Timing chain tensioners

wasz · 5 Oct 2016

Delanor said:
The rattle stops literally as fast as it starts when firing up from cold such as overnight so that suggests its a tensioner not holding pressure I will have to have a listen round with a stethoscope.

Where would I get the correct cam locking tool.

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Del.

Hang on a minute before you rebuild your engine, this is normal for an early car. Most do it with a few miles on. Its just a rattle for the first half second of startup and makes you cringe every time.

Thicker oil quietened mine down almost completely I run 10/40 millers nano.

Its the oil filled tensioner leaking down. Later cars got a stronger spring assisted tensioner. It probably is due to tensioner pads wearing.

Delanor · 5 Oct 2016

Well @ 87K miles it didn`t rattle now on 90K miles it does, surely if a tensioner/tensioners are losing pressure causing excessive contact of the timing chain on the chain guides that is going to accelerate any wear even if it is only for seconds starting from cold!

There are three things I don`t do on cars:
1. Rust.
2. Rattles.
3. Ditch finder tyres.

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Del.

wasz · 5 Oct 2016

Well if you are gonna change the tensioner pads you may as well rebuild everything else thats "at risk" of failing in there.

Where do you stop short of a full rebuild?

Delanor · 6 Oct 2016

I am not going to pull the engine to re-place the chain guides I`m just going to remove the hydraulic tensioners to check/clean or replace them if necessary.

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Del.

Delanor · 10 Oct 2016

Has anyone actually successfully removed the tensioners & cleaned them to see if they are faulty or not if so did it make any difference ie. did it cure the rattle on start up or do I just put 3 new replacements in?

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Del.

deMort · 10 Oct 2016

Ive never cleaned them .. always replaced .

infrasilver · 10 Oct 2016

Delanor said:
Has anyone actually successfully removed the tensioners & cleaned them to see if they are faulty or not if so did it make any difference ie. did it cure the rattle on start up or do I just put 3 new replacements in?

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Del.

It has been done before, that's why I mentioned it.

968bloke · 27 Oct 2016

replace, Porsche updated the early ones!

Harv · 27 Oct 2016

The tensioners have been updated since the 3.4 was first made and I think this happened around 2001.

Simply replacing them will give you the latest version which I know are spring assisted and oil fed (possible the early ones pre 2001 have no spring and these prevent some slack at startup until the oil pressure get going).

There's also a small plastic pad on the ims chain tensioner arm inside the engine that one of the said tensioners presses against (stops metal on metal) and this item wears away. Engine strip to replace it unfortunately.

Pic to follow......

968bloke · 10 Nov 2016

cam chain rattle

having bought my 98 996c2 with 133k on the clock and it was running sweetly, I decided I ought to look at replacing the IMS bearing so bought the kit from design911 the LN engineering roller bearing option which comes with an alternative oil pump drive hex shaft which is fluted to let pressurised oil into the intermediate shaft and on to the bearing, you also get a sharpened punch to pierce a hole into the shaft. so before fitting the bearing I decided to fit the oil pump shaft first and get that job out of the way, all went well and on start up there was the cam chain rattle noise that wasn't there before and it subsided in about 10 seconds, thinking it won't do that next time I start up ,it did! contacted design911 and they didn't know what the problem could be, contacted LN same, so stripped down again and removed the new shaft and blocked the hole up , still same, could it be the oil pressure relief valve? replaced it with new piston and spring still same, new spring was slightly shorter than the old one! so what next, replaced cam chain tensioners with updated ones still the rattle but now takes up to 40secs to subside after a long rest, oil Millers 10/50 and updated oil filter mod. remember it didn't make this rattle before the oil pump was disturbed! any ideas would be welcome :sad: :sad: once the rattle has gone it runs great with good oil pressure!

Harv · 10 Nov 2016

I'm not a fan of this kit, it maybe perfectly fine but I can't see the justification for making a hole in the back of the oil pump to allow oil into a bearing that is somewhat submerged if the oil level is kept topped up and lives in an area of heavy splash lubrication?

