PLS - Help: My 2004 YFM350 has developed a grinding sound

oktrg500 · 2025-03-13T13:42:51-0400

Hi friends,

I am really hoping for some help here, because my local workshop only says the cause could be everything.

Last week I noticed a sort of grinding sound from the engine. It lasted about one minute after warming up the engine. Then it was

not noticeably.

I know I should have checked the engine oil for fragments of metal, but it is still rather cold in Norway and doing maintenance out

in the cold is not what I am looking forward to.

This week the sound has developed and has become much more noticeable. As of now, it still almost disappears when the engine gets

hot.

As far as I know, the ATV has had 2 owners before me and it has been very well cared for. Judging from the condition when I bought it, it is a low mile runner.

I wonder what could this be?

I've been a twostroke only guy for more than 40 years, so I'm in unknown terrain here.

Thank you very much for helping me getting to the bottom of this issue.

Regards
Ole Knut
Norway

beastlywarrior228 · 2025-03-13T21:30:07-0400

Wow that's clean. I would start by going through and checking things like the timing chain and guides.

PineyPower · 2025-03-13T22:21:46-0400

Mine made a very similar noise when the flywheel bolt got loose. The little cover on the left side, pull it off and make sure the 17mm bolt in the crank is good and tight

oktrg500 · 2025-03-14T13:04:39-0400

beastlywarrior228 said:
Wow that's clean. I would start by going through and checking things like the timing chain and guides.

Hi,

Thanks very much for your reply.

I had the ATV serviced before the winter set in, and the person doing the job told me the cam chain tensioner was about half the way in when setting up the tension. I've been riding the bike to and from work daily during the winter. This sound has developed rather fast, which leads me to think the cause is something else. Tomorrrow I will put on a lot of clothes and inspect the oil.

oktrg500 · 2025-03-14T13:15:04-0400

PineyPower said:
Mine made a very similar noise when the flywheel bolt got loose. The little cover on the left side, pull it off and make sure the 17mm bolt in the crank is good and tight

Hi,

Thanks very much for your reply.

This sounds to me like a very plausible cause of the sound.

How did you lock the flywheel so you could tighten it to spec? If it is loose, it sounds like a good time for Mr. Loctite.