Datsun Roadster Forum-311s.org

I am replacing some timing components on a U20 and noticed that there are two different upper tensioners.
One is a little higher (bigger body, so less shims are needed and more stable in the base) and sits in a little more up position ( angle up, which seems the chain sits better on the shoe).
Gaskets that are now sold fits better on this type.
The other is the one that is now still available at the vendors, base is smaller, more down position, not so nice on the chain and not so good fitment of the outer gasket.
Also the shoes can't be changed between these two as the round base is on a different position.
Does somebody knows when this was changed by Nissan?
Will make some pics later to show.

Which new Nissan part number are you showing?

Interesting, I wonder if one of those is for another application that just happens to bolt up. Nissan has never listed a second part number that I’m aware of, that said it could be from a different Nissan engine and happens to bolt up.
Dave

Clearly a difference in look, but I wonder how much in function. I looked at the pics just posted by AmishRoadster under "Engine rattle...." and it appears that his pad slides against the chain a little closer on the leading edge than one and a little less than the other you posted (different, more extended position however). It is interesting but unless those with more experience than I disagree I think they will function exactly the same, and it appears the more the piston extends the closer to the lead edge the fitment may be. Nevertheless, I'd probably use the one that appears to fit "better." Only other thought is along the line of "can the chain more easily catch the edge of the tensioner and somehow damage it." Probably not.

david premo wrote: Wed Apr 12, 2023 9:27 am Interesting, I wonder if one of those is for another application that just happens to bolt up. Nissan has never listed a second part number that I’m aware of, that said it could be from a different Nissan engine and happens to bolt up.
Dave

Already found 4-5 of the large ones between my used parts.

Just checked my stash. "One of these things is not like the others ©!
Bottom one has a different angle and sticks out farther!
Top three shoes won't fit into the bottom one.
Wonder if it is a different vendor?

I see that the top one in your second picture does not have the grooves in the rubber. It’s my understanding the grooves are molded into the rubber during manufacturing, so I would think definitely a different vendor.

theunz wrote: Thu Apr 13, 2023 7:58 am I see that the top one in your second picture does not have the grooves in the rubber. It’s my understanding the grooves are molded into the rubber during manufacturing, so I would think definitely a different vendor.

The upper tensioner shoe is always flat with no grooves when new (grooves are wear from the chain), however the lower tensioner has always grooves on the shoe from new.

The original part number for the upper tensioner is 13080-25500. In a SR catalog dated 1968.6 it shows the part number in the drawing and the parts list as 13080-25500. However, In the back of the book the part number listing supersedes from 13080-25500 to 13080-25501. The last number, in the Nissan part numbering system, denotes a distinction, a change in the part or that the part is being made by a new vendor. This is a very, very early change by Nissan and it would be very interesting to know why it was made.
The part that is not machined on the front, on the left, may be a very early tensioner, but I am not sure. It could be an aftermarket.
30 years ago I did buy Tsubaki Moto originals in plain white boxes from an automotive engine parts distributor in New Jersey. Technically they were sold in the aftermarket but were original OEM maker parts.
I am not aware of any aftermarket tensioners up until 9 years ago when we contracted an after market one to be made. We supplied a recent Tsubaki moto/Nissan tensioner to be remade and then we contracted another maker 3 years ago to make yet another variant of this.

Dean

Good info Dean!
All taller ones I have are not machined on the front.
So they could be used on the 67.5 2000.
Who has an untouched 67.5 2000 engine

Interesting. I am to understand that the tensioner you speak of came off a never taken apart 671/2 2000?
There are people around longer than me that may have more info,

D-

Datsunparts.comInc wrote: Thu Apr 13, 2023 5:12 pm Interesting. I am to understand that the tensioner you speak of came off a never taken apart 671/2 2000?
There are people around longer than me that may have more info,

D-

No, not taken from a 67.5 2000, I bought them over the years with other parts.I found 4 of them between my parts.
What I meant is that somebody who has a never taken apart 67.5 2000 could take look at it.
Maybe Sidney's 43000 mile 67.5 2000.
I just checked a European 67.5 2000 and that one has the early higher one but can't say if it is ever been replaced.

Quote Dean: "The original part number for the upper tensioner is 13080-25500. In a SR catalog dated 1968.6 it shows the part number in the drawing and the parts list as 13080-25500. However, In the back of the book the part number listing supersedes from 13080-25500 to 13080-25501. The last number, in the Nissan part numbering system, denotes a distinction, a change in the part "

The only original number I found is 13080-25501, the "255" stands for the model, which is indicated as a SR(NOT L)311-U 1967.5 2000 U20 series engine low wind screen. I would think if it superceeds in the later 1968 U20 and on engines with the high windscreen model you would think the model number would change . If it was for example "259" it stands for a SR(no L)311-U 1968 2000 U20 series engine high windscreen. But it seems they only changed the last 2 numbers (which are distinction numbers), 00 to 19 are "similarity" kinds of distinction numbers, but no idea what is changed to the part or what they mean with similarity change 00 to 19, because there is also a similarity numbers 60 to 69.
The only thing written about it;

It could be something small like a recess (but could also be a color if it was an interior partnumber).

Other distinction number series are for "material", "processing" and "exclusive service use" but 01 does not fall in those series numbers...
Fact is,

"there is made a very minor change to the part that is not significant enough to warrant a complete new part number"

Anyway maybe DEF (davdav2000?) has or can digg up some books to check/shine a light on this "similarity" distinction number meaning. Or on the given part-numbers for the upper tensioner, which not changed for SRL and/or 1968-1970 2000's.

ladydriver wrote: Fri Apr 14, 2023 8:06 am The only original number I found is 13080-25501, the "255" stands for the model, which is indicated as a SR(NOT L)311-U 1967.5 2000 U20 series engine low wind screen. I would think if it superceeds in the later 1968 U20 and on engines with the high windscreen model you would think the model number would change . If it was for example "259" it stands for a SR(no L)311-U 1968 2000 U20 series engine high windscreen. But it seems they only changed the last 2 numbers (which are distinction numbers), 00 to 19 are "similarity" kinds of distinction numbers, but no idea what is changed to the part or what they mean with similarity change 00 to 19, because there is also a similarity numbers 60 to 69.

The first three digits of the second string mean the model the part was introduced for. It could be used on anything after that - including non roadsters.
I have seen lots of instances where I thought that the part number should be changed, but Datsun wasn't too strict on part numbers.