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#381863 - 07/01/11 2:21 pm Pre unit fork damper  
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machico Offline
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Does anybody recognize this type of pressure tube valve body for the pre unit front fork dampers? confused


They are from my pre unit front forks for mid 50's swing arm models. I have never seen this type of valve bodies before but are they factory original parts? There are 4 holes. I think the parts number is H1012.


The top one looks familiar to me. The valve body has 2 smaller holes.

Thanks,
Machico

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#381875 - 07/01/11 3:47 pm Re: Pre unit fork damper [Re: machico]  
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Deadstiffcatt Offline
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I recently had a set that had the four holes- the front end they were in was the early non clamp type lower legs- pull the axle to remove wheel. Circa 1948-1954. my 1954 parts book shows a pssible p/n of H 395 body, pressure tube valve.





#381886 - 07/01/11 4:28 pm Re: Pre unit fork damper [Re: Deadstiffcatt]  
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machico Offline
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Originally Posted By: Deadstiffcatt
I recently had a set that had the four holes- the front end they were in was the early non clamp type lower legs- pull the axle to remove wheel. Circa 1948-1954. my 1954 parts book shows a pssible p/n of H 395 body, pressure tube valve.

Deadstiffcatt,

Thanks for the pics. My front forks are same type as yours. The oil seals are felt type. But the shape of the valve bodies is a little bit different than mine. I think these forks had been used until 1956. I thought the fork parts were all same so i checked my 1956 parts book only and it shows H1012 for 1956. I checked my 1955 parts book again. It shows H395 which is same as yours. I have no idea what the differences are. confused

I think mine is for TR5 because the fork tube doesn't have the oil filler holes. Do your inner fork tubes have the oil filler holes too?

Thanks,
Machico

#381893 - 07/01/11 4:56 pm Re: Pre unit fork damper [Re: machico]  
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Deadstiffcatt Offline
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The filler hole and bolt was used on the nacelle models, to ease filling the forks with oil. Many replacement fork tubes are found without this hole, as so many nacelles were removed.
Mine had them, BUT they were aftermarket, filled, and needed to be drilled for use with a nacelle. So if your fork tubes are very old, a very good possibility they are tr5. The parts book for 54 shows same part number used for 5t, 6t, tr5, t100, t110, however, there are two part numbers listed for the Pressure Tube ASSEMBLY- H521 for tr5, H521A for the other 4 models. It also lists different springs and stanchions for the tr5 versus the other 4 models. Guessing perhaps longer?

Note, usually the line drawings are quite good and show the tiny little holes, in my parts book they do not on either picture of the pressure tube body, but they do show the tiny little dot (bolt hole) for the nacelle models oil filler.

Hopefully Hawaiian Tiger will chime in, I think he would know this one!!

#381899 - 07/01/11 5:18 pm Re: Pre unit fork damper [Re: Deadstiffcatt]  
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Deadstiffcatt Offline
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Two notes from Bacon's book:

In 1956, the bump stop in all fork legs was modified. This MAY have had an effect on the dampner....

In 1957, the the 3TA had the internals changed to provide two way dampning- could this be the reason for the hole differences? If so, again, they MAY have used it on other models.

They did use this type lower leg up til 57, so some internal mods easily could have been in effect by the time they switched to the cap type legs.

(And who thought just the boys over at Honda had fun changing internals every 3 months of a production year? laugh )

That's all the info I can dig up. Let's see what H T can add.

#381967 - 07/02/11 2:04 am Re: Pre unit fork damper [Re: Deadstiffcatt]  
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machico Offline
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Deadstiffcatt,

Originally Posted By: Deadstiffcatt
The parts book for 54 shows same part number used for 5t, 6t, tr5, t100, t110


The parts book for 55 56 shows same part number used for 5t, 6t, tr5, t100, t110 too even though the drawing of the valve body looks different.



This makes me more confused. confused

Originally Posted By: Deadstiffcatt
there are two part numbers listed for the Pressure Tube ASSEMBLY- H521 for tr5, H521A for the other 4 models. It also lists different springs and stanchions for the tr5 versus the other 4 models. Guessing perhaps longer?

Yes, you are right. I looked at my parts book again.I didn't know that there were differences which you pointed out.

Btw, I have 3 sets of dampers. one set for later pre unit(1957-1959), one used set for early pre unit(46-56), and the reproduction dampers for early pre unit(46-56). The length and dimension is pretty much the same except for the valve bodies.



Thanks,
Machico

#381971 - 07/02/11 2:29 am Re: Pre unit fork damper [Re: Deadstiffcatt]  
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machico Offline
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Deadstiffcatt,

Originally Posted By: Deadstiffcatt
Two notes from Bacon's book:

In 1956, the bump stop in all fork legs was modified.


Ah, Now I understand why the valve body looks different. So the tapered valve body is for the bump stop,,,,am I right? According to the drawing in 1956 part book, I noticed that the tapered valve body except for trophy model was added from 1956. Before 1956, the drawings of the valve body for all models are not tapered but straight and flanged. The reproduction dampers must be copied from the newest damper design in 1956.

