Hmm now what (A Rebore!)



  • You will want to send that head off to be sorted out as well.



  • @Calum yeah you could normally get away with a few dents but that’s completely savaged lol



  • @Pablo13 If you have the cash a full rebuild with a few upgrades aka a modified head to alter the squish would be just the ticket and add more πŸπŸ’¨ !!! πŸ˜‰



  • @DTR-NSR said in Hmm now what (A Rebore!):

    Hard to tell in the pic but looks like the gudgeon pin circlip is missing? Unless you took it out before pic.

    Yeah, and scratches on the side and dome of the piston right about at that point.
    Good eyes.



  • That grey discolouring on the piston looks like death ash, but I suspect that's a result of the failure.

    The head does not look like detonation, looks like something has been crushed into it.

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    That's what detonation looks like



  • @Calum it does have those det marks, they are just hidden under the other damage πŸ˜‚

    Dropped the new piston off today, should be back wih the head and bore tomorrow. Gasket set is here too, so if I get a moment I'll get something done on it over the weekend πŸ˜‰



  • Yes, but I suspect that's a result of the engine going faulty and you continuing to run it. Either way, that bike will be down on power now.

    If the engine was detonating before the incident, then you will definitely want to sort that out, otherwise you'll just kill another engine.



  • @Pablo13 Either way not getting that head fixed would only lead to further problems down the road. Take & post some pics of the newly refurbed parts before you refit them please dude. πŸ˜‰



  • @NINJA Piston, small end and bore have already been fitted. Just a new piston and a bit of cross hatching πŸ˜‰

    I got the old piston off and could inspect in light a bit better. Both circlips were still present. Initial diagnosis was correct, and top ring has lost a section around 10mm long.

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    Looking at the piston, there is more to it than just that IMO. Here is the best pic I can take to give you an idea of the low spot on the crown, to the right side in the picture

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  • I'd be rebuilding that bottom end too. Or chance it and hope nothing went down into the mains...



  • @Calum I've had a little check over and I'll take the risk, I'm more of a when it breaks fix it kinda guy, Plus I'm tired of the traffic in my car, miss giving my 26 year old smelly french whore a daily seeing too 😁



  • So the head.....

    They didn't do much by the looks of it, just a quick clean of the mating surfaces

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    Not particularly happy with that so far so have not refitted yet, gonna sit here and have a play and tidy it up myself. Head is pretty accessible so can always come back to swap it out with another later down the line too.



  • @Pablo13 It's not as simple as that.

    There really isn't much you can do.

    If you take away the marks, you alter the squish band. If you only alter the squishband, then you'll reduce the compression and the bike will be down on power.

    You need to alter the squish, according to a piston dome design, then alter the compression ratio by using a thinner base gasket, or machining the head down.

    It's a very complicated process.

    A tuning company ought to be able to sort it out for you.

    But I wouldn't want to run that head like that, it'll be down on power and increase the likelyhood of detonation.



  • @Calum Yes I understand and will most likely get another head down the line to do correctly. For now I'm going to tidy it as best I can while being sympathetic to the compression ratio but at the same time loosing any sharp edges that will be hot spots and prone to kickstarting a det situation. Basically I'm going to do the best I can with what I've currently available to me πŸ˜‰



  • @Pablo13 Heads are getting rare now unfortuantely. Used to be a time where they were a dime a dozen. Now you'll be lucky if you can get a 3BN head I swear.



  • @Calum The way I see it, whatever I'm removing now is needed and more to be corrected. Its already looking better.



  • @Pablo13 Well, whatever you do, it's likely to affect the fueling.

    So to avoid the engine failing again, make sure you ensure it's jetted appropriately. If it's overfueling, you'll bore wash the engine and risk scuffing the bores. If it's underfueling, it'll detonate and seize again.



  • @Pablo13 Looks like they filed the top of the head and not touched the actual dome part. Personally if you've paid someone to do a job and that's the result of their handywork, I'd ask for a refund. As with everything in life, quality does not come cheap and if you pay peanuts, you will only ever get monkeys!!!
    πŸ˜‰ πŸ˜‰



  • I'll be keeping a close eye on things, regular compression tests and plug chops to see whats going on.

    I think I've done what I wanted with the head for now. I'd say I've given it more of a polish than anything

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    Its far far from perfect, but also a lot better than what it was πŸ˜ƒ

    one of the marks is still fingernail deep, but I'm reluctant to go much further without taking it somewhere knowledgeable with two stroke machining. I'm happy enough to fit and find out for now πŸ˜‰



  • @Pablo13 It looks a lot better for-sure, let us know how it runs once you've finished your rebuild. πŸ‘πŸ»


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