Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board T120 Cylinder head

Hi all, I'm in need of a cylinder head for a 1966 T120 and have seen one for sale but it's a 1976 head with flange fittings for the carbs. Would this head be suitable for the earlier model taking into account rocker box fittings and gear.

Not really. The 76 head has a taper machined on the outer edge of the combustion chamber, which won't suit the smaller bore of the 650. I has two center bolts, where the 650 has one, and in a different position. The cylinder head studs from the 750 have a different thread, and the rocker boxes don't have the structural integrity to support the forces from the through rocker box bolts. Morgo seems to sell 736cc barrels that can be drilled and tapped for the T140 head though, which in your case I'd be wanting to look at.

Proper 650 heads can still be found, but I admit that they are becoming scarcer and the ones available are often scrap. I've been able to save a few with welding, new valve seats, oversize guides and so on, but if you enlist the services of a machine shop, it soon becomes expensive.

SR

PS. LP Williams seems to have a "Routt" kit that can be delivered to fit a T140 head: https://www.triumph-spares.co.uk/750cc-conversion-kit-t120-routt-big-bore-kit-70-6304a

Thanks for the reply. I am wrong saying it's a 1976 head, it's a 73/74 T120 650cc, part number 71-2863, 9 stud, same number as the 750cc 10 stud head. Just need to confirm that the later head is compatible with the earlier (1966) rocker boxes. Besides the carb mountings are there any other differences?

If you go for that head you will need 69 onwards push rod tubes and change the tappet blocks in the barrel to 69 onwards tappet blocks.

You may have to remove the rocker box locating dowels from the head too

The part number you quote is the part number for the head casting.
It becomes another part number for the T140 10 stud head and yet another part number for the T120 9 stud head.
If you look at the central hole in the head you will see the boss next to it where the 10th hole is drilled for the T140 head.
HTH

OK, a very different scenario then,
If it's a 9 bolt head it will fit but needs its own set of head studs, 71 or 72 versions, which are slightly different from each other.
However, it's possible to use the earlier rocker boxes and bolts on these heads. (Often called 9 1/2 bolt heads btw). You may have to remove the dowels as suggested, and will have to alter the push rod tubes and guide blocks to the later versions as kommando said. There may be cross over tubes available from people like Andy Gregory though.

SR

Are the repo heads any good ?

The repo heads are made by (or at least, for) LF Harris, who made the last of the Bonnies under licence, so I would expect them to be as good (or bad) as the originals. I believe that from about 1969 onwards, Triumph used the same metalurgy as BSA for the valve seats, I certainly see lees valve pocketing on the later heads. Of course, if you can find one, and for any repo, you will still need the later PRT's etc for a '66.

The last of the Bonnies, made by Harris, were not as good as the originals.

I bet the frames didn't flex like the 'original' though........................

They were OIF, so they flexed just as much as the darn BSA, which is not.
Flame back at ya!

That's funny i never saw a 59 t120 oil in frame???
Plus most triumphs were 'oil all over frame'............

On that '72 head, they use cylinder head bolts that tighten onto the head surface under the rocker boxes. Prob I ran into was deep recesses where the nuts pushed into the head. If I used the 72 bolts I couldn't get the 72 style rocker boxes on with the motor in frame. But with 68 bolts and boxes there was a gap where the nut depressions were in the head so I know it would blow oil all over the place and not properly torque down. Ended up shimming that space with brass washers sanded down to thickness and 3bond but got disgusted with it and never started the bike like that. Don't want oil all over a clean motor.