Technical Twitchy cam belt tensioner

[gadb]

Greetings all,

Been poking around the engine again, to try and track down a subtle yet still irritating noise since I changed the cam belt (which I did - must be - over a year ago now). But I just can't let these things lie.

During my prodding/listening/observing I noticed the cam belt tensioner "twitching" (bit outlined in red).

Here's an admittedly boring video of it happening.

Is this normal? I recall this wee slotted bit of metal was used to set the tension with a weird looking spanner when I originally installed it. I guess this twitch means the tension is increasing or reducing momentarily during running? Is that something I should be afraid of and deal with now?

Any help most appreciated!

 

[GettinBetter]

I'd say that was a lump in the belt thickness. I've seen it in other belts. Or a minor discrepency in pitch. Look for manufacturing vids on YT, that may shine some light on it?

 

[gadb]

Had a look around on YouTube but can't find anything related to this sort of movement. It's an SKF belt / tensioner / pump so a quality brand. The car did start making a subtle new sound after I'd fitted it though. I've poked around with a stethoscope and the noise is slightly more noticeable near the tensioner but is detectable all around the cam belt. Perhaps I should have gone for OEM. It's double the price though!

 

[GettinBetter]

Sadly even quality brands can supply the odd defective component, you need to remember where they are likely being made.

I was refering to belt manufacturing methods which would give you a clue as to how they were made, not really conclusive though.

TBH, that would bother me too.
The thumping of the idler on every revolution of the belt, is more that likely going to shorten the life of the belt and the idler, do you want to fix the resulting damage if it goes unexpectedly.
Is it an interference head setup?

Your call.

 

[gadb]

Interference engine certainly and a failure would be catastrophically bad of course (I guess your question was a rhetorical one though). But It seems to twitch randomly, not on every rev, unless you were hearing something off from the engine noise?

I've emailed SKF with a shortened version of that clip to see if they have any comments to make about it. Maybe they'll get back or maybe not. I recall when I put the new water pump in it was a fair bit stiffer to turn over than the one coming out but I put that down to newness. This is irritating. Changing the cam belt on this car isn't my favourite job - that engine bracket and belt cover are so damn fiddly and there's no space to work or wiggle bits out. The 1.2 is easier I think - there's more space due to the lack of aircon and separate coolant reservoir.

Will post again if I hear from SKF or decide to do another change. At least I don't have to buy another locking kit.

Cheers,
G.

 

[GettinBetter]

Is there a sticker or label that sits pround on the belt, and would only line up every so many revolutions, which may initially seem random? Clutching at straws here, but suppliers may resort to badge engineering when their products are all
made by the same manufacturer.
Just a thought.

 

[gadb]

Is there a sticker or label that sits pround on the belt, and would only line up every so many revolutions, which may initially seem random? Clutching at straws here, but suppliers may resort to badge engineering when their products are all
made by the same manufacturer.
Just a thought.

It doesn't seem to be doing it this morning although I ran for maybe 60 seconds and didn't let the engine warm up. ¯\_(ツ)_/¯
Nothing sitting proud of the belt. I can see some "Don't crimp" warning in umpteen languages and "Made in the UK" but this has no texture when I run my finger over it. Just been putting the engine mounting bracket back into the side of the engine - this has to be the most sadistic procedure ever invented by a car manufacturer. A few of the bolts are super fiddly but for one (lower front) there's almost no room. Hoping to hear back from manufacturer but have mentally penned in an early replacement for all 3 items. Tiresome.

 

[GettinBetter]

I am beginning to think the designers only have to allow it to go together by robot, in a certain order, and couldn't care less if it has to come apart at a later date. I can hear it now, "Not their problem".