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Help 3LN1 Engine Rebuild

Discussion in 'Yamaha 250cc In-Line 4's' started by camarda, Jul 24, 2021.

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  1. camarda

    camarda Active Member

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    Hey Guys,

    Looking to fully rebuild my 3LN1 engine, just wondering, is there an English translation of all the torque specs. Also, is there a thread in here anywhere that has a good guide.

    Any tips I should know. Are the online pistons for $120ish with a set with rings any good.

    I might need to do the valves and valve stem seals as well as they have sat in the weather and there’s some slight rust on the valves. They might be ok though. I have a spare engine if I need different valves.

    Should I also do the crank bearings? I noticed another thread re conrod bolts, what other disposable parts should I avoid taking off if they aren’t replaceable.

    Are the head bolts reusable?

    Thanks heaps
     
    camarda, Jul 24, 2021
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  2. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Jul 24, 2021
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  3. camarda

    camarda Active Member

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    Thanks, do you know what material are the valves made from, if they have some surface rust looking stuff on them do you think they will be ok or would they be corroded.
     
    camarda, Jul 24, 2021
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  4. camarda

    camarda Active Member

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    Ok so after looking through AliExpress I have managed to find a lot of the stuff I’ll need.

    As no one has managed to find conrod bolts I will refrain from doing the rod bearings at this point. The bearings are cheap but there seems to be no bolts anywhere.

    Here is what I have collated so far, it all seems quite inexpensive however if anyone has any experience of what is and isn’t good that would be appreciated.

    Is this gasket kit fine?
    https://a.aliexpress.com/_mtFjrd9

    I found this valve and valve stem kit, thoughts?:

    https://a.aliexpress.com/_mPzgrsx

    I could also get valves and seals separately.

    https://a.aliexpress.com/_mrS87L1

    https://a.aliexpress.com/_m01iu6F

    And pistons:

    https://a.aliexpress.com/_m0lv3G7
     
    camarda, Jul 25, 2021
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  5. jmw76

    jmw76 Well-Known Member

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    I used chinese stuff in my honda spada rebuild and it was very economical. The only real issue I found is that the suppliers real knowledge of matching parts to particular models is lacking. So you need to double check everything and ask as many qyestions as you dare before buying. Parts marked for one model could be for a previous or next model.
    For my cbr900rr rebuild, I sticking with OEM and well known brands as much as possible. But at a premium price of course. Particulary with bearings, you know you can get the right colour codes for accurate sizing. Who knows what the real tolerance is for the chinese stuff.
     
    jmw76, Jul 25, 2021
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  6. Murdo

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

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    The Chinese pistons I have found to be accurate and of good quality in the engines I have built and the bearings to be within specs when miked (some swapping from different positions gets them closer to specs). Only used one set of valves and as far as I know they are still working efficiently. Why can you not clean up the standard valves?
    Most gaskets are fine although I soak the green paper ones for a couple of hours in water (to swell them) before fitting and always spray the metal head gasket with copper spray before fitting.
     
    Murdo, Jul 25, 2021
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  7. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    If you go for the gasket kit... I would still personally use an OEM head gasket... plus make sure none of the gaskets have ANY Asbestos in them.
    As for valve stem seals... buy good quality Viton seals..
     
    Andych, Jul 25, 2021
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  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I would use the Chinese pistons with OEM rings, circlips & head gasket.
    Mike Norman from G-Force might have rings, but they are still available from Yamaha.
     
    Last edited: Jul 25, 2021
    maelstrom, Jul 25, 2021
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  9. camarda

    camarda Active Member

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    Thanks,

    @maelstrom How do I contact Mike Norman for the oem rings. I’ll need to get the cylinders bored first if they don’t look good. Will give an update when I’m up to that. I read your thread re cylinder boring, I’m still a little bit confused but i need to do some research and figure out what tools I need. I’ll need to find a good place on the Gold Coast that can do it properly.

    What is the exact clearance for 3LN1 from the ring to the bore.

    @Andych where do I get viton valve stem seals.

