640 LC4 Supermono issues

Discussion in 'Thumpers' started by sam_2555, Nov 19, 2012.

  1. gunnerbuck

    gunnerbuck Island Hopper

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    I would say your autodecomp is not working if your compression is at 160 psi... No problem though, the bike will still start as long as you can spin it fast enough... The click of the decomp cam is a good sign, but I am wondering why it is not tipping the valve open... If your valve clearance is excessive then it is possible that the auto decomp would not function.. A worn cam follower roller would also cause excessive clearance...

    By chance if the engine came out of an Adventure model then it would have a vacuum spigot on the side of the intake manifold ahead of the carb on the right side... If you look and see a spigot there, make sure it is capped off as not to allow air straight into the engine...

    I have seen a faulty stator still give spark but not start the engine... This was due to some scoring on the magnet side caused by foreign debris scraping between it and the flywheel... The pickup coil goes south once in a while as well...
    #21
  2. bmwktmbill

    bmwktmbill Traveler

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    Sam,
    Your ignition is not OEM for the engine?...correct?

    Will an OEM ignition module work with your setup?
    bill
    #22
  3. sam_2555

    sam_2555 Adventurer

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    Thanks again for all the responses.

    xy500, I've checked the valve clearances and they were at the nominal values - can't remember what they were now though, suppose I could do a recheck so I have the values written down and they are known.

    Gunner, I'll see if I can borrow a compression tester again this weekend and do a retest. Similar to the valve clearances I can't remember the exact value I just remember doing the test and knowing the value was within the limits. I should've written it all down really. I'll check the condition of the follower this weekend as well.

    I've looked for this spigot before but couldn't see it. There is a cap head bolt in the head close to the manifold that looks like it's plugging something. It;s now screwed into a spigot though, just a hole in the head.

    The ignitech DC-cdi doesn't need the stator to spark, it takes all its power from the battery. That was one of the reason I bought it, it means that I won't need to test the stator as well. Although I have tested resistance across all the coils of the stator and all were within spec.

    Bill, I was originally using an OEM cdi. It still sparked but didn't fire, I thought there might be a problem with it so I bought the non-OEM unit.

    Cheers,

    Sam.
    #23
  4. bmwktmbill

    bmwktmbill Traveler

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    I think you need to pessure test/leak down test it and listen for leaks.

    Gunner has posted an easy way to do this.

    With all you have done and no fire you start to think something is broken.

    Does the oil smell like gas?

    When you open the drain screw on the bowl does gas run out?
    I notice the carb is sitting at an angle.
    bill
    #24
  5. sam_2555

    sam_2555 Adventurer

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    Ok so this weekend I've been in the garage trying to start the bike again to no avail.

    I've tried some easy start, tried getting hold of a compression tester to do a retest but couldn't get hold of one, rechecked all the electrickery. Still no start.

    I have taken the plunge and pulled the engine.

    [​IMG]

    Here it is in my hall way ready to be pulled apart. I'm ordering a clutch removal tool and getting a mate to fabricate a tool to hold the flywheel so I can get the damn thing off. I gave it a good go whilst the engine was still in the frame but I ended up just pushing the back wheel round despite standing on the back brake. I'll order a head gasket in the near future as well.

    After everything I've tried I've concluded that there must be something in the engine preventing it from running. At the very least stripping it will put my mind at rest and I may as well upgrade the main shaft bearings whilst I've got it all apart in the warm flat.

    I'll post more pics as I strip and rebuild it. Hopefully I'll find a chewed up gear somewhere.
    #25
  6. gunnerbuck

    gunnerbuck Island Hopper

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    Look for a left hand thread on the flywheel nut...


    I really wouldn't go past taking the top end apart to inspect unless you have noticeable gearbox issues... The main shaft bearing can be swapped without splitting the cases...

    Your no starting issue pretty much has to be related to one or more of the following: lack of compression, improper valve or spark timing/electrical or fueling problems...
    #26
  7. bmwktmbill

    bmwktmbill Traveler

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    +++!
    bill
    #27
  8. sam_2555

    sam_2555 Adventurer

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    Gunner, I've read a fair few of your posts and respect your opinion............. but, having tried everything I have and dealing with an engine that you have absolutely no history of; what else was left to do apart from look inside?

    At the very least I will know the engine is good once I've put it back together. I have no idea where this engine has been, what bike it was in or what mileage it has on it. For all I know I'm dealing with an engine that's been round the world twice and stored in a lake for the last few years.

