1968 Triumph Bonneville T120R 650

What year heads will bolt up to this? I'm thinking 68-70, but not sure. Did they come with valve stem seals? I read somewhere that the seats were "cast in"? What's up with that? Were the original guides steel or bronze? Any help is appreciated. Thank you.

I don’t see why you can’t fit any 1963-70 T120 head, or single carburettor 650 head.

No seals.

NORTSTER1974 said:

What's up with that?

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What does that mean?

Original guide material doesn’t matter much now. Phosphor bronze guides wear out too fast for me. I use cast iron guides. There are modern aluminium bronze guides that may be better still.

Yes original seats were cast in, which makes it practically impossible for them to fall out, unlike replacement pressed in seats…

So do not be overly in a hurry to replace them !

NORTSTER1974 said:

What year heads will bolt up to this? I'm thinking 68-70, but not sure. Did they come with valve stem seals? I read somewhere that the seats were "cast in"? What's up with that? Were the original guides steel or bronze? Any help is appreciated. Thank you.

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If I remember right, the differences are in 63-65, 66-68, and 69-72. Which has to do with the machining for the top of the pushrod tube. I'm pretty sure they will all bolt on. You do need the matching rocker boxes and mounting hardware that goes with the head/rocker combination.

marshg246 said:

If I remember right, the differences are in 63-65, 66-68, and 69-72. Which has to do with the machining for the top of the pushrod tube. I'm pretty sure they will all bolt on. You do need the matching rocker boxes and mounting hardware that goes with the head/rocker combination.

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Correct. Any of the above CAN fit, but getting a good seal on the pushrod tubes is always the challenge.

Enter silicone seal!!!

Triton Thrasher said:

I don’t see why you can’t fit any 1963-70 T120 head, or single carburettor 650 head.

No seals.


What does that mean?

Original guide material doesn’t matter much now. Phosphor bronze guides wear out too fast for me. I use cast iron guides. There are modern aluminium bronze guides that may be better still.

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What does that mean? What's up with that?--means-- What's the reason for that? I was wondering about the reason for "cast in seats". I've never heard of anyone complaining about pressed in seats falling out.

NORTSTER1974 said:

I've never heard of anyone complaining about pressed in seats falling out.

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It happens !

FE, I believe you, Was this just a thing with Triumphs. I've owned 2 Triumphs, a 69 Bonnie and a 52 something or other pre unit 650. Can't remember the model. I'm not a racer like you but always beat the shit out of any bike I ride. Been riding on the street for 44 years, Harley's, Norton's, Triumphs with buddies who have owned the same. No one ever complained about losing a valve seat. Thanks for your input, and put some more miles on the Fat Boy.

FE, the reason I'm asking these questions is because my buddy/mate just picked up a running 68 Bonneville for 1K USD, from the original owner. It is supposed to only have 10K miles on it. The problem is we like to look deeper into the situation because he had it serviced by a mechanic who used to be good back in the day, but does shoddy work now. Thanks for all your input in regards to what we should be looking into on this bike.

NORTSTER1974 said:

FE, the reason I'm asking these questions is because my buddy/mate just picked up a running 68 Bonneville for 1K USD, from the original owner. It is supposed to only have 10K miles on it. The problem is we like to look deeper into the situation because he had it serviced by a mechanic who used to be good back in the day, but does shoddy work now. Thanks for all your input in regards to what we should be looking into on this bike.

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A ‘68 Bonnie for $1k… Wow!

Whats the plan for it?

I’ve got a ‘68, it was a US bike that got repatriated. I love it. Light, revvy, fast and smooth with great handling and deceptively good brakes.

‘68s have the lightweight crank that some dislike. I like it a lot, makes the motor feel very lively and eager. Totally different to a T140 for example.

Mines had a hard life in the past, the gearbox was shot. I fitted a NOS 5 speed cluster (which works very, very, well on a revvy 650), belt drive, new Premiers, Tri Spark, etc and it now runs SO well. Don't get to ride it much tho coz my Dad ‘borrowed’ it as he couldn’t believe how light it was compared to his Hinckley Bonnie!

The wide western bars are great, perfect riding position for me. But when combined with a twin pull throttle, does lead to the cables being pulled around unevenly, requiring one to keep on top of the carb balancing. I fitted a single pull twist grip, cable and splitter arrangement and now the carbs stay in synch.

The front brake cable is too long and the routing is such that the cable can get stuck, jamming the brake on (so the story goes) I’ve never seen it happen though and imagine it only happens when desert racing or similar.

IMO the ‘68 US spec is THE best Bonnie. It has all of Douge Hele’s development input and thus is fast, it stops and it handles. It also has an iconic overall design and styling. On later pre OIF bikes the styling got busier and busier. The ‘68 has a design simplicity / purity to it that they don’t.

