8 replies to this topic

[bloke]

Hi there, pretty much as the title says, I have been measuring the pressure release valve cap with a vernier caliper and thread pitch tool. 

 

I was convinced that this should be Imperial but things don't seem to add up, thread pitch seems to be 1.75 metric but it doesn't sit comfortably in the grooves, the outer diameter is 20.83 millimetres or .819 inches which is approximately 13/16 

 

Unfortunately I have mislaid my Imperial pitch tool which is annoying and all I can find is a Japanese one. 

 

Anyway, any help will be gratefully accepted, yours, Bloke

[dklawson]

Are you talking about the oil pressure relief valve on the engine block?

[bloke]

Are you talking about the oil pressure relief valve on the engine block?

Yes, that's the one, the little cap that stops the spring and the ball bearing falling out. It's exactly the same size and thread as the oil temperature gauge on an MPI, I'm going to drill and tap it so I can fit an alternative temperature sender. But I also want to make up a few and need to know what taps and dies I need, as some of the sensors that I have will be on the limit for what the cap is capable of.

[dklawson]

Sorry for the delay in replying.  I was too lazy to remove the oil cap from my car and was looking for a drawing I did several years ago instead.

 

I last measured the cap in 2006 and found it to be an odd pitch of 13/16" x 14 TPI.  

[Captain Mainwaring]

13/16 x 16 would be BSF, not that it's much help here

[dklawson]

13/16 x 16 would be BSF, not that it's much help here

 

Hmmm.   Interesting.  The OP (Bloke) said that 1.75mm pitch was close and that would be about 14.5 TPI.  I measured 14 TPI back in 2006.  Bloke also measured the major thread diameter larger than what I found.  It sure would be nice if it were a size/pitch for a common die.

 

When I measured the cap I was going to make my own adjustable pressure relief valve.  I decided to buy one instead.   Perhaps the easiest thing for the OP to do is buy a relief valve cap and modify it rather than machine one from scratch.  Just a thought.

[Dan]

13/16" x 14 is a non-standard BSP size, and this fitting is parallel threaded. It is available as a tap and a die pretty easily as it was quite common on old pumps and stuff. The non-standard size stops you hooking fixed rigid pipe straight up to the pump and forces you to fit a specific part like a hose adaptor or whatever the pump came with to let it move so it couldn't destroy itself.

[bloke]

Thanks everyone, have done just what dklawson suggested, and just tapped a new thread into the end of a relief valve cap. Had to use some extra washers, otherwise I wouldn't have enough thread for a decent joint, but other than that it all seems to be very sound. 

 

At this stage is just a test fixture, if all goes well and the sensor is a good one, I will investigate machining up something a little bit more substantial.

 

All the very best, Bloke. :)

[DeadSquare]

Hi there, pretty much as the title says, I have been measuring the pressure release valve cap with a vernier caliper and thread pitch tool. 

 

I was convinced that this should be Imperial but things don't seem to add up, thread pitch seems to be 1.75 metric but it doesn't sit comfortably in the grooves, the outer diameter is 20.83 millimetres or .819 inches which is approximately 13/16 

 

Unfortunately I have mislaid my Imperial pitch tool which is annoying and all I can find is a Japanese one. 

 

Anyway, any help will be gratefully accepted, yours, Bloke

 

Much too late to be of any use, but it is 1 / 2" water pipe on a pre A+ block