I have dismantled the engine of my 'mostly-2AW-but-with-2XT-frame' TZR250 for inspection. The odometer reads only 10,000km and the external condition of the engine would suggest that figure to be genuine, but only 2,000 of those kilometres were done by me. The engine ran very well before dismantling and I was expecting the internals to be in very good condition. They were...mostly.
There is some weird bore damage in the right-hand cylinder, where it appears that the bottom piston ring somehow got stuck protruding too far from its groove and wore a large deep patch in the bore. The ring peg looks OK, so I'm not sure how it happened. It looks like the bore would have to be made 0.75mm oversize to clean up the damage. Still, that is another story - this one is about the crankshaft.
The crankshaft assembly looked OK and all main and big-end bearings felt good. Unfortunately, my crankshaft man has discovered pitting on the big-end pins after pulling the assembly apart
. I had one spare crankshaft which I pulled out of a 2XT motor a few years ago and stored in a plastic bag, smothered in oil - it also looked and felt similar while in one piece. Sadly, it too had corrosion marks on the big-end pins
.
New genuine complete crankshafts are still available from Japan (for the moment) for about 80,000 Yen. Yamaha no longer supplies the centre assembly (two inner webs with shaft, bearings and labyrinth seal), although a small number of dealers around the world are advertising the genuine centre assembly for assorted prices. I am a bit hesitant to order one from any of these dealers, as the parts could (although unused) be quite old and may have been sitting around on a shelf, possibly with broken packaging, collecting dust (and rust) for several years. Also, I already have the new main bearings and my centre shafts and labyrinth seals from my two used crankshafts are all good. Therefore, I only
need the inner webs with integral big-end pins.
I see that both Yambits and PJME offer (presumably aftermarket) centre assemblies and also individual inner webs:
https://yambits.co.uk/tzr250-crankshaft-centre-assembly-p-42031.htmlhttps://yambits.co.uk/tzr250-crank-centre-web-p-1648.htmlhttps://www.pjme.co.uk/acatalog/Yamaha_TZR250_Engine_Parts_Bottom_End.htmlIt seems likely that all of these parts come from the same aftermarket maker. However, for some reason Yambits is offering the centre assembly 40 GBP cheaper (without VAT) than PJME...!
Before I spend 80,000 Yen on a complete new crankshaft, can anyone offer any advice or opinion about the aftermarket parts available from Yambits and PJME?
Thanks & regards,
James