Lotus Elan

Thread Type - Cylinder Head Tensioner Shaft

PostPost by: Matt Elan » Fri Dec 14, 2012 7:33 pm

Evening All and seasons greetings - does anyone know the thread type and form of the cam chain tensioner quadrant shaft that screws into the front of the head? Mines stripped and needs helicoiling and my engineering company can't ID it - they've measred it and its almost 1/2 inch but not quite, and its almost 19tpi but not quite; they are sure its not UNC and think it may be some obscure pipe thread; but does anyone here know?
Many thanks in anticipation
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PostPost by: billwill » Fri Dec 14, 2012 8:53 pm

BurtonPower seem to think it is 1/4"-18 NPT thread

http://www.burtonpower.com/parts-by-cat ... fl808.html

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PostPost by: Matt Elan » Sat Dec 15, 2012 9:38 am

Thanks Bill - much appreciated!
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PostPost by: CBUEB1771 » Sat Dec 15, 2012 4:32 pm

Matt,
I just ran a 1/4" British Standard Parallel Pipe tap into my cylinder head. It went in, turning by fingers only, and felt like a perfect fit. This thread has a 0.518" outer diameter and is 19 threads per each. I checked my pivot pin and it is definitely 19 threads per inch but only 0.500" outer diameter so it is a little looser fit than I would have guessed. However it is a replacement pin and might not be made to the correct class of thread fit. So go with confidence that it is 1/4 BSPP, definitely not obscure it is still widely used in hydraulics. I don't know why Burton lists it at 18 threads per inch, that is definitely wrong. Here is a US supplier for thread repair kits:
http://www.newmantools.com/recbri.htm
scroll down to "BSP". These must be readily available in the UK.
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PostPost by: alan.barker » Sat Dec 15, 2012 5:06 pm

it's BSPF (fine) and helicoils are available. I had the same problem on my 1973 +2S/130 because the PO had loctited the thread (which is not needed). When i unscrewed the pivot it tore out the thread.
The repair with a helicoil kit is very easy
Alan B
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PostPost by: garyeanderson » Sat Dec 15, 2012 6:39 pm

Not 18 tpi nor was it 20. There is no 19 on my cheap-o-matic pitch gauge so can't try that.

.516 inch is close to what the o.d. is.

Gary

pivot pin dimensions.JPG and
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PostPost by: billwill » Sat Dec 15, 2012 7:06 pm

Confusion reigns as usual

Maybe this will help, wot I found on the Internet.

NPTSizing.pdf
NPT thread sizes
(104.13 KiB) Downloaded 1025 times


That says 1/4" NPT has an OD of .540 which doesn't match Gary's figure.

NPT = National Pipe Thread.... Which Nation?

Looks like Burton got it wrong.
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PostPost by: CBUEB1771 » Sat Dec 15, 2012 9:09 pm

piss-ant wrote:Not 18 tpi nor was it 20. There is no 19 on my cheap-o-matic pitch gauge so can't try that.

.516 inch is close to what the o.d. is.

Gary

The attachment pivot pin dimensions.JPG is no longer available


I don't think this is confusing, 0.516" OD is what I would expect for a 1/4" BSPP fitting, slightly less than the OD of a tap. My 1/4" BSPP tap measures 0.518" OD which is exactly what the tables say it should be. My pitch gauge does have a 19 TPI blade which nests nicely in the threads of the pivot pin. Using a parallel pipe thread on this pin makes sense because Lotus could use any of several types of sealing washers to keep oil in the timing chest. Unfortunately the attached table rounds the OD up from 0.518" to 0.52". Again, my tap is a perfect fit in the female threads in my cylinder head.
Attachments
BSPP Thread Guide.pdf
(43.79 KiB) Downloaded 291 times
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PostPost by: Matt Elan » Sat Dec 15, 2012 9:32 pm

Thanks for all the replys guys....
The shop have the head and an original quadrant bolt/pin so hopefully can work it out..... I'll report back on what they say it is.
Thanks again - hope to get the head back next week but am not holding my breath :roll: :roll:
Matt
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PostPost by: alan.barker » Sun Dec 16, 2012 7:44 am

hi Matt,
sorry to repeat but it's
1/4 BSPF(fine). Supplier Hillcliff tools ltd. <www.hillcliff-tools.com> HIP1412P.
?59.57 + vat for the thread repair kit.
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PostPost by: garyeanderson » Sun Dec 16, 2012 8:57 am

Alan and Russ

This is not one of the subjects that I know a lot about but those two terms (BSPP and BSPF) appear to be the same name for the same terminology.

