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920 engine build waffle (2016)

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fast Eddie, Oct 31, 2016.

  1. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Ladies, I thought I’d do anther ‘engine build’ type thread for those nerds that are interested in such stuff. I thought I’d do it separately to my previous one and title it as a 920 build to help those searching around for 920 build info in future.

    Well, my story is that I bought a Maney crank to put in the ‘Blue Bomber’. Then after a lot of thought, I basically decided that the best place to put such a nice crank would be in some nice strong Maney cases. Then, further thought deduced that such a strong bottom end justified some improvements with regards to output. And so, another 920 project was born!

    So I got a set of cases from Steve Maney, machined to accommodate a standard primary case, this weakens them somewhat, but I really wanted to keep the stock primary case set up. It will still be plenty strong enough for my needs, according to Mr Maney.

    At my request, the cases have no holes drilled from crank chamber to timing chest, this saves me having to plug them for using a Comnoz / cNw reed valve breather. Maney cases come machined to take the Combat style breather at the rear of the case, so I’ll use the cNw style breather that bolts directly into this location.

    As mentioned previously, I already had a Steve Maney crank on the shelf that I bought earlier. I sent this back to Steve for him to fit the main bearings and shim up accordingly to the new cases. I know I could have done this myself, but being in ‘this deep’ already, I thought I’d let a specialist do it right! The cases have been machined to accept a set of Steve’s 920 barrels, which have been finish bored to 81mm in readiness for the JS pistons.

    I have had extensive conversations with Jim Schmidt (thanks Jim) regarding pistons. I have used his high compression 850 pistons very happily hitherto in the Blue Bomber. We arrived at an 81mm 920 design based on the spec of the 850 high comp pistons, with extra material in the crown to allow for a 1mm dish machined into the crown. According to my ‘fag packet’ calculations, this should allow a tight squish and keep the CR at a reasonable 10.5:1 (or there about). I’m aiming for a 030”-.035” squish clearance, which is what I am currently running with no sign of any contact anywhere. The pistons will be hard anodised with the ‘Diamondyze’ process as per my current 850 pistons.

    The fabulous Comnoz ported RH10 head will be used as is, apart from opening up the squish area to suit the 81mm bore.

    I really like the BSA cam followers that I am currently using with my JS1 cam kit, but the flat lined peak BHP graph that I had on the dyno (virtually flat from 6300 to 7500) led me to conclude that a hotter cam might help liberate some power above 6300, plus the increased displacement will have increased breathing requirements, so, after much deliberation, I have opted for a slightly hotter JS2 cam. The JS2 has the same duration as the JS1, but has more lift, and is very similar to the PW3. I will be using a Webcam hard welded JS2 ‘smoothramp’ version. Actually ‘Brooking850’ has a large part of the blame here as his glowing praise for the JS2 cam in his race bike certainly helped to persuade me in that direction!

    Its not likely to be a very quick build, I am aiming to fiddle around collecting the necessary parts (and spread the cost) and hopefully will get the engine built and nailed in to the frame next winter (2017-2018).

    I’ll post some pics of various bits n bobs soon.
     
  2. lynxnsu

    lynxnsu

    Joined:
    Sep 18, 2007
    nice
    like your down to earth info , no bullsh......
     
  3. grandpaul

    grandpaul VIP MEMBER

    Joined:
    Jan 15, 2008
    This should be fun.

    Why not move it to the "Projects" section?

    Oh yeah, pix, please...
     
  4. cjandme

    cjandme

    Joined:
    Feb 5, 2011
    All I can say is Awesome! I look forward to any and all progress that you might share with the rest of us here on these threads. :mrgreen:
     
  5. trident sam

    trident sam

    Joined:
    Oct 23, 2012
    Sounds like a plan mate !
    I look forward to seeing you in the Trident's rear view mirrors :twisted:
    sam
     
  6. BritTwit

    BritTwit

    Joined:
    Aug 25, 2009
    Nigel now I'm a fan of your 920 project too. :lol:

    Keep us up to date.
     
  7. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Where dya get the mirrors that can see through smoke clouds Sam...?
     
  8. trident sam

    trident sam

    Joined:
    Oct 23, 2012
    Smoke Sir,.... :roll:
    I'll inform Neil of your insult my man.
    Now just get it built, don't worry I'll let you catch up now and again, makes it more fun . :lol:
     
  9. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    When you go to that big bore size, how do you seal the bit between the cylinders at the centre of the head, from leaking compression ?
     
