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Cylinder Block Drain plug thread
Posted: Fri Mar 25, 2016 1:09 pm
by vanquishspirit
Hi Guys, I am just trying to it a new cylinder water drain plug in an early Range Rover, 1971 and the threads need cleaning out. I note the new plug I have is tapered and was wondering what thread it is in the block? It looks like it may be a 3\8 NPT but just a guess. If anyone knows it would help me along my way. Also, I will need to buy a tap if it is NPT would it be a standard tap to only clean the thread not take any metal out? thanks in advance. Andrew
Posted: Fri Mar 25, 2016 5:02 pm
by ChrisJC
If I were guessing, I would go for a BSPT thread. No idea what size though.
Chris.
Posted: Fri Mar 25, 2016 6:40 pm
by vanquishspirit
thanks for the feedback. I was thinking NPT as its a US engine, but of course they would be blanks when machined, but perhaps Rover kept with all the tooling from the US? perhaps someone else has a view as well. cheers
Posted: Sat Mar 26, 2016 4:13 am
by unstable load
Take the old plug and using a hacksaw, cut diagonally across the threads to make a groove. that will clear the hole of debris.
Posted: Sat Mar 26, 2016 8:39 am
by vanquishspirit
Another great idea and certainly something I can do if I cannot find a tap. I am a bit worried that the block is alloy, the plug is brass. I could see a right cock up occurring which is why I really want to do it properly with a tap. I have used your method before where I cannot find a tap, my Dad taught me that one!
Posted: Sat Mar 26, 2016 9:20 am
by DaveEFI
vanquishspirit wrote:thanks for the feedback. I was thinking NPT as its a US engine, but of course they would be blanks when machined, but perhaps Rover kept with all the tooling from the US? perhaps someone else has a view as well. cheers
Interesting point. Most of the threads into the block etc are Unified Coarse. Are the Buick versions that or American Coarse? I realise the two are similar.
Posted: Sat Mar 26, 2016 9:30 am
by vanquishspirit
Same thing is it not? UNC and UNF are US threads, where as the UK used until after the Second World War, BSF and BSW (fine and course) and a variety of other threads BCY ( cycle threads etc etc) . I am fairly confident the threads will be the US pipe thread, i.e NPT as opposed to the standard UK BSP. I have ordered a tap so will await to see whether its correct. thanks chaps
Posted: Tue May 10, 2016 10:43 am
by SimpleSimon
Dont be surprised if its BSPT
Posted: Tue May 10, 2016 12:00 pm
by DEVONMAN
As far as I can remember it's 1/4" NPT.
3/8" NPT would be too big. 1/8" BSPT too small.
Pipe threads sizing is not based on the thread diameter but is based on the bore of the pipe you are connecting. So the overall diameter of the thread would be the diameter of the pipe bore plus twice the wall thickness of the pipe. This applies to both English Imperial and US pipe threads.
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