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Help FZR250 - coolant leak in hardline behind block/head

Discussion in 'Yamaha 250cc In-Line 4's' started by skylinerd1, May 4, 2019.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Is it possible to have a problem with one carb where even when you screw the pilot screw right in nothing happens?
    Yes, of course if there is no fuel getting through to meter, or if the compression is too low, or the idle is too high.

    So I guess im going to have to compression test this thing now.
    Should be the first thing to do not the last.

    I rode it around the block and other than that number 3 cylinder causing the engine to bog on quick throttle application you would think this thing runs pretty good.
    You would need to ride a good one to be able to make that comparison or have a lot of experience with engines.

    Im suspecting this engine may have been run without water and maybe the rings (on number 3 in particular have lost their tension). Thats my suspicion.
    It would have seized if run without coolant and rings wear out they don't lose tension. If that engine has done 73000 km on original rings then don't expect them to still be doing a good job of sealing.

    These 4 cylinder 250's are high performance, high maintenance sports bikes. They are, IMHO, the worst possible choice for a learner or someone looking for economical transport.
    Cheers
    Blair
     
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  2. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    Ok fair enough I realize all that I never bought it for commuting its just a one off project I thought I would try tackle. I cant spend every waking hour on it. I have owned an aprilia rs250 in the past and multiple small capacity bikes iv just never had one in this sad of a condition before. So its a bit more of a challenge than I thought it would be for sure. Its no big deal I'll get there in the end all im asking for here is a bit of help nothing more. Im not looking to commute or anything like that. I own plenty of other vehicles.

    Piston rings can loose tension from overheating.
    This previously guy literally pulled it out of his shed and did a burnout and put it back when I pulled it apart I realized it was very low on coolant. I think highly unlikely its been ridden far with no or low coolant. But I think it certainly had been run on atleast pretty low coolant.

    Anyway I will compression test it once I get this gauge rigged up... of course my gauge I have here doesnt go this small and nobody will sell just the adapter.... Anyway I'll butcher a spark plug and make it work.
     
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  3. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    If number 3 exhaust is still pretty warm it's getting fuel from somewhere if the mixture screw can be turned right in.
    I would be double checking the fuel levels / float heights first.

    And with the other 3 cylinders running best at 3.5 to 3.75 turns out on the mixture screws it sounds like they all might have lower fuel levels?

    How did you fix the spark plug cap resistor problem?
    Maybe you could try swapping coil leads 2 and 3 around (if they'll reach) and see if cylinder 2 doesn't run as warm
    That would mean the lead still isnt working as it should

    Sorry cant remember but were your spark plugs new?
     
  4. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    The previous owner claimed he replaced them (there were old plugs in a box). Anyway I just went and bought another set and replaced 3 and 4. checked for spark before and after replacing them no real difference they are sparking and swapped the plug leads over (between 2 and 3) cant notice any real difference although when I turn the mixture screw in just now on 3 the idle did change but it was at half a turn out.
    All 4 cyl are running hot when you touch the pipes.

    I replaced the igintion wires and got two second hand plug boots as when I tested my original ones cylinder 3 was at 10m ohms so I pulled them all apart removed any corrosion on the spring (minor) scotchbrighted all contact surfaces and silicone greased them. The two boots I got as replacements I didnt really like the resistor pills as they were at 15 to 17 k ohms. I retested the pill that was in the boot at 10m ohms at it read 10.5 k ohms....... So I used that one again in one of these other boots I got second hand because their pills were a bit out. instead of the two with higher ohms than the rest.... retested them before assembly all pretty similar 10-11.5k ohms. Retested them assembled to the coils with leads and boots. One coil is 39K ohms total the other coil was 35 k ohms. That didnt seem to bad to me.

    I will check the floats again and if that appears normal will check the compression after that. FFS that number 3 carb is still has the slightest leak of fuel pooling onto the bottom of the bowl and the mixture adjustment screw outer casing? But thats kinda the least of my worries I guess.
     
    Last edited: Jun 25, 2019
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Could be that the float needle seat for number 3 carb is damaged.
     
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  6. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    You could try taking the fuel bowl off and then turn the ignition on to let the pump prime, while quickly lifting the float to see if it shuts the fuel off.

    Those ignition coil readings are a bit high.
    Standard specs for the secondary side is around 15K Ohms for the coil and lead, plus 10K Ohms for the spark plug cap, that equals 25K Ohms.
    Yours are reading 40% + higher than normal if they're 35K and 39K Ohms
     
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    Last edited: Jun 25, 2019
  7. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    You arent times the spark plug caps by two though? I had both spark plug boots on not one. So thats 35k.

    I get what your saying about the bowl.... maybe I should test that before I go pulling the whole bike apart. If I end up rebuilding it id rather have the carbs pretty much sorted than mess around on a fresh engine like I am now.
     
    Last edited: Jun 25, 2019
  8. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    Anyway the rings are farked I reckon.

    I just read some other search results on compression testing it. So im better to take the carbs off and do it? I just held the throttle open and got fairly consistent results at 95psi and then 105psi with oil in the cyl... for cyl 3 and 1.....
    2 and 4 were more like 100psi then 124psi. That seems pretty classic for rings huh?

    But of course the slides stay down as someone mentioned so that could explain the low overall result? But not the jump with oil added into the cyl. The test was done on a engine that had just been running to so it was atleast warm.

    Shall redo it with the carbs off just to make sure?
     
    Last edited: Jun 25, 2019
  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    How are you measuring the secondary Ohms through 2x coil leads?
    Have you jumped them together?

