Timing chain tensioners

10-4

I would have a serious think about what you plan to do moving forwards. I thought you were going to say you had replaced all the tensioners etc. there could be some other explanation like a partially bloked oil gallery or some such and this is just coincidental.

Did you change the engine oil? What was used?

If you are doing the ims bearing inspection it will mean dropping the engine and at that point think seriously about a full refresh. At 120k my main crank bearings were worn much more than the original ims bearing

cam chain tensioners

Harv, my original post covers all your questions, my next step is removing the cam covers and inspecting the condition of the cam chains and wear guides including replacing the vario cam pads and chains, all do-able with engine in situ, the work involved in dropping the engine and trans far outweighs a bit of discomfort sat on the garage floor, for me anyway! :thumbs: :thumbs:

Re: cam chain tensioners

968bloke said:

the work involved in dropping the engine and trans far outweighs a bit of discomfort sat on the garage floor, for me anyway!

Click to expand...

Bought this at the classic car show last week, makes the garage floor much warmer and more comfortable!

I am just about to order new tensioners but I really don`t know what to do about the crank to IMS tensioner which has been updated as apparently both the original and updated tensioners are available and whilst Porsche in a bulletin say not to use the updated tensioner with the external spring some say (mainly in the USA) to fit the updated tensioner.

Has anyone used the later spring assisted tensioner in an early 5 chain engine?

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Del.

I'm unsure why Porsche would update the tensioner then say not to use it? I think I have the updated one with the spring in mine?

The IMS tensioner was updated because the actual timing chain was revised from roller chain to toothed chain the updated tensioner is cheaper not that helps in which one to use it just seems to me the newer spring loaded tensioner is liable to keep in better contact with the chain.

As the early 996 chain set up is the same as the Boxster it is these owners that say the newer spring tensioner is better.

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Del.

Ive recently done this job and the tensioner we was sent was the updated one from your picture , i queryed this as its totally different from whats fitted and Porsche got back to us to say theres 2 listed but no reason why .

They sent the other which was the old type from your picture and thats what i fitted.

I did compaire the two types and this " new " one is about 10mm longer .. IMHO it would put a lot more pressure on the chain.

I for one wouldn,t fit it unless i saw a bulitin saying it was ok for your car , i prefer to replace like for like unless otherwise told.

Could anyone advise if this noise is likely to be the tensioners:


So far disconnected belt (ancillaries not driven) noise remains. Spark plugs checked. My thinking is either the tensioners or hydraulic lifter. Engine was replaced with a full Hartech rebuild 25k ago and the chains were replaced. Not sure if guides and tensioners were at the same time but my guess is it would be strange to replace the chains without the guides/tensioners for a full rebuild at 65K miles.

Could be a sticky lifter but it's always hard to diagnose with sound/video online.

I'd assume the chain guides would have been changed when the engine was rebuilt as they do wear a groove in from the chains quite easily. I had to replace one that had only been in for about 15k ish miles due to it having a crack in it.

I struggled to hear the noise very well but from what i could then it didnt sound like a tappet .. its possible as they can make some wierd noises but i think i would lean towards a tensioner .. it was more on over run than when reving ?

Is it more towards one bank than the other ?


I tend to use a screwdriver to listen to different points on the engine for noises .. old school but it works well enough .

Listen to the tensioners as above and see if the noise is loudest there .. a tappet will be above the cyl on the cam cover whilst a tensioner will obviously be at the tensioner

In the transition from power on, to over run the chain will alternate which side its taught/slack depending which cog is pulling. Coming off the power there would be a rapid too'ing and fro'ing until the engine settles into a steady deceleration?

On that basis a slack guide (due to a duff tensioner) might have a chain slapping against it, or the chain could make the guide move about maybe?

As Demort has described, I've used a long screwdriver or even trolley jack handle to rest on the tensioner bolt heads and listen to noises from inside the engine. The light random tappety noise you sometimes get on a cold start up can clearly be heard coming from the IMS tensioner for instance. Made worse I have found, by using Millers 10w50NT. (though as long as the bearings and bores are well protected I'm not too bothered)

In case anyone finds themselves in the same predicament as to whether to change the Crank to IMS tensioner for the revised tensioner with the external spring the advice from Hartech is stay with the original ie. don`t fit the later one as the timing chain was also revised.

Del.

There is plenty of good advice n here about how to do it - so I won't get into that but the design of the tensioners is IMHI very poor.

Firstly the piston has a flat down most of one side leaving only a small ring to try and seal loss of oil pressure (no other seals) and it soon becomes a bit loose. This small ring plate has two small notches cut out of it to allow a flow of oil at all times leading to the piston.

Then there is no sprung loaded ball valve to maintain pressure - just this minute plate that sits in a space allowing it to flap up and down under oil flow. When the tensioner is trying to press the piston inwards the oil flow moves the plate to seal against a small hole (but some then leaks out from the piston loose fit) and when the oil pressure pushes the plate the other way some oil has to leak past through those notches so it can fill the piston tube and create movement of the piston.

The tensioner at the clutch end sits upside down and as a result the little plate naturally falls to the side of the oil entry hole so gravity acts a bit like a spring and when the engine stops allows the oil in the tensioner to remain (and when you strip them they usually have some resistance still).

The tensioner on the other end sits the other way up so the little plate falls towards the side with the notches allowing oil to leak past emptying the piston chamber/tube (and they never have resistance when you strip them). This also allows the drilled hole feeding the tensioner to empty.

The tappet oil feed gallery also feeds this tensioner at the end of the gallery - so on start up the oil has to first fill the gallery, then fill the tappets and finally the drilled hole leading to the tensioner, filling that.

Inevitable as engines wear the clearances between the tappets and the holes in the tappet housing they sit in - wear, the tappets themselves wear and the tensioner pistons wear so gradually there is more leakage and it takes more time on start up to fill them to quieten them. Indeed some engines will always exhibit this irritating noise (especially when hot) because the engine management system gradually lowers the tickover as the engine heats up and with an oil pump that is also getting worn, tickover oil pressure drops.

It really doesn't seem worthwhile trying to do anything about it unless you undertake a full engine rebuild - but even then few people will add in new tappets, tappet housings, tensioners, cylinder heads and camshafts, oil pump etc etc.

If it is only a problem for a few seconds - probably best to try and ignore it.

Thicker oil would normally help but this particular tensioner design will not prevent oil drain even wit thick oil - when it is hot.

Proper systems have bigger tensioner pistons, often a remote reservoir to maintain oil pressure and of course sprung loaded pistons and/or valves.

Your engine does not need high oil pressure for tickover and the 9A1 Gen 2 engines have a clever oil pressure management system that even lowers the oil pressure when you do not have the throttle open (just steady driving) and immediately increases it as the throttle and acceleration pick up.

Older air cooled engines often ticked over with no oil pressure measurable but still ran OK as soon as the revs rose - but then they had a much better design of tensioner and a reservoir as well.

Baz