Leakdown test - let's talk about 'em.
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  1. #1
    Senior Member turborob's Avatar
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    G'day trendsetters.



    Caveat: I do not know all, but would like to know more. Please correct me if I'm off the mark.



    Contemplating getting a leak down test on the TW, as I hear a compression test isn't a 'tell all' about your top end.



    I assume you receive a number, which relates to how good/bad your top end is. Are there any specs to relate that to other TWs, or service specs?



    More Qs to come, but this will start the ball rolling.



    Over to youse!

  2. #2
    Senior Member assquatch20's Avatar
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    You've got to remember leaks around the rings are still possible. Generally twenty percent or greater losses is when you wanna fix something, but as little as 10 is enough for some folks. You might hear hissing in the exhaust if it's the exhaust valve, intake hissing if it's intake, obviously. You might get lucky and even get hissing out of the crankcase somewhere if you were to have bad rings. Not all the time, but sometimes. Get your valves right before testing. If valves are in spec and you're still getting a poor reading, try a teaspoon of oil in the cylinder. If improvement is dramatic, consider replacing rings. If you open the oil filler cap and the reading doesn't change at all, you have the best sealing piston rings on earth.



    Truth is, with it being a simple, relatively low compression engine, a compression test should be enough. Pretty similar ideas, only you'll be working with PSI's instead of percentages, and you're blowing out instead of in. It won't be as accurate, no, but it should give you a heads up on any issues. If it's running well and you have compression within spec, I wouldn't worry beyond that. Leakdowns are more helpful when there's a cooling system and a more complex head gasket to leak from, PCV valves, turbos, and the like. Still yet, if you can't get good compression and are hesitant to replace rings, then maybe try the leakdown test. There would be a slim chance it's your head gasket, and that's the test to let you know. If you have both testers just sitting around, sure, use the leakdown. It's not a massive difference on a TW.



    That's about all I know. Somebody with more than a shadetree degree should be along shortly to help.



    EDIT: I forgot to mention. Kinda obvious but you'll want to be at TDC on the compression stroke for a leakdown.

  3. #3
    Senior Member turborob's Avatar
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    Thanks Sasquatch, that was a bloody good reply.



    I'm tossing up taking the TW on a longish ride, and want to know if I have to do any engine work, prior to crunch time. I'm a wee bit scared of engine work.



    If a compression test is sufficient, do most of them come with the right thread for the spark plug hole? Might be a worthwhile purchase.

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  5. #4
    Senior Member assquatch20's Avatar
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    Quote Originally Posted by turborob View Post
    Thanks Sasquatch, that was a bloody good reply.



    I'm tossing up taking the TW on a longish ride, and want to know if I have to do any engine work, prior to crunch time. I'm a wee bit scared of engine work.



    If a compression test is sufficient, do most of them come with the right thread for the spark plug hole? Might be a worthwhile purchase.


    Usually they come with a few different fittings. Take your TW's plug to the store with you if you can and try to compare, or if you're buying online, they should usually list the different sizes, which you can compare to your plug at home. Chances are one of the fittings will work. They're handy when buying a used bike if you can look up ideal compression specs before going to look at the bike.



    If you're going on a TW trip, what I would say is know all your maintenance procedures. For stuff you're only supposed to do once in a blue moon, do it before your trip. Change your oil, grease the swingarm, etc. Have your consumable fluids (chain wax, quart of oil, maybe air filter oil, cable lube) with you, zip tie a spare cable to each cable you already have, get familiar with patching a tube, maybe switch to the old style cam chain adjuster and learn to use it right, get familiar with adjusting valves. Carry tube patches (some folks carry tubes), spare chain links (have a good chain and sprockets before you're off, and adjust/wax regularly), a spare plug, get carb-smart and carry some spare jets if you're going through big elevation changes, some folks carry a spare headlight bulb, the list goes on, and it depends on what you're doing and what you're worried about, but the TW is a good bike that's extremely hard to kill. I've read of less than 10 people really having to tear into their motors in the past 4 years or so of me being on this forum.



    Maybe it's all common knowledge for you, which is good, but I gotta throw it out there.

  6. #5
    Senior Member silverhead's Avatar
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    I had to buy a more elaborate compression tester that cost more and had 12mm spark plug thread adapter. Typically the cheapest ones come with 14mm adapters, but not 12mm ones.



    Otherwise a compression tester is a pretty simple little thing. My TW sits at 160 PSI (supposedly high.) It runs fine, so hey



    Like mentioned above, these engines are so simple that a compression test tells you what you need to know. If you're at 100 PSI or lower, it's time to lap your valves and replace your rings. In either case, you're going into the top end, so you might as well do both anyway.
    1993 TW200

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