Would you run this?

Discussion in '2-Stroke Machines' started by Jeff Payton #82, May 15, 2020.

  1. Jeff Payton #82

    Jeff Payton #82 ‘The dinosaurs also thought they had more time’

    Recently had a 125 cylinder replated and a new det ring installed.

    I am not entirely familiar with the process of removing and replacing the det ring on any cylinder, but am seeking opinions of others who may have more experience than myself.

    All of the cylinders I have seen that have a det ring installed are seamless from all aspects - the cylinder I recently received back has a gap big enough for a fingernail on one side between the ring and wall. The bore appears and feels to be even from ring to wall.

    I have already sent the cylinder back once for inspection by the company who performed the work and was told that it is within spec and should seal properly. They went as far as to have a well-known ex GP mechanic sign off on the work as well. This did instill more confidence in the work performed, but I paid extra for the det ring and am uncertain of the quality of work performed.

    I was told that if they did try to re-install a new ring that it could potentially make the issue worse, as the process removes a small amount of material each time it is performed (from what I understand).

    I am a poor boy in a rich mans hobby, and it has taken many months of saving to recover from a fairly brutal failure at VMD last season - so to receive this back in the condition it is I have to admit, I am let down.

    Would you run this with confidence on a fresh fully overhauled 125 motor?

    E953B2F9-427D-42E8-95C9-0B16514F90A1.jpeg D10C0BA0-3407-43E0-889A-2C56558F30BC.jpeg
  2. fastfreddie

    fastfreddie Midnight Oil Garage

    The combustion gasses will blow into that gap. Who knows when or if that will be a problem, potentially lifting or blowing the ring out from underneath/behind? Assuming the det ring is consumable, like valve seats in a 4T, I wouldn't settle for a gap any sooner than I would settle for a gap on the combustion side of a 4T valve seat. Don't care who signed off on it, that's questionable work. IMO, that ring-to-cylinder wall gap should be as seamless as it is in the second pic.
    BTW, that looks like the worst cross-hatching job I've ever seen.
  3. cyclox

    cyclox moving chicane specialist

    On my cylinders with det rings, I've never seen a gap between the cylinder wall and the det ring. I'd want a second opinion if it was my cylinder.
  4. tgold

    tgold Well-Known Member

    Here's the part that makes me raise my eyebrow. That you were told "it was in spec". This is a custom job, so where did they get the specification to begin with? Is the an HRC "this is how you machine and install a det ring" instruction? It sounds a bit fishy like they threw out the word "spec" just to make you feel good even when there's a good chance there may not actually be one. Seems more like two guys standing together and looking at you cylinder and saying something like this: Guy 1- "Hmmm. I'm not sure if that gap is ok or not" Guy 2: Hmmm, yeah, never actually noticed that before. Do we have any other cylinders to look at?" Guy 1: "no, I already looked for one" Guy 2: "Well, I think it'll be ok" I mean it IS a det ring and it's a sacrificial part" Guy 1 :"yeah, that's true, It's probably ok, I mean I'd run it if I had to." Guy 2: "Right, if I had to I'd do it"

    When it comes down to it, I think either the cylinder wasn't square when it was machined, or the det ring was machined and/or installed incorrectly. The tough part is getting them to redo it right when they already did it wrong.
  5. Jeff Payton #82

    Jeff Payton #82 ‘The dinosaurs also thought they had more time’

    Yes I am highly speculative of the responses I received from them.

    Unfortunately, it is not a small local machine shop, rather a well-known facility that my service shop I work for utilizes. So upon sending it back after getting the go-ahead to do so from them, I assumed they would handle the flaw without question.

    This facility was recommended to me by countless individuals, and their reputation preceded them. I keep seeing they are looking to hire so I can’t help but think the person who possessed the skill to do this job the right way is no longer with the company, and they don’t have the right skill set available to make it right.

