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

[dpetterson]

Note - this was originally posted in the "911 Engine Rebuilding Forum" but I think I should have posted it here as it was an issue that happened while driving my car, not something I came across during the rebuild of an engine. Regardless, I feel it's worth a read for those not running pressure-fed chain tensioners.

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!

[proporsche]

you should adjust-check alignment your gear sprockets The gear is very worn out..

Ivan

[Nditiz1]

So did your tensioner fail? If so did the safety collar protect the car from having a catastrophic issue that would force a complete rebuild?

[stownsen914]

I'm with Nditiz1 - was what you experienced really just as bad as a collapsed tensioner? I haven't had to deal with that fortunately, but I always thought the risk with that was enough loss of cam timing to cause valves to hit pistons, etc. Not so? Sounds like what happened to you wasn't as bad.

[john walker's workshop]

That right sprocket is upside down. That throws sprocket alignment WAY off. Then there's the question of how long was the tensioner rattling and ignored? Quite a while from the looks of it. The intermediate sprocket probably looks the same. Good excuse for a teardown.

[proporsche]

Originally Posted by john walker's workshop

That right sprocket is upside down. That throws sprocket alignment WAY off. Then there's the question of how long was the tensioner rattling and ignored? Quite a while from the looks of it. The intermediate sprocket probably looks the same. Good excuse for a teardown.

good eye John...

Ivan

[MBAtarga]

So the left side sprocket is "dish side" out and the right is supposed to be "dish side" in? Had to google search some images to understand the comment so double-checking this.

[dpetterson]

Originally Posted by Nditiz1

So did your tensioner fail? If so did the safety collar protect the car from having a catastrophic issue that would force a complete rebuild?

Yes, the tensioner failed and the collar kept things going until it finally went. I just wanted to raise awareness that if your tensioner does fail, you may not realize it if you have safety collars installed. Not advocating whether to use them or not, just want folks to be aware of this drawback.

[dpetterson]

Originally Posted by MBAtarga

So the left side sprocket is "dish side" out and the right is supposed to be "dish side" in? Had to google search some images to understand the comment so double-checking this.

Yes, the right side should be dish side in. At some point--before we took ownership of the car--the right side cam gear was installed upside down.

[dpetterson]

Originally Posted by john walker's workshop

That right sprocket is upside down. That throws sprocket alignment WAY off. Then there's the question of how long was the tensioner rattling and ignored? Quite a while from the looks of it. The intermediate sprocket probably looks the same. Good excuse for a teardown.

Based on the wear on the safety collar, chain and cam gear, there is a good possibility that we purchased the car with the collapsed tensioner. The car went through a PPI, was serviced by some of the top shops on the east coast and was also driven by mechanics and other people who have owned several of these cars over the years. Not one of them ever heard / mentioned any rattling. If I had previously heard any rattling like that, I certainly wouldn't have ignored it.

[john walker's workshop]

It can be subtle, heard with a practiced ear. What's the plan for the inner gear wear, and all that particulate matter in the engine?

[shoooo32]

I'm with John; tear it down. If the previous rebuilder couldn't install the cam gears correctly, what else is wrong? It's cheaper to do it now than after it spins a bearing...

[RDM]

When I tore down my engine on my new-to-me 911 to fix broken head studs I found a blue tensioner collar in the engine sump and a black tensioner collar on one of the chain tensioners. A mystery to be sure.

Haven't been too crazy about chain collars since.

[dpetterson]

Originally Posted by RDM

When I tore down my engine on my new-to-me 911 to fix broken head studs I found a blue tensioner collar in the engine sump and a black tensioner collar on one of the chain tensioners. A mystery to be sure.

Haven't been too crazy about chain collars since.

Yikes!

[RDM]

Originally Posted by dpetterson

Yikes!

Which means someone had been in there (at least!) twice before my arrival.

And done poorly both times.