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750 Morgo engine build by Fast Eddies Speed Shop

Discussion in 'Triumph (Classic)' started by Fast Eddie, Apr 12, 2018.

  1. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Right then, you know how it is, one things leads to another, right? Yup...

    So, my ‘68 Bonnie has damaged crank cases, it has obviously thrown a primary chain or two in its time. There are several weld repairs and whilst they look ok at first glance, the primary is a swine to keep oil tight. The faces will leak past a new gasket with liberally applied Wellseal. A new gaskets with very liberally applied silicone is the only way.

    Run it dry I hear you say... I’d love to, as I really want to fit a Newby belt kit, but the oil seal housing has a large chunk broken away, there’s no way to fit a seal, so no way to make it oil tight.

    Such damage, and such repairs, have been playing on my mind as to how true the cases may or may not be, could case misalignment be linked to my earlier gearbox failure? And how strong are they after all of this? Stress builds up over time after all.

    I was planning a few upgrades anyway (no rush, just ‘as and when’) but wasn’t happy upgrading on these cases. And I’d really like to strip the bottom end anyway. But could I put it back together with suspect cases?

    So, I called me ole mates Tony and Martin at TMS and bingo, probably one of the last pairs of new 650 cases were sat on their shelf waiting for me all these years.

    Needless to say, those new cases are now sat on MY shelf!

    Suddenly, with new cases in the game, the game plan has become clear.

    So, the plan is thus:

    New cases
    Keep the original lightweight crank
    Lightweight bushless Carrillo rods from JS
    Lightweight billet 750 pistons
    Morgo barrels
    Hyde half race cams
    Kibblewhite 6mm stemmed valves, OS inlets, comical springs
    Re fit the new 5 speed box I already fitted
    Newby belt drive (dry).

    Apart from the rods and belt kit, everything else is already ‘in stock’ here at FESS.

    Anyway, my logic is thus:

    New cases will be a nice strong base, I’m not looking for a massive performance boost, but I wanna ride it like a Bonnie... a proper Bonnie!

    The Carrillo rods and MAP pistons should be no heavier than stock, I think they might turn out lighter.

    The current lightweight crank is a peach, it’s smooth and it’s revvy, which makes it a really enjoyable and fun ride. So, provided rod & piston weights are not very different, I don’t intend to get the crank re balanced, there are too many stories of balancers making things worse. Well, at least that’s my thinking at this stage.

    Morgo barrels will make it a 750 whilst keeping the ‘long rod’ layout and without having to machine the cases.

    I though a lot about keeping the current 3134 cams, I do like them, but Hyde half race cams are actually a 3134 profile but with a bit more lift. So, with it being an extra 100cc’s, I reckon the extra lift will help, but the profile will maintain the current characteristics of the engine.

    The Kibblewhite valve gear should help with gas flow and springs that are both kinder on the valve train and give better valve control.

    Re fitting the new 5 speed box is a bit of a no brainier!

    And then, with the option of a nice dry primary case, I will fit a Newby belt drive, just because I think they’re bloody lovely!

    So there you go, this IS NOT a hot rod project (it would be 900cc 8 valve job if it was) it’s more of a ‘hop up’ project aimed at keeping the Bonnie characteristics, plus some.

    Don’t hold your breath waiting for updates, this will be a slow burner. But here’s some pics to start things off:

    Billet MAP 750cc pistons, lovely looking things, I may round off the sharp edges around the valve pockets (ala Stan Shenton) but I think that’s all. They are slightly over size for the Morgo barrels, which is good, as I can get them finished to my requirements.

