Hitchcocks Forum

Hi

my friend has Bullet 500ccm, carburator engine and some noise comes from his engine. Bellow is his description of issue and what he did:

This noise occures when engine is heated up and when I close throttle- you can hear it on video. I changed recently primary chain and alternator. Noise was present also before this repair, but not always. I thought that it could be caused by too loose primary chain, but it was fixed. Now this noise is present always after heated up.

You can hear noise on video here:

https://www.youtube.com/watch?v=uhD2U8d ... =youtu.be=

Next steps what I checked and did:

-sealed exhaust
-loosen exhauste valve clearence (it was too tight before, now I set clearence to 2mm)
-changed the engine oil
-treated decomopressor by WD40- I thought that probably decompressor is not proper closed
-Add MILITEC into the engine oil

When all above mentioned was done I started the engine and heated up. When the engine was heated up, the noise was presented again, without any change. The engine run about 15min on low and higher revs. I noticed that there is a little smoke around the engine, so I stopped it.

After 10 min I tried to start the engine again by kick start. This time I had to applied full force and weight to move piston. So I let this attempt.

After next hour I tried to kick the engine again- I applied the full force and then I was able to move the piston easy- with ordinary force.

What do you mean about the noise, which could be hear on the video? What to do as a next? Any advise is appreciated.

I had an old Norton that did that.. try a decoke..

I am somewhat concerned about a 2mm (80 thou) valve clearance, that must rattle like a spin dryer full of nuts, bolts, and washers.

How very interesting. It has a light, "tinny" sound a bit like a tin can. It sounds too tinny to be a major engine component, although of course I could be wrong. I'm only giving my impression.



I note especially that it only happens when you close the throttle and the engine decelerates. This isn't what happens if you've got a cracked piston or other major fault.



For all the world it sounds like someone tapping a screwdriver against the silencer, so I did just wonder if it could be a loose baffle. That might also explain why it only happens on the overrun, when the gas pressure from the engine gets very much less.



Or could it be the primary drive chain rattling around inside the case?



I don't think this is a serious fault.

like papasmurf noticed the 2mm is probably a typo and you mean 0,2mm.



but even if you mean 0,2mm that’s way to much, the correct valve play on a dead cold engine is 0,00MM.

the need to spin freely with no measurable play.



are u sure you adjusted them at the correct TDC?

Haven't listened to it or tried to read all this stuff but my guess loose exhaust valve seat

That sounds very much like primary chain to me. I'd take the case off and run the engine without it to check.

Try using a screwdriver or a steel rod to diagnose exactly where the noise is coming from. Example: press the end of the screwdriver against the exhaust port and press the bone just above your ear to the handle end. By moving the screwdriver from place to place you can identify exactly where the noise is, exhaust valve, inlet valve, primary chaincase, whatever. Then you can start looking in earnest! To me, it sounds like a loose baffle in the exhaust, I had something very similar on my very first bike, a Honda CB250 K1 and when I showed it to my more experienced pals they all laughed and pointed out the loose bits inside!

REgards, Mark

Does the exhaust pipe have an inner liner to prevent blueing, if it has the liner may have broken away and is rattling about

Easy way to check if it's in the silencer: take if off and run the bike briefly, if the noise disappears (allowing for the louder exhaust), problem identified. It doesn't sound like engine internals to me. A.