Timing chain tensioner pivot bolt

[Chancer]

Given the cost, hassle and potential risk of damaging/scrapping the head of all the proposed "solutions" i ask myself is there actually a problem to solve?

I would simply re-use the existing modified tensioner pivot, it looks perfectly serviceable, but then I am a practical person not an originality freak, probably just like the person who made the part as a solution to a real problem, that of a stripped thread no doubt.

I have nothing against originality, if your vehicle is as close to original as can be and that is your thing then please just ignore me!

[2cams70]

That would be great. Thanks Rohan

[Craven]

Rule of thumb for tapered or parallel threads when used in a seal type situation, if the face of the hole has a machined flat surface then the seal is probably at this point and the thread is parallel.
If the hole has an unfinished surface then the seal is likely to be by a tapered arrangement.
FWIW.

[rgh0]

I measured up a few cylinder heads this morning to check the tensioner bolt thread.
The thread in the head is 1/4 inch BSPF which is a parallel thread

Note there are 3 types of BSP thread which you may see quoted and the differences sometimes causes confusion. All three types use the same pitch and thread details but vary in fit and taper

1. BSPP - This is BSP Parallel (or Rp series) and it uses a pilot drill size 11.50mm for 1/4 BSPP and has a parallel tight fitting thread

2. BSPF - This is BSP Fastening (or G series) and this has a larger pilot drill size for increased clearance of 11.80mm for 1/4 BSPF and has a parallel thread. This thread is intended for fitting of fasteners which is why Lotus used it for the pivot bolt.

3. BSPT - This is BSP Taper which has a 1/16 taper and a pilot drill size of 11.20mm for 1/4 BSPT


cheers
Rohan

[2cams70]

I received a quote back from full-torque thread inserts for custom made 1/4" BSP inserts.
$880 AUD for a full kit with tooling or $560 AUD for 4 (MOQ) inserts only for local fitment (if I can find someone with tooling). Ouch!!. I think this would be the perfect repair though. Little risk of damage and the insert still just fits within the cast in boss area of the head even though ex-factory it's been drilled significantly offset from centre. See insert details attached. Let me know if you're interested and maybe share the cost?? Much better than a Helicoil even for a first time repair.

In the meantime I'll explore options with the other candidate - Time-sert. A custom "Big-sert" from their range could also work but I'm not sure they do custom orders. Again there's nothing suitable off the shelf that's BSP.

Helicoil also do a "Twin-Sert" spring insert which is essentially two spring inserts one inside the other to accommodate oversize holes. Looks to be available in metric only unfortunately.

[2cams70]

Just to bring this to a conclusion a custom Full Torque FFT insert kit with 1/4" BSPP threads was ordered for this repair and fitted by Crankshaft Rebuilders. The end result is near perfect and in my opinion better than a Helicoil (even though in this case a Helicoil repair was not possible)

I now have a few spare inserts and all the tooling so drop me a line if you need the same. The custom kit was not cheap so any cost recovery would be welcome !

[alan.barker]

Nice job when it's not possible to fit a "Helicoil".
I worked all my life in Aero Space Industry and most things were in some sort of alloy and all threads had Helicoil inserts, Armstrong inserts or some sort of wire thread inserts.
A wire thread insert is stronger than a thread tapped direct in alloy and in general the depth is 11/2 times the dia of the screw.
If for some strange reason the wire thread insert gets damaged then a solid keyed insert can be fitted as a second chance because of damage to the wire thread insert (as you have done).
Just one thing never put Loctite on a screw thread assembled in a wire thread insert.
There are red dyed wire thread inserts which are locking inserts but they are only for assembly once situation.
I have fitted a wire thread insert in the same position for the pivot screw with no problems.
Alan

[ceejay]

Guys, I have an orig stromberg head here.. and recently I bought front timing chest with removable water pump module from Burtons UK... and I just went out to workshop to check thread on the tensioner pivot pin.
OD size measured with vernier" 0.5160"
thread form is NF 18 TPI (thread per inch) and not tapered. it is NOT gas thread.

With regards to your repair, if the head could be set up in vertical milling machine so that part of old thread boss can be accurately over-bored so that a new/machined aluminium threaded insert could be pressed in and TIG welded so that it would be as good as new.

You need to find a machine shop with a mill that has plenty of table adjustment. Lotus head height/length is 18" , then add tool cutter/boring length and milling machine would need about 25"(Minimum) of table drop. The head could be accurate set up/clamped onto the mill bed with a strong cast iron angle plate to do the job.
The job could (With lots of setting up) be also done on a largish lathe. There is always a way around something.

Rohans comment re "Finding it hard to get people to do specialised work" is one of the reasons why I have always carried out my own fabricating and machine shop work.
There are workshops around who will listen to your needs, but often that is not the case.

[2cams70]

Well Ceejay, I just measured the TPI on my pivot pin and from what I can ascertain you are correct and others on this forum have been wrong. Just goes to show, be very careful relying on what you hear and always back it up by checking it for yourself. TPI is 18 and not 19. Therefore the thread is 1/4" NPS and not 1/4" BSPP.

[rgh0]

Yes it looks like I was wrong and I should have dug out a spare bolt to measured the TPI as i could not measure it on the head

measure twice cut once
cheers
Rohan

[2cams70]

That's a bit of a pain now that the insert has already been cut 1/4" BSPP. The pin seems to fit ok by hand though, it doesn't tighten up at all and there just a small amount of "wiggle". I hope it's still ok fully tightened at 45-50Nm.

I expect then that there are no BSP threads on this engine including the head and it's coolant fittings. They should all be to the early 60's Ford standard and Ford being an American company the threads are all UNC/UNF/ NPT/NPS. Mind you, metric fasteners seem to have been progressively introduced from the early 70's on the English Fords.

[2cams70]

Looking at the Escort workshop manual now it's telling me the thread is 1/4" BSP. Which is back where we started and also news I am very happy to hear. What a pain these NP* / BS* threads are. If you are going to create a standard at least make them so they are sufficiently different from existing standards so they can't be fitted together!!

[ceejay]

Making good repairs of these particular parts can be a pain if drastically altered from standard, if the thread on the pin was made to be NC then there would not be a problem.

Next time you have the timing chain tensioner adjuster assembly out of the timing chest, take note of the thread on the large Hex threaded spigot; it is a very coarse thread, the tensioner adjuster stud is 3/8"UNF, both parts are steel and have good strength.

It is generally accepted that fine threads cut into aluminium do not have good mechanical strength, where as a course thread does have the strength.
It is good that individual cross references can be made by various forum members with many Lotus parts that can raise questions and doubt.

[rgh0]

I wonder if the head casting is threaded 1/4 BSPF which is what I measured it as best I could and the pivot pin is threaded 1/4 National Pipe thread straight which is what I now measure that at! That type of confusion could exist with Lotus records keeping !!!

Col - can you accurately measure the head thread form better than I to see what you think it is. The thread is short and internal so hard to get an accurate TPI count

All the other head plugs and other Lotus casting plugs are definitely BSP and all the Ford castings are definitely NP

cheers
Rohan

[alan.barker]

Well it seems a bit strange between the two different tpi 18 or 19.
The most important is that the thread in the head is the same as the thread on the pivot.
I know when i did the repair on my +2S130 i fitted a 19tpi insert that matched the thread on the pivot.
The pivot was the original pivot from new.
I measured the thread on the pivot to determine what insert to fit. The thread in the head was too damaged and difficult to measure.
Anyway HAPPY NEW YEAR and have fun with your Lotuses (Loti)
Alan