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Thread: Megane death rattle - or VVT dephaser. Oh My Gosh

  1. #26
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    Default Tolerances ??

    Hi
    Years ago, many years ago in fact, perhaps when tolerances were not as tight as achieved to day, I did some extra course at Tech Cannot remember what realy except this !!
    We had to do a tolerance exercise on the height of the piston to the block face and the clearance to the head. The production tolerances for all the engine parts from a real engine were given. I cannot remember the actual figures but we were shocked and astonished at the possible variation of below to above the deck face.

    The final statement from the teacher was "that is why you hand select for a standard production race engine"

    So although things have improved, the belt and the idlers position and the keyways and the slots etc all have some tolerances. Also robots may not be good at sorting some things. Whereas they can wack a pulley on a shaft at any angle and then the belt etc and then tighten a screw to a angle measure is easy. Who knows ??

    Some engines I have done a belt on, have had the pulley marks away from the timing marks up towards half a tooth sometimes. Enough to double check the system occasionaly. So there was some noticable variation in the keyed method, and I have not done that many.
    Jaahn

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    Last edited by jaahn; 27th February 2018 at 04:00 PM.

  2. #27
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    Whereas they can wack a pulley on a shaft at any anglewhere and then the belt etc and then tightening the screw to a angle measure is easier

    Manufacturers focus on speedy production rather than ease of service.
    (from post 11)


    Does this mean we have some tacit agreement on the topic ?

    Because a cam belt setup that had correct "anglewhere" decided by keying or other engineering means would certainly be easier to service.
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  3. #28
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    I don't have a problem with a design which is faster to assemble with less componentry and machining (cheaper), when it achieves a "perfect" result every time. And yes, I would agree it is marginally easier to remove a belt from a keyed pulley in service, line up the dots (TDCmarks), and reassemble, with the downside that it is rarely exact.

    A quick calculation is that there are 40 teeth on the cam sprockets in the F4R engine, so 9 deg between teeth, and this would be similar for most engines. The most one could be out when fitting a toothed belt is half a tooth, so 4.5 deg of camshaft rotation. Valve timing is measured by crankshaft rotation, which is twice that of the camshafts, so up to 9 deg error at the crank, huge in the performance of the engine. Of course this is worst case scenario, but easy to see that 3 or 4 deg error at the crank would be common, even normal. I find it quite extraordinary how inaccurate the older designs have been, and in this day of "nth degree" of emission control and fuel consumption regulations, which extend to continued operation throughout the working life of the engine, I guess all manufacturers have had to look at this closely.

    And yes, I agree that with the close tolerances of machining in a mass-produced engine, one would think they could get it pretty damn close these days, with the thickness of the head gasket, and belt tension, being the most obvious minor variables. But then, in servicing, take 0.010" or 0.020" off the head when replacing a head gasket, for instance, and that timing has been thrown out again. With the keyless system it just doesn't matter.

    So, I agree in general with your comments regarding economics of production not always in the interest of easier servicing, but I will defend the Renault cam timing system like Davey Crockett at The Alamo.

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  4. #29
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    but I will defend the Renault cam timing system like Davey Crockett at The Alamo.
    Maybe not the best simile. Davy Crockett was killed on March 6, 1836 fighting the battle you mentioned.
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  5. #30
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    Quote Originally Posted by robmac View Post
    Maybe not the best simile. Davy Crockett was killed on March 6, 1836 fighting the battle you mentioned.
    Ha Ha, yes, hadn't thought of that.

    I was thinking Trooper Duffy from F Troop - "There we were, me and Davy Crockett, shoulder to shoulder, backs to the wall".

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  6. #31
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    Haven't had a chance to pull down the megane engine yet (quite frankly I am a bit scared of what I will find) but will give it a shot tomorrow, no more excuses not to.
    One Youtube cam belt change video had the guy gouging out the cam end plugs with quite a bit of butchery - they looked a bit like welsh plugs on that model. Mine seem to be rubberised, do they still come out in the same way? (punch in one side and lever out?).
    As for the timing tool, is there a template somewhere on how to make one? Otherwise will have to order one online and wait for it to arrive by post.
    Interested in"John W's" post about seizing a/c compressor. Was it intermittent? did it seize and free up, or just seize? what was the diagnosis?