    The underneath is nearly as nice as the top. Lovely:

    The Hyde cams fit lovely in the new cases and turn nicely, almost like new! Morgo barrels just dropped on for the pic:

    And that’s all for now sadly. Will update as and when small steps are made.
    xbacksideslider likes this.
  2. Bernhard


    Apr 20, 2011
    May I suggest you remove , clean and use some locklite in the bottom threads of all the barrel studs & nuts, as these, I believe have a habit of coming unscrewed !:(
  3. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009

    Don't Loctite the nuts. They have to be re-tightened after a few miles on the road, when the barrel settles on the cases.
  4. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Agreed, loctite on studs, nuts free to be frequently torqued. Seems best overall to me gents.
  5. daveh


    Jan 22, 2008
    Pure engine porn, Nigel! A 'warm' 750 conversion AND a 5-speed gearbox in an otherwise stock-looking T120R - sounds intriguing. I'll be interested to hear more.

    Keep us posted,

  6. acotrel


    Jun 30, 2012
    Are 750cc Triumphs faster than 650cc Triumphs or does piston weight take the edge off the 750 ? - The usable rev range is probably different ?
  7. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    All things being equal, a 750 is faster.
    No issue with revs.
    More to the point on a road bike, there’s an increase in low to mid rpm pull.
    My billet 750 pistons will be lighter than the current 650 pistons BTW.
  8. grandpaul

    grandpaul VIP MEMBER

    Jan 15, 2008
    Very nice! All the right stuff...
  9. acotrel


    Jun 30, 2012
    I think it is a simple fact that Norton 750 engines are usually faster than Triumph 750 engines. There are probably several reasons for this. When the guys hot up Triumph motors, getting higher compression means the piston crown has to poke up higher into the combustion chamber, there is no squish band and the pistons weigh more. With Jawa two valve speedway motors, the squish band is up inside the head. With a Triumph motor, it is possible to do similar and reduce piston weight while increasing compression ratio and gain the squish band.
  10. acotrel


    Jun 30, 2012
    How closely do the sides of the crowns of those pistons, fit the Triumph head ? When I did it, I made an aluminium template to guide the machining of the crowns.
  11. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    So, you’re suggesting I build a Nor-umph are you ?!?
    Last edited: Jun 14, 2019
  12. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    How close? About 10 feet currently, pistons are on the shelf and head is on the bike...
  13. acotrel


    Jun 30, 2012
    Not at all
    . Triumphs have the advantage that you can adjust the valve timings of exhaust and inlet independently. But you will never have the same downdraught on the inlet tract. What I am suggesting is the pistons in the photo look as though they might still have the gap between the edge of the crown and the head. However I am used to looking at 650 pistons. the bigger 750 bore might create the appearance that the gap is still there. If you look at any 650 piston after it has been in the motor for a while, it will have carbon on the side of the crown which is away from the plug. What I did in one 650 motor was used low comp pistons out of a BSA DBD 32 - 350. The difference in deck height meant the edges of the crown had to be reshaped to fit the head. The pistons were lighter than normal 650 Hepolites and I gained the squish band. The comp.ratio was high enough, because on a normal 650 piston there is a lot of clearance between the edges of the crown and the cylinder head. But you don't end up with the hump in the centre of the cylinder at TDC.
    The MAP pistons look excellent and if the side clearance between the crown and the head at TDC is minimal, they should work extremely well. Over the years many of us have hotted up 650s using standard type 12 to 1 comp. pistons and methanol. I think we could have done better by opting for a slightly lower comp. ratio with flat top pistons, but incorporating a squish band within the combustion chamber. There is a lot of mystique about needing very high comp. when using methanol - not all we hear is the truth. Methanol still works at low comp and if you run it even slightly rich the motor becomes sluggish - just like petrol but half as critical.
    Last edited: May 23, 2018
  14. xbacksideslider

    xbacksideslider VIP MEMBER

    Aug 19, 2010
    Sweet Sir Eddie!
  15. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    John, this project is on hold for the foreseeable.

    I given my Dad use of my ‘68 T120 cos his Hinckley Bonnie was getting to be too heavy for him.

    The last thing he wants is for me to turn it into a hot snot hot rod !

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