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Discussion FZR250 - Cylinder 4 - big end bearing failure

Discussion in 'Yamaha 250cc In-Line 4's' started by simidau, Dec 11, 2009.

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    All true, assume correct oil viscocity, pump operation, no restrictions that are too tight or clearances that are out of spec

    however when the oil fling at high rpm from the big ends increases flow it reduces pressure, which is why the oil pressure increases with engine RPM - that pressure is calculated to be sufficient with all of the clearances in spec etc,. but it looks like it's marginal at the top end when run there for extended periods

    Now if the pressure release valve opens at close to the oil pressure at peak RPM then I'd say you're going to need a little more pressure to keep up with the increased flow requirements

    An uprated pump which gives more flow would necessarily give an increase in pressure assuming equivalent clearances, not increasing the pressure release valve limit would see you hit that limit earlier

    All of the elements need to work together
     
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  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Since @fnq_fzr has had another big-end failure it seems this thread needs to continue looking for an answer.
    Here are some questions"
    1/ At what pressure does the oil pressure release valve open?
    2/ At what rpm with a hot engine will the release valve open?
    3/ Why always big end 4 and not big end 1? Aren't they equally spaced from the centre gallery?
    4/ Why is the oil pump assy listed for the 3LN6-7 a different part number?
    3LN1 etc - 1HX-13300-01
    3LN6, 3LN7 & Zeal - 1HX-Y1330-01
    Note that Impex report the earlier number as being superceded by the Zeal/6-7 number.
     
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    Last edited: Nov 18, 2020
  3. gregt

    gregt Well-Known Member Premium Member

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    I'll say on this thread what I've said on others. Of the three dead engines I had to build my twin from,one had dropped a valve, the other two had done big ends. On examination I concluded that poor surface finishing on the the oil holes in the crank was largely to blame.
    There were sharp edges at the crank surface where the feed holes broke out onto the big end. this will scrape oil off the bearing surface leading to the results seen.
    The 250 cranks are poorly finished IMO. Certainly less attention has been paid to details than the 400 and above models.

    The first engines I saw this on were Honda V4's in the early series. VF400F and VF750's. They were very bad.
    Even the RC30 I had through recently wasn't particularly well finished in that area.

    My opinion - feel free to disagree.
     
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  4. fnq_fzr

    fnq_fzr Active Member

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    My previous engines had a stock set up. I believe my racing style may have also contributed by over revving the bike when changing down gears placing extra load on the bottom end..?

    My next engine will have the oil pressure relief valve "shim under the spring" mod and will look at the oil pick up design also..?
     
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  5. gregt

    gregt Well-Known Member Premium Member

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    Well, if you've got a crank regrinder local to you, I'd ask them to have a look at the crank and radius the oil holes.
    A linish to finish off and you've prepped it better than the factory did.
     
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  6. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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  7. gregt

    gregt Well-Known Member Premium Member

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    I'd doubt if upstream flow restriction is a factor on the FZR250. The main oil gallery across the engine - from which there are risers to the main bearings- actually increases in cross sectional area as it goes away from the center feed point.

    That article about the shape of feed holes in bearing shells is interesting. I've been known to file the feed holes in shells to align with the holes in the cases. Some Kawasakis - the 16V 750/1000/1100 family in particular - are bad here.
    Multiple holes - with a groove in the bearing recess to feed the holes - are seen occasionally too.

    The Suzuki GSX750 went through a series of evolutions. The upper outer mains originally had a feed hole for a gallery to the cam bearings. In that form they stuffed outer mains very quickly. Then the upper outer main shells got a groove while keeping the feed hole. Stll did the outers quickly.Then both top and bottom shells were grooved. Still failed.
    Then finally they fed the cams from a different point and used solid top and grooved lower shells at the end mains.
    And it works - up to a point. The oil pump is inadequate....
    The first GSXR750 pressure pump rotor set is about 8mm bigger OD and 10mm wider.
     
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  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That's great info, at least there are multiple aspects to look at

    When researching the oil feed radius/chamfer - (I know they're different things) - I saw some interesting chamfers done with a teardrop like shape so that they didn't enlarge the width of the hole

    Similar concept to that hole enlarges into the groove to maintain the contact surface area I suppose.

    Aside from the poor finishing of the oil feed holes, you don't think there's an inherent flow restriction which is an issue?
     
  9. gregt

    gregt Well-Known Member Premium Member

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    Not on current cranks. However, Yamaha for some years had the very bad habit of feeding two big ends from one crank journal.
    This did lead to starvation problems under hard use.
    Somewhere around the introduction of the R1 they changed philosophy on that, spent the extra money on drill bits and it got shitloads better.
    The 250 cranks all seem to be one main feeding one big end. The only caveat I'd have is the angled entry drillings on the mains. The cranks are quite small OD and cylinder spacing is generous so the drillways run at a shallow angle off the mains.
    How much effect this has on the centrifuge assistance in getting oil onto the big ends I can't quantify.

    I've seen teardrop shaped holes as you say. I've seen recessed areas on the surface of the big end journals intended to be a holding point for oil - effective ? Don't know. I've seen grooves ground across the journal surface to distribute the oil. Again, don't know. Probably depends on the pressure and revs it's designed for.