    And I wholeheartedly agree - what is the ‘spec’ ????? Really easy to say that and pass me off.
  6. Boman Forklift

    Boman Forklift Well-Known Member

    Hopefully someone with more knowledge than me responds to you. None of our 125 stuff had det rings, but on any of the pistons we ran, your ring would never go high enough to catch on the possible gap. When you look at what rings deal with between the intake, exhaust and transfer ports, I would imagine this will not be problematic. I do agree it seems that is should be square with not gap.
  7. fastfreddie

    fastfreddie Midnight Oil Garage

    "Not small" and "well known" is not a qualifier for quality. I've seen some eff-ed up Vance & Hines port work. It mighta looked good but, when you went in to measure things, nothing was close to a matched consistency. You're gonna get some difference to balance flow characteristics if you're a perfectionist, but not 1mm differences at port entry diameters or various other measuring points.

    I don't see an issue with ring interference, either. It's combustion gasses blowing out that gap and then getting behind the det ring. The potential is there for the det ring to get blown out if the gasses get behind it. With enough blow out, the top ring land makes contact. It's only gotta blow out a few thousandths.

    I didn't mention it earlier, but it looks like they hogged out the exhaust port bridge pretty good, too. It doesn't need to go above or below the port timing. That creates a potential snag/wear point for the ring(s).
    The bridge in an exhaust port requires a "relief" cut of a thousandth or so inches. This accommodates the bridge's expansion when it gets hot. It should be a concave removal of material WITHIN the confines of the port that blends nicely into the cylinder wall before taking material away from the cylinder wall. The bridges are there to keep the rings from expanding into the port. If the relief cut goes farther into the cylinder wall, it defeats the purpose of the bridge.
    I'll prolly get shit for that last sentence, but I've never eff-ed up a two-stroke ring/piston cuz my relief cut stayed inside the port.
  8. Jeff Payton #82

    Jeff Payton #82 ‘The dinosaurs also thought they had more time’

    Agreed with ring interference and the possibility that det ring might just take a ride through my top end like the circlip I threw last year.

    appreciate all the input. That cylinder had a det ring already, but had unknown miles and the plating was coming up at the bottom of the skirt so I assumed it was time. I actually sent two cylinders, one did not have a det ring and has been heat cycled twice with a VHM piston since fresh replate without any hiccups thus far. The exhaust bridge relief was easily visible on the non det ring cylinder.

    I am really bummed because I entrusted what I’ve been told is a cylinder ported and flowed by carlos neves to a company I thought was overly capable of handling the work. I’m thinking the bridge was adequate before this most recent debacle, and now may be fairly thin as you’re describing.

    I cannot speak to the hone quality, and I am not a machinist or fabricator, but I know deep down when I look at that gap it is not right and they could have at least informed me rather than send it.

    Any suggestions on who I can send this to, that can set me up correctly? Or should I cut my losses and find another cylinder?

    thanks again for the input. Looks like my season has been delayed even further.
  9. mattology

    mattology Well-Known Member

    i think that would be fine for a piston or two.
  10. Jeff Payton #82

    Jeff Payton #82 ‘The dinosaurs also thought they had more time’

    That’s enough for me to have a good time, honestly

    but coming to an abrupt stop mid corner because the det ring comes undone doesn’t sit well with me. Probably wouldn’t sit well with the others on track if something were to go wrong. I guess I have that Keith code dollar mentality, I’d rather this not be in the back of my mind when the green flag drops
  11. Boman Forklift

    Boman Forklift Well-Known Member

    If you are really worried you could possibly ask Carlos Neves or Roland Cushway what they think? Having said that, I agree with @mattology if you are happy with one or two pistons use out of it, I personally wouldn't have a problem with it lasting that long and think it will last much longer.

    Do you remove the head to check on the piston, looking for ringland compression? I used to do that at the end of every day or every other day, and I believe that would give you ample time to notice anything starting to come apart.
  12. humblepie

    humblepie Well-Known Member

    I wouldn't run it.
    The det ring is usable.
    It's the bridged exhaust that worries me. Needs work
  13. Jeff Payton #82

    Jeff Payton #82 ‘The dinosaurs also thought they had more time’

    Appreciate all the input, with all the info I’ve gathered decided it’s best to just have it on hand as a sunday last chance spare

    I’ve since gathered another cylinder, but now have questions of its origin as well. this is the second cylinder I’ve encountered from two different sources that I’m told is for 95-97 but doesn’t have a circlip for the water block off that I’m familiar with - instead uses a hex plug, both identical pugs. Trying to make certain it’s ok to run on my 96, thanks in advance

    Attached Files:

Share This Page