In the middle of rebuilding my 250 and I have ran into a SLIGHT issue. This particular year 250 had two different size conrods, 129mm and a 132mm. You can see where this is going... I somehow stupidly ordered and have already had fitted to the crankshaft, THE WRONG SIZE ONE! It is far too big and pokes out the top of the cylinder at least a couple of mm even with 2 base gaskets. My mechanic mentioned he could stick the head in a lathe to take a small amount off because there are tiny carbon / metal filing pockets where the big end bearing exploded. (I have removed all metal filings don't worry.) I'm wondering if its possible for him to remove the full 2mm - 3mm required to fit the head on nicely, without my head being smashed apart when running. Another alternative would of course be to further increase base gasket size. Would this be a MUCH better solution? In terms of power loss, in not too concerned either way as I don't even get full use out of my 125 let alone this beast. I don't really want to have to tear apart the bottom end again to have another £70 conrod fitted.
Thanks in advance for any help you guys have to offer!
It won't run properly if you do all that work. You'll increase the displacement by a fair few cc's and will alter the squish band and port timings. Even if you upjet it accordingly there is no guarantee it will run properly because of the ignition timing.
It sucks but you learn from your mistakes.
Also when it comes to rebuild for someone else. they will be properly span out why it doesn't fit.
Unfortunately I couldn't find the correct sized conrod for the same price as the previous one as the eBay shop said it would be a couple of months before they have one in. So I had to shell out £105 for a Pro X one :(. I understand its better quality but if you replace the conrod when you have the big end bearing replaced then the conrod is only ever as good as the bearing surely?! Would much rather stick to the cheaper Mitaka but oh well.. £20 quid later once its fitted, fingers crossed I'll have a working, all be it not running perfectly, KTM 250 EXC again!