Fast Eddie said:

It happens !

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And then they do complain about it.

Fast Eddie said:

A ‘68 Bonnie for $1k… Wow!

Whats the plan for it?

I’ve got a ‘68, it was a US bike that got repatriated. I love it. Light, revvy, fast and smooth with great handling and deceptively good brakes.

‘68s have the lightweight crank that some dislike. I like it a lot, makes the motor feel very lively and eager. Totally different to a T140 for example.

Mines had a hard life in the past, the gearbox was shot. I fitted a NOS 5 speed cluster (which works very, very, well on a revvy 650), belt drive, new Premiers, Tri Spark, etc and it now runs SO well. Don't get to ride it much tho coz my Dad ‘borrowed’ it as he couldn’t believe how light it was compared to his Hinckley Bonnie!

The wide western bars are great, perfect riding position for me. But when combined with a twin pull throttle, does lead to the cables being pulled around unevenly, requiring one to keep on top of the carb balancing. I fitted a single pull twist grip, cable and splitter arrangement and now the carbs stay in synch.

The front brake cable is too long and the routing is such that the cable can get stuck, jamming the brake on (so the story goes) I’ve never seen it happen though and imagine it only happens when desert racing or similar.

IMO the ‘68 US spec is THE best Bonnie. It has all of Douge Hele’s development input and thus is fast, it stops and it handles. It also has an iconic overall design and styling. On later pre OIF bikes the styling got busier and busier. The ‘68 has a design simplicity / purity to it that they don’t.

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Well FE, he's going through it top to bottom. Not splitting cases. Considering the old bloke (original owner) who sold it to him did so because he knew my buddy appreciated Brit bikes and loves working on things. My buddy works with the old bloke's son, that's how he found out about the bike. He was able to start it and ride it home, about 10 miles.

His intentions are just to make it a rider. Considering it supposedly only has about 10K miles. So far he cleaned the clutch plates. It had a Boyer in it. He wired in a Shindegin and installed a 3 phase stator. 2 new premiers. LED lighting. He said it was running great.

Upon restarting it once he noticed a lot of top end noise. So off with the head, considering we knew the "Triumph specialist" who has had his hands on it.

Here's what he found .020 over pistons, newer, presumably KW valves and guides, they have a cutout on intake for seals but none were in place. The motor did not smoke. Head gasket leaking, improperly installed rocker spindle gaskets, and it looked like the head was resurfaced with a belt sander. Right now he is just going to lap the valves, and even the head on some glass surface. Valves seem tight and not wobbly. Still wondering if he should install valve seals on the intake, since there is a provision for them.

After that it's onward to the rest of the bike, tires, wheel bearings if needed, brakes, front end, maybe some tapered neck bearings. Whatever, you know the deal. Here are some pics of the top end. Cheers. Sorry I'm having trouble uploading pics, will get them done soon

Fast Eddie said:

A ‘68 Bonnie for $1k… Wow!

Whats the plan for it?

I’ve got a ‘68, it was a US bike that got repatriated. I love it. Light, revvy, fast and smooth with great handling and deceptively good brakes.

‘68s have the lightweight crank that some dislike. I like it a lot, makes the motor feel very lively and eager. Totally different to a T140 for example.

Mines had a hard life in the past, the gearbox was shot. I fitted a NOS 5 speed cluster (which works very, very, well on a revvy 650), belt drive, new Premiers, Tri Spark, etc and it now runs SO well. Don't get to ride it much tho coz my Dad ‘borrowed’ it as he couldn’t believe how light it was compared to his Hinckley Bonnie!

The wide western bars are great, perfect riding position for me. But when combined with a twin pull throttle, does lead to the cables being pulled around unevenly, requiring one to keep on top of the carb balancing. I fitted a single pull twist grip, cable and splitter arrangement and now the carbs stay in synch.

The front brake cable is too long and the routing is such that the cable can get stuck, jamming the brake on (so the story goes) I’ve never seen it happen though and imagine it only happens when desert racing or similar.

IMO the ‘68 US spec is THE best Bonnie. It has all of Douge Hele’s development input and thus is fast, it stops and it handles. It also has an iconic overall design and styling. On later pre OIF bikes the styling got busier and busier. The ‘68 has a design simplicity / purity to it that they don’t.

