A Downside to Using Safety Collars on Non Pressure-fed Chain Tensioners

[dpetterson]

A couple weeks ago, while driving my ‘73 T on my way home from visiting with friends, I suddenly heard a rapid, continuous clicking sound coming from the engine. As soon as traffic would allow, I pulled off the road and shut the car off. Luckily I was able to do this within about 30 seconds. I wasn't exactly sure what the issue was but after the tow truck got us home, I was thinking it could be an issue with the chain tensioners.

With help from a friend, we removed the long piece of engine tin just above the muffler and then the muffler itself in order to access the chain box covers. We removed the driver’s side cover and everything looked fine. We also noticed the non pressure-fed tensioner had a safety collar installed. I've owned the car for about 2.5 years and wasn't sure if any of the previous owners had installed them.

When we took off the passenger side chain box cover, we found the source of the issue: a collapsed chain tensioner and upon closer examination, we noticed the safety collar had been worn down to the point where it finally broke apart. Additionally, the sides of the camshaft drive gear were worn down and some wear was also noticeable on the side of the chain. See photos below of 1.) the collapsed tensioner and broken collar and 2.) the wear noticeable on the cam drive gear and chain.



My friend, who has built many 911 motors over the years, felt that in all likelihood, we’d been driving the car around in this condition since the day we purchased it - well over two years. Our car came with no service documentation and the PPI (pre-purchase inspection) did not entail an examination of the chain tensioners (most PPIs don't).

In Wayne Dempsey's book, 101 Projects for Your Porsche 911, Project 16: "Upgrading to the late-style 911 Carrera chain tensioners", Wayne states:

An inexpensive alternative to installing the pressure-fed Carrera chain tensioners is the addition of a safety collar around the shaft of the tensioner. While not as good as a pure replacement, the safety collar can provide some emergency help when tensioners fail. A potential pitfall is that it is not easy to detect tensioner failure, and the repeated pounding of the collar may cause it to wear and begin to lodge metal bits inside of your engine.

That’s quite startling to read but seems to be exactly what happened in my case.

I’ve since ordered the Carrera pressure-fed tensioner upgrade kit, as well as the newer, more robust Carrera idler arms. Additionally we'll replace the chain. See photo below of the upgraded Carrera idler arm (with the gear) vs. the original arm.



Hope this was informative, especially for those that are running the early spring tensioners with safety collars. While I’m not advocating that people use or don’t use the collars, I wanted to stress the point that Wayne makes in his book, that if you do use them, it is not easy to detect tensioner failure. My friend who helped out with the diagnoses does not run safety collars in his '68 S for this exact reason.

Happy driving!

[boyt911sc]

Originally Posted by dpetterson

DP,

Ask your friend to take another look at your camshaft sprockets. The one shown in your picture is too worn out already. The other side could be bad too. If these camshafts sprockets are worn out, I bet the inner IMS sprockets would be in similar condition. So installing new timing chains with worn out sprockets is not a prudent course of action.

Installing the wider idler gear brackets is a good upgrade.

Tony

[Flat6pac]

The cam drive gear is upside down so virtually impossible to do a chain alignment.
Novice builder not following any book or noticing what he took apart
Bruce

[dpetterson]

Originally Posted by boyt911sc

DP,

Ask your friend to take another look at your camshaft sprockets. The one shown in your picture is too worn out already. The other side could be bad too. If these camshafts sprockets are worn out, I bet the inner IMS sprockets would be in similar condition. So installing new timing chains with worn out sprockets is not a prudent course of action.

Installing the wider idler gear brackets is a good upgrade.

Tony

Hi Tony - thanks for the feedback. Will discuss with my friend.

[dpetterson]

Originally Posted by Flat6pac

The cam drive gear is upside down so virtually impossible to do a chain alignment.
Novice builder not following any book or noticing what he took apart
Bruce

Hi Bruce - thanks for your feedback. I double-checked Wayne's book How To Rebuild and Modify Porsche 911 Engines, and you're right - that cam gear is installed upside down. It should have the flat surface facing outward. I just checked my car and the driver's side cam gear was installed correctly. Whomever worked on our car before we purchased it definitely got that wrong.

[Dpmulvan]

So don’t run safety collars because you won’t know when the tensioner fails?? So it’s better to possibly grenade your entire engine so you know when your tensioner has failed? Makes no sense to me.
That safety collar looks homemade.

