Makes sense Mike. A line bore would be in order if so?
normally in that case the head would have to be flattened in an oven with inserts all removed. after machining this is not so easy so if anything a line bore but is that worth it? I would check straightness of the bearing bore with a straight edge. if all cylinders are at an intermediate height and one cam is removed the cam can be tested for freedom of rotation. a new head and a competent rebuilder would fix this more easily i guess. the problem was described incorrectly. we asked for a video. we did not get one or an excuse. so a lot of fuss could have been avoided.
this thread alone contains questions and hints to work it out. i can fully understand the aggravation.
a correct description would have been: the upper chain has slack taken up, the lower and upper chains move, after turning the crank further (our suggestion), the sprocket moves but the cam does not.oh, it turns around the simple bolt. i make many mistakes and am too worried sometimes but this is a lot.
Not if he passed one bolt through and snugged it down. That alone would lock the part sandwich together, albeit, awkwardly.
If the cams lock up when the caps are torqued down I would suspect that the caps are not with their respective mates?
Many years ago I had a head skimmed which I am fairly sure would have resulted in the cam bearings being out of alignment, that engine ran for quite a while before being taken off the road due to rust in the body.
Skimming the head wonât cause cause a change in the bore alignment of the cams, but it wonât fix a warped head, it only makes it flat. If the cams turn by hand before the skim, thereâs no reason they should not do so after the skim. Any machine shop can mill a head flat. And on cam-in-block OHV engines, thatâs perfectly acceptable. But when you put the cam or cams in the cylinder head, then warping becomes a serious problem.
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If the head is warped and then material is removed so the face is flat, when you bolt it to the block, it is no longer pulled flat by the head studs and so it remains warped. To me this means the bearings are no longer aligned. If that is significant then the cams bind.
Bearing caps in the wrong places sound plausible since apparently it can happen on the crankshaftâŚ
I think we are saying the same thing. If the head is warped, the cams may bind. Milling the face flat wonât fix that.
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Didnât really explain that the head was skimmed because it was presumed to be warped after it blew a head gasket.
I would think he could get a rough idea of the straightness by laying a good straightedge across the head over the cam cover mating surface? It it wobbles badly then the head was likely warped and then skimmed. If it was line bored after then it might be okay but if notâŚ
Just a guess on my part
I too am very confused. On one hand you said the chain was not turning but the sprocket was??? Through my many years of troubleshooting over the phone, there are times when one person talks apples and the other hears oranges. I will assume this just may be one of those times. So you, for me, although I will wonder about this, you need not explain. But, as others have said, the cam bearing clearance is determined by machining, not by tightening the bearing caps. I suggest, unless you are totally sure of what you are doing and we are simply not understanding, I believe someone should check over this before it costs you more money.
Tom
To try to explain the previous post, the chain did not rotate but the sprocket was pulled slightly lower in the head as the chain force caused it to rotate slightly on the single bolt in the plate. Not much a as I did not want to rotate the crank (and pistons) with the can rotating as this would damage the valves.
Sorry that I cannot explain better.
As to the head refurbishment, all that was needed was valve replacement and grinding - no head planing. It could be that the can bearing caps were mixed when replacing but I doubt it as this was at a highly regarded shop.
All I know is that I could barely cause the cam to rotate before I loosened the caps and easy afterwards.
Phillip the caps should all be marked along with the corresponding marks on the head, check that to start with. It may just be a combination of the cam caps not in the correct places and the bolt(s) not being tight enough to keep the plate in place.
FWIW has ANYONE here found someone in the US who can line bore cam bearing on an XK head. My guess is no. I was asked by a well known US racer and major restoration/servicing business to look for one in the UK, as he had been unable to outsource the task here. I eventually found one UK Jag specialist workshop who had developed the necessary fixture.
Unlike normal crank or DOHC designs, the boring bar cannot be supported at both ends because there is no âhalf moonâ cutout that would allow access from the front. Doing this precision task therefore requires rigidly supporting the front of the bar from âinsideâ the timing chain tunnel in the head casting, which therefore cannot move to and fro unrestricted the same as a block or head normally can on a machine table with power feed.
Not surprisingly, most heads just get the snot milled out of them and never see an oven or press unless the bow is huge and/or the machine and customer know of one and are prepared to pay rather than replace.
