How to tell if my engine is any good?

Discussion in '1st & 2nd Generation 1983-1989' started by kiwibob, Nov 4, 2019.

  1. kiwibob

    kiwibob New Member

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    A bit of a weird thread title, but here's the story: I've got three 2nd-gen 750 engines and have to choose two to keep. I don't want to pull them apart to inspect and wreck the gaskets, and they're not all in bikes so i can't ride/dyno them all.

    One is a spare that's not in a bike. It came with the first bike I bought. The clutch-side cover is missing but it looks clean inside.

    Of the other two, one is reported to have about 90,000km on it, and the other was apparently 'rebuilt' (whatever they mean by that) about 5,000km ago. The ones in bikes both start and run fine, though I haven't ridden them cos they're not road-worthy yet.

    I'm going to keep one bike and spare engine, and sell the other bike when it's ready.

    I'm thinking that on each engine I should inspect the cams/rockers for wear, check compression (maybe leakdown test?) and could even pull the engines and visually inspect inside via the oil pans. On the spare I have, I can see the bottoms of the bores when the oil pan is off, and can see cross-hatching on the lower bores. That's a good start, but probably doesn't really tell me too much.

    Any thoughts, advice?

    Cheers.

    IMG_3214.jpg IMG_3212.jpg
     
  2. Captain 80s

    Captain 80s Insider

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    If the cams and rockers look good, it doesn't smoke or make noise, and they had any kind of oil change schedule done on them... they're probably good, I personally wouldn't dig deeper. Those engines are solid as hell. Keep a spare for when you reach 180k km.

    The ones that you haven't heard... if cams and rockers good, probably good.


    Edit: apparently I didnt read your post right. Unless I knew exactly what 'rebuilt' meant, I'd rather have a higher mileage original. There are some hacks out there.
     
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  3. squirrelman#1

    squirrelman#1 New Member

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    compression test would be step #1.

    12-1-17 125.JPG
     
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  4. NorcalBoy

    NorcalBoy Member

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    Sounds like you're on the right track, a leak down test will expose any real issues, but like Sman said, even a compression check would provide useful data. If you have the time and energy, the leak down test would be the preferred method....at least for me.
     
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  5. FJ12rydertoo

    FJ12rydertoo Member

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    Yep, like the man says, leak down test is the way to go. Air compressor and a couple of gauges...
     
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  6. kiwibob

    kiwibob New Member

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    Awesome, thanks for the replies!
     
  7. RS125

    RS125 New Member

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    all great responses. What no one is gonna ask about the rear swingarm?
     
  8. Captain 80s

    Captain 80s Insider

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    I was hoping kiwibob would start a new thread about that project.
     
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  9. Thumbs

    Thumbs Member

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    WiFi or usb endoscope down each plug hole and port is how I check things these days

    They’re on eBay for less than £10
     
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  10. Dr.Инженер

    Dr.Инженер New Member

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    Right, pretty sure everyone who seen that pic raised a quizzical brow. So yes please do elaborate on the swing arm and front forks.
     
  11. squirrelman#1

    squirrelman#1 New Member

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    yes, pleeeeeeze.
     
  12. kiwibob

    kiwibob New Member

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    Ah, great idea. Thanks!

    So the swingarm is obviously 5th-gen, the swap was perhaps first done by @TOE CUTTER many moons ago, here: https://vfrworld.com/threads/single-vs-double.19487/. It's not too hard, just requires patience, a lathe and a grinder. I started on the back foot because when I got my bike as an unfinished project, the PO had started the swap, but only gotten as far as cutting off all the original suspension mounts (don't do that!), so I had to recreate them as part of the process. I probably have as many hours in the subframe as in the swingarm swap.
    Fork is 2006 ZX-10. It's nice and long, as far as modern sport bike forks go. Just run the top triple upside-down to give a bit of extra length and you'll need a GPS speedo.
    No build thread (sorry), but lots of pics on my Instagram @kiwibobb.

    Thanks again for the replies!
     
    Last edited: Nov 7, 2019 at 10:13 AM
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