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What thread is the relief valve plug?

Just had a slight accident re-fitting the plug on the relief valve. It went tight and snapped off.

I dont fancy trying an easy out in case it also snaps off, so as the plug is hollow, thought I could carefully drill out the middle of the steel plug, hopefully meaning I can clean the threads with a tap.

Trouble is I don't have a spare plug on hand to measure. Any ideas?

If all else fails I'll tap oversize in a BSW and make a new plug. Lucky I havnt fitted the crank yet!

Re: What thread is the relief valve plug?

Been there ! you will find that you CAN ease it out... I recalll I got a siutable sized old file and inserted the tang , tapped in home and then turned it out using an adjusable spanner

Re: What thread is the relief valve plug?

Sorry about the spelling , I'm Tired!!

Re: What thread is the relief valve plug?

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Hedd

The thread is 9/16" BSF. The hole for the spring is 13/32", and this goes right up into the head. Thus there is barely .035" wall thickness in the thread relief just below the head - very delicate!

There is about 13/16" left in the crankcase, when the head brakes off, which should come out using Mac's good old fashioned method - the old ones are always the best!!!


Mike

Re: What thread is the relief valve plug?

Many thanks for the info, I was being a numb nuts, it went tight, I tried it a little further, it went tighter, I tried to loosen it off an it broke. My poor wife had to cope with lots of choice language and an angry man for the rest of the evening.

I did attempt to loosen it off with a screwdriver down the hole but started to make a pigs ear of it all. I'll drill it out to be on the safe side. I've spent nearly 150quid getting the lip done, aluminum welding and inserts so far, and have no intention buggering it up now!. Dont you just love 70year old components?

Re: Re: What thread is the relief valve plug?

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Hedd

If you decide to go ahead with the drilling operation do please be careful not to damage the ball valve seating! The ball is still trapped beyond the thread abd should afford some protection. Ball I have is .434" diameter so nominally 7/16".

On the crankcase which I have measured the seat is about 1 9/32" below the face, whilst at the most there is only about 13/16 of steel thread left to be removed.

I would still go for jambing in an old file or similar and twisting out if at all possible- after all you cannot harm the broken bit worse than it is already, whilst drilling out a long section of steel from an aluminium casting like that is fraught with nasties.

However, good luck which ever way you decide.

Mike

Re: What thread is the relief valve plug?

The ball is still trapped. That should save the seat.

Jambing a file or screwdriver into the broken part is nothing but a bodge, both will expand the steel in the aluminium tighter, not a clever idea if I want to unskrew it.

I wont use an 'easy out' on the basis they are made out of HSS steel, hence are very hard. If I snap one of those in the hole there is not a lot of options (I know I've done it), carbide tipped drill bits are expensive, and spark eroding is more so.

Re: Re: What thread is the relief valve plug?

Hedd

We used to have twist drills with the helix the other way. Using them in a reversible drill to drill out jammed studs sometimes loosens the stud/broken bit and unscrews it as part of the drilling operation. If it doesnt unscrew it doesnt matter because you just keep drilling it out and retap/helicoil.

Might be worth a trip to a tool shop?

Steve.

Re: Re: Re: What thread is the relief valve plug?

I have got away with using a small (1/8” or less) ball grinder, grinding two slots opposite each other from front to back as far as your grinder will allow, grind down just to the tops of the threads. Catch the edge with a very small cold chisel, and tap inwards and you should be able to collapse the halves inwards. Any of the thread that remains whole should be able to be screwed out. I have successfully done this, but not on the part you are concerned with, but the principle is the same. Good luck

Re: Re: Re: What thread is the relief valve plug?

There is a little tool now available which is purpose made for unscrewwing "butchered" threaded parts, using a reverible electric drill. I think is is marketed by the same people who sell the "Re-Coil" products. IMHO, extraction of the broken part would be a far better way of going, if you possibly can.

For what it is worth, I have always had more success with the "straight-sided" type of screw extractors, rather than the more traditional "easy-outs"

May the gods be with you!

Regards

Barry R

Re: What thread is the relief valve plug?

"Left handed" drill bits available from Tracy Tools (see google) if you decide to go that way. Probably warm the crankcase first, of course. Good luck.

Regards, Stuart