Motor in bad shape - is there hope?

Discussion in '2-Stroke Engines' started by Molotov256, Jul 21, 2010.

  1. Molotov256

    Molotov256 Member

    After moving what was once my stronger motor over to a different build for the umpteenth time, I noticed a significant power loss. The motor would idle fine, but it could barely pull me past 5mph or so, and it would lurch and shudder terribly. I ran through everything I could think to do on the exterior of the motor such as replacing gaskets and using RTV sealant or hose clamps anywhere I thought there could be an air leak. It passed the carb cleaner spray test fine - no change in idle speed.

    Having exhausted my limited knowledge, I took apart the top end of the engine (thanks to AI.Fisherman's pictorial HT teardown album!), and things aren't looking so great inside. Still, I've never really looked at the inside of an ICE before, so maybe I'm over reacting... There seems to be some noteworthy scoring on the piston and cylinder walls as well as oil/fuel seeping around the head gasket. In retrospect, I remember replacing the head gasket with a metal one from SpookyTooth cycles a summer or two ago, and it looks as though I neglected to use gasket sealer with it... Shame on me. The motor ran like a champ for quite a while, though, so props to the cheap 2-stroke for holding up to the abuse.

    Anyhow, pics are attached. I'm curious what the community consensus is regarding the most cost effective solution. Is it possible to repair existing parts? Am I better off replacing the piston and cylinder with new parts? Maybe this is a good opportunity to upgrade damaged parts with performance parts:devilish:?


    Attached Files:

  2. Luka

    Luka Member

    If I were you...

    Clean it all up.

    Hone the cylinder.

    Replace the piston rings.

    Put it all back together.

    You may also want to replace the rod bearing.

    Use a really good synthetic lube when putting it back together.

    Use metal gaskets, and don't forget the sealant. But don't put so much sealant on, that it seeps inside.

    When you put the rings on, make sure the gaps are not lined up with each other.

    Should be fairly simple, really.

    And that ragged gap in the piston ring that you show, is possibly the reason for the troubles with it running.

    The scoring may be from pieces of the ring which busted out of that ragged gap.

    Get a really cheapo cylinder hone, small enough for this bore. And don't hone it too much.

    Leaving some scoring is ok, as ling as it isn't a 'leak'.

    You don't need to buy a ring compressor tool for this. Just use an old soup can and a couple of hose clamps.

    I clean things with brake cleaner. Not carb cleaner. Brake cleaner leaves no residue.

    If you are thinking, "might as well clean the carb while it is apart"... I'd advise you not to.

    Do the above, to get it back together.

    Getting it running, is going to be less guesswork, if you use the rest of the parts that already had it running... As they were.

    Once you have it running again, if you want to take the carb off and clean it, go for it. At least if it doesn't start again after that, you'll know it's the carb and not something else.
  3. AussieSteve

    AussieSteve Active Member

    If it was leaking at the head gasket, that'll be the cause of the loss of power.
    As Luka says, I'd clean it all up, pop in new rings and put it back together.
    These are a chrome bore, I think, and very cheap to buy, so if the scoring is too bad I'd consider a new barrel.

    Nothing wrong with cleaning the carb, in my opinion. Just don't change the needle or float height at the moment.

    Luka, there's no 'ragged gap' in the rings and definitely no pieces busted out and scoring the cylinder wall. That's how the ring-ends are supposed to look, to fit around the locator pin in the ring groove.
  4. Luka

    Luka Member


    I wondered about that.


    Thanks for the correction.

  5. Molotov256

    Molotov256 Member

    Honing the cylinder sounds intriguing, but I'm not sure what all is involved with the process. I googled it and saw some youtube videos of processes which seem more in depth than anything we'd casually throw around on a MB message board, so what exactly does one do to hone a HT cylinder?

    In looking at the rings, they seem to be in pretty good shape to the naked eye, but if it's widely recommended they be replaced, I'll go ahead and do it...
  6. beentryin

    beentryin Member

    some scoring is typical in 2 smokers .check with a fingernail if you can feel it,its a groove and not a rub mark and honing will take most of them out,but the scoring looks typical to me
  7. Molotov256

    Molotov256 Member

    Cool -i ran a fingernail around the cylinder, and it doesn't really catch... I can feel where it's scored, but it's not really catching.

    That being established, I'm inclined to focus more on the head gasket issue. Based on the oil/fuel patterns on the gasket after removal (see pics), does it look likely that I was losing enough compression there to make the motor run like poo? That would be some good news if all I need to do is put a little sealant on it and slap it back together. (I still need to get a new bottom gasket either way cuz the stock one split all apart when I pulled the cylinder off).

    I'm still curious if new rings are necessary... they're cheap enough that I don't mind doing it if I need to, but I'd just assume save the $$$ if I can.

    Can anybody point me and any other readers to a good thread or resource about the process of cylinder honing? Even if I don't have to do it, I'm still curious how that works.
  8. Al.Fisherman

    Al.Fisherman Active Member

    While you have it apart, and if the studs and nuts are OEM..change them out, to grade 8.8 metric (equivalent to a US grade 5). If they are OEM that could be your problem in the fact that they may have stretched. I feel that metal gaskets vs composite need to be coated. I never install a uncoated metal gasket if I can help it. I keep a spray can of copper kote. Sold at almost all auto parts stores. Coat one side, dry, coat the other side, dry and repeat again. Above all good things, except for the fact that you can't put the rings on incorrectly. There is a pin in the ring grove. Goes between the ends of the ring. 8mm studs/nuts are torqued to 150 to 200 INCH POUNDS.

