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71 commando using atlas cylinder

Discussion in 'Norton Commando Motorcycles (Classic)' started by qside, Nov 2, 2018.

  1. qside

    qside

    Joined:
    Sep 8, 2016
    I am working on a 71 commando project. I am sure you all have seen them... a frame on wheels and boxes of parts. The last owner became tired or frustrated so now its my turn.
    I am assembling the motor first. I noticed that the cylinders had a crack in the skirt and I am concerned of it failing so I hunted out a new set of cylinders. I found an atlas cylinder that was in good shape. I had the bolt holes drilled and tapped to match the commando head when I had the cylinders bored. The atlas cylinder has the original atlas lifters. I also have the lifters that are in the damaged commando cylinder if I need them.
    So here is the first question: Are the lifters for the commando and the atlas the same? I plan to use the commando lower end, the atlas cylinders, the commando push rods and the commando head? So which lifters do I need, or does it not make a difference?
    Thanks for any help...
     
  2. bill

    bill

    Joined:
    Jun 1, 2003
    if you are reusing the original camshaft than you will reuse the commando followers and keep them matched to the same lobes. a new cam will need either new followers or a set reground for the new camshaft. so far new followers seam to be hit or miss as to proper hardness more so the old ones.
     
  3. qside

    qside

    Joined:
    Sep 8, 2016
    Thanks, That was just the info that I needed.
     
  4. qside

    qside

    Joined:
    Sep 8, 2016
    ok another issue:

    I switched the original commando lifters into the atlas cylinder. I am using the original commando push rods. When I put the head on the motor without the push rods, it fits snug to the cylinders as it is supposed to. But, when I put in the push rods, there is a measurable space between the head and the cylinder. I loosened the tappets all the way and rotated the crankshaft to try to let all the valves close. No matter what there was always one rocker arm bottomed out on the top of the valve. It seems that either the lifters or the push rods are too long. Is that possible?
     
  5. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    IIRC, Commando pushrods are about 0.10 " shorter than Atlas pushrods.

    If you are using Cdo pushrods AND Cdo lifters, there should not be a problem. There is always at least one valve open, or partially open, at any point in the 4 stroke cycle.

    Set your cold tappet clearances at TDC on the valves that are closed, then rotate engine 360 degrees to TDC on the other cylinder and set those valves to cold tappet clearance. Everything should then be fine.

    Slick
     
  6. qside

    qside

    Joined:
    Sep 8, 2016
    So If I bolt the head on down then the push rod will open a valve as expected. This will snug up the gap. For some reason I thought that there should not be a gap when assembled and not bolted down. I will continue the assembly
    Thanks
     
  7. qside

    qside

    Joined:
    Sep 8, 2016
    OK another related question: I have a few unused copper head gaskets. They are for 750 engines. I am not sure if they are for an Atlas or a commando. Is there a difference? It looks like the holes line up just fine.
     
  8. marinatlas

    marinatlas

    Joined:
    Nov 4, 2007
    The four outer head bolts should be 5/16 in atlas head gasket thus you need to enlarge them to 3/8 as you have done for the cylinder.
     
  9. chris plant

    chris plant

    Joined:
    Nov 6, 2008
    check the distance between the head gasket face and the gasket face that mates with the crankcase,I think the atlas barell is oubout 60 thou longer. chris
     
  10. qside

    qside

    Joined:
    Sep 8, 2016
    So his is what happened. I assembled the engine as recommended above. I torqued to spec and finished the bike. The bike started in 1 kick and sounded great. I was getting grey smoke but i wasnt too worried because it was a new build and it hadnt had time to break yet. But there was a fine spray of air and oil coming from the head gasket seal. I retorqued the bolts and some of the spray decreased but there was definitely oil getting into my cylinder. Worse on the right side. The valve guides were new and the valve seats reground. So the oil had to be from the head gasket.

    I took the head off to look. I could see staining on the head gasket where oil was leaking into the cylinder. I can only think of a couple of potential problems. The cylinder was skimmed for flatness but I didnt skim the head. I also used a new copper head gasket but I did not anneal it. Any other ideas? I was so close to being done!
    Gary
     
  11. marinatlas

    marinatlas

    Joined:
    Nov 4, 2007
    Fit a PCV breather valve (even a cheap one), put some sealant around the pushrod tunnel on the gasket (or try the copper wire around them), anneal it , retorque ........
     
  12. pommie john

    pommie john

    Joined:
    Nov 18, 2005
    I use a copper head gasket and I always anneal it, but I also spray it with silver paint. I can’t remember where I learnt that trick, but it works. Use normal automotive acrylic paint, not epoxy.

    However, I would also check that the head bolts are not bottoming out if you’re using a mixture of bolts and barrels.

    Since the head is coming off, obviously you’ll check it’s flat.
     

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