revilla Posted February 3, 2019 Share Posted February 3, 2019 Trying to work out what thread this is, where the spool valve screws into the HCU housing. I measured the major diameter to be about 19mm and thread pitch seems to be about 1.6mm (around 4.8mm for three as accurately as I can measure it, but definitely larger than 1.5mm). This matches nothing metric but does seem very close to 3/4"-16 UNF (19.05mm major diameter, 1.587mm pitch).Seems really odd to find an imperial thread on the engine where absolutely everything else is metric, but it really does look like UNF.Can anyone confirm please? Link to comment Share on other sites More sharing options...
nickh7 Posted February 3, 2019 Share Posted February 3, 2019 Try Chris at RetroSportCars 01484 715851 he’ll know Link to comment Share on other sites More sharing options...
rj Posted February 4, 2019 Share Posted February 4, 2019 Andrew, Oddly, in hydraulics, imperial threads are often used even on otherwise metric machinery. Don't you have a thread gauge? My friends Lotus Carltons knock sensor has NPT rather than M12x1.5 as you'd expect being based on an Opel (Vx) block. Link to comment Share on other sites More sharing options...
revilla Posted February 4, 2019 Author Share Posted February 4, 2019 Hi Regin,No sadly I don't have a thread gauge. Never need one to date, it's usually been pretty clear what a thread was from just a measurement with a caliper. And I think it is this time too ... I think you're right, they've just used a UNF thread here.I only really needed to know to buy a cap to blank it off ... I'm getting a head bead blasted and to avoid damaging the sealing flange where the HCU attaches I've left the empty HCU case bolted in place (it could do with a good blasting too). I'm blanking off all the threads and ports everywhere around the head to keep blasting media out as far as possible (it will still get everywhere inside I know, but I'm just making sure that critical surfaces don't actually get blasted and threads don't get gritted up). I've ordered a cheap 3/4"-16 blanking cap anyway as I'm pretty certain it will be right. I won't force it in if it doesn't feel right.Andrew Link to comment Share on other sites More sharing options...
John Vine Posted February 4, 2019 Share Posted February 4, 2019 Andrew,I'd take that into a plumbing supply shop, as it may well be NPT (as RJ suggests). You'll likely get a suitable blanking plug there as well.JV Link to comment Share on other sites More sharing options...
revilla Posted February 4, 2019 Author Share Posted February 4, 2019 John,If the UNF cap I've ordered doesn't fit nicely, I'll do that thanks.I've looked at tables of both NPT and BSP threads though and I can't see anything that comes close.Andrew Link to comment Share on other sites More sharing options...
rj Posted February 4, 2019 Share Posted February 4, 2019 AndrewWill everything fall apart if I remove the valve from the head sat on the complete engine I have on the loft? Or can I do it and try to identify the thread? Link to comment Share on other sites More sharing options...
revilla Posted February 4, 2019 Author Share Posted February 4, 2019 No RJ it won't fall apart ... that's very kind but I've already ordered a blanking cap on eBay that should be here in a day or two so I wouldn't go pulling your engine apart to check for me unless I find it doesn't fit!Taking it off:Undo the 19mm plastic hex nut on the end of the stack of solenoids. This lets you slip the two solenoids off the end of the valve (which is a sealed tube so won't leak anything at this stage) and get a spanner onto the nut to unscrew the valve from the housing. It's either a 29mm spanner or, more likely 1.1/8" which is another pointer to it being an imperial thread. At this point if there's any oil in there it might leak a bit. There are a number of O-rings on the spool valve as you can see in my picture so be careful on reassembly, maybe a bit of lube and rotate it as you put it back in. Note the angles of the connectors on the solenoids before removing as you want to put them in about the same positions on reassembly or the connectors will foul the breather pipe (but it's easy enough to turn things around later if you need to). There's a VERY low torque specification for the plastic nut, from memory it's 5Nm but I'd check. Link to comment Share on other sites More sharing options...
rj Posted February 4, 2019 Share Posted February 4, 2019 Ok, I'll wait until I hear you cry in frustration. :-p The engine is likely to have to donate the head anyway as I had the piston/valve-contact issue last time I was out. If not I purchase one of the new heads from eBay that is... Sigh. Link to comment Share on other sites More sharing options...
rj Posted February 4, 2019 Share Posted February 4, 2019 I have just had a look at the thread tables and I would agree: It looks very much like a UNF 3/4-16 Link to comment Share on other sites More sharing options...
revilla Posted February 4, 2019 Author Share Posted February 4, 2019 I'll let you know ... Link to comment Share on other sites More sharing options...
Mechanical Moz Posted February 5, 2019 Share Posted February 5, 2019 Nowhere near as good as a physical thread gauge set but the Thread Pitch app on Android is handy for helping with quick identification. Link to comment Share on other sites More sharing options...
revilla Posted February 5, 2019 Author Share Posted February 5, 2019 3/4"-16 UNF it is. The plug was finger tight all the way in. Thanks for all your input. Link to comment Share on other sites More sharing options...
rj Posted February 5, 2019 Share Posted February 5, 2019 Link to comment Share on other sites More sharing options...
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