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Compression issue

Discussion in 'Norton Commando Motorcycles (Classic)' started by acadian, Apr 17, 2019.

  1. Danno


    Feb 7, 2010
    I've never heard that. Both plugs fire simultaneously with a Boyer (wasted spark). If you foul a plug and it quits sparking, does the black box sustain damage?

    My idea behind this "test" is; you have a good-running engine, but a gauge tells you only one cylinder is up to snuff, so the good one should idle stronger on it's own than the weak one. If it does, that confirms the compression tester's reading. If both idle the same, something is amiss in the gauge or the operator.

    Truthfully, a leak-down test is the best way to assess the compression.
  2. Danno


    Feb 7, 2010
    If your combustion chambers hold fuel turned upside-down, the valves are seating and sealing properly. On a newly-rebuilt engine, it's possible the rings haven't fully seated and just need some break-in.
  3. htown16

    htown16 VIP MEMBER

    Apr 29, 2009
    When you pull a plug wire off one side on a running engine with ei, always ground the wire either with a spare plug or some other method.
  4. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    I think it’s the coil you’re stressing when you open-circuit the HT.

    And on a dual output coil, both cylinders might stop.
  5. kerinorton


    Feb 12, 2013
    HI Titon Thrasher. I looked [ googled ] up 1/ Cycling Proficiency Certificate, AND 2/ Pulteneytown Academy, 1966.
    1/ LOOKS like it is to do with push bike safety ????
    2/ Looks like it is what we call a primary school. ????

    Never mind that though. Perhaps you can enlighten us about about the theory regarding the second ring gap that I have never heard about before.. Perhaps explain in better detail than that discussion above about the Science of second ring technology. It is a bit vague but I get what they are saying.

    BTW, i did my training at Wellington Polytechnic and got my NZ Advance Trade Cert in the mid 1970's. I dealt with regular cars and light vehicles [ LOW REVERS ] and was never interested in racing.

    I retired from the automotive field 19 years ago though and never had the need to update my qualifications.
    Last edited: Apr 23, 2019
  6. baz

    baz VIP MEMBER

    May 26, 2010
    You wouldn't by any chance have fitted one of the compression rings upside down?
  7. acadian

    acadian VIP MEMBER

    Mar 5, 2010
    I did not reverse the rings, but hadn't thought to check that until I was getting ready to put it all back together. Which it is, now, all seems well, I'm just going to run it in a bit more and see where I'm at.

    Valves all checked out BTW

    Attached Files:

    Last edited: Apr 23, 2019
  8. Atlas Commando

    Atlas Commando VIP MEMBER

    Feb 27, 2018
    Decades ago, a friend of mine put his rings in upside down. don't know if it was one or both. He forgot to check the direction so they went in randomly. I do recall that it smoked like a chimney on both sides. Maybe you only missed one ring on the 'bad' side, but if it was both I think you would know immediately by the smoke. Since the barrels are back on I would proceed to running it and doing another test. I'm hoping it was a brain freeze during tappet adjustment on one side and you'll have good compression this time.
  9. Adam M

    Adam M

    Mar 16, 2019
    For me cylinder looks a bit glazed, but this would not cause such a difference in compression.
    If no evident leak is visible in the head gasket area one of the valves was not closing completely (IMHO ).
  10. baz

    baz VIP MEMBER

    May 26, 2010
    It's probably not the rings but I can remember I once put the compression rings in upside down, I can't remember now if it was the two top compression rings or all four
    But I know I couldn't kick it over
    I never did start it, I assume it would have smoked like crazy if it'd started?
    So I just wondered if you had one ring up the wrong way if it would cause the condition you have?
    As you no doubt already know the easiest way to check the taper is to stand the ring on a surface plate or sheet of glass and see which way it wants to lean
    Hope you get it sorted, if it was mine i would give it some really hard bursts of revs when I took it out but not continuous
  11. Nater_Potater

    Nater_Potater VIP MEMBER

    Apr 7, 2013
    In aircraft mechanics school (they're still mostly aircooled, pushrod engines) we were taught to make sure everything's ready to go so it would start as quickly as possible, then immediately go into the open-and-close of the throttle until the cylinder head came up to temp. Shut it off, let it cool down to room temp, re-torque everything, then back to the throttle bit for at least another half-hour. We never had a smoker, and I've used the same technique on both air and water cooled engines with equal success. The rings need that short burst of heavy load to force them to wear against the cylinder walls, but not so long as to overheat them. Once they've made full contact, the heat is carried out to the cylinder walls, and you don't (shouldn't) have to worry about burned rings.