Can you confirm that you removed the engine, performed the oil hole mod and replaced the ims bearing in situ?

Did you do any work to lock cams, and set the timing afterwards and also were all the oil tensioners replaced for new items?

Marky911 · 10 Nov 2016

Re your IMS,
Have you actually renewed the bearing too or did you just do the hex bit and punch hole first and that's when the noise appeared.

If you fitted the whole kit including bearing I know that some people, mainly Hartech go on about pulling sideways on the cam chains (that are wrapped around the IMS) when removing the old bearing. This can put strain on the old nylon guides and weaken or snap a bit off, leading to the chain maybe coming off later. That would be catastrophic though so you'd know straight away, unless some how a guide has become weakened or altered which means the chain is rattling for a while at start up.

I still can't think of how though really as if that was the case I don't know how it would sort itself out once pressurised. That would, as you've checked out, point to a tensioner issue.

Strange one and I hope you sort it. Just thought I'd mention the yanking on cam chain bit that Hartech always mention. I was going to completely ignore it when I do my IMS bearing next spring as my Indy does loads of them,but after reading this I may just flip the seal open on my original bearing if it proves ok during inspection.

40 seconds is a long time for cam chain rattle, even on a cold start. My car does it for literally 1 or 2 seconds sometimes. Can't say I've even noticed it lately. My old GT3 which had been thrashed on track most of its life also only done it for a second or two. It should only be while the tensioners fill up with oil which is almost instant.

Good luck with it. I feel for you. Trying to do some sensible preventative maintenance and ending up with a different problem. Report back with any developments. Might help someone in the same boat in future.

bazhart · 10 Nov 2016

The tensioners are a generally poor design.

They neither incorporate a reservoir nor a non return valve/ball or spring- so rely upon the delivered oil pressure to keep them tensioned.

There is a small flap plate in a captive recess but it has a bye pass hole - I guess it is to slow the back flow from the chain forcing the rail back onto the tensioner piston.

The piston also is not a precise fit and has a flat down one side for most of the length - so it leaks back.

As oil pressure lowers (especially when hot) and always on tickover the gallery that feeds the tensioner is also feeding the tappets and variocam timing system - so needs quite a lot of delivery.

The last component in the gallery is the tensioner and it is possible for it to set up a fluctuating motion shifting the oil back and forward in that gallery when the tickover is slow and the oil thin.

We have made several modified tensioners with a proper ball valve in the small space available - but it only ever removed the noise occasionally.

The tensioner on the right hand side sits downwards and the one for the left hand side is the other way around.

Whenever we strip an engine the one in which the flap valve sits against the return hole is always still full of oil and resisting movement whereas the one that sits the other way up never holds any oil and has no tension and guess what - that is the side the noise usually comes from.

Some rails have a metal insert for the metal piston to push against. The insert starts out with a domed face but the gradual banging of the rail against the tensioner gradually flattens it (further proof of its inadequacy) and the metal insert can be replaced with a plastic one to reduce that noise but beware there are lots of different noise sources all making a similar tick and trying to find yours usually costs more than ignoring it.

Baz

968bloke · 10 Nov 2016

Harv said:
I'm not a fan of this kit, it maybe perfectly fine but I can't see the justification for making a hole in the back of the oil pump to allow oil into a bearing that is somewhat submerged if the oil level is kept topped up and lives in an area of heavy splash lubrication?

Can you confirm that you removed the engine, performed the oil hole mod and replaced the ims bearing in situ?

Did you do any work to lock cams, and set the timing afterwards and also were all the oil tensioners replaced for new items?

Harv. did everything in situ, bearing mod at a later date, all new parts used, no need to lock anything working on the oil pump!

infrasilver · 10 Nov 2016

With the pump cover removed the tension from the chain on the pump end of the IMS will pull on the pump drive end towards the O/S of the engine casing and this could cause an issue, only the pump cover keeps the pump end of the IMS central and at the same time when the cover is removed it pulls the IMS off at an angle at both ends, I'm not sure it would cause an issue but it's not ideal.

Timing chain tensioners

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