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Cylinder head core plug


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Can some kind soul give me the thread type for the 1" aluminium core plug for the 4 cylinder engines. Part N° PS 1603, I believe. I need to order a tap to tidy up the thread.

UNC ?

thanks

james 

Edited by james christie
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i take it you meen the water plug in the centre of the head.

i managed to clean the thread up with a wire brush in a drill and fitted the replacement plug from moss with suitable sealant .   All ok

 

Roy

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Thanks for this info.

Yes it is the aluminium (coolant) plug in the centre of the cyl head

I had an unsuccessful attempt at cleaning the thread with a wire brush. The plug won't screw fully home and as it is in aluminium I don't want force it.

To save me from a mortal end in ignorance can you trained mechanics explain the difference between UNF and NF?

james

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1 hour ago, james christie said:

Many thanks, Roger. Now to find a 1" UNF tap in France.......

james

Tracy tools   They will ship anywhere  the basic tap is under £10.00

https://www.tracytools.com/taps-and-dies/UNF-taps/1-x-12-tpi-unf-spiral-flute-point

 

Peter W

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20 hours ago, james christie said:

 

Yes it is the aluminium (coolant) plug in the centre of the cyl head. The plug won't screw fully home and as it is in aluminium I don't want force it.

james

Are these plugs not tapered ?  so will not go fully home.  Will check on this when i get to the garage.

Roy

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If the thread goes all the way into the water way what stops the plug from screwing all the way in and being lost?  The thread in the head may be tapered.  

In which case I would say .....DO NOT CLEAR THE THREAD IN THE HEAD WITH A TAP. Or the plug may not seal.

The tightness you are feeling after a couple of turns of the new plug may be the tapered thread binding on the plug and making a seal.  

Peter W

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  • 2 years later...

UPDATE.

 

Following this saga as to what thread the plug PS1603 should be

It should be 1” x 14 tpi National Fine.

Pete(BFG) has been sold a plug that is 1” UNF x 12 tpi   that will not screw into his head.
It is the wrong pitch thread for a TR cylinder head, which is tapped 1” NF x 14 tpi.


Moss know about this issue as they had them made wrongly and had them rejected by their customers in the USA.

Cheers
Peter W

 

 

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“sold a plug that is 1” UNF x 12 tpi   that will not screw into hishead”.
 

Yes, I have first hand experience of this!.

In reality the 12tpi into a 14tpi jams up and seals pretty well after a few threads have been wound in, especially if helped with a liberal dose of araldite or whatever it’s called nowadays. 

But why can’t our suppliers get it right before they flog us this **** ??

james

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