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Help FZR 250 R 3LN1 - Unusual sound and struggle between 5 to 9000rpm

Discussion in 'Yamaha 250cc In-Line 4's' started by Hk_Gks, Aug 11, 2024.

  1. Hk_Gks

    Hk_Gks Member Premium Member

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    okay, first of all, is this how you measure?
    IMG_1539.jpeg

    If yes, here is the results

    IMG_1540.jpeg

    Seems to be okay, in between the tolerance I guess.
     
  2. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    As long as you have the pointy bits (cam lobes) facing away from the buckets when you measure, yes. You record the measurement as the largest gauge that fits in the gap. If you want a size that isn't available, you can stack two gauges together to achieve a desired thickness value.

    Those clearance measurements, if correct, are within spec. No adjustment should be needed if your measurements are correct.

    When they need adjustment, you should measure all 16 valves, record the measurements and plot them, then when shims are removed (do so one at a time), record what shim lives where. From there you can calculate what new shims will get the desired clearance (maximum value)

    With clearances being within spec (is that bottom right exhaust 0.15 or 0.25?) , you should quickly recheck compression - make sure you crank the engine over until the pressure on the gauge stops rising if you didn't last time. If you get the same numbers, there are only a few things that can cause low compression across all cylinders.

    One is a badly blown head gasket where the cylinders are leaking into each other as well as the cooling system.

    There are two things you can do to check this - eyeball the pistons through the spark plug threads - you will usually see lots of carbon buildup on the pistons. If the engine has been burning coolant, you will see shiny aluminium of the piston. You can also remove the radiator cap and have the system drained (might have to reinstall it and the radiator first if you have removed them) , and listen for air hissing.

    Other than that, the only other place you could lose compression from is piston rings/cylinders.

    So you might be up for a head gasket if you're lucky, replacement pistons/rings if you are less lucky but the bores are OK, and if you are unlucky you will need an overbore and oversize pistons/rings.
     
  3. Hk_Gks

    Hk_Gks Member Premium Member

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    yeah its 25mm for exhaust

    I think the headgasket is “fine” as the bike doesn’t smoke or anything while riding.

    but yeah it’s either valves that are too dirty and doesn’t close correctly on the valve seat, or pistons/rings for the compression problem.

    if the aliexpress parts are actually okay, I’ll do it this winter, cleaning or changing valves if necessary and looking at pistons/cylinders


    Now I will take everything up again, just cleaning the carbs bowls and try the bike again to see if there is any changes.
     
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  4. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    When my first 3LN1 had head gasket problems, it did not present any smoke out the exhaust. However it was running hot. I don't just mean the temp gauge either, but if left long enough it would get up near the red zone on the temperature gauge.

    The frame was getting hot enough to burn my legs through my pants. The tight valve clearances did not help that, as the valves seating provides cooling for the cylinder head. Tight valves means less time spent seated, more heat build up, it has to go somewhere and the engine/head are bolted to the frame.

    Before you rip the head off the bike, eyeball the valves in the ports. If they are all coated in carbon, it is possible that carbon can be holding the valves slightly open. This will cause lower compression, and it will give you a false reading on valve clearance.

    My suggestion is to run some upper cylinder treatment through the bike with the engine hot. I am not sure what products you have available in france, here we use Threebond Engine Conditioner (Petrol, green/silver can). It is also excellent for soaking carb jets / bowls in so you should get whatever you can get and use it for that. With that amount of dirt in the carbs, you will need to remove and soak the jets. You should remove the mixture screws with the jets and clean them, along with the passageways.

    Just keep it away from plastic and rubber parts as it will destroy them.
     
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  5. Hk_Gks

    Hk_Gks Member Premium Member

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    for the temps, it doesn’t heat up too much or too fast, it cool nicely, even when hitting red zone on high traffic and jam, the ventilation is doing its job, so idk


    Okay i put the multimeter and checked at 5000rpm, got around 13.5v

    I did a video where you can hear that rattling noise I was talking about
    https://youtube.com/shorts/2Jmatc7skF4?si=QcolUesdh3HIg6Vw

    The pump now do a way better noise than before and seems to work correctly except that it leak a bit, gonna need to look at that :v
     
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  6. Hk_Gks

    Hk_Gks Member Premium Member

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    Is it that one? https://www.threebond.com.my/produc...r-engine-conditionerfor-petrol-diesel-engine/
     
  7. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Yes, you want the petrol stuff in the green can. Get two cans, one will not be enough for soaking carb bits and using it for its intended purpose in the engine.