    Thanks for the acknowledgment.

    To hone a cylinder is to break the glaze (smoothness..rough it up a bit) inside the cylinder. The tool to do this comes in two (that I know of) types. One is a set of three stones (like knife sharpening stones), and kind of operate like opening an umbrella. You squeeze the three stones together and insert into the cylinder. The other is a shaft with flexible fingers attached..about 20 to maybe 100 of them. Attached to the fingers are little balls made from the same material as a knife sharpening stone. Both types have a shaft that you chuck up in a drill. You spin these stones inside the cylinder to break the glaze. As you are doing this and at the same time you move the hone in and out, but not far enough to come out the bottom or top, creating basically a X pattern in the cylinder.

    <a href="" target="_blank"><img src="" border="0" alt="Cylinder hone"></a>

    <a href="" target="_blank"><img src="" border="0" alt="Cylinder hone"></a>
    Last edited: Jul 21, 2010
  9. Molotov256

    Molotov256 Member

    Sounds like good advice to me... is this something I can get at the LHS or do some of the sponsored vendors sell rods that are already the right length and thread? I suppose I could just get a grade 8.8 threaded rod and cut it to size, but that's extra work, heheh...
  10. GearNut

    GearNut Active Member

    The rings you have right now are worn out. The heavy carbon build up going down the sides of the piston are the telltale sign. They are cheap and easy to replace.
    Do not re-use the piston pin clips. If and when you order new rings and a base gasket, order new piston pin clips as well. I have seen them called "G" rings or "G" clips in the exploded parts lists at various vendor sites.
    Use pre-mix oil as an assembly lube wherever 2 metal parts may touch each other (but not on the head gasket).
    An alternative to the highly recommended Copper Kote that is also very good (and you may all ready have around) is aluminum spray paint. Be sure that is does in fact have aluminum powder in it. Most do, some do not. Same procedure applies. Two coats on both sides, let dry thoroughly between coats. Install dry.
  11. Al.Fisherman

    Al.Fisherman Active Member

    Buy grade 8.8 threaded rod, and make your own, buy from a vendor, or check out my profile. Use nylon locking nuts and lock tite on the threads in the case.
  12. Al.Fisherman

    Al.Fisherman Active Member

    All good...Have used aluminum paint before myself with good results, I just like Copper Kote, and if you ever see it or use it you will understand. A added feature to CK is it has an adhesive and sticks quite well to both cylinder and head...Don't forget to mill your head before instillation. Used wrist pin retainers ("G" clips) can cause headaches down the road. I use them over again, I know what I'm doing too, but it's a chance.
    Last edited: Jul 21, 2010
  13. GearNut

    GearNut Active Member

    Just a side note, I don't recommend using a ball hone in a two stroke cylinder as the abrasive balls can bugger up the edges of the ports. A bar hone (umbrella type) is the preferred hone for two strokes.
  14. Al.Fisherman

    Al.Fisherman Active Member

    So true.. Was pointing out the types and process. I have the umbrella type.
  15. Luka

    Luka Member


    Spray the hone stones with wd-40 before inserting into the cylinder.

    Also, any time that the hone is in motion inside the cylinder, constantly spray wd-40 in there.

    And it shouldn't take more than a few seconds, to break the glaze in that cylinder.
  16. Molotov256

    Molotov256 Member

    I've been able to find new piston rings and bottom gaskets on several vendors, but I'm having a hard time finding replacement "G" rings for the piston pin. Is it possible to reuse the old ones?

    Edit Cool - found some of the clips on pirate cycles.
    Last edited: Jul 22, 2010
  17. machiasmort

    machiasmort Active Member

    Luka, did the rpm of the motor seem to be normal when you experienced the power loss? PM me!
  18. Molotov256

    Molotov256 Member

    Thanks for all the info on cylinder honing - it doesn't sound as daunting as I thought at first, but I still hope I can get away without doing it this time around. Unless this is a terrible idea, I am going to try my luck without honing the cylinder and just replace the bottom gasket and piston rings as well as using some of that CopperCote spray to seal the aluminum head gasket. At this point I am under the impression that most of my power loss stemmed from the head gasket leak. For good measure, I will also replace the stock rods with grade 8.8 rods and nylon lock nuts as suggested earlier.

    Much obliged, everybody! I'll follow up as the repair progresses.
  19. Al.Fisherman

    Al.Fisherman Active Member

    For a one word answer to your question..."YES"

    I have never replaced the wrist pin clips "G" rings on any engine I've ever had. I break down everyone of them out of the box to upgrade the studs. The trick, if you want to call it that is to use a good pair of needle nose pliers, grip the tab and as you rotate the tab inward to the center, slowly pull at the same not force. Not saying that the clip won't come out while running but I've reused clips about 10 times (different engines) without one incident. Unless necessary, remove only one and slide the wrist pin out.
  20. retromike3

    retromike3 Member

    My first engine kit I used the G clips over again and about two miles down the road it got pretty ruff and then it would not start after I parked it. turns out that it "ate" the clips and scored the piston so badly I replaced the engine. I got a new engine on sale at zipp for about eighty bucks and its been working grate since then. The next time I rebuilt the motor I got new clips and new low end gasket, plus a thinner head gasket from S.B.P. It just ticks over like a watch now.