Engine Knock

Hello, I own a 1994 VFR750F. As long as I have owned this bike, it will sometimes make a knocking sound that seems to come from the front left part of the engine. The catch is it only happens within a certain window of the bike heating up. So if looking at the temperature gauge, C = 0% and the point where the coolant fan kicks on being around 50%ish, the knock usually occurs between 25%-30% of the bike warming up. It stops doing it after that point. Anyone have any ideas?

I will try to remember to upload a video with sound of this happening later.

Thanks.

 

As you can hear, it is like a chattering sound. It may be hard to tell from the video but it is definitely coming from the top left side.

 

Sounds more like a valve ticking, higher pitch than a bearing knock. Going to be hard pin down if only happens for a short time. Hopefully some one with the same vintage bike can help.

 

I would also like to add that the noise goes away above 1500 rpm.

 

Could just be some valve lash that quiets after getting to operating temps.

Also, get a stethoscope and take some body work off. Sometimes you can use a wood dowel to pinpoint noises too.

If it doesn't get worse under a load I doubt it's a serious knock. But video is not the same as being there. Chances are if anybody else except the owner that listens to it every time would say you're fine.

But the only way to know for sure is to start eliminating possibilites which means probably starting with a valve lash check and inspecting everything while you're in there.

 

Also try pulling in the clutch next time and see if it changes. I have some Hondas that have some clutch basket rumble that doesn't sound like that's where it's coming from and can make you think it's something else (worse).

 

Pulling in the clutch doesn't seem to make it any better or worse. I've never done valve work before but I am not afraid to get in there can give it a shot. Maybe when it gets a bit colder (January) I'll take some time to take it apart and inspect/adjust the non typical stuff. Still hoping though someone here has heard this noise before and can tell me what they did to fix it; that would be too easy though.

 

My first thought would be put some flushing oil through and see if that makes any difference

 

Amsoil makes a detergent flush that I've used in cars and it does make a difference in valve noise. No, I don't sell Amsoil.

 

I'd agree it's not a knock (in the bottom end), more likely valve lash. I'd do what Captain 80s says and dig around some more with a stethescope. As for a flushing oil, dump in a quart of ATF, it is a great detergent, just don't go being Ricky Racer while riding. You could try a 5W oil as well to flush. If you are using a 20W oil, perhaps it's a little too thick to completely circulate when cold.... is there a place to hook up an oil pressure gauge?

 

mileage? Have the valve clearances EVER been checked within your ownership?

 

26K miles, I bought it January 2019 at 20k. I've never done any valve or carb work, or checked valve clearances. I have some funds now to replace things on it so I figured I would try to address these issues now. I live in an apartment in the city and I recently cleaned out my Dads garage so I could dismantle it and work on it.

 

checking valve clearance is easy, and nothing much can go wrong, while changing clearance is alot more difficult and includes a risk of problems unless you have proper tools and are meticulous in your work.

 

OK, it sounds most likely to be tappet noise.

I'm not 100% certain what the tappet servicing interval is for the 750 (last time I had a VFR750 was 1998 when I PX'd it for a VFR800), on the VFR800 I have (2000 FiX Pre-vtec) it's at 32K miles.

The choice of oil can be very important, especially if you live in a cold climate.

The standard grade of oil for all VFR750's & early 800's like mine is 10/40 Semi-Synthetic and specifically suited to wet clutches. That's fine for most operating temps a above Zero C (32f).

If you live in colder climate where the temp is often below zero C then use a lighter grade of oil (5/15 for example).

Using older types of oil such as car grade 20/50 is far too thick (viscous) for the narrow oil pathways & pies in motorcycle engines and can starve the top end of the bike when cold starting.

Using simple cheap mineral oils is also a false economy as it does not provide the lubrication and surface adhesion of semi or fully synthetic oils so can lead to significant increase in initial engine wear on startup, especially when the oil is cold and has drained down to the sump overnight.

The other significant issue with cheaper mineral oils is they are far more prone to breaking down and forming acids and waxes when hot and under load, and motorcycle engines generally run hotter than cars (partly due to the high RPM) and also have tighter machined tolerances on all mating surfaces, including pistons, valves gears and bearings making the need for good quality motorcycle oils absolutely essential.

All these can contribute to excessive engine wear, especially the valves and actuators (tappets) at the top end of the engine, .

Checking the tappet clearances is quite straightforward (once the petrol tank and bodywork is removed), but changing the shims isn't quite so easy, which is why it's quite expensive to have done by a dealership with the majority of the cost in labour charges; however, with the correct service manual, tools, structured approach and patience. it can be done at home quite cheaply.