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A Couple Engine Issues - should I be worried?

Discussion in 'The Garage' started by SpongeBobbed, Nov 11, 2017.

  1. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Hey there,

    I built a bobber a couple years ago and have been enjoying it a ton. I went on a long ride in the summer and ended up blowing up the top end. I tore it apart and the culprit ended up being connecting rods that were out of alignment.

    Instead of pulling the crank apart and getting new rods then doing new pistons and cylinders, I found an local used engine with a all the innards in good shape. I figured i would just rebuilt that with new seals and gaskets and keep it simple.

    I'm pulling it apart to aqua blast everything and when I split the cases I found a couple issues. The first is a couple small nicks on the sealing surface between the top and bottom cases. It doesn't look major, but I wanted to hear from others on the forum about what they thought. I've seen other posts where there were major scratches and people advised putting some JB weld on and sanding it to a smooth, even finish. Do you think that is needed here?

    Also, when I noticed a hairline crack on the left side of the case. Can this be welded? Should it be welded? Or do I need a new top case? Any info would be really helpful. Thanks a bunch.

    IMG_1298.JPG IMG_1306.JPG IMG_1301.JPG IMG_1304.JPG IMG_1305.JPG
  2. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    Check that those nicks do not protrude above the sealing surface, otherwise dress them down. The case sealer should handle that.

    The case crack looks like the typical "thrown chain" that bends the sprocket cover upward. You'll want to track the crack's hairline progressions, see if they appear on the inside, oil containing, part of the case. There's no significant loads or stresses on the shiftdrum needle bearing, so no worry there. It's just an "oil leak potential" you'll want to address...
    azman857 and JimD54 like this.
  3. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Thanks TwoMany, I appreciate the insight. Is there anything you would specificly use the file down the nick if it's above? A general file or some sandpaper? I'll follow the crack to see where it goes. It doesn't seem like a big deal now, I just don't want it to get bigger.
    TwoManyXS1Bs likes this.
  4. JimD54

    JimD54 Mechanic, 1968-Present

    Use a fine tooth file. Make sure it lays flat on the mating surface the whole time you're filing. Don't remove all the damage, just look for an even shine on both sides of the nick.
    Above all else, go slow. It's not a race... Concentrate on keeping the file flat.
  5. YamadudeXS650C

    YamadudeXS650C Central New York XS650

    SpongeBobbed likes this.
  6. fredintoon

    fredintoon Fred Hill, S'toon.

    Hi SpongeBobbed,
    you mean, the two halves of the engine started to de-phase themselves?
    It usually takes a 20 Ton press to do that.
    Perhaps the wrecked engine could be the start of a 277º re-phase project?
  7. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Haha, well I'm not sure what happened but the rods were quite a bit over the 0.2mm small end play spec and the piston wrist pins were scored and wouldn't come out of the rod small ends. I purchased the engine from a guy who rebuilt it with high performance rods so maybe it was put together wrong. Either way it's toast. I don't have a ton of extra cash right now so my plan is to rebuild the new (old) engine I picked up with stock parts, and then over the next year build a high performance engine with the 277 and the 750 kit using the engine that blew apart.
    It's the first time I've tackled rebuilding an engine from scratch so I'll be asking a ton of questions :).
  8. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Hi TwoMany,

    I had a follow up question on a different issue if you don't mind. I started looking at the crank in more detail today and the one thing that caused some concern was a line of crud/rust on each of the bearing races. Have you seen this before? There seems to be the same line on each of the bearings so I'm thinking it could be from the engine sitting in the same spot for an extended period. The bearings still spin really well and there doesn't seem to be any seizing or anything like that. Rods also look great. I'm hoping I don't have to split the crank, but obviously I'll do it if these are spent.

    If anyone else has any thoughts let me know. Thanks!

    IMG_1333.JPG IMG_1335.JPG IMG_1343.JPG
  9. JimD54

    JimD54 Mechanic, 1968-Present

    They look to me to be from an overzealous application of case sealant. If the bearings themselves are good, just wire brush/scotchbrite the marks off. Nothing to worry about in my opinion
    gggGary likes this.
  10. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Thanks Jim, that makes a lot of sense. The crud is at the same spot on each race and lines up with the edge of the case where the sealant would go. I appreciate the help!
    TwoManyXS1Bs and JimD54 like this.
  11. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    Agree with Jim.

    I think that the case's steel inserts don't quite fully reach to the parting line, leaving a gap, like shown at the arrow.

    I also believe that if you were to look at other crank pics, that parting line stain will appear, like that pointed to by the arrow.
    JimD54 likes this.
  12. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Thanks a bunch! That was really helpful. I'll hit them with some scotch bright tonight and hopefully that cleans everything up.
    TwoManyXS1Bs, JimD54 and gggGary like this.
  13. Drill a small hole in the case where that crack ends to keep it from spreading. You can get Bernzomatic aluminum brazing rods at Princess Auto to fill in that crack, if you vee it out first. It might not have the same colour as the oem cases, but it would fix the split. Might be easier to find another side cover.

    Probably not hard too find a welder with some free time in Alberta right now who could fix it for you. My brother is in Red Deer and the job market is horrific for all the trades.
  14. SpongeBobbed

    SpongeBobbed 650 Simpleton

    Thanks Mac, I've seen guys drill a hole and then fill the crack. Looks like a good option but i'm cautious not to screw things up even more. I'm going to get the case aqua blasted this week to get everything really clean so I can get a better look. I figure if i'm rebuilding it might as well be clean. It's actually pretty hard to find local used engines right now. I check the local sites daily but stuff doesn't come up to often. When it does the guy is usually trying to get rid of a whole project and doesn't want to sell just engine parts. I'll keep looking though.
    There's definitely a lot of guys looking for work right now. It's been a tough few years for all of us in this industry. There's signs it's going to pick up, but one big move from the guys in the middle east and it can all come crashing down again :(.
  15. SpongeBobbed

    SpongeBobbed 650 Simpleton

    So the scotch brite worked great! Here's the race after a little rub down. Thanks again!

    JimD54 and TwoManyXS1Bs like this.

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