I cleaned the carb and just got my 1972 DT2 250 running! 
I'm looking for help identifying the source of this rattling noise and whether it's normal. 
Possible piston slapping?

Here is my video of the rattling sound on my bike.


I found a couple of other videos on youtube DT2 250 owners whose bike also seems to make this rattling sound. I was wondering whether this was normal or if their bikes were messed up like mine 

Video of someone else's DT2 making the same noise



Any help much appreciated!

Probably just me but i'm a little confused by all the videos so i guess the first one is yours in which case yes it has bad piston rattle. I know ya loading it up a bit in gear but at low revs its laboring & just before it stops its particularly noticable. Even though you're loading it a little before it stops it's sounding flat not happily pulsing on compression. So my guess is its very low on compression & ya gonna have to "Go In" i'm afraid. Might've been seized at some point & rings partly trapped in their grooves. Or just plain worn out from unfiltered air--sand--dusty etc. Full of joy aren't i lol.

Just thinking--it wouldn't be a good idea to try starting a 360 the way the lady starts the 250 although that's pretty impressive i must say. & if that's the same bike from original poster it does sound very rattly but from more of a distance. So same answer applies as above.

So I opened up the cylinder head expecting to see a gouged cylinder wall from the piston slapping around.. Looks pretty clean to me. Think we can rule out piston slap as the cause for the rattling noise?

Thoughts?

If it were me i'd now lift the cylinder & remove the piston then do some simple measuring first just using a feeler gauge at the piston skirt base [not the top]. Remove the rings makes it easier to slide the piston up the cylinder & doing that in about the same angles as it was when running ie holes in the shirt pointing back towards the inlet side.. I'll leave it there for now & look forward to your results. Did you clean the piston crown or was it like that [been cleaned recently]. Ok maybe i'm going on about nothing--& hope its nothing.

It looks like to me that someone took the cylinder off, did a hone job on it, cleaned the top of the piston off and put it back together. Like Morley said the top of the piston is way too clean to have any run time on it and you can still see lot's of cross hatch on the cylinder walls.

On your vid at right on 39 seconds the piston is very audible on the overrun when closing the throttle. Problably more times through the vid but i just caught it right there so picked 39. Very similar to the ladies bike in audible noise.

@airbornsilva - I did clean the top of the piston actually. First I gently removed the carbon with the dull edge of a hacksaw blade, then gave it a light scrub with WD-40 and a scotch brite pad. Below is the beginning and end result. 

 
 

@Rt35 - I removed the cylinder jug today, initially NOT to measure the bore and piston because when I saw how clean the bore was, I figured the bore/piston fit was still fairly precise. I removed it because I broke one of the 10mm bolts where the exhaust pipe and cylinder meet   But since its out, I do plan to measure the spacing between the piston and bore with a feeler gauge, then take separate measurements of the bore with a telescopic gauge/digital caliper.

I tried extracting the broken bolt by drilling the center out and using a left-handed drill bit - but no luck. I ended up just hollowing out the bolt and probably slightly flared the opening of the entry point... Pictures below.

 
 

I'm thinking about bringing the cylinder jug to a machine shop or motorcycle repair shop to see if they can salvage my shotty attempt... Im hoping they can remove the leftover bolt stuck in the threads, then if needed, retap the threads to the next size up.

Any suggestions if there was anything else I can try? 

Don't ya just hate it when that happens--& it's happened to all of us at some time. The bolts are actual 6mm with a 10 spanner size & if you can get it removed & thread is ok just use a 6mm allen head bolt. They're high tensile & you won't overtighten it with an allen key. I must say you've done a good job of drilling central. Worst case is go bigger to 8mm thread. All mine have gone to 8mm. Not sure if my trick would work now it's drilled but i've had luck sitting a bit of flat steel with a hole over the broken stud & arc welded it to the stud then it just winds out [if ya lucky]. I know the stud is flush with the cylinder but works for me. Maybe an 8mm hole in the steel plate & a small arc rod with good amps & do a circle into it. Not as easy as it sounds as the rod flux wants to get in the way. Tig weld might be good & wish i had one.
 Here's the only pic i can find & no help, but i had a broken cyulinder stud in my 360 crankcase. It broke truing to remove them all to use in another case but must've been locktighted in i think. Hard to imagine breaking those 10mm long studs unscrewing with a stud tool. So i made a plate, then some more lol as kept breaking my weld. But after many tries i got some slight movement so forward & back a mm or so & it eventualy came free. Was broken flush with the case but welding using special rods in this case & didn't damage the alloy crankase mouth--luckily. 

Thank you for the tips @RT325!
Ill keep them in mind for if and when I run into this problem again.

I took it to a shop and one of the owners was able to drill out the remainder of the old screw, use a time-sert and did so for $40. Good price given that other shops quoted between $100-$250...

 

Now time to clean out what carbon I can from the exhaust, clean out the rusty cylinder bolt ports, scrape off the melted cylinder jug gasket and get some piston/bore measurements.