Lotus Elan

tensioner pivot pin

PostPost by: bill griffiths » Mon Jul 26, 2021 1:44 pm

On tightening the tensioner pivot pin which has about 50 ft lbs, I recently thought that the thread in the head was stripped.
It was not getting much feeling of tightness!!
But the thread was fine. The problem was that the pin was in two parts.
Around the slightly thicker base of the shaft at the bolt end, the thread in fact formed the outer part of a tube
which was pressed over the shaft.
How it was meant to be kept in place at the required torque I do not know!
The bolt pulled out, leaving the threaded tube in the hole. It was easily removed with an easy out, but is this the method of munufacture? And if so, why? Surely machining the pivot in one piece would be fool proof?
And how might the "tube" be reattached to withstand the torque? And if that is not possible, any suggestions as to who might supply a useable version?
Regards,
Bill
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PostPost by: bill griffiths » Wed Jul 28, 2021 1:17 pm

pin.jpg and
To better describe the strange device with which I was confronted after removing the pivot pin from the chain tensioner, I shall attach a photo.
It shows the TWO components of the pin.
The bolt with shank.
AND the anulis, with thread on the outside and of a size which is a tight fit over the thicker part of the pin nearest the head.
Surely such a contrived arrangement was not original?
Where might I obtain a one piece version or must I ask my machinist to make a one off replacement?
Reards,
Bill
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PostPost by: seniorchristo » Wed Jul 28, 2021 2:15 pm

Kelvedon has them

HOME » LOTUS TWINCAM ENGINE » TIMING CHAIN TENSIONER PIVOT PIN

TIMING CHAIN TENSIONER PIVOT PIN
£15.52 ex vat
2 in stock

Timing Chain Tensioner Pivot Pin quantity Add to basket
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SKU: X026E0011Z Category: LOTUS TWINCAM ENGINE
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Description
Product Timing Chain Tensioner Pivot Pin
Part Number X026E0011Z
Description Timing Chain Tensioner Pivot Pin.
Crush Sealing washer also required, and available at extra cost (Part Number DW13)

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PostPost by: bill griffiths » Wed Jul 28, 2021 11:27 pm

Thanks for that.
Regards,
Bill
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PostPost by: avro » Thu Jul 29, 2021 9:14 pm

Bill

Just a thought :- The only reason that l can see for a pivot bolt to be modified in such a way is that the thread in the head has possibly been stripped at some time in its life and has been tapped out to a larger size. If this is the case it would be a relatively easy job to machine off the existing thread from the pivot bolt and then machine a new oversize threaded sleeve to suit. This could be made from a section of threaded bolt or bar and then pressed onto the machined pivot bolt. Looking at your pictures it’s possible that this has been done. Perhaps Loctite had been used on the threaded sleeve but tightening the pivot bolt a little too tight has broken the seal between the two parts allowing the bolt to turn but not tighten.

The original thread in the head is 1/4”NPT and this is the same as the brass oil gallery plug adjacent to the front exhaust port outlet. A quick check before you order a new pivot bolt would be to simply unscrew the brass plug and see if it screws into the the pivot pin location. . If it doesn’t fit then buying a new pivot bolt will unfortunately not cure your problem as that won’t fit either.

Regards

Nick.
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PostPost by: bill griffiths » Thu Jul 29, 2021 11:56 pm

Thanks, Nick. Your are correct about a damaged thread in the head.
I have ordered a replacement pin but in the meantime borrowed one and on installing it discovered indeed that the existing thread is standard...but indeed that it is stripped!
I now have a helicoil of the same thread and hopefully I can install it after blocking the hole from the back to avoid
contaminating the chain casing.
Any comments especially from anyone who has had a similar problem would be appreciared.
I am unsure why such a high torque is specified for the pin; I think 40 -45 ftlb.
Perhaps a little less with some locktite?
Regards
Bill
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PostPost by: rgh0 » Fri Jul 30, 2021 11:18 am

Hi Bill

I tighten to much less torque by feel and use a medium strength Loctite as that torque on the relatively short thread in the alloy casting is to much. The bolt carries no tension load and you only need to to seal with the alloy washer and not unscrew which does not require a high torque.

cheers
Rohan
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PostPost by: 2cams70 » Fri Jul 30, 2021 2:43 pm

The 1/4" BSP threads are very fine as fine threads can withstand a higher load before stripping than threads that are more coarse. The problem with fine threads though is that it's easy to cross thread them when inserting the male part. Most of the problems tend to be caused by a combination of cross threading and previous owners tightening fasteners not using a torque wrench rather than the torque specification itself being wrong.

In your case you are probably lucky in that the thread has only been damaged once so a Helicoil can be used to repair the damage. If you are going to repair with a Helicoil do not use Loctite on the fastener. This is specific advice from Helicoil themselves. Helicoiled threads should be stronger than original and I would recommend keeping to the factory torque figure - the lower end of the range if you wish to be cautious.

In my particular case I was not so fortunate. A Helicoil could not be used because the thread had already been bodged using a Helicoil once before. "Lock and Stitch" made some custom inserts and tooling for me to make the repair. 1/4" BSP parallel is not a common thread size particularly these days! In the unlikely event it happens that you can't do the repair with just a Helicoil feel free to send me a PM because I have the tooling and custom inserts just sitting here to repair something that's been badly bodged and requiring a special oversize OD.

See previous threads below:

viewtopic.php?f=39&t=40164&start=

viewtopic.php?f=39&t=40164&start=15

Also when fitting the Helicoil if at all possible I'd recommend removing the head and putting it in a fixture so it can be drilled true perpendicular and central to the original hole. The far end of the tensioner pivot sits in a location spigot. If the front thread is in incorrect alignment the end of the pin may not line up properly with this spigot.
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