Should I crack open my LC4?

Discussion in 'Thumpers' started by Umarth, Jan 12, 2013.

  1. gunnerbuck

    gunnerbuck Island Hopper

    Nov 19, 2005
    N.V.I, B.C.
    The scratches that show for the most part are pretty minor... The deeper scratch is pretty narrow likely will not have much effect.. But then again you are going on a long journey, the top end is apart, so now would be the time for a complete refresh if you have the funds... The scratching is likely caused by hard particles getting past the filter...

    The budget fix would be to order a new set of piston rings and have the cylinder honed... You would probably be looking at $100-$120 total to restore to 95%...

    To go 100% you'll need to have the cylinder replated or replaced and go with new rings or a new piston... Replating usually costs around $300 and a stock piston $350 VS $180 for a Pro X or $220 for a Wossner... Stock rings are about $60...

    Wossner piston are the lightest and there have been some claims that they smooth the engine out, but I have noticed that with a refreshed top end regardless of piston brand, the engine will feel smoother...

    The 02 and prior 640s with the low flo head used the thicker base gasket.. The low flow cylinder has larger alignment dowels so this difference in the gaskets will have to be addressed... Some have just installed the gasket filling the dowel gap with sealant while applying it to the cam tunnel area as recommended in the manual... My plan is to sacrifice one of the four gaskets I have and cut out little filler donuts to make up the difference...

    One of my 640s has the compression reduced via combustion well milling and it is noticeably smoother than the other which is in stock form... The power between the lowered compression bike VS the stock is hard to compare because the lowered bike has an SM exhaust vs the others oem cored unit...
    With the SM pipe the comp reduced bike has less low grunt end but more on top and uses a slight bit more fuel, maybe about 1-2KM less range per liter... These differences may be due to the freer flowing exhaust and nothing else... The only way to tell for sure is to switch exhausts and see how it compares...

  2. rob748

    rob748 resident alien !!!!

    Jan 17, 2005
    traveling somewhere :)
    i replaced the piston and had a sleeve put in and put two new valves in and decided not to do the bottom end. its lasted 5000 miles and went boom, it needs new bore, piston rings plus the bottom.
    if i did it again i would have refreshed the bottom at the same time.
    mine was raced a lot so the miles don't mean a lot
  3. Umarth

    Umarth Been here awhile

    May 16, 2011
    Tramping arround the world for a bit with Big O
    I do but it's also countered by the "if it ain't broke, don't fix it". Especialy since this would be the first time I ever take a motor completely apart and would be a hands on learning experience. Kind of like learning to drive standard: you do it with someone else's car...

    I'll go with gunners recomendation which makes a lot of sense.
    But yeah, really would of liked to crack it open! :drif
  4. bmwktmbill

    bmwktmbill Traveler

    Jul 16, 2005