    Compressions are low but could be because the valve clearances need doing, may have some carbon on the valve seats and valve heads too?
     
  10. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    The picture on the coil measuring page has the multimeter leads into each coil ignition lead (two per coil)... Which is 15k. I have my leads into each fitted plug boot two per coil so thats how I measured 35k and 39k respectively for each coil pair. With both boots on each coil you are adding approx 20k+ of resistance. Its the same difference.

    That to me is correct the 39k one is a touch high sure but I cant see that causing the issues im having. Its the same as the pic below but with the boots fitted on the plug leads. I dont see the issue?

    https://www.2fiftycc.com/index.php?attachments/coil-test-2-jpeg.34800/

    I checked the valve clearances a couple pages back they looked good. I will compression test it again tomorrow with the carb's off.
     
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    Last edited: Jun 25, 2019
  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Sorry my mistake, my head wasn't with it when i replied,
    i had to take my wife to the doctor's where they were discussing lady's business
    Spec's say 12K Ohm's to 18K Ohm's so no problem's there then

    Hopefully your compression's read a bit higher with the carby's off the engine
     
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  12. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    Guess I have now jumped out of the frying pan into the fire. I bought a second hand motor all honed and decked sort of ready to assemble. Thing is it needs a C stamp rod as one rod is to tight on its clearances according to the owner it has 4 rods still on the crank with two pistons and two pistons slid into the honed bores (old used pistons). Its a 3ln3 motor with a 3ln1 sump. I will have to measure the cams I guess to make sure they are fzr cams. Came with chinesium pistons of course.... These pistons are either chucked around in shipping or they were seconds from manufacturing from yamaha. Has anyone else brought these alibaba pistons? EDIT: Now that I see the other guys thread I see why the pistons are a bit mullered.... Still dont quite get how but anyway it is what it is.

    I guess im going to have to strip that bottom end or atleast remove the rods and just check whats going on. The extra rod I have looks damaged in the small end to me.

    Is it possible to purchase rods from yamaha or yahoo auctions japan might be my best bet?

    I dunno about these new pistons... three of them are beat up around the top edge. Im hopeful I can just debur them but yeah not good im thinking I might just risk ordering another set for what these chinese things cost. I might trip down to the local engine machinist and get a solid opinion on them.

    Whats your experiences with these pistons guys?
     

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    Last edited: Jun 28, 2019
  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  14. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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  15. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    Hmm even just looking at the rod thats in there now in the same position as the rod that was cooked. I can see almost blue nuts on it compared to the other three rods which have normal coloured nuts..... And cyl two rod next to that one is deff tight on its crank journal which is the only non C stamp rod again....

    So yeah looks to me I need to find a C stamp rod at minimum.

    Is it possible to purchase rod bolts from yamaha? ****** if im using that pair thats most likely been on an overheated rod. So the overheated rod thats out of the motor has its own fasteners on it that are overheated brown like the rod itself is in that area so those two fasteners arent from it.... Have you guys seen bolts on rods a different colour from the rest before? Im very dubious about how they could be blue like that?

    Heres a pic on the left is the normal colour of all the other rods on the right is in the blue nut... Maybe its just the manufacturing blueing?
     

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    Last edited: Jun 28, 2019
  16. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    I have fitted four sets to CBR's and one to FZR. Three CBR's are road bikes (well used)and my CBR drag bike that has had the freckle worked out of it for two years without any signs of piston trouble (I do let the engine warm up properly before use). When measured the pistons are all (per set of four) withing .0005" (half of one thousands of an inch, dunno what that is in metric as my micrometer is Imperial) of each other which is as good as any 'factory' pistons. I believe they are being made in the old factory dies as the casting numbers are the same.
    That engine you bought had burnt a rod and I would strongly suggest that you check the main bearings and oil galleries for debris or blockage before any assembly work.
     
  17. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    Thats what I thought when I saw them they looked like they've been cast out of the same mold as yamaha originals. They are pretty cheap so I think I'll just get another set and use these to throw at the neighbours cats or something.
     
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  18. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    I can only say that I have had no problems with them and for the price have put five bikes back into good condition and back on the road/track.
    Go with a new set and be careful when fitting them.
    Check and clean that bottom end before you go any further, I would hate to see you put money/effort into putting it together and have it go bang because of some hidden fault. So check it!
     
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  19. skylinerd1

    skylinerd1 Member Premium Member Contributing Member

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    The original overheated (spun) C stamp rod.... I do wonder weather I should look into reusing this. Its straw brown in colour sure thats hot. But thats still nowhere even remotely close to changing the temper of the rod. Im thinking I was overreacting a bit to the colour of everything after looking at this rod the first time.

    To my mind all it need to be checked for is dimensions and square and that the little end hasnt been too chewed up from debris?

    All im seeing in the little end is signs grit from this rod bearing has got in there and put some faint discoloured marks nothing I can feel with a finger nail or even remotely close to that.
     
  20. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I have not looked at the service manual, but the parts book shows only one type of rod and 4 versions of shells. These shells are usually coded (colour, numbers, letters) to give fractionally different sizes for a standard journal. There are no undersize bearings, take it to your local car engineering shop and regrind the crank type things. You do all your measuring and determine which bearing version you need. All of the bearings fit all of the rods. The only difference will be the assembled ID. Any number, letter or colour on a rod just indicates which bearing option it was assembled with. New rod bolts and nuts are listed as separate parts. This is my understanding of most 4 cylinder Japanese engines and I can be completely wrong.
     
    Last edited: Jun 29, 2019

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