Hi,I first posted in new members about motor I am looking to repair , big end bearing damage on two rods, crank has cleaned up and looks usable but I cannot find parts in the UK I have new bearing shells from AHL , having called various bike breakers I can get 250r parts, so do any of you guys know if a 250r crank rods and pistons would fit as a complete unit in to a fzr250 motor or could I use the cylinder head from my motor on a 250r engine .any help much appreciated
3LN rods are 2mm longer than 2KR. Use the part numbers as a guide. If only the last two digits are different you might be able to use them.
@Mike Green and @gregt are both authorities on the differences in the 250 cranks - if I recall correctly Mike noted the differences (development) from the 2KR - 3LN cranks As @maelstrom has correctly identified , the rods differ in length and use pistons with differing crown heights As far as main and big end shells go, I cannot say for certain that there is any difference, I don't think the cases differ between 2KR - 3LN, so you can play mix and match, same for barrels, and heads also Cylinder heads - valve sizes differ - 4mm stem diameter for 2KR, 3.5mm stem diameter for 3LN series, cam timing differs a little between the two and valve sizes differ but I cannot recall the differences. The 3LN service supplement is a good resource for the 2KR -> 3LN changes, especially cam timing, slight change in timing and duration from memory
BTW - good threads on the big end failure so that hopefully you can avoid it reoccurring - there's some good knowledge https://www.2fiftycc.com/index.php?threads/fzr250-cylinder-4-big-end-bearing-failure.6927/ also https://www.2fiftycc.com/index.php?threads/fzr250r-the-rebuild-is-progressing.10794/
AFAIK the rods will interchange onto any model crank. Wise to check clearances though. Sets must be used together - long rods with short pistons and short rods with long pistons. Either will work with any model barrel or head, the total height to the top of the piston is the same for both types. Having said that, one of the blown motors I was given had one short rod.....The proverbial previous owner, lol.
Crankshafts are different but the bearing journals all seem to be the same, it's only the counterbalance weights. Crankcases are different but the only real difference is the underskirt oilers on the 3LN. It might just be for marketing but then it might also help with the life of the lighter slipper pistons in the 3LN. As far as I know you are good to mix and match 2KR and 3LN parts
number 4 big end bearing is a problem. if a 2kr motor check the cranks oil galleries and the feed holes in the block.
I wouldn't expect that marketing would make decisions about oil squirters. There will be an engineering reason.
Oil squirters help cool the pistons down as well as providing lubrication. I found on my 3LN's that I pulled apart, there was lots of burnt oil residue on the underside of the piston, which took multiple rounds of threebond and ultrasonic cleaning to fully remove it.
Which begs the question regarding the big end failures on No 4, have 2KR's ever had this problem? Maybe the addition of the oil squirters without upgrading the pump was just too much to ask under racing conditions.
The oil squirters become active above 1700rpm according to the manual. It only takes around 50g of pressure against the ball/spring inside to allow oil to flow through it. One of mine had an interesting issue. The top part of it felt wobbly when I removed it from the engine and it came apart in my hand. I wondered if oil was escaping from it around the join and reducing the oil flow to useful areas. When they are installed the top sits level with the bottom of the cylinders which trap them in place but there is a chance they could still leak.
