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Hi; I am trying to start my old pre unit but does not want to cooperate.
I have spark; gasoline and compression (...) but no start
Checking by the plugs holes, I noticed that one of the exhaust valves is not "showing" all the traveling so I was trying to remove the inspection cap but is just almost seized there. Like welded.
Perfect hexagon to fit a wrench and now is just rounded almost useless, due to impossible to remove it! The other 3 can be removed in a breeze so I have now a more difficult scenario to try to move the damn cap.
I have a big wrench and did not moved a bit also I sprayed WD40 without any success.
What about warming the rockers? or could be even worst? though the only thing that I have to heat there is a hair drier.

Thanks

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boil the jug and pour hot water over it?

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A small dull chisel and hammer......gently tap the chisel on the outside edge to loosen it...Yes it will scar the cap that is already ugly


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I’d use a paint stripping hot air gun
Obviously taking precautions like tank removal

I came close to blowing myself up once, when a still red hot element on a switched off hot air gun got a whiff of butane

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They more usually come loose and get lost of their own accord. If a spanner won't hold on the hex, or even a pipe (mole) grip, then you must do as HB says.
They are readily available, though Uruguay may not be so straight forward.

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get out your set of 6 point box wrenches .
pick one thats close to your rounded over hex head mess , but a little smaller .
hand file 6 new flats using the 6-point wrench as a pattern .
Obviously you don't want to file off too much , but you do want six points to catch .

If you can get six points to catch you have a better chance of loosening the cover .
The only other alternative is a pipe wrench or
A set of vice grips like these .
these can grip the outside circumference lip ... without making too big of a mess
[Linked Image from m.media-amazon.com]
model# 04-12LC
Locking Large Jaw ... vice grips
Ideal for plumbers, mechanics , welders and britbike backyard Bodgers .

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My vote would be for a pipe wrench (Stilsons) if you can get them on there. They are designed to grip round pipes, so won't struggle with your rounded off hex. Just might be difficult to get them on properly and have a decent amount of rotation.

They will trash the cap, but sounds like that's the least of your worries.

Screenshot 2021-10-13 at 18.34.46.jpg

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reverb Offline OP
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Yes; in a distant past I had the 4 caps in iron (chromed) then with vibration came loose several times then lost them. Each time a buddy machined one for me in Aluminum; no more loosen caps. Do not know what happened with this one though.
The HEX was perfect so if I file to use an smaller wrench will be the same.
The problem that I see with a pipe wrench is that there is no space (thickness) on the HEX to put it so the best way could be use it on the edges of the cap but I so not think that remove it that way...
I do not have a heat gun only a hair drier as mentioned.
I need to remove it due I think something happened there with the valve etc

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Why not just pull off the rockerbox and work on it off the engine? You would probably save time overall and less likely to damage something else.

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...of course; but removing the rocker box out of a 48 is not as easy as in mine 79; included all the hassles about leaking oil of the iron head not so perfect surface and ultra thin rocker boxes then the problem with the pushrod tubes and on and on.
Then still the cap will be seized in the box and at this time I need to go to a machinist to makes another...

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How about freezing the cap. Pipe freeze or something similar. Might break the bond between the cap and the rocker box.

I would maybe try hot water on the rocker box then freeze the cap. I wouldn’t try it the other way round though as you might fracture something.


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Jeez, don't complicate it...A chisel and hammer it would be loose just like that....


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HB's right, the cap is already damaged. Just remove it with a dhisel. Subtlety belonged to an earlier stage, long past.

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...well; I can use a grinder too...
I am trying to not damage the threads of the box and the box itself
I will try the chisel etc Tomorrow and see if the box is too fragile to continue with that method.
Cannot believe that it did not moved a bit. The hexagon is for a 1 inch wrench, so is bigger than the originals; you know to in theory have an easy removing of the cap...

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...still seized there. Pipe wrench did not worked; Normal vice grips did not worked so I started with the chisel and hammer near the edge around the cap; still not worked and the cap is starting to looks very damaged. I am really concerned to not damage the box thread.
Cold welded?

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You just might have to carefully break it up in pieces. Sounds like you've tried everything else.

Some times the threads get damaged to the point the darn thing won't stay tight......but usually you just lose it because it falls out. I could see someone getting tired of it getting loose and using epoxy.......ugh.

You'll get it........it's not like replacements are that hard to find.

Gordon

Last edited by Gordon Gray; 10/17/21 12:33 am.

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Reverb:
“Yes; in a distant past I had the 4 caps in iron (chromed) then with vibration came loose several times then lost them. Each time a buddy machined one for me in Aluminum; no more loosen caps.”

Were caps on the early motors iron? I didn’t know that.

But your current caps have been custom made in aluminium, one at a time as needed.

So perhaps it is possible that this one cap was made with a slightly oversize thread which has somehow locked into the rockerbox thread? Just thinking.

I think DMad’s suggestion of removing the rockerbox might be the safest.
You could them drill out most of the middle of the cap, and then collapse the remaining outer.

You would need to get some new caps (or at least one) but in your situation you had might as well buy 2 or more sets.

