Lotus Elan

Oil gun for trunnions

PostPost by: MarkDa » Wed Feb 28, 2018 3:35 pm

Isn't grease basically thickened oil?
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PostPost by: JonB » Wed Feb 28, 2018 5:24 pm

Bit more to it than that, I think. I'm no expert, but I believe it has soap based agents to help it maintain "greasiness" and this stuff dries out (or maybe the oil content does) over a period of years leaving a waxy, cake-like cruft that looks like dried earwax - which I had to scrape off my trunns, and which indicated to me they hadn't been lubricated in, well, years. :roll:

Not to kick it all off again, but my reading says that thick grease can be displaced from the trunnion causing voids which (subsequently) collect water. As Rohan says, the trunnion top seal is basically ineffective here, and I'd say that is true whether you lubricate with grease or oil. Yet since oil is runny, it will be pulled down into the trunnion by gravity and stay there, whereas displaced grease will not. Flip side is that grease will help the top seal do its job, but oil won't. Pros and cons.

That said, I think that the choice of grease or oil is less important than the regularity of service. In other words, if you pump the trunns full of [insert lubricant of choice here] really often, and displace any water or dirt that got in there since you last did it, you should be OK. If you accept that, the only decision you need to make is "how often", and I'd say monthly during the summer and fortnightly in winter, assuming average mileage. And definitely just before laying the car up in winter, if that is your normal usage pattern.
Last edited by JonB on Wed Feb 28, 2018 5:36 pm, edited 1 time in total.
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PostPost by: ericbushby » Wed Feb 28, 2018 5:32 pm

" Once a month" !!.
I do mine once a year without fail.
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PostPost by: JonB » Wed Feb 28, 2018 5:40 pm

It's a personal choice, Eric and I am not saying you are wrong.

However... after reading several horror stories of catastrophic king pin failure due to corrosion, I concluded that there is no such thing as "too often" with these things. It's a pity the design doesn't allow you to dismantle the trunnions for inspection very easily (the brake rotor prevents this, so you need to remove the caliper and hub first), otherwise I'd be doing that annually myself.

I am probably being over cautious. That comes with middle age. I try not to think of all the Spitfires I drove in the past, blithely ignoring the condition of the trunnions... and I did some pretty epic miles in one of them.
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PostPost by: MarkDa » Wed Feb 28, 2018 6:27 pm

I'd certainly agree that regular maintenance is the key to long life - goes for most things and people I reckon!
For what it's worth the workshop manual says check suspension for tightness every 3k and lubricate (now there's a neutral word!) every 6k so that would be twice a year in the day.
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PostPost by: joe7 » Wed Feb 28, 2018 8:56 pm

Checked my manual under "lubricants" and it references several brands (BP, Mobile, Shell etc) of 90 oil for the swivels/trunnions.
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PostPost by: JonB » Wed Feb 28, 2018 9:05 pm

Thread is drifting off topic and I played my part.

Apologies to the OP.

For my trunnions I bought a small, cheap grease gun similar to the Clarke model previously mentioned. My plan is to use EP90 as I had seen a good video on YooToob that demonstrated using a standard grease gun to push oil into a Spitfire trunnion. It made a bit of a mess, so the guy demonstrating it laid a rag under the joint, covering the bottom of the wheel. You could see all the dirt being pushed out of the top seal by the grease gun pressure. He continued until the oil ran clear, then used the rag to wipe up the excess.

I think it took about three minutes, if that.
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PostPost by: Orsom Weels » Thu Mar 01, 2018 9:31 am

Being a Norton Commando owner & also having a couple of Seagull outboards, I always have a bottle of 140 oil on the shelf, & this is what I have been using in my trunnions for many years now. The oil is thick enough to stay in a Seagull gearbox which has no seals, just relies on the fit of the shaft in the bush & the water pressure outside to keep the oil in, & 'runny' enough to wick through a Commando swinging arm spindle & keep both ends bushes well lubricated. I use a Wanner grease gun to pump it in to both the Commando swinging arm & the Lotus' trunnions, & as long as I take the spring tension off the plunger with the chain, the oil stays in the gun in storage with no mess at all. To use, I just release the chain, clip the guns end on the nipple & give a couple of pumps every now & then. Works perfectly for both applications.

wanner-grease-gun.jpg and


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PostPost by: rgh0 » Thu Mar 01, 2018 9:37 am

As long as it is a stiff enough water proof grease to help seal the top of the trunnion and prevent water migration down the threads, then what type does not really matter as from a lubrication perspective almost anything will work on what is a relatively lightly loaded and slow moving bearing surface.