[dpetterson]

Originally Posted by Dpmulvan

So don’t run safety collars because you won’t know when the tensioner fails?? So it’s better to possibly grenade your entire engine so you know when your tensioner has failed? Makes no sense to me.
That safety collar looks homemade.

I don't think my post said anything about not running them. Just alerting people to the fact that it's difficult to tell when they collapse if you run the collars.

[MichaelSJackson]

Collars worked for me. Stopped at intersection before I noticed loud rattling coming from engine compartment. Stuck my head in and could quickly tell something was wrong on the driver side chain area. When I opened the chain housing there was the collar I'd heard described at the Bruce Anderson - Jerry West engine class. Saved my ass just like it was supposed to. Found a tooth missing from the cam sprocket and lots of wear on the idler arm shaft.

I bought a new set of collars when I put it back together. I'm a believer!

Michael J.
'78 SC

[ficke]

Originally Posted by MichaelSJackson

Collars worked for me. Stopped at intersection before I noticed loud rattling coming from engine compartment. Stuck my head in and could quickly tell something was wrong on the driver side chain area. When I opened the chain housing there was the collar I'd heard described at the Bruce Anderson - Jerry West engine class. Saved my ass just like it was supposed to. Found a tooth missing from the cam sprocket and lots of wear on the idler arm shaft.

I bought a new set of collars when I put it back together. I'm a believer!

Michael J.
'78 SC

Sounds like you experienced the same thing as the OP. Your tensioner failed, you drove with a failed tensioner not noticing the failure because of safety collars, damaging the engine for how many miles? till it failed enough for a loud rattle then you made the repair.

[Flat6pac]

When you loose a tensioner, it’s immediate, you lost tension, jump time on the cam, wipe exhaust valves, break rockers, damage pistons.
The guards set the tensioner into mechanical mode with a minimal chain slap but doesn’t destroy one side of the motor.
As a note, the Carrera tensioners can fail and cause a loose chain and chain noise.
Bruce

[ficke]

Many people are driving around on weak or failed completely tensioners destroying their engine slowly because they have these safety collars on and need to wait till their engine has eating itself enough for them to hear a problem, by then more damage has been done than if they did not have a safety collar and heard the weak tensioner right away and not continued running their engine. Tensioners usually give warning and not fail immediately with catastrophic results; they lose their oil slowly getting weaker, but nothing is absolute, and I am sure there are instant failure examples.



Having said that safety collars have a place and serve a good purpose for a lot of people. But, If you run safety collars, unless you check them once in a while you will not really know if your tensioners are failing or have failed., you cannot trust hearing them either because you do not have the ear or they were adjusted so tight, or? I do not know why, but people obviously cannot hear the failure when it happens and drive on the broken or weak tensioner because of the safety collar.



There are a lot of nuances, and pros and cons to different systems. That is why it is difficult when people say is this "safe" are the" best way" None of them are failproof. But some defiantly have way more upside than others. I would put the new arms and pressure fed tensioners as having the most upside for the average 911 driver.

[Henry Schmidt]

The design of the "safety collar" is not to prevent tensioner failure. It is designed to alert the user to a failed tensioner. If you pay careful attention the your engine sounds, the safety collar will make a knocking noise on start-up after the tensioner fails. If you ignore the noise or just aren't in tune with your engine sounds, the collar can cause damage if perpetually exposed to stresses/ pounding.

If you're looking for a tensioner safe-guard, you can install a Teflon or Delrin collar [6-7 mm] that will prevent engine damage from tensioner failure. It will not alert you to the failure but it can save your engine.

[Rosco_NZ]

Yes, Carrera tensioners can fail too .. but check out the Jerry Woods mod to help reduce risk. Also Carrera tensioners localised area for sludge buildup and reduced operation .. these should be disassembled and cleaned with any rebuild .. but often aren’t. New tensioners have also been known to fail .. just a small ball bearing and seat keeping valve train chains tight .. never did such high value sit with such a simple cheap part!!

[dannobee]

+1 on the Carrera tensioners with the Jerry Woods mod. That little retainer for the air bleed ball at the top tends to blow out, leaving a slack tensioner. The spacer used with the Jerry Woods mod eliminates any engine damage if that should occur.
If you have Carerra tensioners and you see a tiny ball bearing stuck to the magnet on the sump drain plug, it's from one of the tensioners and needs to be addressed ASAP.