To Hone or not to Hone; Chrome-plated Two stroke bore

Discussion in 'Old's Cool' started by Quickv4, May 11, 2010.

  1. Quickv4

    Quickv4 Pro Turd Polisher

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    I was going about replacing the blown base gasket on our Aermacchi/HD SS250 today. When I went to put the cylinder back on the piston, I miss aligned the rings, and snapped the top compression ring. The bike had excellent compression considering the mileage (over 10000 miles estimated), but of course I will need to install new rings.
    This means going through the whole "refesh" process, but this has me confused.
    It is a chrome-plated aluminum bore, and Im wondering whether I should hone it or not.
    I have found in multiple resources that one should use a ball/flex hone to do the job, but im so afraid on wrecking the bore by honing it through the coating, if it is not needed, I will not hone it.

    My father already honed this bore once using the above method, will it stand up to another light honing?

    The bore has no deep scratches or gouges, except it is taking on a gloss towards the bottom, and the cross-hatch that is still there is not as defined as I think it should be.

    Like I said before, the engine had a good 125psi of compression the last time I checked.

    So to hone or not with new rings, that is the question!:ear
    #1
  2. JPSpen

    JPSpen At Large

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    I think I'd just leave it alone..Especially since it's been honed once already.
    Just wonk on the thing when you first get it running to get the new rings seated quick.... No high rpms but large throttle openings at lower rpm's.

    That'll put a lot of pressure on the new rings and get them seated asap..

    Good Luck

    John
    #2
  3. caponerd

    caponerd Kickstart Enthusiast

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    I don't think you want to touch chrome plating with a hone.

    My guess would be that the hone marks will last longer than the new rings.

    (assuming you don't accidentally hone right through the layer of chrome)
    #3
  4. Grider Pirate

    Grider Pirate Long timer

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    Anything below the top of the highest port doesn't seal combustion chamber compression, so I wouldn't worry about the 'gloss'.
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  5. norton73

    norton73 drinkin'

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    :nono

    You should not hone a chrome plated cylinder. The chrome is harder than your hone.
    Also, you risk the hone catching the chrome next to one of the ports and flaking of a big chunk.

    And definitely do not use a ball hone on a two smoke, the ball ends will go up in the ports, might ruin only the hone if you're lucky.
    #5
  6. concours

    concours WFO for 44 years

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    +1... Chrome is not to be honed... and the rings must be specific for it, that is, NOT chrome.
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  7. mark1305

    mark1305 Old Enough To Know Better

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    I thought the HD Italian singles, both 250 and 350 were all 4-stroke. And I'm from that era. Do I need an Alzheimers test? (I had a HD Hummer 165, so I do remember they were 2-strokes.

    But I also vote in favor of not touching the bore and put in new rings. Break in with increasingly aggressive and longer rides with equal cool down time between each ride. Ie., ride 5 minutes with off & on heavy throttle but moderate rpms. Cool 5 minutes. Ride 10, cool 10. Ride 20 and cool 20. Ride a normal 30 minute ride, cool it all the way down and call it done. Or something like that.
    #7
  8. Quickv4

    Quickv4 Pro Turd Polisher

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    Nope, alot of people think they were all the 4 stroke Sprints. Nope, not so, They had the two strokes also, the X90, Z90, SS/SX 125/175/250, Rapido, TX 125.

    What we have...

    [​IMG]

    (not mine, this is the one at the Museum)



    Sprint 250.....

    [​IMG]
    #8
  9. mark1305

    mark1305 Old Enough To Know Better

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    Cool, thanks. The Sprint 250 is the one I remembered with the horizontal cylinder,
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  10. Pigford

    Pigford British

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    Lots of bike have chrome (nicasil) bores - Old Suzunki GT550 to name one :wink:

    DO NOT HONE :huh
    #10
  11. YamaGeek

    YamaGeek Ancient trailbike padwan

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    Are you sure it's a chrome bore? If it has cross hatching, it's not a chrome plated bore, it's either a steel or iron linered bore. I know of no chrome plated cylinder that has cross-hatching, it's usually a pretty smooth surface.
    #11
  12. Quickv4

    Quickv4 Pro Turd Polisher

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    Im 100% sure it is a chrome bore.
    However, my father honed it in his (and the bikes) younger days. I think your right with the chrome bore being shiny in its unmolested state.
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  13. YamaGeek

    YamaGeek Ancient trailbike padwan

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    Is it the same bike in the second picture you posted? That's definately an cast iron cylinder on that bike. I own a Ducati 250 and it has a steel liner with a heat shrunk aluminum outer cylinder.
    #13
  14. Quickv4

    Quickv4 Pro Turd Polisher

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    No, it is a SS250 two stroke, like the orange one in the museum above. Its not a Sprint.

    I got some opinions from the Aermacchi guys, including a major parts supplier. They all said also not to hone it.

    Looks like I will NOT hone it, and do a lively break-in routine, based on the collective opinions of almost 10 agreeing people.
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  15. concours

    concours WFO for 44 years

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    Chrome lined bore is N O T Nikasil!!!! Two totally different animals. Nikasil is a spray welded lining that is then honed to final size. (and can and should be diamond honed when re-ringing)
    Chrome is an electroplating of the bore. It has a very smooth surface finish, NOT the cross hatch of iron lining and Nikasil. The rings are specific for that purpose. Chrome lined cylinders existed WAAAYYYYY before the technology to apply Nikasil exised.
    Considering them one and the same with interchangable terminology is inaccurate and could cost somebody an engine if they read these posts as gospel.
    Carry on.
    #15
  16. Quickv4

    Quickv4 Pro Turd Polisher

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    Concours, you are very correct. Nikasil and Chrome bores are two different coatings.

    But it so happen when many chrome bores wear out, the best replacement for them is Nikasil, since (from what Ive read) Chrome bore plating isnt to widely availble anymore.

    Ironically, I live about 1 mile away from one of the few places in the US that do Nikasil liners. UsNicom.
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  17. Pigford

    Pigford British

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    Please accept my humble appologies - obviously I am not perfect, unlike you..... :huh
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  18. Strong Bad

    Strong Bad n00balicious

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    I worked as a 2 stroke "Porter/Grinder" back in the 70's. I ported for EC Birt's Precision cycles and I was the first and only grinder at FMF (known as Flying Machine Factory back then) for over a year. I've seen lots of chrome, cast iron and even Nikasil. I've been told that you can't port a chrome bored 2 stroke because the chrome will peel. Well that's bull shit as is a lot of other crap and miss-information people with no experience will spew. People also get mixed up and confuse the difference between a glaze breaker (squiggley/balls) and precision stone or diamond hone (like a Sunnen hone) used to give a precise bore. A ball "hone" can be used to "clean up" a chrome bore but it really won't do much at all. We used to always run one through the chrome bores after porting and NEVER saw or heard of ill effects. No the little balls don't get ripped off in the transfer ports and it does help blend in where you cut into the barrel. A glaze breaker will have a much greater effect on a cast iron liner or barrel and it is possible to go over board and ruin the bore with one.

    Bottom line: DO NOT run a Stone hone through a chrome bore, you can run a ball/squiggley glaze breaker through a chrome bore but with little to nil effect.
    #18