Hodor
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| posted on 18/8/15 at 09:56 PM |
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M8 1.5mm pitch thread bolt anyone?
I stupidly overtightened and snapped in half a valve that screws into my fuel rail. It is (was) an M8 sized fitting but with a 1.5mm thread pitch.
The valve was just like a tyre valve, which you could use to release the fuel pressure in the rail, or attach a pressure gauge.
I've had a good look round workshops at work and home but cannot find that combination, an M8 bolt with 1.5mm thread, they are all the standard
1.25mm. Same with Google, eBay etc, doesn't seem to be a thing that exists.
Can anyone offer any help in either locating that our an equivalent? Perhaps it's a common thread for some valve but I'm searching the
wrong thing??
I'm only after a blank, not fussed about the valve.
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owelly
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| posted on 18/8/15 at 10:34 PM |
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ISTR there's a banjo fitting that is M8x1.5 so perhaps have a google and see what turns up. Perhaps a blanking banjo or banjo-bleed screw?
http://www.ppcmag.co.uk
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craig1410
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| posted on 19/8/15 at 12:30 AM |
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You seem very sure that it's an M8x1.5mm so I expect this is a daft question but how sure are you in actual fact? Is there any chance it's
a UNC or some other non-metric thread? The normal thread for M8 is 1.25mm pitch as you probably know so just playing devil's advocate.
Any time I need odd sized fasteners I always go to my local hardware store here in Kilmarnock. It's an old school type store who do a lot of
work for agricultural vehicles and they have stacks of odd sizes. That said, I usually go there for non-metric stuff when I need it so not sure how
well stocked they are for metric stuff. I see you're in West Lothian so might be worth a try. Contact details here:
https://www.yell.com/biz/william-young-kilmarnock-ltd-kilmarnock-717725/
Note, these guys tend to be a bit "old school" in terms of customer service too so don't expect friendly service. Maybe that's
partly because I only ever go in there for a single bolt at a time! 
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britishtrident
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| posted on 19/8/15 at 05:34 AM |
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5/16" UNC is most likely candidate. 1.44 mm pitch
UNC was thread of choice for fittings in aluminium especially for US and Uk manufacturers
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Hodor
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| posted on 19/8/15 at 06:38 AM |
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You are both right, it could well be an imperial thread, I should have said it is either 1.5mm or something similar. I did check for 5/16ths as well,
but no joy so far!
Will see if I can locate a hardware store locally. Not aware of one in Livingston though.
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r1_pete
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| posted on 19/8/15 at 07:15 AM |
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I've a quite a lot of 5/16 UNC studs and blanking screws from stripping early Jag Heads and Manifolds, if you don't get any joy locally
let me know I can drop a few in the post.
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Brian R
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| posted on 19/8/15 at 12:12 PM |
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Crossflow inlet manifold, engine mounts, thermostat housing etc are all 5/16" UNC.
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craig1410
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| posted on 19/8/15 at 02:12 PM |
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You could order a 5/16" UNC set screw from Namrick here: http://www.namrick.co.uk/acatalog/Home_U_N_C__Hex_Head_Set_Screw_10.html
I previously ordered one of each type of UNC and UNF set screw from Namrick for thread identification purposes. Not sure what they would charge you
for delivery of a single set screw but I doubt it would be much. Might be quicker and cheaper than visiting your local scrap yard and at least it will
be shiny and new!
Edit: From website: "Most orders we can send via Royal Mail 1st class post, with charges ranging from a £2.93 to £7.45 depending on the size and
weight."
[Edited on 19/8/2015 by craig1410]
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Hodor
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| posted on 19/8/15 at 08:27 PM |
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Thanks folks, I think you have set me on the path of enlightenment, every day is a school day. Ordered a couple of 5/16 UNC bolts, 1/2" long
from ebay. Just a couple of quid, so thanks for the help. Hopefully that'll fix it.
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craig1410
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| posted on 19/8/15 at 08:34 PM |
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Glad to hear it, hopefully it is what you need.
I found my 5/16th UNC 75mm long set screw in the garage still fresh in its zip lock bag. It's just a tad under 8mm diameter and about 1.4mm
pitch so is certainly pretty close to the M8x1.5mm you thought you needed. Fingers crossed...
Note, if you over tighten it this time it's the fuel rail thread that will go first. I'd suggest using a nice fresh copper washer to get a
good seal and just nip it up carefully. Halfords usually have them in the little plastic boxes next to where you get fuses and other odds and ends. I
wouldn't be tempted to use PTFE tape or sealant as they might end up blocking an injector.
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Hodor
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| posted on 19/8/15 at 08:57 PM |
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Good point. Currently I have an M8 with PTFE in it. Seemed OK, but at the risk of spraying petrol all over the engine bay and alternator, I need to
get this properly bunged.
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craig1410
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| posted on 19/8/15 at 09:09 PM |
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Yeah, you certainly don't want high pressure fuel on the loose!
I once had exactly that situation in an Austin Mini 1275GT with an MG Metro Turbo engine in it when the fuel hose split and sprayed a beautiful
fan-shaped fuel pattern all over the turbocharger just after a fast run! The fuel instantly turned to a thick white foggy vapour but amazingly
didn't catch fire. I just stood back with fire extinguisher in hand ready for ignition but it never happened. A scary moment though!
I think I've read that ordinary white PTFE plumbing tape is not petrol resistant and that there is a special petrol resistant tape which is
yellow in colour. Don't quote me on that though. You can use liquid sealant and there is a special aviation sealant which is recommended. It has
a catchy name like form-a-seal or form-a-gasket or something like that. Personally for a non-tapered thread such as yours I would just use a copper
washer.
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Hodor
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| posted on 23/8/15 at 04:30 PM |
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5/16 UNC bolt worked a treat. Fits perfect. Copper washer fitted and all good. Thanks for the help
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craig1410
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| posted on 23/8/15 at 07:16 PM |
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Sounds like you've had a more successful day than me. I wrapped my exhaust manifolds in exhaust wrap last weekend in the hope it would reduce
under bonnet temps and finally got around to "cooking" it today with a 30 minute run. Initially it seemed to do the trick and my engine
temperature stayed nice and low around the 75-80C mark (74C thermostat) but then half way through the run, after a brief stint through a town at 30
MPH, the temperature came up to 90C and stayed there for the rest of the journey. Even on the main road at steady 60MPH on light throttle the
temperature wouldn't come back down and yet, earlier in the journey before I got to the town, the temperature actually reduced slightly as I
descended a long hill where I was using almost zero throttle. I think the exhaust wrap has helped but I seem to still have a cooling gremlin
somewhere. No fear, I'll get it fixed!
Anyway glad you got your fuel rail sorted! 
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