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Thread: Engine rattle on cold start up - timing chain tensioner? (Update: no)

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    Engine rattle on cold start up - timing chain tensioner? (Update: no)

    I am beginning to think that the timing chain tensioner is the issue. That isn't valve noise.... it's the loose timing chain hitting the timing chain housing until oil pressure builds up and the hydraulic chain tensioner finally pushes the chain guide out and tightens the chain.
    The old 2.5 four-cylinder engines that Mitsu made back in the 90's had the same issue. Worn out chain guides and weak tensioners.
    I am researching Mitsubishi hydraulic chain tensioners to see if I can use one from an Evo or other Mitsu engine.
    Either that or take off the original tensioner and see if I can put a longer, stronger spring inside that will keep the chain tight after the engine is shut down.
    Unfortunately there is very little info on the 'net regarding the tensioner on our little 1.2 litre engines.
    I'm going to hit up a junkyard tomorrow and pull some tensioners out other chain-driven Mitsu engines and see what is compatible.

    Stay tuned.....perhaps I can find a way to stop the notorious "Mirage rattle".

    3Banger



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    Senior Member Cobrajet's Avatar
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    Quote Originally Posted by 3banger View Post
    I am beginning to think that the timing chain tensioner is the issue. That isn't valve noise.... it's the loose timing chain hitting the timing chain housing until oil pressure builds up and the hydraulic chain tensioner finally pushes the chain guide out and tightens the chain.
    The old 2.5 four-cylinder engines that Mitsu made back in the 90's had the same issue. Worn out chain guides and weak tensioners.
    I am researching Mitsubishi hydraulic chain tensioners to see if I can use one from an Evo or other Mitsu engine.
    Either that or take off the original tensioner and see if I can put a longer, stronger spring inside that will keep the chain tight after the engine is shut down.
    Unfortunately there is very little info on the 'net regarding the tensioner on our little 1.2 litre engines.
    I'm going to hit up a junkyard tomorrow and pull some tensioners out other chain-driven Mitsu engines and see what is compatible.

    Stay tuned.....perhaps I can find a way to stop the notorious "Mirage rattle".

    3Banger
    I believe this is the tensioner out of the old engine in Fummins' 2014. It appears to have a kind of pawl mechanism on it which would seem to keep the tensioner from collapsing as you describe when the engine is off and oil pressure ceases.

    I always assumed the noise was due to the fact that there was little or no oil in the top end on cold starts. Once oil pressure is up and the cams start getting lubed, the noise stops...this takes just a second or two.

    I have also noticed that when I do my first startup after changing my oil and filter the same noise is present, only it is slightly louder and lasts about twice as long. This is because the filter needs to fill up, which extends the time the top end isn't being lubed from one second to about three.

    In any case, Mitsubishi says the noise is 'normal'. I have about 185k on my car and it has made this noise since it was new. No problems to report. In 2017, the 3A92 got roller rockers...anyone know if the noise is better or worse?

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    The timing chain tensioner has a ratchet mechanism which stops the chain from getting slack with missing oil pressure, which is the case when the engine is off or is just begining to be started. See picture above. A few VW and others did not have that sort of ratchet, and a mild bump to a parked car in gear brought some timing chains to jump a link and damage the engine later upon startup. Ours is a more thoughtfull construction.

    The usual cold engine startup rattle is because too much oil has drained back into the pan, and the bearings etc are practically dry. There is only air where oil should be. It is the crankshaft rattling in the main bearings and also the dry conrod bearings that make the rattling noise. The cams have very little play and the valve springs are constantly pushing them in upward direction. They can't rattle, even if they were dry. With a better oil filter that includes a built in non-return valve, the no-oil-rattle will be very much less and often practically non-existant. There are several threads about that in this forum, and some good filters are listed in those threads.
    It may be hard to believe for some folks that this rattle is actually a "no oil rattle" but a better oil filter does the trick which proves the fact. Btw, the cheapo OEM oil filter has nill anti-drainback valve!