  7. #32
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    For the basic tool dimensions see my recent thread, post #5, photos 9 and 10:
    Gates Timing Belt Kits with STEEL idler pulleys for Renault engines.

    The cam alignment tool doesn't need to be fancy, a bit of flat steel bar, say 60mm wide, with a recess cut into one side to clear the head between the 2 cams, and ground down on that edge to 5.0mm (maybe 4.9-5.0mm) to fit the slots in the cams. The little angle bracket in the photo is just holding it in place so it doesn't fall out.
    This is the one I use, but it doesn't need to be as fancy:
    Megane death rattle - or VVT dephaser. Oh My Gosh-p1100728_red.jpg Megane death rattle - or VVT dephaser. Oh My Gosh-renault-cam-tool_reduced.jpg
    (Actually, looking at the photo, maybe that little semicircular cutout may be necessary to clear the thermostat housing boss?).

    The cam end plugs - the genuine ones are like a welsh plug, yes, but the in the centre is about a 12mm dia hole, then covered with rubber/neoprene. So a screwdriver can pierce that rubber, but don't go too deep and then hook the screwdriver sideways to hook the plug out - note the end of the camshaft is only maybe 5mm behind the plug, and you don't want to damage it. This method destroys the plugs and you will need new ones later to seal it back up.

    I will say it again - because there is a good chance the timing has slipped, there is no way you will locate the crank TDC slot unless you remove the sparkplugs, and get a rough TDC using a thin screwdriver down onto the #1 piston. This isn't the normal way, which is to line up the cams first, then the TDC slot should normally be close to the pin hole.

    If it were mine, I would at first just be interested to check if the timing has moved, and if it has then you know why you have the rattles and bangs. Resetting the timing is another matter, and if there is damage to the valves, requiring head removal, I would be inclined to pull the engine out for access to the head removal, and the realignment/replacement of the belt, etc. It would all be a piece of p... with the engine out. But first, just check to see what has happened, then "regroup".

    Cheers.
    Last edited by Fordman; 2nd March 2018 at 03:06 PM. Reason: Add photos.
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  8. #33
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    Quote Originally Posted by Bluemegane View Post
    Haven't had a chance to pull down the megane engine yet (quite frankly I am a bit scared of what I will find) but will give it a shot tomorrow, no more excuses not to.
    One Youtube cam belt change video had the guy gouging out the cam end plugs with quite a bit of butchery - they looked a bit like welsh plugs on that model. Mine seem to be rubberised, do they still come out in the same way? (punch in one side and lever out?).
    As for the timing tool, is there a template somewhere on how to make one? Otherwise will have to order one online and wait for it to arrive by post.
    Interested in"John W's" post about seizing a/c compressor. Was it intermittent? did it seize and free up, or just seize? what was the diagnosis?
    It was hot weather and the AC stopped cooling. My wife doesn't like it hot so I moved quickly to get it fixed and that's when we discovered it was beginning to seize and starting to chew the accessory belt. So by luck we caught it before anything nasty happened.
    JohnW

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  9. #34
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    Well, the story so far some of you have read. However, in a nutshell:
    Broken accessory belt with no clear cause. Replaced belt and it broke - taking harmonic balancer with it.
    Put a new h/balancer and belt on so I could get it to A/c specialist because I suspect a/c compressor.
    In replacing H/Bal I didn't know the timing was affected - and when I started it up, there was a frightening rattle.
    Aussie frogs folk (finally) enlightened me to my error (cos I was convinced I hadn't been near the valve timing. (so wrong!)
    Did I bend valves? - dunno yet.
    So what I did was; make up the tools (see pic. rough but effective)- on advice from this website, reset the timing and put it all back together


    Megane death rattle - or VVT dephaser. Oh My Gosh-renault-tools.jpgClick image for larger version. 