    Last night I pulled the head. Whilst I was taking the head off I took a coolant pipe off the barrel that I missed before and some fluid came out, a sort of mixture of water and oily looking stuff. It look pretty grimey. The inside of the head is pretty much made of rust. The water ways in the barrel are a bit better but not by much. There is a lot loose of crap in there, I would like to pull the barrel just to give it all a proper clean. I dread to think what I'm going to find in the water pump (which will be rebuilt imminently). I think I'll put some new valve seals in and check the guides for wear whilst the head's off as well.

    A couple of pics of what I found last night:
    [​IMG]

    Barrel coolant outlet:

    [​IMG]

    Cylinder head:
    [​IMG]

    This filth won't stop it running I know, but it's a clue to how well cared for the engine was before I got it. The coolant system on the bike was using a rs125 filler tank and the coolant in there always looked clean, I guess I didn't feel the need to drain it before - probably should have done.

    Good points: cylinder and piston look ok, no glaringly obvious faults. Valves look ok to.

    I'll post more when I get more work done.

    Any advice on what to do next or how (if at all) this coolant situation would effect the rest of the engine would be appreciated, as always.
    #28
  9. gunnerbuck

    gunnerbuck Island Hopper

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    I would pull the barrel off and have a good look at the piston, then you can assemble the head and barrel off the engine and flush out the passage ways with a mix of hot water and vinegar... Use your gasket to keep the sealing properties when you bolt them together and block the upper hose port... sit the cylinder on it's side and fill with a mix of vinegar and boiling water and let stand... Empty , flush with clean water and repeat the cycle several times... :http://www.advrider.com/forums/showthread.php?t=132369

    You will be able to inspect the crankshaft for play and smooth operation at this point as well as cycling the gearbox to make sure it turns and shifts smoothly... If all is good you shouldn't have to go farther than this:http://www.advrider.com/forums/showthread.php?t=73558


    [​IMG]
    What's that, a bullet hole in the valve or a photo defect?
    #29
  10. sam_2555

    sam_2555 Adventurer

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    Cheers Gunner. That's a photo defect on the valve there.

    I've just been turning the engine over to check the whole barrel for any obvious scoring and can hear a fairly loud clunking coming from the gear box. It sounds a bit like the auto-decomp which is why I didn't pick it up before. I'll post more details when I strip back the engine further.

    Here's a youtube vid of the noise: http://www.youtube.com/watch?v=69yQLcdKFWE
    #30
  11. gunnerbuck

    gunnerbuck Island Hopper

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    #31
  12. bmwktmbill

    bmwktmbill Traveler

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    YIKES!!!!

    bill
    #32
  13. beek-02

    beek-02 blazing a trail

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    Dollars to donuts it has a bad crank/connecting rod. I bought an lc4 a bit back with a bad crank and although I did get it to fire/run, it barely ran, and not for long. I ended up buying a pro x con rod kit to rebuild the crank and then came across another motor that I got lucky on. I don't need the con rod kit if that is the way you decide to go shoot me a pm. The crank on these is about as mechanical as it gets. It has to be shimmed to the proper clearances for the main bearings and will have to be redone if you put a new crank in. If you go the route of rebuilding the crank a good reputable shop should be able to mimick the current width of the crank and not require any shimming, (repeat should). This is only good if the main bearings are still good. Also, check/replace the seal on the clutch side cover that goes over the end of the crank. This is the seal that directs the flow/pressure of the oil through the crank and to the con rod.

    A whole other direction is to get a crank with a longer stroke and build a big bore. I think you can go up to almost 700cc with the right combination of crank and piston. Of course this gets a lot more expensive as it would require a longer cylinder to get the right compression. Munn racing might have more info on the big bores, I know he has a lot of knowledge on the lc4, or at least used to. There aren't as many out there building the old lc4's now that the new FI 690 is out there.

    Good Luck and keep us posted,

    Beek
    #33
  14. sam_2555

    sam_2555 Adventurer

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    Thanks for the help guys. Gunner, those threads are really useful, I've started reading all of them and not quite finished any yet. I've learned a fair bit by just going through them though.

    Beek, thanks for your input. If it is the crank that's bad I'd like to go the big bore route but finances might limit me a bit. We'll see, if I need a new crank or if it'll cost a fortune to get this one sorted I'll look into it more.

    Mean while, I've been taking more parts off. I got a mate to make a flywheel holder for me from a rough drawing I gave him and it worked like a charm. The clutch nut was a pain to get off though, I ended up flattening out the entire tab washer not just the bit that was bent over the nut. Got it off in the end though and saw this little beauty when I did:
    [​IMG]

    Now correct me if I'm wrong but that's a SKF roller bearing isn't it? So it would appear that the upgrade has already been done. This would lead me to one of two conclusions, either the previous owner was a fan of preventative maintenance OR the main shaft bearing failed and it was replaced. Going off the position of the oil drain plugs this is a pre 2001 engine so the bearings are definitely not OEM.

