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Blown engine (19/8/2018 update)

Discussion in 'Norton Commando Motorcycles (Classic)' started by Adam_R, May 12, 2018.

  1. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    My guess would be insufficient clearance at the rod bearing. I've had that problem a few times with a newly ground crank. [like the last one I had ground]

    The spec only says <.001 clearance, but it better not be much less than .001 or this can happen. I prefer just over .001 clearance. Jim
  2. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Jul 8, 2011
    That's why I alway plastigauge.
    SteveA likes this.
  3. Bernhard


    Apr 20, 2011
    Bottom end failure is usually caused by lack of oil – the filter in the feed pipe of the bottom of the oil tank can get blocked up over time, oil pump failure, blocked crankshaft oil holes there is a whole range of possible faults that need to be looked at. Does your oil tap allow maximum oil flow for the double speed oil pump/ it may only be flowing X pints per min. when y pints p.m. is required. HTH
    Last edited: May 15, 2018
  4. auldblue

    auldblue VIP MEMBER

    Nov 20, 2012
    What is the history of the motor? On start up did you check the oil return and level on start up? Was the bike wet sumped after a run and what was the oil level in the tank after use? When you changed the oil was it contaminated with metal and was the motor getting noisier? Do you service the bike yourself or get it done elsewhere? Anyway ,when it comes to auld bikes these things happen so no use getting upset, nobody's died and it can be fixed!
    Nater_Potater likes this.
  5. chaztuna

    chaztuna VIP MEMBER

    May 5, 2017
    Another possible cause could be from fuel dilution of the oil, due to a leaking [or left open] petcock.
  6. grandpaul

    grandpaul VIP MEMBER

    Jan 15, 2008
    I'm with Fast Eddie, the interior of the engine did NOT get all black from THIS failure, that is BUILDUP (over time). Also note the BURNED rod, it's black!

    Do you have photos of the overhaul as work was in progress? You should have a photo of very nice clean crankcase halves. Could be the overhaul was not as advertised. Same goes for the sludge trap, could have been overlooked previously, crank never un-bolted and inspected.

    I'm not saying that IS what happened, I'm saying it COULD BE what happened. Sure looks badly built up and burned, from the photos...
  7. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Adam rebuilt the motor himself GP...
  8. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Jul 8, 2011
    All the black in the engine and the black rod end could have been a result of a long and drawn out big end rod failure. Too tight upon rebuild and/or lubrication problems.
  9. grandpaul

    grandpaul VIP MEMBER

    Jan 15, 2008
    That would explain it. Wow, what a grenade...
  10. grandpaul

    grandpaul VIP MEMBER

    Jan 15, 2008
    Went back and looked at Adam's other threads, and it sure looks like this was a "problem child" engine from the beginning.

    That sure stinks, right when the weather is good...
  11. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    This seems to be the leading suggestion at the moment.

    26 miles is a long way with no oil supply, but JimC got 12 miles.

    Maybe Adam’s bike had some oil around, but not enough.
  12. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    That’s kinda what I thought TT, my hypothesis goes something like this:

    He had an air lock to start with, the engine suffered, but pulled enough oil through to survive, he stopped just in time to prevent a seizure, but too late to prevent the damage, so when he re started, a seizure was inevitable.

    And / or incorrect grinding of the big end giving insufficient tolerance.
  13. Adam_R


    Nov 20, 2015
    Ive not had a chance to strip the engine any further,
    but to answer some of the comments.

    The engine was rebuilt towards the end of last year, a circlip had escaped and gouged the bore. At this point i found the big ends worn and the cam was marked as well as the followers.

    I decided to rebuild myself, (this is not my first bike engine build) the rebore and crank grinding was out sourced.
    I cleaned the cases thoroughly using good old elbow grease both internal and external. they were dried and put to one side.

    It was at this point i ordered a 4s cam from norvil
    The superblends and shells came in a bottom end rebuild kit from RGM whom also supplied new followers.

    I picked up the crank and barrels from my engineer.
    the sludge trap was cleaned by myself. and the crank re-asembled with new bolts

    Oil pump was stripped and cleaned then rebuilt as per the book.

    The new followers were fitted to the barrel and the camshaft trial fitted to ensure even contact on the faces.
    The Rods were fitted to the crank using engine build lube and torqued to book spec.
    Everything was spinning freely.

    the crank was put in the case along with the cam (using the supplied lube) with a light smear of sealant on the joints. bolts were tightened up and once again the assembly was checked to make sure it span freely.
    Timing set and chain on and tensioned

    accralite pistons fitted with NOS accralite rings (I had an issue with the new rings on my triumph)

    Barrel on then cylinder head.
    ready to go back in the bike.

    the oil tank was removed and cleaned out as well as the pipes.

    engine back in

    bike was run in as per norvils cam instructions.
    oil was returning at tank

    Had some issues with the boyer so replaced with a trispark, (running better but still not quite right)
    so bought a pair of premiers.
    had some isolastic issues so wasn't used much.
    changed oil after a couple of hundred miles with a new filter over the winter
    Oil is Castrol XL40
    nothing out of the ordinary in the oil.
    Re-torqued the head and barrel.

    start of the summer

    fitted a PCV valve as per recommendations on the forum.
    Ran for a bit more still trying to iron out the tuning issues, no leaks and no smoke.
    was running fantastic, went out on the Sunday running spot on.

    Got to St Andrews, traffic was a bit heavier so some filtering didn't have me waiting about.
    stopped by the beach, (on the road) and caught up with some mates.

    started up and headed out to Anstruther, made it around 6 miles before it went bang.

    Im still a bit gutted and it hasn't quite sunk in yet.

    Grandpaul is right in saying that its been a bit of a "problem child" its certainly been a rather expensive journey so far.

    I understand what has been said about airlocks in the system and the possibility of incorrect big end clearance, and i hope to pull the engine and strip it down this weekend.
    ive not got a lot of pictures from the rebuild but here a a couple

    Thanks for the reply's its helping me to figure this out, not that i can do much now, just got to decide if its worth fixing.
  14. JimC


    Oct 12, 2007
    When you rebuild, get rid of that damn manual valve in the oil line. There should never be anything other than a hose between the oil tank and oil pump.
  15. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Jul 8, 2011
    Ditto on removing the manual valve, plastigauge the journals.

    Consider yourself lucky, very lucky. It may not feel like it now but when you reflect back on the "other" possible outcomes, most of them are not pretty.
    cliffa and SteveA like this.
  16. oldmikew


    Jul 25, 2015
    Exactly .
  17. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    No oil pressure light, gauge or indicator?
  18. Adam_R


    Nov 20, 2015
    The valve will be going in the bin, and if it does get rebuilt i will be fitting an oil pressure indicator of some sort.
  19. dynodave


    May 28, 2003
    Probably the most sensible approach...
    even though my oil pump testing procedure it not super refined , By testing them I saved 2 club guys from almost assured blow up since their pumps were SO BAD it was pittiful. two other club members came to me AFTER a "fresh" rebuild blow up such as in this thread...you guessed it ...bad pumps.
    How some one can "look at the gears" and tell if the pump is good or bad is magic...
    New pumps are let's say 100%. What do you think when you put new tight rod shells and the pump can only flow 20% of a new pump. NO cooling flow and the rod shells melt.
    Was it a good pump?? then why the shut off valve to stop wet sumping.
    Every Norton I own will have a gauge on it.
    delagem and JimC like this.
  20. JimC


    Oct 12, 2007

    No gauge or warning light is akin to playing Russian Roulette.
    delagem likes this.