DT400, my engine is now fully stripped but I'm concerned about my crank.
My thoughts are, the seal will not seal around the crank because of previous deterioration, so the crank is scrap. 
Any comments welcome.

My engine has obviously been left and deteriorated, somebody has cosmetically "tarted" up my bike, listed it for sale, for then some old guy with rose tinited glass to buy. Act in haste, repent as leisure....... .

   

That can be repaired by installing a speedi-sleeve over the damaged area (after crank is installed in cases). 

Several brands available: www.skf.com/us/products/industrial-seals...es/skf-speedi-sleeve

Otherwise, a good specialist shop can hard weld and re-machine damaged area...  not that uncommon and since it sounds like you're in the UK, you can probably find someplace to repair. 

Or replace with a crank in better shape.

 

Tim- that is a pretty suspicious looking seal area, I would be wary myself as to how long a new seal would last. Was the rod assembly replaced or a rebuild done on it? Or do I understand that the bike was cosmetically improved but not necessarily mechanically renovated? 

Mark that is a fantastic solution! Had no idea something like that was available. Very good to know, much appreciated, I have saved the website for possible future reference.

Kudos to you! 

Tim- are you in the UK? and what year DT400? 
(P.S.- don't feel alone in getting bit buying something that was less than purported to be. there are probably more than a few of us geezers that this has happened to)

Thank you MarkT, I didn't even know something like that could be done, I suppose anything's possible really.
I'm going to send it to my machine shop now I know and let them decide.

Yes, cosmetically beautiful, mechanically dogs dinner  .

UK based, N W Wales, mine a 400C.

Get it spray metal transfer welded they shoot powdered metal out of a torch that fuses to the base metal and is very hard then it's machined back down to size good as new. Any engine rebuilder will know someone who dies this service 

I used a speedy sleeve on my bike it was quick to install and cost about $15

That crank is definitely in need of repair or replacement.  I like the speedy sleeve idea for the seal area but it can't go into the area where the bearing sits as the increased OD will not allow standard bearing reuse.

Read my original post carefully.  Speedi sleeve needs to be installed AFTER crankshaft is installed. 

And yes, if you need to press the crank out of the bearing in the future, a new sleeve will need to be installed. 

The crank definitely needs an overhaul, big ends etc but the threads look a little suspect too, so with so many issues I'm heading towards a replacement but there opens up another minefield