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Old 29th November 2022, 23:08   #1
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Timing Belt in Oil/Wet Belt. Are they reliable?

This is not new and seems to have started with the Ford 1.8TDCI engine as a timing belt, but the Peugeot predates the ford in using a wet belt but to drive the fuel pump. Ford and PSA have collaborated to create a bunch of shared engines in the past so the connection is quite natural. It seems the Honda and a few others have also joined this wet belt bandwagon. For the owners of the Ford 1.8TDCI there is a chain conversion kit available for the wet belt.

What i gathered is that this timing belt in oil is not in the interest of the end consumer, these are for the benefit of the manufacturer who has to meet certain emission and fuel efficiency norms on the whole across their product portfolio. So they look for avenues to extract the tiniest of efficiency gains from wherever they can and reliability be damned. The belt in oil has 30% less frictional losses than a timing chain system for a net 1% fuel efficiency gain.
Timing Belt in Oil/Wet Belt. Are they reliable?-underhoodservicebeltinoiltimingdrives.png

But they don't seem to be very reliable going by the information available on the internet. The most common issue is the belt gradually wearing off in the oil and the belt dust settling in the sump and then blocking oil pump intake. There's a new belt of another chemistry which is supposedly better. But ironically the manufacturer recommends reduced replacement intervals with this new belt.

Ford's Ecoboost 1.0 and the new Puretech 1.2 by PSA are two engines with wet belt systems sold in India per my knowledge.

Timing Belt in Oil/Wet Belt. Are they reliable?-uknewsgaragewiremagazinedaycoissuesbeltinoiltechnicalupdatefor12litrepuretechengine.jpg
Timing Belt in Oil/Wet Belt. Are they reliable?-puretechbeltinoilthebestpractice.jpg
Timing Belt in Oil/Wet Belt. Are they reliable?-newct1228timingbelt.png
Timing Belt in Oil/Wet Belt. Are they reliable?-continentalaftermarketenenmagazinetechnologyproductswhyournewbeltinoilrunsforalongtime.png

In the french portal L'argus there was article which mentioned about the manufacturer changing the wet belt system to a timing chain to solve the reliability issues. But the article is edited and that part removed on what is available on their website now.

Timing Belt in Oil/Wet Belt. Are they reliable?-largus_puretech.png

Original from wayback machine:
Timing Belt in Oil/Wet Belt. Are they reliable?-largus_puretech_original_waybackmachine.png

"Techniquement, la 308 SW accueillera une évolution de la plateforme EMP2 au niveau de l’architecture électronique qui sera compatible avec de nouvelles aides à la conduite. Sous le capot, pas de révolution… ou presque. En essence, la gamme s’appuiera sur le 1.2 PureTech, décliné en trois puissances (100, 130 et 155 ch). Afin de résoudre ses problèmes de fiabilité, ce moteur va troquer sa courroie de distribution pour une chaîne."
Translation of the last sentence in the above para is "In order to solve its reliability problems, this engine will swap its timing belt for a chain."

So they don't build it like they used to is a phrase very much apt for some of these modern engines. Good while it lasts but not built to last a lifetime.
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Old 29th November 2022, 23:53   #2
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Re: Timing Belt in Oil/Wet Belt. Are they reliable?

Thanks for this thread. I believe a timing belt system itself is a step back from timing chains. Timing belts have the following drawbacks over chains in my opinion:

- Have to be replaced periodically. Chains on the other hand last the life of the engine in most cases (especially petrols)

- Belts have a tendency to get brittle with age and develop cracks. I have seen this for myself on a couple of low mileage TDIs. Chains on the other hand don't face this sort of an issue

- Belts typically just snap without warning. Chains on the other hand give audible warning in most cases if they are going to go bad

Here's what chains can't do as well as belts:

- Timing chains are typically a bit noisier than belts. Though I haven't noticed a stark difference on petrols between the two, timing chain driven diesels do sound louder to me

- Chains are expensive if and when the time comes to replace them. Replacement is also slightly trickier

- Chains are lubricated by oil. While this does guarantee excellent life, timing chain covers are a potential weak spot for oil leaks. Additionally, you do need to adhere to oil change intervals and use good quality oil to ensure good timing chain life

Coming to belts immersed in oil, I think it's a rubbish piece of technology. I am a part of a Ford Transit owners group on FB and I see numerous owners complaining that pieces of the timing belt were found in the oil sump strainer!

