Chain tensioner safety collars

nick3814 · Sep 17, 2007

Hi folks, my 1983 911SC has the regular chain tensioners still fitted (94,000mls) and I've been pondering over fitting the Carrera style tensioners this winter when I take her off the road for a couple of months. However I've been party to a a few conversations on other sites about the sudden failure of these units with catastrophic results. With this in mind I have purchased a pair of safety collars from PP, a much cheaper option and piece of mind as well.
Has anyone on here fitted these recently? They seem simple enough but my problem is getting the plunger (end of the tensioner that moves back and forth) far enough out to fit the collar with the correct allowance which is a total of 9mm. I've attached a photo of one of my tensioners to show how short the plunger appears at about 4-5mm at the most.

jamescharnley · Sep 17, 2007

whats the tension like on the chain? Have you checked the tensioner itself? Whilst you're in there in might be a good oportunity to rebuild & bleed your existing tensioners

nick3814 · Sep 17, 2007

Hi James, these pics were taken last December when I checked them, the tension was spot on, the chain was rigid, no play in it at all, since then I've done a couple of thousand mile including Lemans with no problems I'm just looking at avoiding the cost of Carrera tensioners when there seems no need other than a little piece of mind.
Can you rebuild standard tensioners??
What does it involve??
Can you relace the spring etc??

Cheers

Cheers

bones · Sep 17, 2007

ORIGINAL: nick3814

Hi James, these pics were taken last December when I checked them, the tension was spot on, the chain was rigid, no play in it at all, since then I've done a couple of thousand mile including Lemans with no problems I'm just looking at avoiding the cost of Carrera tensioners when there seems no need other than a little piece of mind.
Can you rebuild standard tensioners??
What does it involve??
Can you relace the spring etc??

Cheers

Cheers

There's nothing wrong with the original design there are plenty of SCs still running around with the originals in there. If all you want is peace of mind buy yourself some new original tensioners and new chain ramps and leave it at that for 50,000 miles and then check them again.

jamescharnley · Sep 17, 2007

Mike Bainbridge ( http://www.mbporsche-engineering.co.uk/ ) over at Kendal showed me how to rebuild tensioners. As usual with these things they gone in one ear & out the other [8|] , but it is not difficult, just important you bled all the air out of them when you refilled with oil.

I have the safety collars too, but have not fitted them either as I have also had new chains fitted & these have not got enough slack in them to allow enough shaft for them to be fitted. Same boat as you then [

]

nick3814 · Sep 18, 2007

Thanks Phil thats good news, can I ask why you were having yours bled and when you look at the photo of mine at the start of this thread does the plunger seem any shorter (further in) than yours before or after you had it bled??[

]

Cheers

jamescharnley · Sep 18, 2007

Hi Nick

this is mine shagged .. spot the gap between the tensioner & the arm due to seized tensioner ... also spot the pulley on back to front [8|]

this is the new one fitted + new ramps & chains

As you can see there is a lot more shaft exposed than on yours for some reason ?

vitesse · Sep 19, 2007

It looks as if your old chains were not that badly worn when comparing the positions of the various components in the 2 pics.I can't spot the sprocket being the wrong way round unless you mean the camshaft sprocket;no holes showing around the securing bolt/nut.The chains look to be the original Renold versions,Duplex 3/8" pitch.These have a wear limit of 2% so if the chain length is 24",a worn chain could be almost 1/2" longer before the bearing pins and bushes reach the limit of their casehardening treatment;the sprockets being designed to last several chains.The "ramp" pads are not tensioners,they are designed to eliminate chain vibration and therefore are set to slightly engage with the chainplates which then cut grooves which allows the chain rollers to run along the high spots.Renold "run in " automotive chains to eliminate the fast initial bedding in of all the components due to production tolerances,etc.They are kept within a tolerance band by adding either fatter or thinner pins during assembly but it is possible that 2 different cars with different dated assembly,different batches of drive sprockets,chains,engine castings,machining plus a different tensioner could exhibit the different characteristics your two cars show.

Sorry for the anaorackism;I used to work for Renold Chains many years and was involved with camshaft drives at times.Had many a discussion with Keith Duckworth over the 'phone-clever guy!

jamescharnley · Sep 19, 2007

Some numpty in the distant past had obviously been into the motor & put the cam sprocket on back to front so the chain was running at an angle, to the point where the ramps had been worn smooth [:-] . This was the reason for new ramps & new chains. On my 1st pic the tensioner was seized so the full extent of the chain stretch can't be seen although irrelevant of wear it was decided to change these anyway whilst we were in there .... the origianl chains were pretty noisey though before [

] . As it turned out when we opened up the other that tensioner was failing too.

We did all this at Mike Bainbridge's who is very experienced with Porsche engines & gearboxes

In the end after retiming the cams ( they were different on both sides originally [8|] ) , new injectors, rebuilt the throttle bodies, new backbox etc etc I got 198bhp @ 7190rpm on Bob Watsons Rolling road [

] Not bad for a 1973 2.4S [

]