Timing chain sprocket shaft wear

[derm.1785]

Hi all, after a full strip down and inspection of my early 3.0 sc engine I have noticed that the timing sprocket support shaft has a fair bit of wear on it. I know that I can buy new sprockets with bushes but wondered if there is a replacement for the shaft other than buying a complete new chain box. I’m sure this has been covered in the past but need a straight yes or no and if a yes then who or where I can get new shafts from. I see this as a common wear issue so should be loads of options ( hopefully ) thanks in advance.

[pampadori]

which number in the diagram are you referring to?

[IMG]https://www.*****************/uploads/diagrams/911_1973_1_03_103-20.jpg[/IMG]

I see that ECS is stripping the domain name from the link to competitor sites now. Sigh...

Here let me upload a screenshot to their servers so you can see what I'm trying to post:

[derm.1785]

Hi. The part is not shown on that screen shot. The wear is where the timing chain sprocket pivots on a shaft which is attached to the chain box. See photos of wear, I would consider this to be quite bad but I’m taking suggestions.

[Jack Stands]

Perhaps have Henry Schmidt at Supertec rebush the idler arm with the longer bearing surface as used on the Carreras?

[db_cooper]

It looks like that chain case idler post is worn. If it is very rough have someone take a good look, for a second opinion. A roughed up steel post will wear on a new idler too. A common issue when the cars are not driven much. If you are planning on keeping the car, look at new chain cases.

The part numbers for new chain chain cases are 930-105-061-02 (left) and 930-105-062-01 (right).

[pampadori]

Does the idler move much there on that post? I wouldn't think it would move much at all once the tensioner has taken out the slack of the chain.

However, couldn't you just press that old post out and push in a new one made from similar steel?

[derm.1785]

Pampadori, that was my initial intention. I believe these posts/shafts are pressed in and can easily be replaced but can’t see an aftermarket part for this. Does anyone have any suggestions or a fix for this. I could ask a machine shop to make new ones but I’m sure someone has already thought of that and has some for sale but can’t find them. Help is greatly appreciated.

[derm.1785]

If anyone knows where I can find some timing sprocket support shafts I’d be a happy man. Please message me or post here.

[UROParts]

We're working on those shafts, but realistically production pieces are 18-24 months out, so unfortunately we're of no help for this build.

[eastbay]

There is a thread on here about a guy turning a set of posts on his lathe. Faced with the same issue myself I bought a used set of chain boxes with good posts for $100. They are out there.

[derm.1785]

East boy, I was already looking at buying a second hand pair but thought it would be better to try the forum first as I would prefer to install new posts into the original boxes. Hopefully someone will jump in.

[Walt Fricke]

$100 for two good used housings sounds like less than a machine shop would charge. These were not made to be replaced, so it might take more than just pressing out the old and in the new.

If you want to be inventive, you can find a thin brass or stainless steel sleeve which fits your shaft tightly, maybe with some epoxy underneath to fill the grooves, and have Henry Schmidt bore his fix for your need to be updated arms a bit larger. The longer bushing avoids the off kilter loading which led to this wear, or exacerbated it.

[Jack Stands]

I figured the larger bushings that Henry provides would allow them to ride on other sections of the shaft that weren’t as worn.

[stownsen914]

Years ago I had some chain boxes with worn shafts. I noticed that the shafts were worn mostly on one side, so I pressed them out, cleaned them up a bit with some crocus cloth, turned them 180 degrees, and pressed them back in. And with changing to the later style idlers, they were sitting on a different spot along the length of the shaft. I decided that was close enough to being a new wear surface on the shafts.

[derm.1785]

Thanks for all the input guys, I’m going to see if a local machine shop can turn me some new shafts but failing that I’ll keep an eye out for a plain of second hand boxes, although I think $100 is a little optimistic for a pair.

[UROParts]

URO Parts' replacement Timing Tensioner Support Shaft 930 105 060 S is now available! This shaft is not available from Porsche - use it to replace worn shafts without having to replace entire housings 930 105 062 01 / 93010506201 and 930 105 061 02 / 93010506102.

Pelican should be adding it to their catalog soon, we'll add the link once they do.

[Jonny042]

URO, the description in your signature says it only fits up to 1974 I think that must be wrong?

[75 911s]

Nice. Glad to have these being made.

No one mentioned it yet, but a bad fix on pre-hydrualic fed tensioners was to use a fixed tensioner (modded with a bolt to be fixed). This sort of fixed the short term problem of the tensioner collapsing but negated the entire reason for the tensioner which was to allow the chain to move under thermal expansion.

When a fixed tensioner is used on a street car, massive force is placed on the idler shaft and chain housing. On my 2.7, the idler shaft actually worked its way out the backside of my housing due to solid tensioners. The soft mag chain boxes and old JB weld material was no match for the stresses of the steel shaft wobbling back and forth.

[UROParts]

Originally Posted by Jonny042

URO, the description in your signature says it only fits up to 1974 I think that must be wrong?

Thanks for catching the typo Jonny, it's corrected now.