Its engine rebuild time after 90,000km and I'm a good 98% sure the cams in my 2kr are not EXUP. Anyone got ideas whether a set of exup cams would fit up to a non exup head? Has anyone ever measured the degrees on the cams to see the differences between em? Service manual says the valve lift is virtually identical, based on serviceable lobe diameters. Bonus question, how cross compatible are cylinder heads? And has anyone tried the aliexpress valves? $25 for 16 does not spark confidence but $150 does slightly more...
I've just been sorting through potential bearing shell candidates for the FZR250 engines - nearly every bearing shell for them is NLA - same goes for conrod bolts - ZXR250 ones are the go and nothing else is available - literally It's looking very much like CBR250rr MC22 shells will work for the crankshaft main journals - to be verified AND CBR250rr MC19 [27mm crank pin] will likely work for conrod journals - again to be verified but I am hopeful I will make a table to convert the Yamaha bearing colours to the respective Honda or potentially ZXR250 counterparts once I have a few more accurate measurements I believe [subject to vefification] that cylinder heads are identical - valve stem diameter being the difference 2KR 4mm - 3LN 3.5mm I bought 1 each of 2KR inlet and exhaust valves to assess the quality - the valve heads were nowhere near concentric - so much so that the face width varied by 50% from one side to the other YMMV I'm fairly certain that the cam timing difference between 2KR -> 3LN are in the 3LN supplement from memory it's 1 to 2 degrees more duration and a 1 degree shift - on which cam I cannot recall off hand, but it's in there A 3LN cylinder head 'should' go straight on
Pistons and rings are different as well, there is a height difference, I believe the 2KR pistons sit higher than 3LN. Not sure about the rods. I'd be careful mixing and matching 2KR/3LN engine bits.
Is it the oil scraper ring pack which differs between them? Yes pistons are different - that is in the 3LN supplement rod went from 80mm 2KR -> 82mm 3LN and the pistons changed to accommodate that difference in rod length
Some good info cheers. @ruckusman do you remember which seller you got the valves off? I've found a few and I'm thinking of buying a sample pair of the better looking ones. I'm very tempted to leave the bottom end alone since it's turning very smoothly and I haven't found anything in the oil. Mainly though because I cannot get the flywheel off to save myself. Made a thread about it about 9 months ago but no replies. Even the local yamaha was clueless after taking a look... That table would be pretty handy for the bearings if I do dig further in. Has there been any solutions for the no. 4 bearing going yet? Shimming the oil pressure spring was the last I read. Although I don't think I'm good enough rider to reach that limit Current shopping list is new pistons and rings and doing something about the head. The exhaust valves are a little pitted and the shims are all close to the smallest size
I would get info from @Murdo as to which seller he purchased the CBR250 valves from I bought mine a long, long time ago - OK just checked It was this seller - although I suspect that they're all coming of of the same factory so no blame against the seller, unless some are buying the stuff that fails quality control and palming them off... https://yismay.aliexpress.com/store/922726?spm=a2g0s.9042647.0.0.58734c4dIqFPeE I did manage to get the flywheel off - posted how here - let me find the post... Here it is https://www.2fiftycc.com/index.php?threads/tool-of-the-week.10190/page-3#post-118274 Only caveat is don't undo the conrod bolts without replacements ready - OEM are NLA so go for ZXR250 ones - we've had a thread here recently https://www.2fiftycc.com/index.php?threads/fzr250-rebuild-but-cant-source-conrod-bolts.11456/ Ping me by DM if you want to split shipping on some parts - conrod bolts mainly from impex Apparently the FZR250 doesn't have the thinner oil gallery section which afflicts the FZR400, but the oil restrictors backing out does need to be checked Personally I think shimming the oil pressure relief valve is sensible, if you've read that thread you know why BTW, you've obviously still got the cases together - record the 6 main journal shell numbers on the back of the case and if you can read them, record the numbers on each conrod, hopefully legible - stamped in black /ink/paint - down the side edge of the rods towards the front of the engine
