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Why did Triumph change to parallel ports?

Discussion in 'Triumph (Classic)' started by Fast Eddie, Mar 6, 2019.

  1. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    Why did Triumph dispense with the splayed head in favour of the parallel port head on the T140E in 1978 ?

    Anyone know ?
     
  2. L.A.B.

    L.A.B. Moderator VIP MEMBER

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    Nov 20, 2004
  3. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    Thanks LAB but unfortunately the question still stands...

    A ‘revised head’ due to ‘emmisions’ as quoted in the article is a tad vague on detail.

    As far as I know, the head changes where:

    1. A move to parallel ports
    and
    2. a ‘revised combustion chamber’.

    What I’d really like to know is why they did those.

    What did moving from splayed ports to parallel ports actually do? What changes occurred to gas flow etc and what was the effect?

    Same question to the ‘revised combustion chamber’.

    I’ve heard one version that Triumph went to parallel ports in order to use a link between the choke levers. I don’t buy that at all, cha going the ports would have been a very expensive exercise and they must have had good reasons for it.

    I’ve heard folk say the parrelel head burns better and gives better performance, others say the ports are obstructed and perform less well, etc.

    I’ve heard it was to save money by have a common casting for twin and single carb heads.

    There’s lots of folklore, most of it baseless, even the literature available is poor on detail and full of errors (in general, not just this topic). I therefore wondered if anyone on here could actually offer any logical reasoned hypotheses for these changes?
     
    Last edited: Mar 7, 2019
  4. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    I thought that cylinder head was the earlier single carburettor version modified (manifolds) to take twin Mk2 Amals not a new for the 1978 model item in total but the Mk2 fitment might have been ?
    There was some mention of the straightened inlet port adding to swirl as far as the splayed exhaust port but that might have been wishful thinking after the fact.
     
  5. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    I always thought that twin carb heads and single carbs heads were a different casting, having differences around the intake port areas.
    However, a quick google image search would seem to quash that idea. They look like the same casting to me, machined differently of course, but it’s the same casting a think.
    Maybe cost saving was a big factor after all?

    0246BA88-AF55-418A-A628-E6B10EC8A7B7.jpeg DD2F8FEE-59BF-4A70-A495-F9DFD2F7CC6B.jpeg
     
  6. L.A.B.

    L.A.B. Moderator VIP MEMBER

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    Nov 20, 2004
    It was a more efficient combustion chamber design:

    http://www.britbike.com/forums/ubbt...ngine-pinging-when-hot-ok-when-cool#Post95834

    "In a return to an earlier parallel port design in the 1979 T140D*, Triumph engineers were able to introduce more swirl in the combustion chamber producing a more even burn. This markedly reduced the combustion temperature to a point where they had to abandon Champion N3 plugs for ones two heat ranges hotter (N-5) to prevent plug fouling. In turn it lowered the octane requirement."

    *(& '78 T140E)
     
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  7. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    That’s very interesting LAB, thanks.

    Indeed, my genuine Triumph workshop manual states N5s. And the bike does run very happily with them.
     
  8. oldbeezer

    oldbeezer VIP MEMBER

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    Nov 2, 2017
    Per J. R. Nelson's book Bonnie The development history of the Triumph Bonneville "The T140E model was introduced on January 1st 1978 fitted with Amal Concentric MKII carburetters, and revised engine breather system to comply with U.S.A. Federal legislation"
    Still vague, perhaps the MKII carbs or breather system were the reason. Not being familiar with MKII carbs I ask the question did they have seperate cables like the MKI or were they connected similar to madass' mod for the Norton carbs which would require them to be parallel?
     
  9. L.A.B.

    L.A.B. Moderator VIP MEMBER

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    Nov 20, 2004
    Last edited: Mar 7, 2019
    nortriubuell likes this.
  10. L.A.B.