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FE, I'm sorry I haven't been able to post any pics. Something to do with the format. I'm sure the pics are nothing you haven't seen before. Nothing drastic. It's easier to work on the Triumph, than it is to post pics. Thank you for your recommendations. Will keep everyone posted of any updates. Thanks to everyone again. We are Norton/Harley riders, and I haven't owned a Triumph since 1980, when I was a kid. 69 Bonnie. 52 pre unit 650 something or other. P.S. In the 80's I got a dog from the pound in Philly. He was about 4 months old. Wheaten gold in color, white patch on the chest, black snout. When I would walk him around the hood, folks would say "Is that a Ridgeback"? WTF, I had no idea and looked it up. Used to hunt lions in Africa. Someone said that breeders would discard them if they weren't perfect, Sammy must have had a slight mix, he didn't have the ridge going down his back. Best dog I ever owned. friendly with other dogs, unless they Fu@ked with him. Good with everyone, unless I told him to attack. Awesome dog. Sorry I don't have any pics. While walking him around the hood in Philly, we were attacked by Pitbulls, Rottweilers, and other big dogs. Sammy had them on the ground by the neck in a few seconds. Loved old Sammy! Take Care FE.

The 68 got the good geometry & the beefed up swing arm . And other things .

OIL SEALS , would stop them sucking oil through . So theyed run dry . its notta pressurised top end feed , like a Norton . So dont really needem .

Pity no pictures . Youd get the recessed valve lecture . The outer edge should be unimpeedeed in the chamber . STRAIGHT THROUGH ' Mufflers '
were recomended . Or Better . And orrible olde TERRYS valve springs were goodfor 8500 held the world L S R . Copper Coat & retourque after
a good heat cycle or two - on the top end. and CHECK the base nuts ( barrel ) till its settled in their .

Thats 1 9/16 & 1 7/16 , tho Jo Mo did 1 5/8 intakes . AND the W&S Springs ( and collets & keepers ) were NORVIL . Or V.c.V. . so goodfor 8.000 No Sweat .

Yer actually do intake bore to 1 1/8 , with 1 3/16 carbs . as per T. T. if ya wannit to Really go . Wiff the 1 3/4 pipes , too . To blow off Harleys .

NORTSTER1974 said:

FE, I'm sorry I haven't been able to post any pics. Something to do with the format. I'm sure the pics are nothing you haven't seen before. Nothing drastic. It's easier to work on the Triumph, than it is to post pics. Thank you for your recommendations. Will keep everyone posted of any updates. Thanks to everyone again. We are Norton/Harley riders, and I haven't owned a Triumph since 1980, when I was a kid. 69 Bonnie. 52 pre unit 650 something or other. P.S. In the 80's I got a dog from the pound in Philly. He was about 4 months old. Wheaten gold in color, white patch on the chest, black snout. When I would walk him around the hood, folks would say "Is that a Ridgeback"? WTF, I had no idea and looked it up. Used to hunt lions in Africa. Someone said that breeders would discard them if they weren't perfect, Sammy must have had a slight mix, he didn't have the ridge going down his back. Best dog I ever owned. friendly with other dogs, unless they Fu@ked with him. Good with everyone, unless I told him to attack. Awesome dog. Sorry I don't have any pics. While walking him around the hood in Philly, we were attacked by Pitbulls, Rottweilers, and other big dogs. Sammy had them on the ground by the neck in a few seconds. Loved old Sammy! Take Care FE.

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RIP Sammy.

He could well have had some Ridgeback in him by the sound of it.

They are great dogs. SO soft with their own, but they change completely if they sense a threat, or even just something out of the ordinary.

I knocked on the window one night to jokingly scare my girls. Two Ridgebacks (only had two then, up to three now) came charging around the corner to get at me. They seemed twice the size they are normally and looked freakin’ terrifying! Fortunately they recognised me in time !!

Beautiful dogs FE. I have pics of Sammy, but they are on paper and in the basement. Sammy wasn't pure but as close as you could get. Never really knew what he was crossed with but could only speculate. He probably has a little Norton in him, based upon how quick he could catch a rabbit or squirrel. Quick out of the hole and great top end once he reached the right rpm. If you happen to think of anymore 68 Bonnie tips, please do post them. Thanks, JZ

Here is a pic or two of the bike it's been repainted but it starts first kick with new amal premieres and the boyer that was already in there. Needs a bunch of other stuff tires clutch plates wheel bearings gone through maybe neck bearing conversion to tapered not a bad deal for $1,000. Now it only leaks oil from the plug in the crankcase. The original 80-year-old owner had it repainted, but it will be corrected.

Fast Eddie said:

RIP Sammy.

He could well have had some Ridgeback in him by the sound of it.

They are great dogs. SO soft with their own, but they change completely if they sense a threat, or even just something out of the ordinary.

I knocked on the window one night to jokingly scare my girls. Two Ridgebacks (only had two then, up to three now) came charging around the corner to get at me. They seemed twice the size they are normally and looked freakin’ terrifying! Fortunately they recognised me in time !!


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Just love, love, love them dogs FE

Best deal I've heard of in YEARS!