Torque Just to hold Plug in Place

[JCReynolds79]

Hi all,

Hopefully a very simple question...

I have a 'plug' made from steel, M22 X 2 thread, which is going into a cast aluminium threaded hole. It is acting purely as a plug, i.e. not clamping anything down.

All I want to know is how to work out a sensible torque to do the plug up to so that it is not going to work itself loose.

Thanks in advance

Regards,

Jon Reynolds

 

[Ron]

Since it is used as a plug, I would assume it is under some level of pressure. Is the pressure cyclic? Will there be a land at the bottom of the plug or is the threaded hole all the way through the piece (torque irrelevant)?

If there's a land, and low non-cyclic pressure, I would say a snug-tight condition. If higher pressure or cyclic, I would torque to a safety factor of at least 1.25 on the pressure equivalent.

That's just "gut feel" from a structural guy! I'll yield to the gearheads for a real answer!

 

[JCReynolds79]

Hi Ron,

Thanks for the answer.

The plug bolts down onto its underhead area. It actually clamps a collar between itself and the workpeice, but this is purely to adjust its distance into the piece.

There will be a constant force of ~170N from the inside (a spring).

How would you quantify 'snug-tight condition'?

It seems like a silly question, as most engine builders will have a feel for whats good enough not to come out...but I just think there must be some maths behind this to support it. Plus the builder really would prefer to be given a number (so he isn't held accountable probably).


Regards,

Jon Reynolds

 

[unclesyd]

Generally oil pan drains plugs are tightened to 15 ft-lb-20 ft-lb with 18 being the norm. These numbers are with a new gasket and will vary a little for different gasket and plug size materials. Some of the bigger engines with a heavy boss have went to 28 ft-lbs.

I would get in touch with the manufacturer of the oil pan for their recommendations

 

[MintJulep]

M22 is a pretty hefty bolt. Too much torque could crush your collar or strip the threads in the aluminum casting. I'll assume that the size was selected because that big a hole was necessary, not because you had big forces to deal with.

So calculate your preload and torque for those two cases and select appropriately.

Consider using Loctite to prevent it from loosening.

 

[CoryPad]

Sensible ways to determine proper torques include calculation (such as VDI 2230), reverse engineering (competitive assessment), and measurement (simple torque wrench to expensive torque transducer with angle encoder).

Do you have any gaskets or o-rings in the joint? Soft copper washer or other? Without one of these, in general, mating standard metric threads will not be leak proof. You will need some fastener magic, such as thread sealant (Loctite being one brand), thread masking (e.g. PTFE tape), or thread forming fastener (e.g. Taptite).

 

[unclesyd]

The torque spec is given in manuals for every engine in use. I just looked up mine for 5.7L engine in a Camaro and it 15 lb ft.

All drain plugs should have a washer, nylon, fiber,aluminum, or copper, They do make drain plugs with a built in O-ring.

Torque is a little misleading if you changed from the O,E.M. one as there are some have longer threads, which have tendency to bind during insertion.

If you strip the threads in the pan and have to go over size the torque values for said plug is on the package./

The standard technique practiced by the roll in, roll out oil changing bunch is to use a standard box wrench and pull it tight using one finger.

 

[MintJulep]

There will be a constant force of ~170N from the inside (a spring).

It's not an oil pan drain plug. I'm guessing timing chain tensioner.

 

[JCReynolds79]

Hi guys,

to be a bit more specific perhaps might help.

This is a plug holding a spring into a hole, which in turn is acting against a plunger for a pressure relief system.

There is no seal as 100% leak proof is not a requirement. This part just holds the spring in the hole against the underside of the plunger.

There is a steel collar between the plug and casting, which allows us to vary the spring pre-load.

I just want to make sure we torque it enough not to work loose but not too tight to risk stripping the alum casting.

Thanks again.

Regards,

Jon Reynolds

 

[Twoballcane]

If this exists or something close, get yourself a torque wrench and actually torque it in till you feel it is sufficient. Then read torque. Most of the time it is when snug, quarter turn more.

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[MikeHalloran]

For about the same amount of machining, you could use an internal retaining ring to retain the spring, and do away with the plug altogether.

Mike Halloran
Pembroke Pines, FL, USA

 

[JCReynolds79]

The plunger goes into a blind hole, I don't see how we could do away with the plug. Plus I am not looking for alternative designs thanks.

Regards,

Jon Reynolds

 

[MintJulep]

So what part of my first reply was not clear?

 

[JCReynolds79]

MintJulep,

None. Your reply made sense to me thank you. I was just following up with more detail as other were starting to guess what was going on.

Thank you.

Regards,

Jon Reynolds

 

[IRstuff]

I don't see where you've mentioned the vibration environment. Wouldn't that have some bearing into how tight you need to make it?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[unclesyd]

If it is the oil pressure relief valve spring;
Depending on the engine the supply house should have a list. The last one I saw was from Crane-Cams

 

[MikeHalloran]

If it's really important that the plug not loosen, I wouldn't rely solely on assembly torque to do that, particularly where you won't be storing much energy in bolt strain.

At least use Loctite.

I'd try to turn the spacer/collar into a French lock.




Mike Halloran
Pembroke Pines, FL, USA

 

[JCReynolds79]

Well from the responses it looks like there is no obvious calculation I could be doing, which is fine. I am happy to do it up til it 'feels' snug (maybe 30 - 40 Nm) plus a bit with the addition of some Loctite.

I just wanted to run it past people here in case there were some obvious calcs I could run.

Thanks for all your thoughts and feedback.

MikeHalloran, I am curious as to what a French Lock is. I can't find much on Google about it. Could you possibly enlighten me?

Regards,

Jon Reynolds

 

[MikeHalloran]

A French lock is a malleable washer with ears or tabs.
After the fastener is seated, one ear is hammered up against a flat of the fastener, and another ear is hammered down over or into some feature of the substrate.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Here are some pictures of tabbed lock washers from Bokers,as MikeHalloran posted. The two tab ones are/was very common, especially the 2 eared one, which was called a cat ear washer. Around steam equipment they are called pant leg washers.
The last one of the French Locks I saw called out as such was used on the Chevrolet Caviar exhaust manifold.

http://www.bokers.com/tab_washers.asp