After crash engine problem.

[ridders]

Hi, unfortunatly I came off my nc30 last week in a average speed crash, the bike has been lay on its side for a small period off time with the throttle stuck on whilst i picked myself up (no more than 30 seconds). I have switched the motor off via the key whilst the bike was still lay on its side and still under revs as the throttle was packed with mud and grass. I have got bike home via a van and cleaned it up as much as I can to inspect the damage, which was mostly to the front nose cone and right side fairings, but the major concern I have is now with the engine, it now has a terrible knock/rattle when turned on, I am thinking that this is going to be a dropped valve but could well be wrong with out further inspection. So my question is does this sound right (dropped valve) or does any body else think any thing different and what I should do from here. Thanks

[arsey30]

Rev limiter should prevent top end damage, but bent valve more common than a dropped one.

Sit bike on rear stand, engage a low gear and turn engine over forward by hands on the rear wheel or a spanner on the wheel nut to check all 4 compressions. First gear will be too hard to turn, top too easy, so choose one that gives some feel.
Remove clutch cover timing hole bolt to see where the firing points are as they are not equally spaced [90-270 degrees]

The oil may have run from the sump to the side of the engine [perhaps into the clutch cover as it seems that it was on its right side? ] so that the pump pick up was above the oil level, so starving the big ends of an oil supply.

Is the noise from the top or bottom of the motor.

[skinnydog0_0]

Rev limiter should prevent top end damage, but bent valve more common than a dropped one.

Sit bike on rear stand, engage a low gear and turn engine over forward by hands on the rear wheel or a spanner on the wheel nut to check all 4 compressions. First gear will be too hard to turn, top too easy, so choose one that gives some feel.
Remove clutch cover timing hole bolt to see where the firing points are as they are not equally spaced [90-270 degrees]

The oil may have run from the sump to the side of the engine [perhaps into the clutch cover as it seems that it was on its right side? ] so that the pump pick up was above the oil level, so starving the big ends of an oil supply.

Is the noise from the top or bottom of the motor.

+1

I would suspect main bearing rather than valve, unless the bike was running at max revs and you don't have a standard ignition?

[ridders]

Hi thanks for reply I will do as mentioned and see how I go, it sounds top end to me but I am no bike mechanic to be honest, I have done bits on the carbs and so on but this is new territory for me. I run a standard ignition and the bike didnt seem to be reving that high when I killed the engine.

[skinnydog0_0]

Best get a compression tester only way to know for sure if it's a valve and which cylinder.
Also get a large screwdriver and place the flat end against the engine and the hard plastic handle against you head just I front of your ear, this acts a bit like a stethescope and will give a better indication of where the noise is comng from as you turn it over.

[arsey30]

I was looking at a first quick way to check compressions, [do you have a compression tester, access to front heads] before going any further.

A faster way to check is to run the engine at 3000rpm for 30 seconds and check each ex headers to see if 1 or more is cold.

[RickOliver]

`terrible knock/rattle` - my bet would be that the oil starvation has taken out one or more of your big end bearings...

Rick

[ridders]

Ive just had a good listen with a friend that knows abit more than myself and think that its the big end/crank thats gone, so I am thinking that it will just be cheaper to buy a new engine or bottom end. Any other/better ideas would be nice to hear tho please. Cheers

[skinnydog0_0]

Yes would probably be cheaper to replace the engine than repair the one you have.
Where are you based? I have a spare engine I was going to keep for my race bike but would consider selling it.

[ridders]

I live in manchester (gee cross/hyde), do you have a price in mind, what is the condition of the engine you have?
Cheers