    Another question is, what is this stuff around the bottom of the barrel? You can see where the piston travel stops and theres some discolouration around there. It's the same on the other side but not as bad. Is this just a coating that's worn off in places or something else?
    [​IMG]

    There is some fairly minor scoring on the piston skirt as well but since I've never done anything like this before I don't know what could have an adverse effect and what is acceptable. You can feel the scores with your finger and if you drag a nail over them it gets caught on the biggest score, I guess that's the best description I can give really.

    [​IMG]

    There aren't any marks that I can see at the crown just those up the skirt.

    I've been thinking about carburation recently as well. When I get this thing back together and running on the old BST I think the next upgrade will be fuel injection. It'll cost about £100 more than an FCR but for the tunability and potential performance gains I think it'll be worth it. Plus I might learn some stuff along the way, which is never a bad thing. What say you advriders?

    One more thing, when I eventually got the clutch off the oil on the shaft smelt really bad. Is this normal? It really didn't smell like engine oil, I've smelt something like that before but can't remember what it was now.
    #34
  15. gunnerbuck

    gunnerbuck Island Hopper

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    Did the oil have a rotten gas smell to it? Sometimes if the carb float/needle are not doing their job fuel leaks past, goes through the intake and ends up bleeding through the piston/ring seal and into the base... Are the discolored patches on the cylinder wall sticky like fuel varnish?

    The cylinder itself looks serviceable {unless you have visible scoring that doesn't show in the pic} but could probably use a hone, at the same time the shop could measure it to make sure the bore is within spec...

    The score marks on the piston skirt should not be much of an issue as it is the rings that seal the bore, they should probably be changed for new ones...

    At the point you are now you can diagnose the crank, lift the rod up and down to see if the bearing has excessive up and down slop.. Use a feeler guage to then measure the side play.... You can spin the crank and hold a pointer to the gear end of the shaft to kind of observe if it has excessive run out, a dial guage will give you a correct # if it looks to have a lot of wobble...

    You can now spin the gearbox with the mainshaft and shift through all the gears a few times to see if you pick up on any of those clicking noises...
    #35
  16. bmwktmbill

    bmwktmbill Traveler

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    Sam,
    Are the rings free or are they stuck?
    bill
    #36
  17. sam_2555

    sam_2555 Adventurer

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    Gunner, I've checked the side play on the crank at less than 0.7mm and max in the manual is 1.1mm so that seems good and no radial play at all. I haven't checked the cylinder discolouration yet but will do tomorrow.

    Bill, the rings are free and the gaps in them don't look too big. I reckon when I put it back together I'll measure the assembled end gap and if they're out of tolerance I'll replace them.

    I found the clicking noise. It's coming from the kickstarter assembly. As the kickstarter intermediate gear spins something in the assembly is clicking. I've got no idea what it could be, any educated guesses? Ratchet gear maybe? The engine has never had a kickstart fitted that I know of, the guy I bought it off said he took it off because it wouldn't fit around the fairings.

    Before I can split the cases to have a look at the kickstart assembly I need to get the gear off the end of the crankshaft. The manual says this nut is torqued to 170Nm! What should I use to get it off? Remount the flywheel and nut and use those maybe?
    #37
  18. clintnz

    clintnz Trans-Global Chook Chaser

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    Check that big end carefully, I couldn't feel much play in mine when I did a rebuild but it was obviously well shagged when I removed it. Having said that my piston was also well worn by that point, your fairly unmolested piston should give some hope that the engine isn't too buggered.

    To get the crank gear nut off just put the piston pin back in & put a block of wood under each side between it & the cases to chock it. Leave the base gasket on to protect the surfaces & use good size blocks of wood. It might have been Gunnerbuck I learnt that one off actually :D This is about where an engine stand comes in real handy - if you have fabrication capability its well worth spending an hr or 3 knocking something up.

    Maybe check your crank end float before you split the cases too so you have a baseline just in case.

    Cheers
    Clint
    #38
  19. gunnerbuck

    gunnerbuck Island Hopper

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    Do you have the kick start lever? It comes in handy to hold the spring tension when you loosen the stopper bolt at the back of the engine, it also comes in handy to wind the spring tension back up upon reassembly...

    If your not using the kick start you could always just remove and run without the intermediate gear to eliminate the problem... Personally, I would tear it down and fix the issue...
    #39
  20. wrk2surf

    wrk2surf on the gas or brakes

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    have you checked the regulator and also have you clipped the ignition wire on the plug end..
    #40