    Needle on the temperature gauge should not reach the red zone in normal operation, including traffic. Fan should cycle on and off, needle should be in the middle of the range once at operating temperature.

    You should check running temperature of the radiator with a non-contact thermometer, cooling system in good order should not exceed 110c. If it does, you have a problem.

    First suspects are radiator cap. The seals can swell, if so replace the cap. They can also just be bad even if it looks OK. They are 1.1 bar pressure. Do not fit a higher pressure cap, as instead of the cap venting you will pop a water pump seal, internal o-ring or radiator hose. Worst case cooling system will explode. The caps are designed to vent at a certain pressure, the fluid will then boil as it is no longer under pressure. The boiling of coolant itself releases steam which in itself is a last resort cooling measure. This is why all 'anti-boil' coolants are nonsense. They are solving a problem that doesn't exist.

    Next is thermostat. Remove it from the housing. It can be tested in boiling water, it should open fully. And start to close when placed in cold water. It should start to open again at 85c. If it jams partially open, or fails to open, it needs replacing.

    Physically inspect water pump impeller under the cover. Requires removing lower left hand coolant pipe. Watch the o-rings aren't old and brittle. Litetek has new o-rings for cooling system too: https://litetek.co/CoolingSystem_O-Rings_Yamaha_FZR250.html


    The noise in your video, I am sure it is cam chain rattle. It is how I remember mine sounding when it needed a chain. So new chain required.

    You can watch my old videos and compare

    This video is first start after sitting for a long time. It has a cam chain rattle and also leaking exhaust gaskets. I tightened the flanges after which helped, but they bend easily. Sounds like a lawnmower beforehand. The pops out of the exhaust pipe were a sign of the head gasket being blown. My symptoms were: popping out the exhaust as per the video, getting up to red zone on temperature gauge, extremely hot frame, coolant bubbling in the radiator when ran with the cap off, and with the cap on the coolant bottle in the tail section was dumping coolant all over the rear tyre and ground. The cap was venting pressure because the system was over-pressurised due to engine compression leaking into cooling system (blown head gasket), overflow hose leads to coolant bottle which pressurises and forces coolant out of the drain hose on the bottle.




    This one is after timing chain, head gasket, valve clearances, tuning, sounds a lot healthier.




    This was my other 3LN6 that was in good condition. Still had a little bit of chain noise at low RPM




    13.5V at 5000rpm is acceptable, but on the low end. Could be better. You should clean/sand the battery terminals, main earth and positive leads, and the regulator/rectifier connection. Inspect the pins, if they fit loosely, as a temporary fix you can close up the curls of the female pins so they bite properly. If the plastic casing is discoloured or burnt, new connector and pins required.

    Test the stator next.

    A/C voltage output across each of the phases (the three white wires at the regulator plug) - at idle at 5,000rpm again. Should read similarly across all three phases. One dead phase? Replace stator. If the voltage output is low across all three, the magnets in the flywheel are weak = needs a new flywheel.

    Resistance between each phase - 0.5-1.5 ohms is about normal. Zero resistance is shorted = replace stator.

    Resistance of each phase to earth/battery - should be open circuit. Any actual reading, even if kilo ohms or mega ohms means it is shorted to earth = replace stator.

    If the stator tests good, test the regulator.

    You can use multimeter in diode check mode to check the diodes. This regulator is body earth, so the casing of the regulator is the earth. One meter lead on red terminal, earth lead on the three other pins, then swap the leads. You should get a voltage reading one way and not the other. Test the same way for the earth side, but one meter lead will be on the casing.

    If any of the diodes get a voltage reading both ways, replace the regulator.

    If the diodes are in good order but the charging voltage remains low, replace the regulator IF the stator is OK.

    Check A/C voltage at the battery. Yes, you read that correctly. Sometimes a regulator will appear OK when measuring DC voltage, but it is pumping A/C voltage into the battery. A/C Voltage on the battery should not exceed 0.15 Volts. If it does, replace the regulator.
     
