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#735822 05/19/18 12:09 pm
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Dibnah Offline OP
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Afternoon All

Reassembling the front (started as just tyre replacement and then escalated), taking the opportunity to change the fork oil.

The manual states ATF, I have in stock on the shelf:
ATF
15 weight Silkolene fork oil
20w50 engine oil
10w40 engine oil
5w40 engine oil
5w30 engine oil

Is the 15 weight fork oil too heavy?

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As long as it's fork oil I think it's a matter of personal preferance. I have a 15w and a 30w. Can't remember what's in what. The manual 46 years old. There are better products available today.

Last edited by desco; 05/19/18 12:50 pm. Reason: addition

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I like thin oils, I find the added comfort is worth the sometimes too fast rebound.
My 72 Trident forks have had their innards modified by Richard Darby and can’t really be compared to the standard issue, I use 5 weight fork oil, but find 10-15 better on standard forks.
By the way, I can really recommend Richard's mod. I am however toying with the idea of fitting “emulators” for a degressive dampener action.

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Dibnah Offline OP
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Thanks Stein and Desco, I'll use the 15 weight SIlkolene fork oil

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HI Dibnah, I have '73 Tiger which as basically same fork. I did a lot of experiments with fork oil. I used Belray fork oil. Like motor oil, fork oil is a can of worms.

Comparing ATF to fork oil on road, to me ATF feels like 7.5w fork oil.

10w fork oil felt way too stiff for me. Harsh ride & wanted to chatter on fast bumpy curves. I felt dangerous.

5w felt much better on my bike. I'll say way better in every way. Gave me a good 5mph more safely in same curves. I had a road test route to evaluate.

You weight will make a difference too. I'm 160# ready to ride. The heavier you are the deeper into springs you'll be & thicker oil will not stiffen ride as much. Still my hunch is 15w will be too harsh.

How does motor oil compare to fork oil on weight? Seems similar from my tests of flowing oil through a pin hole in cup & timing flow.

Going from 7.5 w to 5w in these forks makes a very decided difference. With springs removed you can feel it just pumping forks by hand. On road very easy to feel.

I would recommend use what feels thinnest you have. If you felt forks were rough or harsh I'd buy 5w fork oil. I used Belray because it's sold close by & many said it was good. Other brands 5w may feel different, I don't know.

Not a huge job to change so have so fun experimenting. Removing drain screws & pumping forks will indeed remove all oil.
Don


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Dibnah Offline OP
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Thanks Don

I'm a sturdy but svelte 215lbs or so ready to ride, I blame the beer and the pies.

All front end fixings loose, poured in 190cc of the Silkolene 15w fork oil, fork caps on, bounce the forks a few times, tighten all fixings working downwards, tighten mudguard/fender fixings. Forks seem OK with the bike at rest but topping out on rougher roads. Operation under compression seems OK.

The old oil I drained out was a lot thicker, about 30W I would estimate, although age and use uncertain. Would thicker oil reduce topping out?

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Not so sure about that, these forks seems to top out no matter what in my experience.
I notice TR7 Don is with me on thin oils, but with you being a full grown beefeater you may want to start with a 10 grade fork oil? I’m about 200 lbs net and 215 “on the road” and find 10w ok for a standard fork.
Bear in mind that new seals will add to the dampening by increasing the static friction. The surface finish on stock Triumph stanchions isn’t comparable to anything new, and it may take a few thousand miles for them to achieve a smooth surface. It usually happens just before the chrome is worn out...

Last edited by Stein Roger; 05/21/18 7:20 am.
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Thanks Stein. It is possible that the 15w oil is preventing the forks initially compressing when hitting a minor raised bump, meaning that the forks are fully extended when the front wheel rides off the raised bump and into a depression = "clang", if that makes sense!? The bike has US style bars.

I'll try some 10 weight fork oil.

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If so, there's a least one other problem. The majority of forks have bump stop capability. Some work better than others. I personally like bump stop springs and they always do the trick, but done hydraulically, it can be overcome by too fast or too slow movement. When done hydraulically, there is usually an oil pathway that is occluded by the moving parts right before contact is made. This pathway can be modified if necessary. In some cases, the parts have possibly been assembled incorrectly as is possible with the Triumph steel forks.

Cheers,
Bill


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Thanks Bill

I tried the bike with no oil in the forks, no "clanking". Poured in 10 weight and there is a "clank" over one bump on my backroads test route, the forks almost certainly topping out. I'll run it as it is for a while, probably change to 7.5 weight at a later date.

60-0779 fork top nut spanner is useful

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When changing fork oil remove RHS top nut, remove LHS drain screw, doing opposites stops oil gushing out the top as the bike settles.Read that in the manual, after doing it wrong for years, this saves a lot of mess. I like to flush the old oil with a little kerosene to get the last of the muck out.
I use 10 W in my 71 forks, have tried ATF and 20/50, prefer 10.


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Originally Posted by gavin eisler
When changing fork oil remove RHS top nut, remove LHS drain screw, doing opposites stops oil gushing out the top as the bike settles.Read that in the manual, after doing it wrong for years, this saves a lot of mess. I like to flush the old oil with a little kerosene to get the last of the muck out.
I use 10 W in my 71 forks, have tried ATF and 20/50, prefer 10.


i never thought of that.


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Dibnah Offline OP
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Originally Posted by gavin eisler
When changing fork oil remove RHS top nut, remove LHS drain screw, doing opposites stops oil gushing out the top as the bike settles.Read that in the manual, after doing it wrong for years, this saves a lot of mess. I like to flush the old oil with a little kerosene to get the last of the muck out.
I use 10 W in my 71 forks, have tried ATF and 20/50, prefer 10.


Thanks Gavin

For the first draining, I had the forks off the bike to change the gaiters (again), now using gaiters supplied by Norton Andover.

The biggest issue I have with "wheel off the ground" works is the lack of centre stand, it's been on the list for a while, £99 or so. My 40 year old cantilever tool box with some wood on top supports the bike adequately, albeit not as convenient as a centre stand.

I used a gigantic yoghurt carton for the second draining, the oil probably tasted better than the rancid cow's milk that previously occupied said carton.

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I'm with TR7RVMan in 5W fork oil + plastic rings exchanging orings in my 73 front end.
Sticking terrible before a change and giving really jarring ride on orings and ATF.

Last edited by Adam M.; 06/02/18 5:44 pm.
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A good test for the forks yesterday evening, an approaching Audi driver obviously thought I should use the verge on a single-track road, said verge had two big potholes, I thought I was going over the bars, but the trusty TR6 took it all in its stride. US bars and standing on the pegs helped.

It's at times like that i have visions of Apache + Hellfire. What is it with Audi drivers in the 21st Century?


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