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PostPosted: Thu Jul 14, 2011 5:57 pm 
Well I'm really scratching my head! I've owned my sprint for 9 + years and it has never been the quietest. However, I've put it back on the road after some major work and a engine strip down and head skim. However, I think it maybe noisier than before now, but maybe my memory.

The car hs done 79,000. I know its had a re-bore at sometime and the pistons are nice and tight. The sump came off and don't recall any obvious issues there. Refitted timing chain (which is reasonably new) I did note a bit of wear to one of the front cover webs as if something had been rubbing but nothing to suggest it was very new. I've not checked the oil pressure yet, but the indications are that the pump should be in good order, but have ordered a new one and will fit it to be sure.

The noise sounds like a small end type sound and seems to improve a bit once warmed. it is there on rev but dies down. I've done the screwdriver bit but cant be sure and was considering it maybe a camshaft or follower worn or possibly a chain thng. I'm not desperately happy about the end float on the jackshaft. Had new water pump nothing obvious.

Inspiration please!


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PostPosted: Thu Jul 14, 2011 9:22 pm 
Just been reading some old posts and done a check on the timing chain by turning the engine over on a socket wrench both ways and watching the dizzy and no concerns there. There is also plenty of compression and no obvious free play in engine, which would support what I suspected, that engine rebuild bas not that long ago and quite extensive!


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PostPosted: Thu Jul 14, 2011 9:22 pm 
Just been reading some old posts and done a check on the timing chain by turning the engine over on a socket wrench both ways and watching the dizzy and no concerns there. There is also plenty of compression and no obvious free play in engine, which would support what I suspected, that engine rebuild was not that long ago and quite extensive!


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PostPosted: Thu Jul 14, 2011 9:49 pm 
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So, it's not there at tickover, comes in a little above idle then at much higher rpm is gone again ?


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PostPosted: Thu Jul 14, 2011 9:55 pm 
there at tick over. tends to be initially there at rev then settles down. It could be that the noise blends with revvs. The engine is so 'tight' I can't imagine a small end. Seems to be more towards front. Even contemplated if the valves were hitting pistons if the head had been over skimmed but ruled that out as I remember checking if they protruded before I put the head on. Doesn't sound like that either. Was going to ask if there is any measurements I can take


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PostPosted: Thu Jul 14, 2011 9:57 pm 
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I'm thinking timing chain tensioner. Hold the revs at about 1200rpm and check the timing mark. It should be steady. If it's jumping backwards and forwards I'd suspect that the tensioner has reset itself.


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PostPosted: Thu Jul 14, 2011 10:08 pm 
ok will try that tomorrow. I've got to say never been a fan of the hydraulic type


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PostPosted: Thu Jul 14, 2011 10:24 pm 
its not a light tapping btw, thats whats bothering me!


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PostPosted: Thu Jul 14, 2011 10:58 pm 
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Block worn where there ought to be a bearing for the jackshaft to run in?
Had this on an old engine of mine-oil pressure was fine until the oil got hot,but the noise was always there.


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PostPosted: Fri Jul 15, 2011 7:11 am 
the only thing noted was the end float in the jackshaft, which appears to be taken up by the gears. Can't say I'm amazed by the design, but there is no end float figures. certainly no other play in the shaft. Surprised there wasn't a thrust button in the end either. I've got more chain checks to do and a bit more tuning so will keep you all updated. I'm wondering if it may be a worn valve bucket, in which case not very happy with the man who did the head!


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PostPosted: Fri Jul 15, 2011 1:09 pm 
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How about a worn rocker finger. I had this on mine...clearly blocked lubrication hole which ruined a cam lobe too.

Annoying but not too hard to sort.

Jonners

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Note from Admin: sadly Jon passed away in February 2018 but his humour and wealth of knowledge will be fondly remembered by all. RIP Jonners.


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PostPosted: Fri Jul 15, 2011 5:41 pm 
I noted one lobe was a bit scored but didn't think it was that bad, but destined for a new cam in the near future. The noise doesn't sound like a cam, but I bow to greater knowledge on this engine , as I know they don't really follow the normal rules. I am sure the former keeper has spent a lot of money on the engine. New pistons are certainly not cheap and to stick with this lump opposed to a second hand engine would not have been a cheap route. Must have happened a good 10 years ago . I'm no stranger to engine work and am pretty methodical and sure I would have picked up any mysterious play in jack shaft. The only thing that did bother me was this wear on timing case web, but not sure if it is old. They are such an unusual set up or should I say award wining design, that I am sure things present noises completely differently in this engine to the more conventional set up. Triumph OhV engines are usually so sweet and I know them backwards! I wonder sometimes if it was the rover influence over Mr Webster's more conventional thinking!


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PostPosted: Fri Jul 15, 2011 9:56 pm 
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Ah ha Rover had very little if any input to the slant 4.
Take a look at the Coventry Climax engines of the late 50's and early 60's and you will see likenesses appearing, and the wonderful Hillman Imp engine.
Sure these engines have faults but if there was money and the will to do it such as Ford would have execised if it were one of theirs, the engine would have been a legend. Saab certainly took it to a much higher level.

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PostPosted: Sat Jul 16, 2011 7:45 am 
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There is an endfloat tolerance on the jackshaft. I think it's about 8 thou but i'd need to check. Broadspeed used to fit an adjustable nut in the timing cover with a nylon or PTFE bush on the end which was adjusted to just touch against the jackshaft sprocket bolt thereby taking all the forward load off the shaft when the engine is running. I have one such modified cover that I'm going to fit once I've taken some measurements off it.

My money is still on the chain tensioner. Have you checked the timing mark as I suggested ? Basically, as the cam lobes move past the cap/rocker arm the valve spring pressure pushes the cam causing a momentary increase in tension on the chain. If the tensioner has reset ie there is no spring pressure it gets pushed back against the housing with a sharp tap. It also affects the rotation of the jackshaft resulting in the timing mark appearing to jump backwards and forwards (in time with the tapping noise you can hear).

The only other thing I could think of, based on what you've described is a loose camshaft sprocket.


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PostPosted: Sat Jul 16, 2011 11:31 am 
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I got 969 running again yesterday with it's newly refurbished cylinder head clearances set meticulously to 18 thou. I was dismayed on start up to find a rythmic "tap tap" from the valve gear.

I read this thread this morning and it inspired me to check the chain tension.

So initially Carl I angled a torch with a screwdriver down the oil filler hole to find that sure enough the long run of the chain is "slack". I then went and borrowed a fibre optic camera to check out what was going on with the tensioner. Sure enough once the oil pressure has dropped down it's falling back in, not holding on the ratchet so as you describe Carl as the chain snatches it's going to "tap,tap,tap" on the tensioner body.

I'm going to strip out the front cover on monday and probably replace the tensioner which is a new Rolon item having done only 500 miles. Is there another "superior" tensioner that can be had.

Sorry slant4 for the minor thread hijack.

Mike.


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