So, no slippage at all.
Looking back on the thread, we had ruled out your guesses and sorted out the basic answer early and certainly nailed it by halfway. The only reason for the more speculative side tracks was your insistence the crank and lower chain were rotating but the upper chain was not, when clearly the intermediate gear was moving them in unison until you ceased turning beyond very few degrees used to take up slack!
PH:â⌠the upper timing chain is too loose and will not rotate when I rotate the crank and lower timing chainâŚthe adjuster cannot pull the chain tight enough to engage the crank driven intermediate timing gearâ.
PH â⌠that still does not explain why my chain slips with eccentric downâŚâ
J-L âMost here I believe are having trouble as to how this chain could be that loose that it totally drops below the intermediate sprocket and does not even try to engage.â
PH ââŚI can clearly see that 15 and 16 are turning together but, for some reason, gear 15 is not engagingâŚâ
J-L âSo how did his chain get so long? He said he could rotate the adjuster 360 degrees and the chain was still not engaging.â
âPH ââŚthe 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 canât see but assume the upper chain is not engaging the intermediate sprocket.
- I can clearly see the lower chain rotating the intermediate gearâŚ
- I have carefully studied all of your posts but none answer my question of why isnât top chain rotating?â
At least we can now safely assume that the experienced head rebuilder and everyone else implicated is likely perfectly innocent. The answer to the mystery of why the upper chain didnât move is as expressed by several peopleâŚdrum roll)âŚ
âŚbecause you stopped turning the crank.
Phillip, this was my suggestion about a month ago. It sounds like this is what you said the problem was, after the cam applied resistance to turning.
But again, maybe I just am not understanding what you are stating.
Tom
I am just confused. But if the problem is fixed to your satisfaction then letâs move onđ
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I am now on a new theory about my problem as I have concluded my last theory about stuck cam shafts was wrong. Apologies for wasting your time on this bum idea.
My new speculation is that the idler adjuster gear is not low enough to create enough tension on the chain to get the chain and intermediate gear to engage.
Up until today I have been rotating the serrated adjuster through 360 degrees to achieve the most tension. Today I found, however, that the serrated plate is turning but the actual eccentric shaft is rotating only a small amount i.e. The flat spot on the plate does not stay engaged with the flat spot on the shaft
Taking off the adjuster plate and just directly rotating the shaft, I find the shaft will only turn about 30 degrees from stop to stop in either direction. This, in turn, moved the idler gear up and down by about 0.3 cm when I.believe a 1.0 cm movement would be achieved by rotating the eccentric by 180 degrees
In any case the max adjustment I can achieve in not enough to get the top chain and intermediate gear to engage.
A long story - apologies - but my question.now is what is preventing the eccentric shaft from rotating more than about 30 degrees?
Incidentally, I have rotated the lower chain and intermediate gear to ensure that a gear tooth is not impacting on a chain roller, which would prevent the eccentric from turning.
And finally, I bought a small inspection camera at Erica Mossâs suggestion but I still cannot see under the intermediate gear where I believe the separation with the chain is occurring.
And just to reiterate, after I first found this âloose chainâ problem, I completely dismantled the entire timing chain apparatus and changed the top chain in case the old one was worn and loose. Everything else in the system looked in very good condition.
Where are you probing? If youâre looking for slackess at the intermediary pulley, then youâre probing the top and bottom side of the lower chain segments. If youâre trying to get in to see the tensioner pulley then youâd probe the top and bottom of the upper chain segment that loops over the cam gears.
In total, side to side, or from full loose to full tight? Either way it seems low. It depends on the age of the chain though. New chain, little travel, old chain, more travel. From memory Iâm thinking that side to side stops would be more like 90 degrees, perhaps more. Hopefully someone can confirm or deny. What if you remove the cam gears and hang them from the aluminum bracket with zip ties or something and push the chain fully away from the tensioner gear?
At that point I donât think there is anything to prevent the tensioner from rotating a full 360. As youâve seen, it simply rides on a shaft with a cam on it.
I think someone above pointed out that itâs possible for the two prongs on the adjuster wrench to be too long, which causes them to foul against internal aluminum webbing behind the circular toothed adjuster plate. Have you confirmed that is not happening? That has definitely happened to other people here.