Bellville Lock Washer 1

[TChronos]

I'm designing an oil filter head for a six cylinder motor. The head will be made in two pieces, I'll be fastening them using low grade steel bolts. I'm thinking of adding a bellville under the bolt head to compensate for thermal expansion and contraction of the parts. I don't think locktite works for this particular joint, because it will need to be broken down from time to time.

 

[IRstuff]

Loctite is not exactly permanent; it simply resists unscrewing more than the friction does.

TTFN

FAQ731-376

 

[Bribyk]

As IRstuff said, you can get different strength grades of thread-locking compounds.

I take it your filter head is aluminum and you're worried about the difference in thermal expansion rates from the bolts. I've seen plenty of aluminum oil and coolant outlets that worked fine with standard bolts and no thread-locker. I would hazard a guess that there's a gasket in between these pieces as well which, being the least rigid part of the joint, will account for any change in the joint preload by deforming.

Use as long a bolt as you can to increase the joint's tolerance to thermal expansion.

 

[Bribyk]

Came across this today in NASA 1228 "Belleville washers are... used more for maintaining a uniform tension load on a bolt than for locking... [and] unless they have serrations on their surfaces, they have no significant locking capability."

 

[TChronos]

Thanks for the input, guys. The bellville washer would be hardened and serrated, that's easy enough.

The filter head componentes are aluminum, which is why I have a concern about thermal effects. The filter will be screwed into the outer half of the unit, which will mount horizontally. I need the bolt to hold snugly to maintain even compression on the o-ring, rather than the o-ring expanding to maintain sufficient tension on the bolt.

I'm not comfortable with using threadlockers, because this is being designed as a field replacement. Not sure I trust a mechanic of unknown reliability to apply the right threadlocker.

 

[IceStationZebra]

Obviously the bellville washer is just another spring. If you clamp it tight enough to flatten it, it becomes in essence a flat washer. For the sake of discussion lets say it takes 100 lbs of clamp load to flatten the washer, but the bolt is torqued so that it produces 200 lbs of clamp load. If the bolt loses clamp load, due to loosening or thermal expansion, the bellville washer does not help maintain clamp load until it drops below 100 lbs. After this point the clamp load will remain at about 100 lbs until the bolt loosens enough to unload the washer. So if you go this route you should choose a washer that collapses at 125-150% of the torque it takes to keep your O-ring joint from leaking.

As far as the threadlocker goes, you could supply a bolt with pre-applied threadlocker. Of course this doesn't get around your reuse issue though.

ISZ

 

[IRstuff]

This thread might be of interest: thread404-231093

TTFN

FAQ731-376

 

[Bribyk]

Can you tell us which engine you're designing this filter head for? From "field replacement" I read "stationary engine" and I think I might have an idea which make/series. I have one of these on my to do list and am interested if you're already designing the system (and selling?). We have customers requesting this for a particular engine but I haven't found the time to work on it yet.

 

[MintJulep]

The annulus of a hardened belleville is likely to damage the aluminum where it contacts.

As noted above, a belleville is a spring. It can be used to maintain relatively constant tension to compensate for thermal expansion. It isn't a locking device.

You might consider a pellet or strip bolt, or a stud and elastic stop nut.

 

[mkkessel]

Rather than bolts, can you redesign utilizing studs with nyloc nuts and flat washers?

 

[dicer]

So why won't the average spin on filter work?
What is the application? Meaning aftermarket performance, industrial etc.
Saftey wire it if your so concerned about it loosening. That is what is done in the aircraft world.

 

[richkeogh]

In the past I've used an aluminium housing with a steel threaded adaptor screwed and loctited into the aluminium head, that the filter will screw onto.
Never had any issues with unscrewing with thermal expansion, as long as the filter has been torqued up correctly.