Quote:
Originally Posted by Tambohamilton
If the spring and ratchet were enough on their own, why would they be supplemented by oil pressure?
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Damping and lubrication.
Look at a standard BMW chain tensioner. Most people think that the inside is the oil filled chaimber that builds pressure, but it isn't.
It's the small narrowed portion of the piston that is the oil filled chaimber.
The chamber where the spring sits has a hole in it, to get rid of the oil in the direction of the chain/chainguides (lubrication, and without oil the tensioner itself would wear like crazy too ofcourse).
Also because the oil pressure isn't constant (it varies greatly, especially when the engine is cold, and that can be around 8 bar, where at running temperature it can be as low as 2 bar), the chain would not be at a constant tension, but there would be a difference of 4 fold!). Therefore you want the oil pressure to play very little role in chain tension.
So that is why there is always a spring inside. The chance it jumps timing on the chain with no oil pressure is really small imho.
If the spring wasn't enough, every car would jump their timing chain at startup (where the eninge is cold, so friction on the moving parts is greatest, and there is no oil pressure), or after a big overhaul (it can take up to a minute to reach full oil pressure when you had your engine apart (it's the reason you use assembly lube on cams bearings et), I speak from experience)
If timing looks wonky (which is basically what the dealer said) my guess is, it's something to do with the camshaft variable timing system (what bmw calls vanos, don't know what hyundai calls it).
Like the TS said that the dealer blamed a variable valve timing pin. (so no skipping of the chain; it probably needs a new vanos/vanos overhaul)
Standard bmw chain tensioner disassembled:
