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#712092 - 10/21/17 5:15 am T140 Ported Head Question?  
Joined: Sep 2017
Posts: 5
Mike Austin Offline
BritBike Forum member
Mike Austin  Offline
BritBike Forum member

Joined: Sep 2017
Posts: 5
Murrieta California
My first post here, so hello everyone. I need an opinion on a head decision for a T140 Bonneville engine to be used for Sportsman Open Twins (motocross). Its being built on Johnson Cams version of the Spitfire cam set, and MAP forged 9 to 1 pistons set at .035" (ish) squish. The plan was to lightly prep a stock head and rebuild it with Kibblewhite guides and valves, but the head I bought was not stock... So run the ported head as described below, or find a stock one???

Like everyone I shop eBay for parts and I bought a generally nice T140 head but I got a surprise... The head was ported :cry, the intake ports match the example shown in Stan Shenton's book "Triumph Tuning, including opening the ports up to 32mm as shown below...

[Linked Image]

At some point after the head was ported someone attempted to add "texture" to the port walls and made things ugly but did no real damage. the plan is to clean the head up and rebuild with Kibblewhite guides and valves using the Norton spring set recommended by Johnson Cams
[Linked Image]

The plan is to run the MAP 3 inch tapered manifolds (port matched by boring on my lathe), with 32mm VM Mikunis.
[Linked Image]

The exhaust ports look like this, the plan is to get the ports threaded for stubs and run 1 1/2" exhaust.
[Linked Image]

The chambers are nice and the gasket surface is flat.
[Linked Image]


Thanks For Your Time And Comments: Mike


"An ill-assorted collection of poorly-matching parts, forming a distressing whole."
#712098 - 10/21/17 7:12 am Re: T140 Ported Head Question? [Re: Mike Austin]  
Joined: Dec 2013
Posts: 3,280
kevin roberts Online content
BritBike Forum member
kevin roberts  Online Content

BritBike Forum member

Joined: Dec 2013
Posts: 3,280
ohio, usa
run the ported head first and see how it works. you could probably avoid the cost of tbreading tbe exhaust by using push-in pipes and springs. or weld on external aluminum stubs.


Into the distance a ribbon of black
Stretched to the point of no turning back
A flight of fancy on a windswept field
Standing alone my senses reeled
A fatal attraction is holding me fast how
How can I escape this irresistible grasp?
#712179 - 10/22/17 1:20 am Re: T140 Ported Head Question? [Re: kevin roberts]  
Joined: Sep 2017
Posts: 5
Mike Austin Offline
BritBike Forum member
Mike Austin  Offline
BritBike Forum member

Joined: Sep 2017
Posts: 5
Murrieta California
Originally Posted by kevin roberts
run the ported head first and see how it works. you could probably avoid the cost of tbreading tbe exhaust by using push-in pipes and springs. or weld on external aluminum stubs.


Hi Kevin.
Thanks for that, I'm close to the Los Angeles area so I'm lucky to be in a "Triumph specialist" rich environment, I may take a day off his week and collect a few opinions as to what my options are with this head. The exhaust port has been opened up enough that the push in pipes are not well supported by what's left of the support ring that the pipe butts up against, I am afraid the pipe will chew it way through the support ring and end up in the port, and the push in inserts are thick wall so that won't work with this port without partially blocking it, so I will probably have to bite the bullet and go with a thread in conversion that will butt against the support ring, assuming the head is not so over ported as to be useless in my application.
I would like to run this head but there are a lot of unknowns with it, and as I am relatively new to Triumphs I do as much research as I can and make conservative decisions based on others experience and successes.
So I have found myself sort of out in the weeds with this head as its a circa 1967 full road race port job and I have no idea how flat the power will be below 3K RPM.
The Spitfire grind cams are reported have a smooth power delivery so that may be this heads saving grace as I'm 60 and no longer have the attention span to race a bike with peaky power delivery banging handlebars with other old men. So its kind of a blurry line as to what's ridable and what's not.

Thanks: Mike


"An ill-assorted collection of poorly-matching parts, forming a distressing whole."
#712223 - 10/22/17 11:06 am Re: T140 Ported Head Question? [Re: Mike Austin]  
Joined: Oct 2012
Posts: 3,108
Hillbilly bike Online content
BritBike Forum member
Hillbilly bike  Online Content
BritBike Forum member

Joined: Oct 2012
Posts: 3,108
Running from demons in WNY
The "Spitfire" cam is a stock 750 intake cam?....Modern porting isn't always about big ports but more about high velocity from smaller properly shaped ports ...This is especially true on a street bike ...My opinion based on my 650 race bike...That head with Spitfire cams will have reversion problems and a big flat spot around 3500-4000 rpm....Perhaps a two into one or crossover pipe exhaust will help out...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#712266 - 10/22/17 6:47 pm Re: T140 Ported Head Question? [Re: Hillbilly bike]  
Joined: Sep 2017
Posts: 5
Mike Austin Offline
BritBike Forum member
Mike Austin  Offline
BritBike Forum member

Joined: Sep 2017
Posts: 5
Murrieta California
Originally Posted by Hillbilly bike
The "Spitfire" cam is a stock 750 intake cam?....Modern porting isn't always about big ports but more about high velocity from smaller properly shaped ports ...This is especially true on a street bike ...My opinion based on my 650 race bike...That head with Spitfire cams will have reversion problems and a big flat spot around 3500-4000 rpm....Perhaps a two into one or crossover pipe exhaust will help out...


Hi Hillbilly bike,
That's Information I need. The Spitfire cam set is from Johnson Cams, so yes its their version of the Triumph inlet and exhaust cams. A flat spot in that range would make this head useless for a motocross engine. Not good news but I kind of suspected I was hosed when I got my first look at the ports, I have read enough of your posts here on Britbike that I value your opinion. I have poured enough money into this project a little more won't hurt, I guess its time to shop for another head. Thank you for taking the time and for an honest opinion.

: Mike


"An ill-assorted collection of poorly-matching parts, forming a distressing whole."
#712270 - 10/22/17 7:09 pm Re: T140 Ported Head Question? [Re: Mike Austin]  
Joined: Oct 2012
Posts: 3,108
Hillbilly bike Online content
BritBike Forum member
Hillbilly bike  Online Content
BritBike Forum member

Joined: Oct 2012
Posts: 3,108
Running from demons in WNY
Have you talked to Johnson Cams about the head? If you have money into the head then maybe just run it to see how it goes with the cams and whatever carbs and exhaust you're using...It's no big deal labor wise to swap heads if it doesn't suit your needs.


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#712334 - 10/23/17 2:25 am Re: T140 Ported Head Question? [Re: Hillbilly bike]  
Joined: Sep 2017
Posts: 5
Mike Austin Offline
BritBike Forum member
Mike Austin  Offline
BritBike Forum member

Joined: Sep 2017
Posts: 5
Murrieta California
Originally Posted by Hillbilly bike
Have you talked to Johnson Cams about the head? If you have money into the head then maybe just run it to see how it goes with the cams and whatever carbs and exhaust you're using...It's no big deal labor wise to swap heads if it doesn't suit your needs.


You have a very good point, I have a set of tappits that has to go to Johnson cams for a regrind, I will give them a call in the morning and if they can do something for me, if so I will find a bigger box and ship the head to them and not worry about it until I hear back. It's one of those things one way or another I have to spend money If Johnson can fix my problems, I'm more than happy to pay them.
I wish I wasn't so OCD life would be much simpler. an example would be the Husqvarna wheel swap into the OIF swingarm. I didn't want to reduce the diameter of the rear axle from 5/8" to the 15mm Husqvarna standard, so the challenge was to find a bearing that fit the Husqvarna hub that had a 16mm ID. Motobecane moped crank bearings are dimensionally the same as a 6302 bearing with a 16MM ID, problem solved except the OIF axle is now too small, easy hard chrome the Triumph axle and grind the od to .6285... I had to buy a 16mm reamer to size the spacers and backing plate. But now I'm happy and it only took 2 weeks to figure out. this is that result...
Yes I'm nuts, I build everything with the same attention to detail and I am really enjoying this build and thank you for your input it's spot on, your advice has gotten me out of my funk and on to something productive. I will keep everyone informed on my progress.

[Linked Image]

Thanks Again: Mike


"An ill-assorted collection of poorly-matching parts, forming a distressing whole."
#712880 - 10/27/17 5:54 am Re: T140 Ported Head Question? [Re: Mike Austin]  
Joined: Sep 2017
Posts: 5
Mike Austin Offline
BritBike Forum member
Mike Austin  Offline
BritBike Forum member

Joined: Sep 2017
Posts: 5
Murrieta California
Well things are going quite well, a 10 bolt T140 head has been located with good seats and a unnamed shop on the west coast that has a great reputation for supporting vintage flat track racing has agreed to build my new head, nothing exotic, Kibblewhite valves, guides, norton springs, steel pushrods, and porting that complements the cams, things are looking up. There was some confusion over the Spitfire cams from Johnson, in their catalog their called T65 cams described as "Between a Q and a Jomo 15. Good for hot street, short track, and TT in 650 and 750 twins" so that should clear things up a bit.
Its been a good week for hunting parts as I have a line on a pre 1965 T120 frame with less rake than the later models, this works in my favor as the turn in should be better for motocross, I still have to figure out the offset for the triple clamps, that will happen when I can mock up the chassis with the 13 inch shocks and the 1973 Husqvarna forks and wheels, yes the bike is a "bitsa" but a well thought out one. I scored a 1960's Webco oil tank in great condition (it should look nice with the TR5T alloy tank) so Its the prize of the week and the Carrillo rods showed up... Woot.

[Linked Image]

[Linked Image]

: Mike


"An ill-assorted collection of poorly-matching parts, forming a distressing whole."

Moderated by  Allan Gill 


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