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    Quote Originally Posted by Cobrajet View Post
    In 2017, the 3A92 got roller rockers...anyone know if the noise is better or worse?
    Of course I've never heard one make this noise besides mine. But because mine makes what I believe to be the exact described noise for the exact described time upon start up, I have to assume it is the same. Which would stand to reason that the noise is unrelated to the roller rockers.

    On edit:
    I don't know the route of oil flow. But if I were to guess, I would have to guess that there needs to be pressure to push it through the filter. So, it would go from pump, to filter, and then get plumbed up to the top of the engine into the valvetrain area. The reason I mention this is that because I don't believe the oil up at the valvetrain is under much pressure. Just valve cover atmospheric pressure. High pressure from the pump to the filter, where it will see a large pressure drop on the other side of the filter. Then enough pressure to push it up to the valvetrain. Then it gets slung around.

    Now these are just my "guesses." As I don't know the fact. But if these guesses are correct, oil pressure would not have a factor in the valvetrain. Of course there are exceptions. Seems like Honda did, and may still, use oil pressure to in some way to run the infamous VTEC. But after oil is slung around in the valvetrain, I don't think it is under pressure anymore. It just slings around until it can find a path back down to the oil pan, to start the whole process over again. Note: I'm admitting I may be wrong, I don't know the oil system at all. Just guessing how it works.

    With that said, that is why on another thread my guesstimate was that the noise was related to the pump to oil filter area ... where the pressure changes from 0 to whatever upon start up.

    7milesout
    Last edited by 7milesout; 10-11-2021 at 08:56 PM.

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    My '17 with roller cam makes the very same startup noise that the two '15s that I had did. That being said I am much more inclined to believe that the startup noise is coming from inside the MIVEC variable valve timing hydraulic unit before it fills up with with oil, rather than anything else in the valve train, or crankshaft/rod bearings.

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    With the oil pan off, grab a conrod and pull it back and forth vigorously, and you can hear exactly the same rattle sound.
    If you want to get rid of the "out-of-oil-startup-rattle" you could replace the inferior oil filter with one that has a good non-return valve. There are plenty on the market and they don't cost much either. You can change one by yourself in less than five minutes, even without any tools.

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    Senior Member Cobrajet's Avatar
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    Quote Originally Posted by foama View Post
    With the oil pan off, grab a conrod and pull it back and forth vigorously, and you can hear exactly the same rattle sound.
    If you want to get rid of the "out-of-oil-startup-rattle" you could replace the inferior oil filter with one that has a good non-return valve. There are plenty on the market and they don't cost much either. You can change one by yourself in less than five minutes, even without any tools.
    This doesn't sound like bottom-end knock or piston slap to me. Definitely sounds like it is coming from the head. That said, what filter would you suggest? I have used OEM Mitsubishi filters, Mobil1 filters, and Fram Ultra filters.

    Fram claims the Ultra filter has a silicone anti-drainback valve. None of them have alleviated the start-up rattle. Is anyone NOT getting the rattle on cold starts? If so, what filter are you using?

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    Quote Originally Posted by Cobrajet View Post
    This doesn't sound like bottom-end knock or piston slap to me. Definitely sounds like it is coming from the head. That said, what filter would you suggest? I have used OEM Mitsubishi filters, Mobil1 filters, and Fram Ultra filters.

    Fram claims the Ultra filter has a silicone anti-drainback valve. None of them have alleviated the start-up rattle. Is anyone NOT getting the rattle on cold starts? If so, what filter are you using?

    With the OP575 made by Filtron the rattle is gone. They sell it almost all over the world except for the Americas.
    The rattle is certainly not piston slap. The head has no hydraulic lifters, adjusters or anything else like that, nothing that can rattle. Cam adjustment is made by the oil pressure that a dedicated valve applies to the adjuster, much like Toyota, but a bit different to avoid patent issues.
    If you were using a too thick oil, eg. 15W-40 the oil takes a bit longer than with 0W20 and consequently rattles longer at startup.



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