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Diagnosing engine noise...

Discussion in 'Technical and Troubleshooting Torque' started by mattb, Aug 16, 2007.

  1. I have some questions regarding what I should do about a tapping noise in my engine. I've also posted in an SR500-specific forum, but I thought I'd get some trusty opinions from you guys as well.

    I’ve had the SR500 for two months. I love doing the mechanics but actually have very limited knowledge for it. I’ve got a tapping sound in the top of the engine (though I have trouble locating it). Importantly, this sound only comes on, or gets worse, when the engine is hot. The noise is quite noticeable at that warmed up / hot point (toward the end of a long run it’s very noticeable), and has a kind of lightness to it, rather than a clunkiness etc – it could also be described as a ‘light metallic click’. It is regular and relatively in synch with the revs. I notice it more after I rev the bike hard (I’m gentle on it, but say if I go unusually hard from the lights). The bike has frequent oil / filter changes by me and the previous owner. The engine was reported to me to be a grey import of only 7000kms. I tensioned the cam chain recently, and had the valve clearances done by a mechanic this week ($90! - I only paid them to do it, so as to make sure this 20 minute job was definitely done right in order to isolate this problem).

    Dilemma : this is my only transport so I need to keep riding it, and as I student I don’t have the money to throw at a general replacement of internal parts ; but, I have a loan on this, it’s my true love, and so I want to do whatever is needed to make sure this engine doesn’t explode (that happened last time – ouch!). So…

    a) Without taking out and opening up the engine, what else can I do (or ask a mechanic to do) to diagnose the problem? (I heard talk of “piston to valve clearance†– is this such a check which can be done?)

    b) If I do take the engine out and take it to a mechanic, what should I ask them to check and on principle replace?

    c) I’ve heard it said that the SR engine is mechanically noisy (certainly the old SR185 is – really is! – and she just keeps going!). Have people ridden for extended periods with such a noise undiagnosed, and been ok, or should I *necessarily* be seeking it out, and avoiding bigger rides until this is sorted? (This is a question about people's experience, but also I'd like to ask : in principle can the typical sort of problems this might denote, assuming it’s not the cam chain and valve clearances, be of the sort that don’t destroy the engine, or at least not all at once as happened with my last bike? If so, which potential problems are yay and which nay regarding this?)


  2. gut reaction: wouldn't be too worried about piston to valve clearance, that is in the combustion chamber and if the cam chain is fine and the valves are fine (ignoring valve springs), you should not get any problems. Valves hitting the piston would only happen at high rpms, and you'd know about it - you would not have a happy motor, at all.

    If you've had a mechanic check the valve train, and you have checked the valve train, and nothing is amiss, would just put it down to bike character, whilst it seems illogical that it would get worse as it warms up, upon further thinking about it, the problem may be general valve tap (normal, and a good thing).

    But as the oil viscosity gets lower as the oil heats up, less oil remains on the tapette contact surface, hence a clicking sound might increase. Could try using a thicker hot temperature oil, see if it remains. If it does, the specialists on the other forum might have some tips
  3. Tappets.

    In some alloy engines the tappet clearance actually grows as the engine warms up.

    So set your tappets right and anything after that you may just have to live with.

    If it goes away when you rev it, it may be the cam chain (tensioner likely), but I'm guessing tappets.
  4. Valve Guides may be shot mate thats waht the soft click usually is its the valve seating and clicking sideways when the cam lobe comes fully off
  5. Has there been any increase in oil consumption or exhaust smoke from the engine? if valve guides go, more oil would leak down past the valve seals into the intake/exhaust chambers
  6. Actually no : it once drank a lot of oil quickly, inexplicably, but otherwise seems to be using almost no oil. And there is exhaust smoke as a black puff when I start the engine, and disappears immediately to no smoke at all.

  7. I would be looking at the condition of the tappets. It is very posible that the end of the valve stem and the adjuster are worn. You will be able to adjust the clearance but it will be false as the feeler guage will be making contact with the highest points of the adjuster screw and the top of the valve stem.
  8. Nah, it remains / gets worse (depending on the RPM) when I rev it harder – for instance it’s really noticeable after I have to push the bike in overtaking out in the country (and it remains louder thereafter, at any RPM, even idle). Indeed, in the first week of owning it, it wasn’t until after the first time I gave it a bit of stick in a sticky situation that the sound came on (before that I had no such sound (that I noticed)).

    What’s the result of this? – I’m guessing it’ll just wear further over time and need replacing, but could it result in something that does damage to other parts (just as the cam chain would if it were the problem)?

    A friend has a friend (who is a lawn-mower mechanic) who is rebuilding her GN250 engine for her at real mate’s rates – I might contact him and see about arranging an affordable session where together we pull the engine out and inspect its innards. Better safe than sorry (like the sorry old GT!)! I'll check out the oil and heat issue as well.

  9. This tells me the valve stem seal are no good and chances are the valve guides are on the way out.

    This should be an easy job on a 2-valve single.

    Get some guides, bung the head in the BBQ and push the old ones out. Push the new ones. Take the opportunity to lap the valves in and then bung the head back on with a new head gasket.

    take your time and it's only take a whole Saturday.
  10. Thanks for that tip, will remember that one. Too hard to get the kitchen oven to that temperature (use the oven for curing paint though, 30 minutes at 100, baste regularly...)
  11. Thanks guys : I'm hearing a valve guide consensus (as well as the need to check the wear from the valve stem / tappets and have a look around).

    An important question : I'll get to the job asap, but given that it might just as easily be a month or two before it's all attended to, am likely to be causing serious damage if I continue to take it for country runs etc? (I'm pretty gentle on the revs)

    A couple of minor questions:
    -What is it to "lap the valves"?
    -I'm guessing that if the valve guides are shot then as the oil thins at heat the sound increases possibly because the oil's lubing and buffing less well?

  12. You won't do any major damage, though things may get a bit coked up if left too long.

    The rattle is probable getting worse at temperature due to increases in clearances.

    Lapping the valve is putting a cutting compound on the face of the valve and "rubbing" it into the seat. It helps get a good seal. You should note that it will only work if the valves are in reasonable condition.