If so, my dampers may be for not only TR5 but other models if the drawings in the parts books are correct. But Do all dampers before 1956 have 4 holes??? confused

Thanks,
Machico

Last edited by machico; 07/02/11 2:30 am.
#381983 - 07/02/11 4:25 am Re: Pre unit fork damper [Re: machico]  
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Deadstiffcatt Offline
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Originally Posted By: machico
Deadstiffcatt,

Originally Posted By: Deadstiffcatt
Two notes from Bacon's book:

In 1956, the bump stop in all fork legs was modified.


Ah, Now I understand why the valve body looks different. So the tapered valve body is for the bump stop,,,,am I right? According to the drawing in 1956 part book, I noticed that the tapered valve body except for trophy model was added from 1956. Before 1956, the drawings of the valve body for all models are not tapered but straight and flanged. The reproduction dampers must be copied from the newest damper design in 1956.

If so, my dampers may be for not only TR5 but other models if the drawings in the parts books are correct. But Do all dampers before 1956 have 4 holes??? confused

Thanks,
Machico


It appears that the tapered valve body would indeed be for a certain type of valve stop, as the shape would also have an effect on the dampening. From experience with front ends, unit and preunit, there are definitely different types of valve stops, as well as restrictor tubes.

Can't say for sure on the 4 holes, as this becomes a question of, "If memory serves me right........"

Don't have enough detailed first hand knowledge still tucked in my brain,(over the years remembering the difference between what-had-2-itty-bitty-holes and what-had-4 gave way to the let's-just buy-the-damn-parts-book-and-look-it-up-when-I-need-to....); and what written info I could find hasn't supplied any further knowledge.

Now to have a little bit of fun regarding ancient knowledge- I had an old 60's Ford van with an inline six. I needed to know the spark plug firing order. Asked the old codger at the parts shop years ago, and he told me, "Too young, Too old, and Just right."

What does that make the firing order? crazy

(Point being-some knowledge that was easy to access because in 1956 everything was still fresh and a simple phone call to the distributor or even your mechanic could get an answer, today there will be fewer left alive that will have the answer to questions as simple as yours.)

I do hope some of the others on the board have a bit more knowledge regarding your question, now that you have made me curious, I wanna know too....!

By the way, the correct firing order answer is.............

#382332 - 07/04/11 12:14 pm Re: Pre unit fork damper [Re: Deadstiffcatt]  
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machico Offline
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I asked old triumph guy who has bought a brand new pre unit triumph in 1961. I'm not sure if his opinion is correct or not but here is what he said.

The fork oil was not available during 50's. So the engine oil had to be used for front fork. Only thickened oil such as SAE 40 or 50 was available at that time. That's why the 4 bigger holes were needed.

However, according to the lubricant chart in work shop instruction manual, triumph recommended SAE20 for front fork. The thinner oil should be available.

I'm getting confused again. confused

Thanks,
Machico

#382371 - 07/04/11 4:55 pm Re: Pre unit fork damper [Re: machico]  
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Deadstiffcatt Offline
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That's what I mean by, "If memory serves......"

It partially makes sense, but still doesn't answer your basic questions of when and which models.

On another fairly recent thread, there is a little discussion about oil thickness, particularly trans oil- basically pointing out that today's oils are thinner than 40 years ago.

"However, according to the lubricant chart in work shop instruction manual, triumph recommended SAE20 for front fork. The thinner oil should be available." Ah, the time warp! Key wording is "should HAVE BEEN available."

As a young gas jockey in the early 70's I remember selling CANS of 20wt through 40 wt, as well as 10w40. (What 20w50 or 5w30? Many of the modern grades did not exist at that time! FORK OIL? That new fangled stuff ya get at the Honda shop????)

Taking that and combining it with what your friend says leads us more to the function of those holes and their relationship with the oil. He is correct that those holes are a metering device. As the fork compresses, the oil is squished out those holes, and the number of holes, combined with their diameter and the thickness of the oil would help determine 'cush rate'.
(Please excuse me if I don't use formal mechanic terms.)

Some of the more advanced racers of the time would use any combination of the above- number of holes, size of holes, and oil grade to achieve just the right amount of cush for their own personal use. The springs themselves, although a matching pair bought brand new, could have minimally different compression rates due to the manufacturing process, adding another factor. So the real nutcases would work all four points together, and in some cases would run, as an example, 30 wt in one tube, and 40 wt in the other to achieve their desired balance in individual fork operation! (Picture a race being run in a basic oval. In an extreme example, one fork would always be toward the inside of the track, and COULD have a tendency to absorb more of the compression of the forks, especially on the turns, depending upon a rider's individual style.)

So I know this still doesn't answer the original question, but perhaps the above illustration will shed just a little light on part of the WHY of 2 holes, no holes, or 4 holes. I don't have a copy of a 1950, 51, 52, or 53 parts book, but I wonder if one would show the little itty bitty dot representing the holes that we don't see in our later copies.

Hope the 4th is treating you well! I'm happy that I can darn near walk normally again after two weeks of evil and wicked spider bite, still feel like I've got a 2" circle of 1/4" thick leather stuffed between the kneecap and my skin, but the bad stuff is gone and it feels GREAT to be able to stand in the shop and work again! Definitely a good 4th for me!!!! Cheers! Joe

#382373 - 07/04/11 5:01 pm Re: Pre unit fork damper [Re: Deadstiffcatt]  
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Deadstiffcatt Offline
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P.S......... 15, 36, 24, too young, too old, just right.......1-5-3-6-2-4!!!


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