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#895374 11/14/22 7:28 pm
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How can I find out the year of the engine on my Triumph? The engine numbers start with T120VKJ.

Thank you in advance

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Originally Posted by mrcarb
The engine numbers start with T120VKJ.

K = September
J = 1974 model year.

KJ = 1974 model year manufactured September 1973.

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mrcarb-- you have a really good engine there.
Triumph started making the T140s (750cc) in 1973 and thereafter the quantities of T120s (650cc) made tailed off.
However these last of the T120Vs and T120RVs incorporated some of the good features of the t140.
For example they have the front disc brake, a triplex primary chain and the 6 bolt tappet inspection cover.
IMHO they are the best of the OIF Triumphs with the advantages noted plus the revviness of the 650 motor.
It would be great if you could give the full engine number (maybe star the last two digits) as I think all of those in US might have come from the same batch.
FYI I have T120RV KJ 581** and T120RV KJ582**.

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T120VKJ58561 is the complete engine number. The frame is a pre-OIF, where can I find the number and information on the frame?

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That should be stamped on the left side of the steering head.

If it isn't there, it's:
A. been ground off,
B. a dealer replacement new frame, never stamped, or
C. a non-Triumph aftermarket frame (chopper, or racing.)

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Originally Posted by mrcarb
T120VKJ58561 is the complete engine number. The frame is a pre-OIF, where can I find the number and information on the frame?

Scroll to the top of this page and open
the pull down tab marked
Serial numbers

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Your engine would originally have been housed in an OIF frame with the frame number and engine number matching each other.

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1974 model year started with JJ58014, although I can't say whether or not that they started with the early 724cc models or the late 650s with the triplex primary chains. According to JR Nelson, The first 1974 Bonnevilles released between July and November 1974 from Meriden after the commencement of the strike in September 1973 were 1974 model T120V models JJ58080 through KJ59067.
-Dave


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i also am interested in the last of the 650s.

i have three 9-1/2 bolt 650 cylinder heads, the ones with the ten-bolt splayed-port casting but with only a single central head bolt hole drilled, in the 650 position.

what exactly was the origin of these heads? were they thr 724s?


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Originally Posted by The Bonneville Shop
1974 model year started with JJ58014, although I can't say whether or not that they started with the early 724cc models or the late 650s with the triplex primary chains.

According to JR Nelson, 1974 T140 production commenced from GJ55101.

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1958 5TA / T100
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I think the Triumph B-range is quite extraordinary for its longevity (1937 to late 1980’s).
It is also remarkable for amazing racing achievements “in the day” as well as its popularity with domestic sporting enthusiasts and special builders.

Of course there were BSA and Norton models offering similar performance. But their parts over the decades are not so interchangeable.

The Triumph B-range is a wonderful set of mix-and-match parts to play with, of course to be mixed with care.

But to be able to use cranks, cams, primaries, even gearboxes from most years, is amazing.

Tinkerer does some amazing stuff using T140 top ends on 650’s, showing what can be done, as well as his 4 to 5 speed conversions.

I think a company like Triumph would have been thinking about development from the get go. So they made the 5T with the T100 in mind (an off the wall development of the racer from the RAF generator being an interesting variant).
Early post-war success brought the 650. Just a series of modest changes to get to the Bonneville in 1959, then to the unit version in 1963.

Right up to the last 750’s nothing really changed in the fundamentals, which is what makes them a playground of parts (again with caution).

Back to the 9.5 cylinder head. You just know that they were working on making a 750, so cast a suitable head that could still be drilled for the 650 (wouldn’t want to make 2 different ones).

I suspect the 750 head is pretty much the same as the 650 head in terms of chamber diameter. That allows the “squish band” to be created in the 750 (no squish in a 650 as far as I know).

So to make a long story even longer, Triumph yet again adapted old parts in a Darwinian way.

Just thoughts…

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That's a very romantic view on trumpets, in reality they didn't change anything as they
were too skint to develop anything and had a domineering MD who didn't like change.
By 1972 the firm was dead but wouldn't lay down, machine shop worn out etc.
Any forced change was done on the cheap like that head casting.

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what years did the 9.5 head appear?

on what motors?


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Does anyone inow the CC volume of the 750 head? I have several 650 heads at 69-70 cc's


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It was Nick, because of the fun it has allowed me over the years!
That is a fair-dinkum alternative view.
I’ll hold to mine though!
To my mind the original design was pretty smart and worked well for decades, some of the fiddling in the late 60’s – 70’s doesn’t make much sense.
For instance I would say the best engines would be the pre-70 ones (actually I would say the pre-63 ones).

It is good that the 70’d T140 engines have a main bearing solution for the timing side, not needed for the original design.

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I think that they realized that they needed the 10 stud head when moving from 650 to 750ccs.
They probably modifed the moulds to the have ability to make new 750 and 650 heads while ongoing also being able to make new 650 heads for the spares market.
Hence the bare casting for the 9 1/2 and the 10 stud heads are the same.
The land in the center can be drilled for a 9 1/2 or a 10 stud head.
So I reckon introduction in 1973 for the introduction of the 750s.

BTW if you have one of these late 650s look carefully at the top of the gas tank.
When I walked through Meriden in 1974 these machines were all stored sort of under cover.
They were in a building with sides and a roof but no ends.
Under the roof there were dozens and dozens of pigeons nesting with pigeon crap being deposited on the bikes parked below them.
The bikes had no covers and were tightly packed together so no protection for the paintwork!

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so the 9.5 heads went on the 724s.

what years were the 724s?

edit ^^^this is wrong

Last edited by kevin; 11/15/22 3:57 pm.

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Originally Posted by kevin
what years were the 724s?

The first T140s were 724cc (up to XH22018 according to JR Nelson) so 1973 model year.

Last edited by L.A.B.; 11/15/22 8:21 am.
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Originally Posted by L.A.B.
Originally Posted by kevin
what years were the 724s?

The first T140s were 724cc so 1973 model year.
I'm so lucky to have a NOS 9.5 stud T120 head in stock, awaiting a worthy bike to put it on! I have a couple of 1970 projects, but the bolt-on carb adaptors just won't look right. A late T120V would be perfect but I haven't seen any later than 72 around here.

SR

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If you feel you need some of the '71/'72 rocker boxes with the tappet adjusting inspection holes, I have at least 2 sets all refurbished - I sort of collected them for a while!

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Kevin- I can't speak to the 9 1/2 bolt head on 750's but they are apparently sought out because the intake side supposedly flows better than the earlier heads.

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i asked rob hall what 650 heads he preferred to work with and he suggested tbe 73-on, if i could find one.

mine has been opened up for 35mm carbs on the intake. havent measured the actual diameter.

when i saw two more for sale on ebay i snapped them up

Last edited by kevin; 11/15/22 3:50 pm.

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Originally Posted by kevin
so the 9.5 heads went on the 724s.

what years were the 724s?

i said ^^^this and it is obviously wrong.

the 9.5 heads were tbe 73 650 heads, not 724.

unless tbe 724 T140 only used tbe one head bolt.


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The T140 heads have a sort of squish band to the edge of the combustion chamber, the T120 just has a radius.

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