The integrity of the belt is compromised, but more importantly, the engine head could potentially be starved of oil and seize if bits and pieces of the belt choke the sump strainer enough. These belts are also expensive as compared to traditional timing belts. I don't see the point of having these if they need replacement as well in the first place and are only going to last slightly longer than the traditional stuff. To me, a timing belt immersed in oil is the worst of both worlds.

If you thought timing belts were perfect examples of engineering obsolescence, the auto industry just one upped you . As always, I think it was better to stick to the good old timing chains than come up with these rubber contraptions.

Last edited by vishy76 : 29th November 2022 at 23:54.
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Old 30th November 2022, 09:06   #3
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Re: Timing Belt in Oil/Wet Belt. Are they reliable?

Regular rubber/polymer timing belts (belt-in-air ) are perfectly ok. Some seems to last long enough and some don't. Same with the chain, not all chain drives are great eg: 1.3 multijet timing chains.

I have seen the timing belt on vag cars deteriorating early. On vag cars its not just the belt, but some plastic/rubber parts on the cooling circuit seems to have a set expiry date which is ~ 7-8 years. Personal experience. On Suzuki and toyota the timing belt in air seems to last long enough reliably to not be a problem for the user. Changing them are also easy.

Anyway cheers to the guy who thought it was all ok to mix rubber/polymer belt and oil in an engine. Neither inspection nor change is easy.
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Old 2nd December 2022, 14:35   #4
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Re: Timing Belt in Oil/Wet Belt. Are they reliable?

Originally Posted by vishy76 View Post
Thanks for this thread. I believe a timing belt system itself is a step back from timing chains.
i don't think so.

Advantage of chains: Durable, Less width (saves some packaging space in Z direction)
Disadvantages of chains: Costly (& costly sub components like chain guide/tensioners), High weight, Needs lubrication, noisy, Sensitive to temperature (cold/Hot engine), Now biggest one is the tendency to not allow any stretch (Chain system works in relatively high tension which takes more energy from the engine - parasitic losses), Need for higher cleanliness specification

Advantage of Belt: Weight less, Stretchable (Can handle some tricky situation without snapping), Can work in low tension (as compared to chain), Low cost, no sealing required, low cost (of belt & subcomponents like tensioners)
Disadvantages of Belt: Durability (as compared to chains, But modern HBR belts are durable till 300K Kms), sensitive to side tracking (edge wear possibility), Low replacement intervals (some OEMs have even as low as 100,000 kms)

Belt in oil: is now a mix approach of the above two, where the advantage of belt are achieved with the sealing lubrication (that's why called belt in oil). Here we get advantage of chains and belt both but looses on the major risk of the contamination & loss of tensioner damping in oil environment.

Traditionally European customers prefer more of a timing belt, while Japanese OEMs prefers Chains. American have mixed approach to this. But as far as i can see in the business world, the timing belts application are getting reduced.
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Old 2nd December 2022, 16:30   #5
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Re: Timing Belt in Oil/Wet Belt. Are they reliable?

In the past when I had ICE cars, I used to do maintenance myself and topics like this get my attention straightaway. But moving to electric mobility few years ago and never have to deal with understanding hundreds of components and tens of replacement every service interval, I am feeling that I save a lot of time now-a-days.

This is a quick note (of nostalgia) to myself and some others on this forum if they are still sitting on the brim of switching to EVs.
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