I always thought they were the same on all pre-units.

The way I stopped losing them was to make clips that fasten beneath the lower nuts, that press onto the outer of the caps.
Ideally these would be made of a spring steel, but I made mine from thin stainless sheet (~1.5mm or so), and periodically at long intervals I have to tweak them to contact the cap.

Even if they have a small gap with the cap, they still prevent loss of the cap, even if it were to loosen enough to take up the gap. That’s as far as it goes.

I took the idea from the arrangement used on unit 500’s, which used a simpler spring-steel clip on the upper surface of the box, contacting the serrated edge of the cap.

Cheers.

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Hi Reverb, nit the clearest of pics, but you should be able to get the idea of what I was describing in my previous post.

[Linked Image from i.postimg.cc]

Cheers.

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Hi Gordon; this is a 48 pre unit; yes; are hard to find.
Hi Koan; as mentioned, actually is more complicated to remove the boxes in the 40s pre units. I have the boxes "oil tight"...and that is a veeery difficult thing with this older worn out engines. I did not remember how I did it but I spent time for sure. That is what I do not have right now. For the free time I need to work on other 2 engines.
Sadly the cap was perfect. These caps are not flat like those; have a dome and are more bulbous. The hexagon is for a 1 inch wrench.
Cut it with a grinder is what remains...but I am afraid of that way might be the threads still could be welded there so even more difficult to remove the pieces and no cap to prevent oil leaking...I mean; both threads there and an open rocker box hole

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I've switched to Viton orings for the rocker caps and find that they stay perfectly oiltight and it seems to grip and not come loose. I've also tried them this season on my 71s little side tappet inspection holes and fully expected them to leak but so far so good!


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Originally Posted by reverb
Hi Gordon; this is a 48 pre unit; yes; are hard to find.

OUCH..........yes, I know nothing about parts availability for earlier bikes. But it sounds like you will have to replace it anyway.

Never had that problem but I feel your pain.

Gordon


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Hi Reverb,

I don’t understand why that rockerbox would be so difficult to remove, is it just the resealing of the gasket area that concerns you?

Anyway, if you’re determined to keep the box in place, then I can see only 2 realistic approaches:

1 – chiselling, but rather than using a sharpish chisel from the beginning, you need to prepare a surface for a blunt drift to hit. This could be done with a file or careful work with a small sharp chisel. This will give the drift better impact transference with short, sharp Shocks.
If this doesn’t work, then

2 – cutting/grinding the cap into pieces so that you can collapse the remaining threaded collar enough to release its grip. I cannot imagine doing this without much horrible material getting into the engine (including grinding wheel abrasive particles, if you employ such a tool). Even hacksaw blades and files leave nasty bits, that’s why they wear out.
If I were to do this (which I wouldn’t) then I would want to strip the entire engine, not just the rockerbox.


If the chiselling method in #1 above doesn’t do the job, I would just bite the unpleasant bullet and remove the box, get the job done and worry about resealing the box afterwards. You may come to regret taking a shortcut because of lack of time.

Unless you are going to get another unusual cap made, it is likely that you will need some new standard caps.

I believe they are the same for all pre-unit models (other than 3T) from the very beginning to 1962. The parts manual for 47/46 shows them as E1564, and they look the same as the ones in my 1960 engine, which have the same part number.
No where are early iron caps mentioned, I am doubtful such things ever existed.

Those caps are readily available in the UK, I would imagine that CBS and many others would have them in the Americas. Of course shipping to Uruguay may have its difficulties/delays.

Apparently the caps are also used on some other models and marques, as mentioned in these links:

https://www.aceclassics.co.uk/products/pre-unit-triumph-rocker-box-caps-e1564-1938-1962/

https://www.feked.com/triumph-pre-u...-sump-plug-on-unit-350-500cc-models.html

Best of luck!

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Sounds like the threads are galled. If that’s the case, you should start shopping for a replacement rocker box for the least hassle.

Chris

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It appears that early original valve adjustment cap covers were diecast , making the nut part hollow .
... but if it's an after-market cap ... there's a good chance then raised nut part is solid ...
if so ... you could ...
drill a quarter inch hole ( or metric equivalent ) straight across the center of the rounded over nut
to allow you slide a Phillips head screwdriver into and across the nut
The screwdriver blade and handle will provide a lot of extra Leverage to un-twist the cap
Extra /extra leverage can be added with some judicious Taps of a hammer .

Last edited by quinten; 10/17/21 6:36 pm.
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“It appears that early original valve adjustment cap covers were diecast , making the nut part hollow”

I wouldn’t doubt that, all the ones I’ve seen and bought since 1976 have looked the same. You can see the remains of the sprues on them.

Reverb’s custom-made replacements were possibly made in a higher dome shape so as to keep the hex solid (the hollow allows a bit of space for the top of the valve adjuster, as well as saving metal money in production).
If so, then your idea of drilling across the hex for a torque handle will be a good one, though I’d doubt it could be anything like a quarter inch, unless the hex is an organ-stop of a nipple.

If Reverb would show us the inside and outside of one that he can remove, then we would have more idea of what we’re dealing with.

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