I have an LN3 with a damaged plug thread, and an LN6 with a nasty rattle (31000kms... CCT only halfway out so guess it aint stretched camchain). Thinking of dropping the head with torquier cams onto other eng. Neither had great compression, so doing rings too. Guess the block and pistons are incompatible (LN3 suffix-01; LN6 suffix-02 on part numbers), so need to swap them also. Any warnings appreciated pls?
Rings wouldnt necessarily be the culprip with lower compression... if it was low across all 4 cylinders...maybe. Compression pressure is really hard to get a good reading on these little 4 cylinder machines. A better indication is a leak-down test. Before you pull anything apart make sure you check the valve clearances... its a really good bet both engines they are too small. pointless doing all the work and then having to re-do half of it to set all the valve clearances. Best to do that when you have the head off after you have taken measurements... depending on the condition of the valves as well.
Valve clearances are done to upper half of range ie over 0.15 and .25mm Comp gauge is pretty rough fit - but 40 to 100psi etc whereas I get 120 on my 3rd bike Is there anything special about the rings, anybody know if they're plated?
Well LN3 pistons measure up the same as LN6 (3ln-11631-02), so I gave up on getting gudgeon pin out. Rings from 4 Sets Piston Rings Kit For YAMAHA FZR250RR 3LN ZEAL250 FZX250 3YX STD Bore 48mm | eBay came with the correct thickness oil control. Compression OK, running fine.
