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Engine rattle - Seems to come from top end - Your thoughts?

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I picked up a 2005 Honda crf150f for my son about a month ago. It's been running good, starts right on first or second kick, no smoke and good power...but a couple days ago it started developing an intermittent rattle noise in what sounds like the top end. With in minutes or so of start up it starts a rattle noise...then maybe goes away for a few seconds and comes back. This noise is different than the usual noise (ticks) it makes...and it stuck right away and is somewhat loud. You can definitely hear it when it starts. My son actually came to me and said what this noise?

The oil has been changed and air filter cleaned, running new gas in it as well (91).


We've been running it every couple days for the last month and are just now hearing this rattle sound. I don't want to cause more damage by ignoring it...but I'm afraid to take it to a shop to be told I need a complete top end rebuild or something if of course that's not the case.

Could the valve clearance need adjusted? My understanding is that this bike has a self adjusting/automatic cam chain tensioner?...it it possible that it failed and the noise could be coming from a loose cam chain?

I posted a video on YouTube to see if anyone can help and possibly tell me what is. The rattle is constant in this short video.

Here's the link:


You're thoughts/suggestions/advice are greatly appreciated!


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You might as well properly adjust the valves to narrow things down a little.

There supposed to be adjusted regularly any way so why not?

Seems like you would have done that before you posted.

Just think, that could be the problem the whole time?

Just follow the adjustment procedure step by step like it shows in a factory Honda OEM shop manual.

If you do the adjustment properly, you question could possibly be answered?

Edited by adnohguy

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