Engine blown ......... updated with more pics

[Mincehead]

Errrm nope, fraid not, it`s been `shaved` by the cranks excessive movement. Get those crankcases split and have a good inspection, clean, degrease, better still steam clean.

[zednine]

Ok will do ....seems a little odd though as the shaved bit is identical on both sides of the engine and the area of the shaved part is much greater than the radius of the crank .... im in engineering and would have expected some aluminium residue as well ...... there is none ....engine and oil clean as a whistle , however Ive not rebuilt one of these before and I am asking for advice so will take it ......... Thanks Mince

[pabxxv]

Just glue it.. it will be fine

[pabxxv]

That bike had the least vibey trsx motor ive ever ridden. Ive owned maybe 5 of em and ridden a few more

I think that motor went because whoever put teh alt bacvk on after rebuild, fuk't up... and the rotor jammed and caused teh crank to go... fek all to do with vibes

[Mincehead]

There may be more to this than currently meets the eye. You`ll have to split the cases anyway so all will be revealed as it comes apart.
There are some marks on the top of the crank web and the crank the other side of the con rod that doesn`t look as though they were left that way by Mr Yamaha too.
Like I said, never seen a crank go quite like that one!

[zednine]

Definitely some marks on the crank web .... someone must have a crank out there with stripped camchain teeth ......... that end of mine is perfect so can make one out of two hopefully

[Mincehead]

Yep you sure could, been done by at least one of our members but he was lucky in as much as he could utilise part of a 180 degree TDM crank, he needed the crank sprocket only to repair his crank.
There is a thread on here about it too, I think it was Tarwetijger, search under his name for threads he`s started.

[NWS870R]

Your crank has previously been welded as a quick repair (very poorly!) you can still see 'cut in' marks where the weld has penetrated & then ground off. It's also been welded 'off true' which is what is causing the crankcase wear & ultimately it's demise. Did you say this was a recent purchase?

[zednine]

fairly recent ........ive had the bike 7 months but only ridden it regularly in the last few months

[NWS870R]

Might be worth contacting the previous owner & seeing what work had been done to engine prior to your purchase - i'm 100% about the crank being welded tho, i run a welding business so spot these things at a glance

[Mincehead]

It was also the impression I was getting, those `tell tail` air pockets in the ground off sections, but was holding back from saying so as the crank was coming out anyway and it would have been far more evident once it was.
Could also explain why the motor seemed smooth if it had been critically balanced after it had been welded, likely balanced to a better standard than it might have left the factory.

[Smithers]

Your crank has previously been welded as a quick repair (very poorly!) you can still see 'cut in' marks where the weld has penetrated & then ground off. It's also been welded 'off true' which is what is causing the crankcase wear & ultimately it's demise. Did you say this was a recent purchase?

Ive got to agree with NWS870R ..... going by the evidence ie. weld porosity or undercutting, discolouration and the linished areas either side of the journal, it looks like the journal has been welded .... it,s sad to see what you have there, good luck with it

[zednine]

Ok crank is out and the problem become obvious

The crank has had a previous repair ...... the left hand journal has been built up with weld and reground presumably altering the hardening of the crankshaft

All has been well until the alternator winding came adrift locking the motor momentarily until the shock has sheared the weakened crankshaft

Fortunately I have come across a Tdm 4tx engine which is seized but should provide a crank that is suitable for regrind

[Mincehead]

Ahaaa, I was right about the alternator coming loose first. That welding really was VERY poor and maybe a few degrees out which could have been why the bike seemed `smoother` than other TRX`s too.
How are the crankcases looking zednine?

[zednine]

No problems at all with the cases fortunately ......... half way through getting the crank out of the tdm too so fingers crossed should be able to send one to SEP in a week or so