My son's 1997 300 4-Trax 2WD started making a noise in the upper cylinder area. Utilizing the shade tree doctor technique, I placed a large screwdriver to my ear and ran along the engine cylinder area. The noise is coming mid cylinder and upward. Not very noticeable at idle, but increases as you increase RPM. I removed the top cover, cylinder, etc off the other pm,,everything appears in excellant condition. No broken rings, no piston damages, cylinder wall "slick",,just a minor carbon build up ring at the top of the cylinder, valves appear to be seating properly,etc.. I am lost as to what it could be. The noise did sound somewhat "soft - metallic" for lack of words and as RPM increases, the noise level increases ,although the frequency did not appear to increase at the same rate as the RPM.
I am lost as to what it could be. Looking for all possible suggestions. Son panicking as weekend approaching and he appears to be "gounded" until problem resolved.

Thanks in advance....
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Check you cam lobes or rockers they could be worn thus causing a 'soft-metallic' noise

 

Did you check the valve clearance before you took it down? Crackhead right about cam and rocker being the obvious cause, but you should see obvious wear there. Was the oil just changed? If so make sure the oil filter is put in the right way otherwise the cam rocker area will starve for oil bigtime. Are you sure about the piston? If piston\cylinder clearance is much over .004" it will be a bit noisy. Also the wristpin sometimes wear their fit to small end rod. If you feel any wear on the wrist pin at all, make sure to replace it. If you do find excessive piston clearance it indicates it was run with low oil level or dry air filter. Did you check the valve lash before you disassembled? Hard to say without hearing the noise. How about the cam chain\tensioner?

 

Sorry about asking you about the valve lash twice in the previous post, it was due to my lack of proofreading. Good luck!

 

Thanks for the replies.
Re-inspection of the ATV this pm reveals visible piston pin wear area at connecting rod surface. Neighbor just happen to have a piston/pin out of collection of misc parts he bought off of EBay. Very noteable difference.
Also discovered the connecting rod has considerable side to side clearance. I do not know how critical this would be on a small engine as such. Could not determine any excessive "slack" rod to crank,,only side to side clearance seems somewhat excessive to me in comparision to my past automotive engine experiences. Virgin trip for me into a single cylinder engine as such ,with exceptions of Briggs, etc. It maybe acceptable. Need to get specs and feeler guage .
With the exception of removing timing chain and performing a side to side comparsion with a new one, is there a way to determine excessive wear/stretch ? Physcial appearance of timing chain and gears appear good.

 

Honda does have specs for the crank big end clearance, but it seems to me a lot is the norm. I would be more worried about the small end wear, if your wrist pin is considerable wore. There is also a clearance spec for this, but I don't have a bore gauge that small so I just usually feel for excessive play with a new wrist pin. From there it's kind of a judgement call. If that was causing your noise, A new wrist pin may quiet it a bit, but if the small rod end is in tough shape, it may still make noise. The best way to diagnose the chain\tensioner is by the sound it was making to begin with. You will have to remove the tensioner end bolt to install it on the cylinder when reassembling. When you turn the small flatblade clockwise (accessed by removing the end bolt), you will observe that the plunger retracts, when you remove your screwdriver it should extend fully. Now push into the assembled top end. You can make a guess as to how far the chain is stretched by seeing how close the tensioner body is to cylinder when the plunger is fully extended. With new parts you can barely get the bolts started. If you can push the tensioner close to mating with the cylinder, your chain is stretched a lot. Make sure you retract the plunger and hold it when you bolt it to the cylinder. If you don't know what noisy cam chain sounds like, you can simulate it on a running machine. Remove the end plug of the tensioner while idling, then carefully turn the flatblade clockwise, putting slack in the chain and listen. good luck