http://www.malonespecialtyinc.com/Malon ... fchart.htm

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British Standard Pipe Threads (BSPP, BSPF)
Dash Size Nominal Thread Size - t.p.i. Basic depth of thread (h) (in.) Basic Major Dia. (in.) Basic effective Dia. (in.) Basic Minor Dia. (in.) Recommended tap drill size
size Rp (mm) Size G (mm)
-1 1/16-28 .0229 .304 .2812 .2583 6.60 6.80
-2 1/8-28 .0229 .383 .3601 .3372 8.60 8.80
-4 1/4-19 .0337 .518 .4843 .4506 11.50 11.80
-6 3/8-19 .0337 .656 .6223 .5886 15.00 15.25
-8 1/2-14 .0457 .825 .7793 .7336 18.50 19.00
-10 5/8-14 .0457 .902 .8563 .8106 - 21.00
-12 3/4-14 .0457 1.041 .9953 .9496 24.00 24.50
-14 7/8-14 .0457 1.189 1.1433 1.0976 - 23.25
-16 1-11 .0582 1.309 1.2508 1.1926 30.25 30.75
-20 1 1/4-11 .0582 1.650 1.5918 1.5336 39.00 39.50
-24 1 1/2-11 .0582 1.882 1.8238 1.7656 45.00 45.00
-28 1 3/4-11 .0582 2.116 2.0578 1.9996 - 51.00
-32 2-11 .0582 2.347 2.2888 2.2306 56.50 57.00
-36 2 1/4-11 .0582 2.587 2.5288 2.4706 No Sizes of B.S. (British Standard) drills are recommended in B.S. 1157:1975 for this range
-40 2 1/2-11 .0582 2.960 2.9018 2.8436
-44 2 3/4-11 .0582 3.210 3.1518 3.0936
-48 3-11 .0582 3.460 3.4018 3.3436
-52 3 1/4-11 .0582 3.700 3.6418 3.5836
-56 3 1/2-11 .0582 3.950 3.8918 3.8336
-60 3 3/4-11 .0582 4.200 4.1418 4.0836
-64 4-11 .0582 4.450 4.3918 4.3336

British Standard Pipe(BSPP, BSPF)
Thread Form

r = Basic Radius = * 137329 p

h = Basic Depth of Thread = *640327 p

p = Pitch = 1/t.p.i. (Threads per Inch)

ISO 228, DIN 259, BS2779, JIS B0202

In Japan this thread is known as (PF)

Use prefix G for parallel thread. Example: G1/2
Ref. Catalog Page 42 (Chart 2)


One chart (sorry the chart does not transfer as formatted, please look at the link posted) does not make it so and I certainly have no clue but a name is a name and some times things (and people) have multiple names.

Gary
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PostPost by: CBUEB1771 » Sun Dec 16, 2012 11:14 am

piss-ant wrote:This is not one of the subjects that I know a lot about but those two terms (BSPP and BSPF) appear to be the same name for the same terminology.


Gary,
Thanks, mystery solved. Apparently there has been no end to confusion on terminology for these thread types:
http://www.ring-plug-thread-gages.com/t ... itting.htm
BSPP and BSPF are actually the same thing! What had me scratching my head was the meaning of "F" in "BSPF". Pipe threads are not segregated into fine and coarse categories, there is only one pitch per nominal size. I checked a few sites and in this case "F" most commonly means "fitting".
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PostPost by: Matt Elan » Sun Dec 23, 2012 4:20 pm

All sorted - it was 1 x BSP-GAS 1/4-19. Recoil insert repair kit bought and new thread and insert successfully fitted.
Thanks for all the replys and yes Burton was wrong!
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PostPost by: CBUEB1771 » Sun Dec 23, 2012 4:40 pm

Matt Elan wrote:BSP-GAS 1/4-19.


Good heavens, yet another descriptor for the same thread! I am glad everything worked out for you.
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PostPost by: SJ Lambert » Wed Aug 16, 2017 8:41 am

alan.barker wrote:it's BSPF (fine) and helicoils are available. I had the same problem on my 1973 +2S/130 because the PO had loctited the thread (which is not needed). When i unscrewed the pivot it tore out the thread.
The repair with a helicoil kit is very easy
Alan B



I reckon BSPF is BRITISH STANDARD PIPE FASTENING and they're "G" (parallel threads) and the tapered versions in the same pitch are BSPT - British Standard Pipe Tapered (on the Goliath chart in front of me the BSPT chart describes them as RC Series.
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