What is a trunnion?

[JimB]

Numpty question - sorry.

 

What exactly is a trunnion - I have wanted to know for ages but never got round to asking.

[Crudders]

It's a threaded swivel joint Jim, usually brass and filled with grease or heavy oil. The vertical link or upright has an external thread and the trunnion has a matching internal thread.

 

It's a legacy from the small Triumph (Herald/Vitesse/Spitfire/GT6) range of cars from which our 7s take their front suspension. Most modern cars, including later Caterhams, run a spherical bearing.

 

If I've typed this before anyone else has replied I'll be very surprised

 

Crudders

 

Edited to add that although 'our' trunnions are threaded it doesn't necessarily follow - you can have a smooth trunnion in which a kingpin upright swivels for example.

 

 

Edited by - Crudders on 26 Apr 2006 13:00:05

[Crudders]

Well, you could knock me down with a feather

 

Crudders

[Sheds Moderator]

I'm surprised too Crudders. Good explanation, and I'd add that its purpose is to act as a joint that allows pivoting in 2 axes.

[Dave Rothwell]

Wasn't failure of the trunnion the reason why you were always seing Morris minor 1000's at the side of the road with a front wheel cocked at a crazy angle (going back a few years). ??

 

Who needs a Helmet - Get an Affro !

Clickhere to see Car and AFFRO !

 

Member 6790

Superlight 0075 - K7 LYT

[Tom_C]

Yep, exactly that, so keep them oiled.

 

 

Cheers

 

Tom

 

FH54WLX - only the car supports ManU, honest!

 

see here

[irrotational]

more than you ever wanted to know! :-

 

http://en.wikipedia.org/wiki/Trunnion

 

---

this is a local sig for local people!

[MartinS]

Most modern cars, including later Caterhams, run a spherical bearing.

 

Hi, quick question hopefully, do these spherical bearings ever need lubrication? If so, what should I squirt on them?

 

M.

 

Martin Saunders

ohh, is it upgrade time? :)

[Crudders]

Hi Martin,

 

You'll probably get as many ayes to the right as nos to the left on that one

 

As I understand it though (prepares to duck for cover) they are designed to be self lubricating and do not need any help in that department - any grease or oil added may lubricate the joint but will also attract damaging grit.

 

I haven't done any mileage on mine yet but intend to leave them alone.

 

Crudders

[Andy A]

 

We had an old Hillman Super MInx (lovely) that went trunnions-up in a multi storey carpark!

 

BOSS - 2 axes???

 

 

[J A T Richardson]

thx for all the feedback. Additional question: I've been told NOT to put grease in the trunnions - but they have a grease nipple on them? I've tried putting oil in a grease gun to lube them - doesn't work and VERY messy. The only other way I know is to undo them, unscrew them, fill and reassemble. Pain. Is there any other way of doing it, or can I just use grease?

 

Stinky toy driver - and proud of it!

[Sheds Moderator]

Yes 2 axes, at least in the Spit/Caterham 7 application. One axis is up and down the thread, the other is the top hat bushes that allow the wishbone to pivot. They are 90deg apart.

 

Interesting- are there trunniaeae that have only one axis, ie turning the thread only?

[Normans_Ghost]

JATR, you should fill a grease gun with 90EP gear oil. This will not run out and can be pumped into the trunnion. You may need to "seal" the bottom which has a core plug but often leaks oil. If you clean the core plug (the round penny size disc) and put some thick super glue around the edge to stop the oil running out.

 

When you have finished drian the oil from the greas gun.

 

ed to ad that if you turn the wheel from side to side when pumping oil in all the better.

 

Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here

You and your seven to The French Blatting Company Limited

 

Edited by - nverona on 18 May 2006 12:25:01

[Sheds Moderator]

I have found filling them with oil like this, then grease a few weeks later, and repeating regularly, gets you round the problem of the oil leaking out of the bottom and/or the grease drying up. A mixture of oil and grease does neither.

[susser]

I've added another description of the use of Trunnions;

Having nothing to do with cars, but more to do with Chemical Engineering.

susser (1/2 🙆🏻d Chemical Engineer)

[Mark Gregory]

BOSS: Would that be called 'groil' or 'oise'?

[Sheds Moderator]

😬 Should have known you'd be along Mark, any mention of a thread and he's off.

 

ISTR I put some CV boot slime in mine in the past, certainly it was as black as the ace of spades when it eventually wore out and I replaced it.

 

Oh, and I reckon "groil" sounds much better. 😬

[Mark Gregory]

Whad-da-ya mean? You were there well before me & I never mentioned the thread. Anyway, what's all this stuff about trunniaeae??

I think I prefer groil, sounds like a cross between groin & gruel..............the mind boggles! 😬

 

BTW, the Grads are at Cadwell on the 27/28th May (testing/racing).

[Sheds Moderator]

😬 I'm in Slovakia on 27 May. Tough life I know, but then I am unemployed. (actually I'm still on full pay, but that won't last for ever)

 

Trunniaeae, trunnia, trunnii, who knows. I'm certainly not going to start calling them anything as boring as "trunnions" when I have an alternative.

 

Going out to the shed now to mix up some groil. Sounds like something from Macbeth.

"Groil from longdead reptile's head, fresh found in Battered's shed...finger of birth-strangled babe, ditch-delivered by a drab..."

[Andy A]

 

Battered old Shakespearean,

 

2-axes - I guess so in the tri/moggie/cat case. Not strictly generic trunnion functionality methinks?

In fact never considered running along the trunnion as significant. It almost seems its meant to lean the vehicle into the bend?

 

 

 

[Sheds Moderator]

I think it is meant to induce geometry change on turning, yes. Will depend on kingpin angle of course.

 

OED has "cylindrical support for cannon, mortar or sim" which gives the shape but not the threaded bit.