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    Last edited: Aug 31, 2024
  8. Hk_Gks

    Hk_Gks Member Premium Member

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    I have a spare cam chain so, I guess I will have to open the top again (not happy) the operation to change it without splitting the whole engine sound hard but I’ll see, I have the tool to dismantle the chain, this one
    IMG_1544.jpeg


    I did a little ride, so the original problem is back, so after 6000rpm, weird sound and power struggle, I can reach around 16 000rpm in first gear but that’s it, all other gear are struggling to get pas 10 000rpm.
    I can do like, 120mk/h.
    The new plugs and cap start the bike way faster, so at least that good


    i think the next suspect is still the carbs, I will see once I can order all parts and clean it.

    i just don’t get, it just came a day from another without doing anything special, and specially the problem is random and not always at the same moment, sometimes it does it sometimes less


    And for the heat needle, I meant just before the red zone, fan start to cool the bike
     
    Last edited: Sep 1, 2024
  9. maelstrom

    maelstrom LiteTek Premium Member 250cc Vendor Contributing Member

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    Again, the entire fuel system needs to be overhauled. Fuel tank, taps, lines, pump, carbs, air filter, everything.
     
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  10. Hk_Gks

    Hk_Gks Member Premium Member

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    yeah I’ll check on that too, I think the rust come from the fuel tank itself, not in the best shape inside, but what’s weird is the state of the carbs bowls, while the fuel pump is clean as new
     
  11. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    It is very fine rust and dirt, so small that the filter doesn't catch it. It accumulates at the lowest point in the tank, goes through the tap, filter, pump and sits in the bottom of the bowls. Extremely common.

    If that cam chain is not pre-split, do not split it. Buy an open ended chain.
     
    Last edited: Sep 1, 2024
  12. Hk_Gks

    Hk_Gks Member Premium Member

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    Tutorial didn’t mention that
    IMG_1552.jpeg
     
  13. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    That guide was made before I was even an apprentice let alone a qualified mechanic, and doing a home job. It is recommended to buy an open ended chain with joining link if you are going to replace it without splitting case, that is the reason for the open ended chain in the first place.

    It can be done with an unbroken chain by breaking it and rejoining it, but you will run the risk, and need to very careful with the pins and plates.

    I don't want you to have problems or cause damage to your engine.

    Being a mechanic with access to a workshop these days, I would just open the cases and refresh everything at once. Which I will probably do with my 3LN6 at some point.
     
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  14. Hk_Gks

    Hk_Gks Member Premium Member

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    hmmm, that’s a bummer, any link to a opened chain?
    I will check the chain tensioner again before changing to see.

    yeah I’d love to open the engine and do new stuff in it, but for that I’ll need another bike first, working on a bike with no another to ride, is boring


    I have a appointment next week, I need the bike since I don’t have any parts for carbs and all right now, I’ll put it apart again next week
     
    Last edited: Sep 2, 2024
  15. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Yes that is how the measurements are taken and as @Linkin has mentioned, the cam lobes should be pointing up, you are measuring the heel (back) of the cam for the clearance.

    Those numbers look good BTW.

    Usually combining two feeler gauge fingers is easier as they're more flexible, you should feel some drag as they go in and through when they're the correct thickness, then to check go to the next thickness which shouldn't go in.

    If you have to force it, which is possible, then its too thick, go to the next lower.

    Also worth mentioning that for cleaning jets - if it's necessary to use wire then use soft wire, you can get copper wire strands out of electrical cables for example.
     
  16. Linkin

    Linkin The Mechanic - Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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  17. Hk_Gks

    Hk_Gks Member Premium Member

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  18. gyro gearloose

    gyro gearloose Active Member

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    compression tests and readings...

    1 atmosphere, 1 bar, is 15psi ABS... 14.7 if you must nit-pick.
    101.3 kpa.
    i vaguely recall its also 1kgfcm...

    and from there, its pretty easy to figure out compression ratios...

    15 psi (gauge, or 30 psi ABS) is 2:1.
    30 is 3:1...

    and so forth.

    so generally the reading you get in bar or kgfcm is the compression ratio... remembering to add one or subtract depending if its gauge or absolute...
     
  19. Hk_Gks

    Hk_Gks Member Premium Member

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    I

    I will also try to test everything in relation to electricity, this week I hope, I’ll be able to order everything for the carbs

    i think I will also try evapo rust for the fuel tank because yeah it look bad
    IMG_1553.jpeg

    And once everything is cleaned and checked, I hope it will finally be good.

    then this winter if I don’t ride that much or get another bike, I’ll check the valve/piston/cylinder problems
     
  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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