I think there is some mechanical failure that needs investigating, and is no oneâs fault, especially not your wrongdoing.
David:
Thank you for absolution from guilt 
I stopped at the garage on my way home yesterday, which was before I saw your email. I went to look at the arrangement of the chains to better understand what happened.
On the day of the incident, three of the setscrews were in place, two on the intake side and one on the exhaust side. When I tested them yesterday, the two on the intake side were very tight. The one setscrew on the exhaust side was only moderately tight. I was able to make 2 or 3 revolutions of the one looser setscrew before it was tight.
I should also explain what I was doing on the day the damage occurred as that may give a hint of what occurred.
As I mentioned, the two setscrews on the exhaust side were in place. However, only one setscrew was in place on the exhaust side. In fact, the incident occurred when I was attempting to line up the hols for the setscrew in the adjusting plate with the hold in the exhaust camshaft flange.
When I attempted to install the last setscrew, the adjusting plate whole would not line up with the camshaft flange hole. The manual says that when that happens, you should disconnect the camshaft sprocket from the camshaft flange and turn it 180 degrees, and it will fit due to the eccentricity of the plate.
So I had removed the circlip on the exhaust side, and the one setscrew. Then pulled the camshaft sprocket forward, so it was separated from the adjusting plate. I then pulled the adjusting plate forward and rotated it 180 degrees, in an attempt to get the two holes to line up. But when I rotated the adjusting plate, it did not line up with the camshaft flange threaded hole. So I returned it to the original position so at least one screw would be in place. I think that is when the accident occurred.
As a test yesterday, I turned the crankshaft less than 5 degrees to see what movement would occur. The top chain, #7 in your attached drawing, on both sides, (exhaust and intake) moved when I move the crankshaft. Also, I can see the top of the sprocket. #9, in your drawing, turn when I turn the crankshaft. But that motion does not transfer to the two sprockets.
It appears to me that the motion of the #11 sprocket is not being transmitted to #7 sprocket and itâs twin the exhaust side of the engine.
I donât think I can see the back of the #7 sprocket which is where the problem may be.
Any thoughts?
Thanks
Lou
SoâŚ
The lower chain turns alright.
The intermediate sprocket that transmits the power from the lower to the upper chain is turning.
The upper chain is moving and so is the idler (with the upper chain tensioner function).
A sprocket, to me, is the geared wheel the chain rides on, so if the chain is moving, the sprocket must move too. There will always be some slack to be taken up in the chains when the engine is turned.
Is the sprocket moving in relation to the camshafts? Everything has to be mechanically connected. You will need to make out a certificate point at which a part is moving in relation to another even though they must be connected.
David
the situation you describe is perplexing.
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a couple of thingsâŚyou cannot try and rotate the engine with only one camshaft screw in, unless it is dead tight, or the shaft may pivot on the sprocket ?
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if you undo the camshaft to sprocket bolts, and completely back of the cam bearing cap screws, that should mean the valves are all fully closed, and you can carefully attempt to rotate the engine and see what is the issue
Take a 2nd opinion on the above !
If there is some fault in the timing chain area, those parts need R&R,
which is not easy with the engine on the car
I also never work on these engines without stuffing the timing chest with rags
**
The manual says âturn the adjuster plates through 180 degreesâ, Lou - though admittedly, either may have the same effectâŚ?
But since the damage has already been done; turning the engine to verify cause is, sort of, safeâŚ
Frank
xj6 85 Sov Europe (UK/NZ)
**
But nothing excuses turning the engine if the cams do not follow.