    Also, does anyone know a good source for oem head gasket.
     
    camarda, Jul 25, 2021
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  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    My bad, Mike doesn't do rings for the FZR. Impex Japan have them.
    You mean piston to bore clearance - please check workshop manual. If you don't own some precision measuring instruments then finding a "good" place that can do the job will just be a guess. The sleeves are very hard and don't wear much. Just a de-glaze and new rings might be all you need.

    The OEM valve guide seals are Viton, that would be your good quality, and the Chinese ones will be who knows.
    The head bolts will be fine.
     
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    maelstrom, Jul 25, 2021
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  11. camarda

    camarda Active Member

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    Thanks,

    1 other question, is it ok to use 3LN3 carbs on a 3LN1 engine.
     
    camarda, Jul 26, 2021
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  12. beano

    beano Well-Known Member Premium Member

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    Yes, bolts straight on.
     
    beano, Jul 26, 2021
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  13. driftwood

    driftwood Well-Known Member

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    Got std rings from ZFMotor via Ali, impressed by fit of comp & 2nd (0.15mm & 0.3mm gap on a good barrel, spot on spec), but oil control trio added to 2mm wide - all 3 were quite wrong. Happy enuff at $USD3 per piston tho'
     
    driftwood, May 10, 2022
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  14. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    You probably ordered 2KR rings by mistake, or the listing was wrong. Check what you ordered. I made the same mistake the first time.

    The top rings will work, but you need the correct oil control rings and spacer. Guaranteed at this point the originals are worn out and not worth reusing, you'll end up with oil consumption problems.

    Also worth doing the valve stem seals, and also check the o-rings on the bottom of the cylinder block, if one of those is broken you will get coolant in the oil - had that problem too.
     
    • Agree Agree x 2
    Linkin, May 10, 2022
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  15. jmw76

    jmw76 Well-Known Member

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    I had a similar issue when buying rings for my Honda Spada VT250. the suppliers site had them listed as appropriate for the Spada but what was delivered was for an earlier VT250F. The top 2 rings were usable, but I ended up using the old oil control rings which were still servicable. Next time I will ask the supplier to provide all dimensions of all rings to check before they are sent. Also had a similar issue with bearing shells. The lesson is, do not believe the details on the listing. Get the supplier to check as much as possible before they are sent.
    Otherwise quality seemed to be quite acceptable although colour coded bearing sizes will not be available from Chinese suppliers.
     
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    jmw76, May 10, 2022
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  16. driftwood

    driftwood Well-Known Member

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    Re-assembled and spun, OK compression. Oil ring gap spec is 0.8mm, no wuckers reusing eh!
    Lesson learned: eyeball buckets before dropping cam in, in case a shim has gone cocked over.
    And a Xi Xie to 2021motouk on eBay . He asked that I cancel my head gasket order due to lockdown. "Nahhh mate, I'm ordering off Yam also, and have 2 engines to do." So he's snuck out, risking being shot, and got item from storage to some mule, which beat the other order by 2days.
     
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    driftwood, May 19, 2022
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  17. driftwood

    driftwood Well-Known Member

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    Eng had 150psi on 3cyls, 60 on another. So took barrels off while doing stem seals to check alignment of gaps, now 60 on all four! Leakdown shows valves OK, crankcase has air. Closer examination of rings ie with specs on and find I've got a dogs breakfast of rings. Etch-a-sketch brain, and poor record keeping so confused as....
    Chrome gaps all .2mm, blacks 0.3mm but the black 2nd in my unused packets sit at .2gap (surely it'd be better?) Does anyone have specs for rings pls, seems I'm mixed up
     
    driftwood, Feb 7, 2023
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  18. jmw76

    jmw76 Well-Known Member

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    Typical rule of thumb for ring end gap is 3-4 thou (inches) per inch of bore diameter.
     
    • Informative Informative x 1
    jmw76, Feb 7, 2023
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  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Compression test???? You have lost me.
    You have honed the bore?

    This is what I do. I don't care what anyone else thinks.
    First of all, I would only use Chinese rings as a last resort.
    Hone the bore, get engine together and give it a flogging. It has to run to redline. Yes, just like the factory does on the dyno before your brand new bike is ready to ship. No "running in" (it is not an Austin A40), but don't overheat it.
    Finally after all that you can do a compression test.
     
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    maelstrom, Feb 7, 2023
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  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    ruckusman, Feb 7, 2023
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