How I fixed my "rocks in the motor" noise -- thanks to the board for all the help!

[motoxer65]

For those that are interested, here's my story:

I have a 2006 Honda CRF450R that I bought new from FBC last year (my first four-stroke). Due to work being so busy last year and some non-MX injuries, the bike only has about 20 hours on it. At one point the bike sat for about two months, and the first time I brought it back to the track (Amago) the motor was making some new / bad noises under load.

Bike sat for another six weeks before I had a chance to work on it (kept in storage unit), and I figured I'd trying just changing the oil (and praying) first before tearing into the motor. Problem was, when I went to start the bike to warm the oil before draining it, gas started just pouring out of the carb overflow lines.

Tore the carb down to clean everything (jets were gummed up by old fuel), and finally got the bike started but couldn't replicate the motor noise on asphalt. Changed the oil and went riding at Elsinore the next weekend, but the noise was back. Had a friend with many years of non-CRF four-stroke experience take a ride, and he thought it was probably the valves needing adjustment. I brought the bike to FBC service, and they ended up adjusting all four valves (good). However, went riding on my first desert trip the very next weekend, the noise was still there in all its glory.

Came home and read an hour or two of previous posts to this forum about motor noise, and decided to check the cam chain tensioner. Unscrewed the center bolt, and the spring still had tension (seemed fine). However, instead of just releasing the spring to its natural tension, I twisted an extra 1/8 or 1/4 turn to put a little bit of extra (manual) pressure on the cam chain.

I'm relatively new to California, and so far the best pump gas I've been able to find is 91 octane (whereas back in Mass we could get 93 at any Mobil, and 94 at Sunoco). So, since I figured there was a chance the motor noise could actually be detonation (something I was very familiar with from previously owning a modified Ford Lightning), I decided to buy some VP-C12 race gas as an extra precaution (to make sure it couldn't possibly be detonation).

Went riding at Elsinore this past Sunday, and between the cam chain adjustment and/or race gas, I'm happy to say that my motor noise was 100% gone (and the bike was a rocket)!! I'm gonna bo back to Elsinore this Sunday and run straight pump gas. If the motor noise is still gone then my manual cam chain adjustment to the auto tensioner fixed the issue, but if the noise is back then I'll have to start mixing race gas with pump gas or running some type of octane booster.

Oh, and for those that I'm sure will ask, all the internals of my motor are stock (cam, valves, spring, piston), but I do have a bunch of bolt-ons.

Thanks for all the help (from previous posts).

[basilbug]

I thought Honda made the bikes to run on super, no?

[Tony211]

They run on 91 fine.

[Shawn_Mc]

If youve got that kind of detonation going on with 91 there's another issue. Too lean, or the cylinder is oiling for some reason...geared too high...its over heating for some reason etc.

[motoxer65]

Thanks for the advice Shawn. Like I said, I'm gonna run it this weekend on pump gas at Elsinore and see what happens. I'm 85% sure it was the cam chain adjustment that fixed the noise, so the only thing race gas did was put a smile on my face. Shouldn't be jetting because I went UP by 1 or 2 sizes on the pilot AND main when riding in the desert. Shouldn't be the gearing because I'm +2 on the back and stock up front. No idea about the cylinder oiling, but bike has less than 20 hours and has never sucked sand (i.e, airboot intact). I've seen coolant drip from the radiator overflow once or twice, but that was only if I let the bike idle too long while stopped to talk with a friend during a ride (no airflow). I'll take all those things into consideration though if my bike decides to act up again (naughty bike!). Later...

[PSD_Sun]

Everytime I hear someone complaining about engine noise I tell them to remove the skid plate as those things reflect noise and make the bikes sound broken.

[motoxer65]

PSD -- I heard many other members say the exact same thing when I spent hours on here reading previous posts trying to self-diagnose, but the problem is that my bike has had a WC skidplate & engine guards AND full Unabiker radiator guards since its virgin ride, and the noise I'm talking about didn't happen until recently (12 rides / 15 hours in). I didn't do anything to their mounting bolts last weekend, but the noise went away (which to me means it wasn't the skidplate). Thanks for the advice though...

[skychicken]

Arent we supposed to be running 93 octane?

[motoxer65]

Sky -- unless you buy race gas, the best "test" you can find out here is 91.

[the_tinman]

I had a loose skid plate alarm me to engine noise. After tightening all was good.

I also had a cam chain tensioner fail. Toward the end of a race I noticed engine noise. It was more prominent at low rpms so it was easy to diagose.

As far as octane, depends on your altatude. Lower altatude requires higher octane. Usually the region you live in has the apropriate levels. I run 91 pump gas at 5k ft with no detonation.

Tin