NC30 engine rattling noise.

[ptroy]

Alrighty, a new noise has started coming from my vfr400.


Its a rattle / clacky type noise, not noticeable at idle. Increases with RPM and I only really notice it when on throttle / engine accelerating. With engine deaccelerating the noise stops.

Dosent make any difference with clutch in or out or in neutral.

When riding it sounds like it is coming from the top end, though with it on the stand it is hard to tell, sounds like from bottom end but depends where you listen it always sounds like its coming from somewhere else. Have gone around listening with a screw driver all over the engine and cannot hear the noise at all through the screwdriver, only time I heard something similar was with the screwdriver on the side of the carbs.

With the bike on the stand and in neutral, the sound seems to be most prominent around 3000rpm, especially if you blip the throttle at idle.

Events leading up to this happening:

Got new tyres, and dropped the bike at about 20kph leaving a stop light turning right (doh, didnt realise how slippery new tyres are, or there was something on the road). No damage appeared to be done other than cosmetic damage to the right hand side fairing. I didnt notice the noise after this, so I dont think its related.

Later on going for a ride I accidently over revved it changing gears where I must of selected neutral between 1st and 2nd. I think it may have seen 16k rpm. I noticed the noise almost straight away after this happened. I rode home very gingerly about 40km and the noise did not get any worse.

When I got back to the workshop and was checking the engine I found the oil was extremely low (bottom of dip stick, must of done more km's than I had realised before checking it).


So my thoughts were maybe damaged big end bearings, or cracked piston.

I have drained the oil and it looks fine, no metallic particles. Removed the sump, nothing suspicious in the sump. Looking up at the bottom of the pistons I cannot see any cracks or such things.

I have removed both side covers and nothing suspicious here either.

Any input on what the noise could be? Where else to look, could it infact be the carbs making the noise?

If it was bearings I would of expected to see metal in the oil, and maybe make the noise more consistently.

Before I strip the engine I want to make sure I have not overlooked anything, I would hate to strip it to find nothing wrong.

[AllanB]

Later on going for a ride I accidently over revved it changing gears where I must of selected neutral between 1st and 2nd. I think it may have seen 16k rpm. I noticed the noise almost straight away after this happened. I rode home very gingerly about 40km and the noise did not get any worse.
.

That's the clue ............. extremely low oil, over rev, noise from the top end, everything lower you have inspected looks good ...... bent a valve maybe?

[ptroy]

It appears the noise is coming from the top end while riding, but when next to the bike it seems to be from lower end, and listening with a screw driver cannot be heard at all.

It also still runs very well, other than the noise, not loss of power etc.

But I will be removing the tappet covers shortly and inspecting.

[Akzle]

cc or cct. .

-edit-
or yer fuken valve clearances. When were they last done?

[ptroy]

cc or cct. .

? Not familiar with these abbreviations.

[Akzle]

? Not familiar with these abbreviations.

starts with C and rhymes with cam chain.

[ptroy]

these are gear drive.

[tigertim20]

cc or cct. .

-edit-
or yer fuken valve clearances. When were they last done?

NC30 = gear driven cams

[Akzle]

well then. It wont be your fuken cam chain.

[spanner spinner]

there are scissor gears on the cams on this model to quiet down the cam gear drive and these can spit out or fracture the springs that tension them and they then become noisy. the bikes run fine after this has happened they just get noisy. have seen this happen mainly on race bikes run at high RPM but the big over rev would do the same. take the rocker cover off and check the gears on the cams just to make sure it is not this.

[ptroy]

there are scissor gears on the cams on this model to quiet down the cam gear drive and these can spit out or fracture the springs that tension them and they then become noisy. the bikes run fine after this has happened they just get noisy. have seen this happen mainly on race bikes run at high RPM but the big over rev would do the same. take the rocker cover off and check the gears on the cams just to make sure it is not this.

Alrighty will check this.

How high a RPM to the race bikes run? How high is safe for a standard NC30. I dont like having no rev limiter for this reason

[spanner spinner]

Alrighty will check this.

How high a RPM to the race bikes run? How high is safe for a standard NC30. I dont like having no rev limiter for this reason

the race bikes usually run to normal red line or just above but running high rpm for long periods seems to do the springs in. red line is the safe maximum for a standard engine, the factory did a lot of testing to find this limit.

[ptroy]

the race bikes usually run to normal red line or just above but running high rpm for long periods seems to do the springs in. red line is the safe maximum for a standard engine, the factory did a lot of testing to find this limit.

Alrighty.

Defiantly wasnt for an extended period of time, just missed a gear and over revved.

I have checked the scissor gears, and they are not loose or flapping around. I can 'tension' them up against the springs with a large flat head screwdriver.

I cant find anything obvious. Though it could still be a bearing or cracked piston / ring ? Cant know for sure unless I remove them.

[ptroy]

Ok, problem found.

Broken a valve shim and thrown it out, along with one half of the retainer. Lucky it didnt drop the valve!

[Katman]

Ok, problem found.

Broken a valve shim and thrown it out, along with one half of the retainer. Lucky it didnt drop the valve!

Good old valve bounce.

Sounds like you were very lucky.