Hello everybody,
I'm preparing for a new build starting with a fresh new factory block. It will be replacing my original 1986 block which for reasons I won't go into here is now a candidate for re-sleeving...It might not have been the wisest decsion, but since I could get a new block for just a bit more than the cost of getting my old block sleeved, I decided to go that way.
So now I've got a block with the latest updates, and among the things that are different with my existing stock of parts, there's the spring tensioner, and I thought I'd save a few bucks by looking for a used one, instead of ponying up 650€ for a new one, even though it's available.
During my search, I found a late alloy one, which turned out to have exactly the same problem as the one that Tom showed in his Wall of Shame post. A bad heli-coil repair on the pivot stud boss. Now I've got a couple of the second generation iron tensioners around (with the adjustment tool holes), and considering that stripped out stud bosses seems to be a problem with the alloy version, I'm thinking I might be better off using the iron one, even though it weighs a good kilo and a half (almost 3lbs) more.
Anyone have any thoughts on the topic?
Iron or alloy timing belt spring tensioner?
Just a little follow up if someone else is dealing with a spring tensioner for the first time.
I was considering just installing a stud and using the older eccentric tensioner, but new studs are unavailable, and I've read somewhere (Clark's?) that the stud should be renewed after a few roller replacements, so re-using my 30year old stud from my old block doesn't seem like a great idea.
I couldn't see on any parts diagrams for the post 87 924S/944 what bolt was supposed to go in the hole where the stud used to be. I found it on the 968 parts diagram, and it is the same shorter bolt used for the engine mount brackets, an M10x45. I thought i'd share that if it might be of help.
I was considering just installing a stud and using the older eccentric tensioner, but new studs are unavailable, and I've read somewhere (Clark's?) that the stud should be renewed after a few roller replacements, so re-using my 30year old stud from my old block doesn't seem like a great idea.
I couldn't see on any parts diagrams for the post 87 924S/944 what bolt was supposed to go in the hole where the stud used to be. I found it on the 968 parts diagram, and it is the same shorter bolt used for the engine mount brackets, an M10x45. I thought i'd share that if it might be of help.
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Tom
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Iron tensioner? Have a picture of the one you say is iron? Does a magnet stick to it? I've never seen one made of iron, so I'm intrigued. 
For the life of me I have no idea how those threads get stripped. Makes no sense to me. Only thing I can guess is that people are wildly over tensioning the pivot nut -- but even that seems unlikely. I almost wonder if the factory helicoiled those threads for added strength and they sometimes pull loose when loosening the nut? Interesting that you came across a stripped one -- the one in the wall of shame is the only stripped one I've ever seen. In the grand scheme of what's reliable and what's not, I wouldn't worry about the spring tensioner being fault prone.
The later 951 blocks have three studs that hold the tensioner to the block (using nuts). It would not surprise if those studs are sold as part of the block, without their own part numbers. There are quite a few examples of studs like that on the block. Nothing special about them though, so I'm sure you could find suitable replacements if needed.
I plan to do a 'how to rebuild' post on those tensioners at some point, including how to calibrate them to actually produce the factory-specified tension level on the belt. Most of them I've seen under-tension belts on their own -- not sure if that's because they are older with more pivot friction or if that's just how Porsche made them.
And good call on finding a good short block. Sleeves can work, but they add way more execution risk than a spring tensioner ever will...
For the life of me I have no idea how those threads get stripped. Makes no sense to me. Only thing I can guess is that people are wildly over tensioning the pivot nut -- but even that seems unlikely. I almost wonder if the factory helicoiled those threads for added strength and they sometimes pull loose when loosening the nut? Interesting that you came across a stripped one -- the one in the wall of shame is the only stripped one I've ever seen. In the grand scheme of what's reliable and what's not, I wouldn't worry about the spring tensioner being fault prone.The later 951 blocks have three studs that hold the tensioner to the block (using nuts). It would not surprise if those studs are sold as part of the block, without their own part numbers. There are quite a few examples of studs like that on the block. Nothing special about them though, so I'm sure you could find suitable replacements if needed.
I plan to do a 'how to rebuild' post on those tensioners at some point, including how to calibrate them to actually produce the factory-specified tension level on the belt. Most of them I've seen under-tension belts on their own -- not sure if that's because they are older with more pivot friction or if that's just how Porsche made them.
And good call on finding a good short block. Sleeves can work, but they add way more execution risk than a spring tensioner ever will...
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Last edited by Oringojin on Fri Mar 27, 2026 1:50 pm, edited 1 time in total.
The new block does come with the 3 spring tensioner studs. Of course it doesn't come with anything in the big hole for the old eccentric stud, so that's what I was writing about in my follow up post. i was getting frustrated not being able to find the dimensions of the bolt that replaced the old stud in 1987 and later engines.
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