    As a teenager I watched over the shoulders and listened to my old man and a friend of his sorting the crank on a 2.5L Ford V6 used in a speedboat locally. Both men AMIMechE engineers - and clever bastards too.
    The drillings went straight from mains to the outside of the big end journals. One hole on the outside radius of each big end. It was starving the mains at constant high revs. They agreed to cross drill the big ends and plug the holes on the outside radius.
    The crank was acting as a centrifugal pump and sucking oil from the mains.
    Job done. The boat set a new world record for 200CI hydros, won a big meeting in the US. And ran to 9000 rpm....
     
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  10. jmw76

    jmw76 Well-Known Member Premium Member

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    Is there an opportunity to increase the capacity of the pump? I have modified the pump on the GSXR1100 engine I run in my race car. You might be able to find a slightly larger pump from another model. I fond a larger set of internals for my pump and just made up a spacred for the pump body to make it all fit. There was also a little relieving required to the crank case.
    I needed more oil flow not only for bearing life but also for improved cooling. Arguably you might loose a little power. The tradeoff being that it might survive longer. SAM_0393.JPG
     
  11. gregt

    gregt Well-Known Member Premium Member

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    Currently I don't have a 250 oil pump outside an engine. I do have a complete 400 bottom end here. Without looking at either I'd suspect that the 400 pump may be a direct swap. Several other bits are. The primary drive and clutch basket will swap in from the 400 - with work. So I'd suspect the pump may be the same. Part nos may tell the story. But if it is exactly the same pump all that says is that it's a bit small for the 400.

    There's a well known upgrade for Honda 350/400 sohc four oil pumps which involves using a shortened 750 rotor set.
    I did it on a big 350/4 I built a few years back. But I used CBX550 rotors as a friend here has blown up at least half of the 550's which came to NZ. He has a good supply of pumps - free. It's been raced for five seasons now and the bottom end hasn't been touched.
     
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  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That's a godo idea and I don't know which oil @fnq_fzr is running, but 30 weight oil is specified for the 250
     
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    OilPump_FZR250.jpg
    250 oil pump

    OilPump_FZR400.jpg
    400 version

    I am with @gregt 100%. Even if you can't get a direct swap, so long as you can find a matching rotor with greater depth it won't be too hard to machine down another 250 pump body to add the required thickness. Failing that I would be thinking about welding a slice of rotor to the original to make the thickness.
     
    Last edited: Nov 22, 2020
  14. gregt

    gregt Well-Known Member Premium Member

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    On the Honda pump I mentioned above, the end cover spigots in to the body. It's fairly simple to reduce the spigot to a very narrow shoulder - then cut longer rotors down to suit. Gained about 4mm in length from memory.
     
  15. fnq_fzr

    fnq_fzr Active Member

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    Wow guys. This is getting deep. The 'shim under the oil pressure relief valve' mod is about as far as I can go myself. Does anybody have any recommendations on how thick the shim should be and can explain how this mod will help?

    Thanks guys!!
     
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  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Here's a quick google result
    https://www.zx-10r.net/threads/increasing-oil-pressure.65848/

    FWIW - springs can be measured accurately, if you can remove the spring and measure - spring place can help to measure it accurately, how much force it's exerting at it's compressed length inside the relief valve, some simple math for the surface area will be able to determine what pressure it's resisting when closed to the open point.
    I don't think we have a spec for the oil pressure relief valve

    Then you could measure the increase in compressed length to get an increase of a known amount that you consider reasonable.

    I'm going to put this out there and say a 10-20% increase might be a sensible amount to aim for - and I really want @gregt to chime in on that suggested amount.

    Out of interest, what weight oil are you running?
     
  17. fnq_fzr

    fnq_fzr Active Member

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    I have been running Motuls 7100 4T 10W-40. Maybe they don't like full synthetic? upload_2020-11-23_8-2-10.png

    I just found this in some docs I have.
    upload_2020-11-23_7-59-9.png

    Relief valve operating pressure: 441kpa = 63.9616psi ~ 539kpa = 78.1753psi

    Not sure what the Bypass valve is?

    Anyone know if it is possible to install an oil pressure gauge and oil temp gauge and how to do so?
     
  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Well done, I hadn't gotten around to searching for the relief valve spec - their name for the oil pressure relief valve

    The two mentions, one for bypass valve and the other for relief valve is somewhat confusing, however given that I think that sheet comes from a translation, perhaps the bypass valve setting relates to the oil filter bypass valve - surprised that it kicks in so early.

    Now when you disassemble the oil pressure relief valve you can measure the installed spring force, then aim for an increase in that spring force of a known amount, which is a decrease in compressed spring length = that's your shim thickness

    EDIT - I've also been pondering if an oil cooler similar to the one which goes onto the FZR600 could be fitted to the 250.

    It should be possible to at least fit an oil pressure sensor, wondering if a sensor is available which measures both pressure and temperature

    Caveat - vibration = premature failure
    https://www.efisolutions.com.au/bosch-fluid-pressure-and-temperature-sensor-pst-f1
     
    Last edited: Nov 23, 2020
  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Another point where oil pressure can be lost. The piston oilers.
    Oilers.jpg
    You should replace all the o-rings that are used in the oil galleries as a matter of course. The oilers, release valve, gearbox etc
     
    Last edited: Nov 23, 2020
  20. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The FZR400 1WG shows as follows:
    FZR400_Pump.jpg
    After a bit of a manual read the bypass filter is referring to the oil filter.
     
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