    An acquaintance built a Hon-dog 500cc 4-banger into a "big-bore" 600cc track racer, but kept pussy-footing around the track "to make sure it's fully broken in". It never stopped smoking, so he knew it just needed more miles. Well, I went out with him on the hot-rod Ya-mama-ha 650 twin and started pestering him. Apparently, he forgot about taking it easy, and, guess what; it wasn't smoking when we came back in!

    Put it together, fire it up, make sure you have good oil flow, seat the rings, then rod the $h17 out of it.

  12. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    Some info on bigger 2nd ring gaps cropped up on Britbike.com recently. http://www.britbike.com/forums/ubbthreads.php/topics/772800/re-rings-to-oil-or-not-to-oil#Post772800

    This link appears to be the source of it. https://www.fordfe.com/ring-end-gap-input-please-t76170.html

    A nice man called Barry says:

    “Actually the big second gap process was defined from OEM research work at Federal-Mogul and Perfect Circle. As a result of the research, every OE I am aware of went from having a smaller second gap to having a larger second gap over a period of five years. Did not matter who - Ford, Chrysler, and GM all went that way.

    The guy who worked for me at the time is likely to be one of the best ring guys on the planet, and he got them to run the same simulations (using F-M's Cray - not exactly a desktop dyno sort of deal) with input data from a then current Cup engine. He got similar positive results. We then tried it with a couple selected teams and went "public" with the info in a Jeff Smith article article in Chevy High Performance magazine, which was very well respected for tech at the time (mid-90s).

    We had positive feedback on bigger second gaps from the OEMs as noted, as well as from numerous cCup and Pro Stock teams - essentially anybody who had the resources to do a controlled test with isolated variables so either no change or a positive one. Gap changes in an otherwise optimized package are going to be like that - incremental single digit or low,low double digit changes. Anybody that claims you'll get 30 or 40 horsepower from a gap only ring change is blowing smoke - or smoking something.

    You'll get the biggest gains from ring stabilization at loads where pressures can approach equalization above and below the top ring. Part throttle operation or under bore distortion at high load. The more tightly sealed the top is, with the least distortion, the smaller the benefit. At some point other variables will outweigh most ability to verify any benefit in a street engine without A-B-A testing, but the trends are pretty clear.

    Speed-Pro, Perfect Circle, JE (outsourced from NPR, Riken,F-M) and other ring providers have gone big 2nd gap on recommendations. Total Seal is the single exception to this. They cannot really promote the change since it goes against everything they've preached regarding the gapless deal for 20+ years. You will notice that subsequent to the big second gap deal they quickly moved to the topless top ring as a primary marketing piece and are comparatively quiet about the second.

    Barry Rabotnick
    Last edited: May 6, 2019
    Nater_Potater likes this.
  13. o0norton0o

    o0norton0o VIP MEMBER

    Apr 27, 2015
    Triton thrasher, that can't possibly be true. Perhaps they didn't consult the NZ counsel of fully qualified engineers...:p
    Nater_Potater likes this.
  14. jbruney


    Jan 5, 2019
    I've been tracking the same thread over there and it appears to have considerable backing...Not that I'm willing to break tradition over mere printed word. I believe test results though.
  15. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    It is now common practice to use a second ring gap that is larger than the first.

    The reason for it is to prevent a buildup of pressure between the top ring and the second ring. They want the second ring to leak more than the top ring.

    If there is pressure buildup between the top ring and the second ring then the pressure that forces solid contact between the top ring and the cylinder wall is reduced. With less pressure behind the top ring, in comparison to the pressure below the ring, the ring does not seat as well and ends up leaking more. Jim
  16. MexicoMike


    Jan 31, 2010
    jbruney likes this.
  17. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008

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