A conventional No2 lithium soap based grease works fine semi liquid greases or blends of grease and oil will all work from a lubrication perspective but are probably not as good from the water ingress prevention perspective.

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PostPost by: rgh0 » Thu Mar 01, 2018 9:42 am

MarkDa wrote:Isn't grease basically thickened oil?


Grease is basically oil combined with a hydrocarbon soap that bonds to the oil and holds the oil within a stiff matrix and stops the oil flowing out. The oil within the grease matrix is what does the lubrication

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PostPost by: JonB » Thu Mar 01, 2018 9:48 am

@Rohan

Seems to me that all lubrication options being equal, one may as well use grease in order to benefit from the improvement to the top seal's function. Just need to remember to service them regularly.

Here's a question, though (with apologies to the OP). When steering, the thread is turning into the trunnion or out of it. This compresses the grease slightly, then uncompresses it. Doesn't that mean the top seal is going to be compromised quickly? After all the grease has nowhere to go other than up, and wouldn't it tend to push the seal off the top of the trunnion? Then, when the wheel is turned the other way, so the thread is unscrewing, wouldn't that tend to draw water and dirt into the joint? Or more likely, contaminated grease?

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Last edited by JonB on Thu Mar 01, 2018 9:57 am, edited 1 time in total.
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PostPost by: rgh0 » Thu Mar 01, 2018 9:50 am

JonB wrote:Bit more to it than that, I think. I'm no expert, but I believe it has soap based agents to help it maintain "greasiness" and this stuff dries out (or maybe the oil content does) over a period of years leaving a waxy, cake-like cruft that looks like dried earwax - which I had to scrape off my trunns, and which indicated to me they hadn't been lubricated in, well, years. :roll:

Not to kick it all off again, but my reading says that thick grease can be displaced from the trunnion causing voids which (subsequently) collect water. As Rohan says, the trunnion top seal is basically ineffective here, and I'd say that is true whether you lubricate with grease or oil. Yet since oil is runny, it will be pulled down into the trunnion by gravity and stay there, whereas displaced grease will not. Flip side is that grease will help the top seal do its job, but oil won't. Pros and cons.

That said, I think that the choice of grease or oil is less important than the regularity of service. In other words, if you pump the trunns full of [insert lubricant of choice here] really often, and displace any water or dirt that got in there since you last did it, you should be OK. If you accept that, the only decision you need to make is "how often", and I'd say monthly during the summer and fortnightly in winter, assuming average mileage. And definitely just before laying the car up in winter, if that is your normal usage pattern.


Jon
I agree regularity of service is important. However I don't see how voids are created in the grease. as the trunnion is full of grease with no air. An air pocket could only be created if the grease was forced out the top which it does not. Even if voids are created it would not matter, think of your wheel bearings they are lubricated by grease and there are lots of voids as the bearing cannot be filled fully with grease like the trunnion can.

If you pump out the used grease in a grease filled trunnion the initial amount that comes out is discoloured from water but the subsequent material is translucent like new grease. This demonstrates to me that the grease does form an effective barrier to water penetration. On the other hand with an oil filled trunnion, the water that gets in will sink to the bottom and build up and start to corrode, when you pump in new oil you may not displace that water :shock: and it continues to sit there and corrode

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PostPost by: JonB » Thu Mar 01, 2018 10:00 am

Now that's a very good point, Rohan.

What do you say to my last post? Is it possible the pressure caused by screwing the king pin in and out of the trunnion through steering can displace the grease at the top of the trunnion?

I'm beginning to think grease is a better approach!
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PostPost by: rgh0 » Thu Mar 01, 2018 10:16 am

JonB wrote:Now that's a very good point, Rohan.

What do you say to my last post? Is it possible the pressure caused by screwing the king pin in and out of the trunnion through steering can displace the grease at the top of the trunnion?

I'm beginning to think grease is a better approach!



In my experience it does not , the grease stays fully filling the trunnion, the small movement of the volume inside the trunnion is accommodated by the grease pushing up or being sucked back down, try filling a grease gun tube fully and then watching what happens if you put a rod into the grease. You will see the grease push up as the rod goes in and suck back down as you pull the rod out. The volume change in the trunnion is very small in comparison and is slow to occur and is easily accommodated by grease flow and the seal flex. Any contamination is very small and will stay trapped at the top by the grease just under the seal. Oil will move in the same way but if any contamination is drawn in it will then be able to sink down through the liquid oil.

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PostPost by: JonB » Thu Mar 01, 2018 11:50 am

Grease it is, then.

:D
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