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ID question T120
#797238 02/01/20 8:01 pm
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MikeG Offline OP
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I've recently acquired a T120R engine, serial number DU80XXX. Should be a 68, but it has the oval valve adjust covers which I thought were used on the T140 engine? Have done nothing more than a cursory inspection so far, but how much of the cylinder/head/rocker boxes were interchangeable between the T120 and T140? It's been 40 years or more since I've delved into a Triumph engine so if I sound like a NOOB I am.
Thanks
Mike G


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

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Re: ID question T120
MikeG #797244 02/01/20 8:56 pm
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The oval valve covers were introduced on the 1972 650's but will fit any oil in frame cylinder head, 650 or 750. You could have a 1968 engine with a later cylinder head.

Eric


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: ID question T120
MikeG #797247 02/01/20 9:27 pm
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As far as I know, the later rockers fit the earlier heads? The factory did as little as possible and the bikes evolved rather than major redesign
It was only when larger changes were made to castings that you'd have issues? Until the stroke of the engine was changed, the 750 was the same as the 650 but witha larger cylinder? (724)

Re: ID question T120
AngloBike #797250 02/01/20 9:48 pm
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Originally Posted by AngloBike
As far as I know, the later rockers fit the earlier heads? .....


The other way around, the early rocker boxes fit the later cylinder heads. Triumph changed the shape of the cylinder head to rocker box mating surface for the OIFs when they added the 4 rocker box to cylinder head dowel pins and the late rocker box/early cylinder head set up leaks oil.

Eric

Last edited by BikeVice; 02/01/20 9:49 pm.

1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: ID question T120
MikeG #797254 02/01/20 10:48 pm
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if you use the early rocker boxes on a later head you have to use the early head bolts as well. you don't need to pull the dowels from the newer head- they don't interfere.

i believe you can fit the later boxes to an early head if use the correct two-piece headbolts and figure out a head steady. the late boxes used a central stud and a single steel strap hooked to the OIF, while the early ones bolted four steadies to the four inner head bolts. i don't know whether not having the dowels wouldcause leaks.


every day you do not take a chance is a day of your life that you will never get back.
Re: ID question T120
MikeG #797255 02/01/20 10:56 pm
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MikeG Offline OP
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Thanks All. Were there differences aside from bore between the 650 and 750 cylinders? A quick look at my engine tonight and I count 10 head bolts. I've been offered a good used cylinder but it only has 9. Was a later model 750 top end a bolt on affair or something else?


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

Re: ID question T120
MikeG #797259 02/01/20 11:25 pm
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Mike,

I think at this point, it would be a good idea to post up a picture of your stamped engine numbers. Is there also an elbow at the rear of the primary side of the cases for the crankcase breather ? I am somewhat suspect of a restamped engine.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

Re: ID question T120
kevin #797260 02/01/20 11:26 pm
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Originally Posted by kevin roberts
i don't know whether not having the dowels wouldcause leaks.


It's not the lack of dowels that causes the leaks but that the cylinder head to rocker box gasket surface on the head doesn't extend out to where the dowels would be. The late rocker box overlaps the cylinder head. Put a late rocker box on a bare early cylinder head and look through the valve cover. You'll see daylight where the dowels would be.

Originally Posted by MikeG
I count 10 head bolts


10 head bolts is 750. A 750 top end on 650 cases is quite a bit of work. The 750 connecting rods are 1/2" shorter than 650 rods and the cylinder spigots are larger and siamesed so 650 cases require boring to accept them. Are you sure you don't have a 750 engine renumbered as a 1968 650? Does it have a crankcase breather at the top of the primary?

Eric


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: ID question T120
MikeG #797412 02/03/20 1:16 pm
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MikeG Offline OP
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Well, it does have the breather at the rear of the primary, but it is a right hand shift so I can assume it is somewhere between a 72 and 75?


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

Re: ID question T120
MikeG #797437 02/03/20 4:54 pm
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Originally Posted by MikeG
Well, it does have the breather at the rear of the primary, but it is a right hand shift so I can assume it is somewhere between a 72 and 75?



It could be a '77 with a RH shift conversion for all we know at this point. Pics.....


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"


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