Unpleasant cylinder noise - bad wrist pin?

[erik_w]

Hello!

I am getting some unpleasant noises from my four stroke Ural (650 boxer twin) and I would like to know what might be causing it.

- Noise comes from the cylinder area on both sides (one more frequently) and sounds kind of like when you making machine gun noises with your lips. Not like a metallic clink but a more muted, fast vibration sound.
- It occurs randomly while running, at 30 km/h as well as 80 km/h, it comes and goes without an apparent cause. Pulling back the throttle quickly will make it stop temporarily.
- Both plugs are light brown and engine pulls strongly across the whole range, there is no effect on performance.
- Grounding out the cylinders produces a nasty metallic clinking sound on the grounded cylinder.
- My wrist bin bushing are not 100%, I did them up with sandpaper but they weren't perfect.

I strongly suspect something is wrong with the wrist pins and / or bottom end? I want to rule out ignition problems since the plugs look so nice?

Would a wrist pin to loose / to tight cause this?

Thanks!

[unclepete]

What did you do to the wristpin bushings with the sandpaper ?

[Chuck in Indiana]

Wrist pins sound like a rattle when you back off throttle.

and sounds kind of like when you making machine gun noises with your lips.

Normal BMW/Ural exhaust note..

My wrist bin bushing are not 100%, I did them up with sandpaper but they weren't perfect.

Now, that's an understatement..
Obviously, I'm clueless though.. at least this will bump it to the top.

[Peter from Sch'dy]

I don't know much about Urals but if the wrist pins were tight on assembly I wouldn't think they'd stay that way very long.

Best,
Peter

[erik_w]

I don't know what to believe, some say that wrist pins are diagnosed by grounding the cylinder and some say that wrist pins cannot be identified by this.

what has me wondering the is randomness of the noise, it comes and goes like it wishes and I can't seem to cause it on my own. if I cut the throttle quickly while it is going on it stops temporarily.

if it where detonation due to pre ignition, wouldnt the spark plugs be white and nasty looking? I haven't touched the ignition timing recently.

1. what are symptoms of detonation?
2. what are symptoms of a bad wrist pin?

[LaMojo]

Detonation shows up on hard acceleration  -  also, sometime during high ambient heat, when lugging the motor.   

Wrist pin noise generally goes away with dead cylinder.  Rod bearing louder on acceleration and deceleration.

Neither noise will come and go.

I would look at the valve train.  Maybe a loose valve guide.

Pull cylinders and have a look see.

[Chuck in Indiana]

2. what are symptoms of a bad wrist pin?

I've already told you. Loose wrist pin will rattle when you let off the throttle.

[erik_w]

Hello!

ok, gotcha on the wrist pin.

loose valve guide? I've had that once before and the symptoms was massive oil smoke and bad running. I don't have that now...

I'll have to open up and see.

[Farmer Dan]

I'm not familiar with Ural's but it sounds like it could be a loose sleeve.  If they have them?

[erik_w]

What is a sleeve in this context?

[Chuck in Indiana]

A sleeved cylinder. I dunno what they use..

[erik_w]

there is of course a cylinder sleeve, which is a part of the cylinder and in no way detachable, I have a very hard time imagining this coming loose.

the engine is very similar to an old guzzi two valve, just the bare essentials, no extra technical nonsense.

[Chuck in Indiana]

there is of course a cylinder sleeve, which is a part of the cylinder and in no way detachable, I have a very hard time imagining this coming loose.

the engine is very similar to an old guzzi two valve, just the bare essentials, no extra technical nonsense.

Sleeves *have* come loose before. Depends on the quality of the assembly job. I'm not saying that is your noise, but..
Ural? Uhhh, the same company that totally misses the timing marks on the flywheel? Sometimes? 

[acogoff]

A loose valve seat will also make a whole lot of clackety racket and is usually easily detected with a simple finger over the sparkplug hole "compression" test.

[erik_w]

yes, a loose seat or guide would result in almost total loss of compression? 

some urals indeed have incorrect timing marks.

[Chuck in Indiana]

yes, a loose seat or guide would result in almost total loss of compression? 

some urals indeed have incorrect timing marks.

Not necessarily.

[luthier]

Might be a bent push rod too. Why not pull it apart and have a look? They are simple enough.
Otherwise just ride it and wait for the big bang.