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    I did this because I didn't know if I had bent the valves so wanted to just run it with the timing right and see- I figured if I put the timing right the rattle (if pistons were touching valves) would stop knocking but engine might run rough if valves stuck or sticky(bent).
    I started it up today after doing the timing setup - and it still rattled something awful.
    I'm pretty disheartened.
    Yes I am
    What have I missed this time? sigh

    Megane death rattle - or VVT dephaser. Oh My Gosh-blue-megane.jpg

  10. #35
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    One more thing, and this may be where I went wrong. When I was setting up the timing I locked the cams and noticed that I was able to rotate the dephaser pulley. From memory I was able to move it anticlockwise about 10 to 15mm whilst it was locked with tool, I could hear oil moving within it and then it felt as if it had locked in (?) I couldn't turn it at all after first moving it. So I set the timing with the dephaser pulley wound anticlockwise as far as it would go. I have read as much as I can on Renault valve timing (and watched endless Youtubes in French and Russian(I think) that I didn't understand but tried to figure it from the pictures) but couldn't find anything about setting the dephaser.
    Any tips?
    Thoughts?

  11. #36
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    Woe. Best wishes for the evolution of the story.
    JohnW

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  12. #37
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    Quote Originally Posted by Bluemegane View Post
    So I set the timing with the dephaser pulley wound anticlockwise as far as it would go. I have read as much as I can on Renault valve timing (and watched endless Youtubes in French and Russian(I think) that I didn't understand but tried to figure it from the pictures) but couldn't find anything about setting the dephaser.
    Any tips?
    Thoughts?
    This is from the Haynes manual, may be of help. I don't know, but removing the solenoid might release the pressure in it?? I haven't touched the dephaser when I have changed belts.

    Megane death rattle - or VVT dephaser. Oh My Gosh-img_20180307_123525235_red_li.jpgMegane death rattle - or VVT dephaser. Oh My Gosh-img_20180307_123716790_red_li.jpg

    Soooo - was the timing way out, or just a bit, or not at all?

    If you think it is now correct, a compression check (as mentioned above somewhere) will let you know if valves are bent - no compression, may be bent - or timing still out.

    Cheers.
    Last edited by Fordman; 7th March 2018 at 05:34 PM.
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  13. #38
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    Hi
    I can only ask a few questions to help.
    Did you turn the engine several times by hand with the plugs out to see if there was no interference, after you had redone the timing ?
    If you put one plug in at a time and turn it over by hand you should feel the compression in that cylinder. Repeat the four individually.
    No interference YES OR NO.
    Was the timing out by much as fordman asked . ??YES OR NO.
    Compression on any cylinders YES OR NO ? How many. You could check the compression properly, but only if the hand turning showed no interference.
    I do not believe the dephaser should be able to be turned easily. But have had no experience of them. It may be stuffed after the other problem.
    Jaahn
    Last edited by jaahn; 7th March 2018 at 07:48 PM.
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  14. #39
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    Default Dephaser ! Musings !

    Hi
    My thoughts on dephasers after some Googeling. I have not had to look at them before and when i did or assisted with a timing belt change i did it "by the book" as Fordman has shown, and the dephaser was not touched and did not need any attention.

    There is a spring loaded locking pin in them that should lock the actuator in the 'normal' slow speed position when there is no oil pressure. Normally it will be locked when starting and oil pressure is nil. So when stopped it should be locked and the cam and pulley should not move relative to each other. Removing the electro valve or similar should not make it fail or be free. If it can be moved then the unit is faulty. Then it will likely be noisy. Broken parts may jam the locking pin from moving.

    When the engine cam timing is correctly set and the dephaser working as it should and advances the cam timing, the change of timing will not give valve contact with the pistons. It is internally limited so it cannot. So even if the dephaser fails in the fully advanced position it should not cause bent valves. The noise would only be the broken internal parts and the uncontrolled movement perhaps. Like the utube video ! https://www.youtube.com/watch?v=dey5wFJLODM

    Whether the timing being out would cause contact depends on how far the timing was out. But worth checking further IMHO. I would take the dephaser front plate off and see what is broken in there. If you can take out the broken bits and check the locking pin will lock back in place with the spring pressure, it should be safe to run it for a test. But I have not done any of that ever.
    Cheers Jaahn
    Last edited by jaahn; 7th March 2018 at 08:25 PM.

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