    L.A.B. Moderator VIP MEMBER

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    Nov 20, 2004

    https://www.classic-british-motorcycles.com/1978-triumph-bonneville.html

    "NEW HEAD FOR THE 1978 TRIUMPH BONNEVILLE
    UNF threads were still making their way through the engine & it finally got a composite head gasket in place of the prehistoric copper one. But the biggest change was just north of it. A new cylinder head was cast which now placed the intake ports in parallel paths aiming straight back, ending forever that time-honored Triumph Bonneville tradition of splayed carburetors. The new head also had revised combustion chambers & reworked valve guides & seats.

    NEW CARBS
    Again, emissions-driven, a new set of carburetors was installed, the 30mm Amal Concentric MkII, suddenly making the old standard Amal Concentric the Mk I. These new carbs were boxy-looking on the outside, but besides the elimination of the tickler valve, very little was different inside. An enrichening lever was located on the left carb that operated both units via a common linkage. The whole point was satisfying the new EPA rules forbidding the escape of any fuel or oil vapor to the outside air. The old round-bodied Amal Concentrics (now called Mk I) vented their float chambers to the atmosphere via the tickler valves, which themselves were messy & had to go."
     
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  11. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    I was referring to the T140E Lab, despite its parrellel ports I always thought it was a different casting to the TR7 head, but it is clearly the same, which makes good sense.

    They’re good pictures you posted, it’s easy to see that the later head has a bigger squish band area and thus a slightly smaller combustion chamber.

    FWIW, often on T140s that squish band is largely wasted because the gap is too big, it’s very easy to skim the barrel or use a thinner head gasket and get a good squish.

    Regarding the carbs, after all the time and faffing around I just spent on mine, I now consider myself an expert in the field of EPA vs non EPA T140 carbs !!
     
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  12. Triton Thrasher

    Triton Thrasher

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    Feb 10, 2009
    Was there something wrong with the prehistoric copper head gasket?


     
  13. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    That’s a good question...

    I only ever fitted copper gaskets to numerous road and race Triumph twins. It was never something that showed up on my (long) list of problems to solve / things to improve !
     
  14. L.A.B.

    L.A.B. Moderator VIP MEMBER

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    Nov 20, 2004
    Meriden seems to have thought so.

    Quote from 'Triumph Service Bulletin 9-79' (Jan. 79) :

    "... the Klinger cylinder head gasket was introduced to prevent failure to which the copper gasket was prone."
     
  15. Triton Thrasher

    Triton Thrasher

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    Feb 10, 2009
    That reads like something between forlorn hope and sales talk.
     
  16. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    Thing is, back in t’ day they were owned by teenagers with no tools, no money and no f***ing brains!

    They got cobbled together with warped heads, no torque wrenches and a scabby old re used copper gaskets that had never seen a blow torch.

    So yes... they used to leak from time to time.

    Truth is that today, a bike owned by a reasonably sensible enthusiast is gonna be fine whichever gasket is used.
     
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  17. Onder

    Onder

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    May 11, 2010
    Probably more accurate to say owned by young men not teens as Bonnies were a bit pricey for most of us at age 17.
     
  18. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    I’m not necessarily talking about those who bought new ones...

    I was 18 when I got my first Bonnie, on poverty line apprentice wages too.

    And you’re just being sexist...!
     
    Last edited: Mar 8, 2019
  19. Geoff Lather

    Geoff Lather

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    Nov 18, 2018
    Possibly swirl induced by the splayed inlet ports directed incoming flow to exit straight out the exhaust port during the valve over lap period, not good for emissions

    The straight inlet ports would send the intake charge at the exhaust valve face and not at the open area of the exhaust valve inducing tumble instead of swirl
     
    Time Warp likes this.
  20. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

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    Dec 3, 2012
    Even though 500 unit construction had stopped before 1978 I wonder if the 500 and 750 head had anything in common, the 500's did go well on the track.
    (Personally I think the last 500's were one of the best 'Brit engines built)
     

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