  10. gortnipper

    gortnipper VIP MEMBER

    Joined:
    Nov 11, 2013
    Well, based on our PMs, you know that I think this is a mistake. Or are you going to use the FA head on you primary motor? :mrgreen:
     
  11. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Nigel, will you use the stock transmission with this 920?
    If you add it all up, it sounds like a lot of power will be running thru the box with this new motor.
    I know Jim Comstock is doing something similar with his bike and it has kept it in one piece by exercising restraint.

    With all of these Tridents gunning for you, it seems you might need to go a bit harder on the power train.
    I see a TTI box showing up soon.

    Glen
     
  12. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    It would be nice Glen, as would the FA head that Gortnipper suggests. Sadly though, those two items would probably double the budget, so I'll have to manage without.

    I will swap my belt drive from Norvil to Maney, which speeds up the primary gearing and eases the loads on the gearbox and will probably fit a Maney outrigger. Both of these items are already 'on the shelf' and I'm already using a strengthened AN gearbox shell.

    So I think my direction here has already been set.
     
  13. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Well, hopefully, with a head gasket.
     
  14. Matchless

    Matchless

    Joined:
    Dec 23, 2010
    On the subject of head gaskets, I wonder if Jim Comstock is any closer to having Cometic 920 head gaskets made. If he doesn't read this I'll send him a PM.
     
  15. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Anyone can send a pattern gasket to Cometic for reproduction in one of their chosen types.
    The cost is pretty low, if I remember correctly.

    Glen
     
  16. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Cometic will only do them in copper without making a large investment for dies to make a multi-layer gasket.

    I have been doing the cylinder head o-rings which have been working excellent. No gasket- no leaks.

    [​IMG]
     
    chaztuna likes this.
  17. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Like Fast Eddie said, with a gasket. Or maybe now with comnoz's trick O-rings. That really is slick.

    But for the old school methods, as you can see in this picture of a 920 cylinder, there is plenty of material between the bores for the head gasket to seal. I used the copper O-rings around the bores in addition to a copper gasket because this was a high compression engine. I've also run 920 engines without the copper rings, just the usual .040" copper gasket, with no problems. For race engines, I like the extra safety margin the O-rings provide.

    [​IMG]

    FWIW I don't recall ever having a head gasket fail on a Norton between the bores, but I have had them fail at the pushrod tunnels and at the outer edge of the bore.

    Ken
     
  18. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    I've got a couple of different thickness of copper head gaskets coming from JS so I can fiddle with squish gap. I don't intend to use anything on the barrel base apart from Wellseal. I intend to use the .005" copper wire loops around the pushrod tunnels and oil drain hole along with the copper head gasket.

    I just have to decide what goo to use. JS swears by plybond. Matchless has an oil tight Maney 920 using BMW silicone sealant, 2 tubes of which I have on the shelf. And I have always had good results (but not used on the head/ barrel interface) with good old Wellseal. I don't want to be pissing around taking the head off to fix oil leaks...!
     
  19. B+Bogus

    B+Bogus

    Joined:
    Jun 28, 2009
    No problems here using Welseal around the pushrods tunnel with a copper head gasket, but mine are just plain old wussy 850s....
     
  20. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Yeah, we all have our favorite magic goo, don't we? Ron Wood turned me on to using Pliobond on copper head gaskests years ago, but I've also used pretty much every other goop there is at one time or another, from spray on aluminum paint to Yamabond. The latest 883 engine I did I used a copper head gasket with .005" wire set in Hylomar around the pushrod tunnels and oil drain hole (and it still weeps oil). They mostly all leaked some oil eventually. Jim Comstock suggested a high temperature pipe jointing compound, but I haven't had a chance to try that yet. The only engine I recall not having oil weeps was the stock 750 in my first Commando, a Production Racer that I only used stock flame ring gaskets in. Once I started modifying the engines for higher compression and bigger bores, I don't think I ever had one that didn't eventually start showing some oil around the head and cylinder fins at the joint. I think using a reed valve crankcase breather will probably help a lot, but I don't have any significant experience with that yet. Using Jim's waisted ARP head bolts should also help, but I don't have any experience with that yet either. Always something new to try.

    I'm really intrigued by Jim Comstock's latest gasket free technique, and looking forward to seeing how it holds up to his high mileage riding.

    So, is the gasket goo topic now up there with the infamous oil and tire threads on the list of perpetually repeating topics?

    Ken