Hmm now what (A Rebore!)
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@Pablo13 I would be surprised if the heavy braking incident caused all that damage, by the looks of it your engine was in decline and had suffered some internal damage most likely from detonation, over an extended period of time. The incident was just the tip of the iceberg and the straw the finally broke the camel's back. You were dead lucky the engine maintained power and you were still able to ride her home. Sadly the price we all have to pay from owning a used bike and not knowing the true history of our pride n' joy.
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@NINJA Yeah I agree. She is a French import, although it was the runt of the litter so to speak, and had expected stuff to go wrong and I guess the mileage is about right for a top end. Just surprised that any plugs I pulled looked fine and it always started first or second kick right up until that incident.
I've run it on super while I've had it, so I guess it must have had some crap French fuel a while back and just managed to hold it together pootling about French lanes until I got my hands on it :grinning_face:
On the upside this may well go to explaining why it wasn't too happy revving over 9k, so if it solves that issue at the same time, I'll be happy. 0.5mm oversize piston, small end and gaskets have been ordered today and the bore and head are at the machinists. Hoping for a quick turnaround :grimacing_face:
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@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. -
@Calum it does have those det marks, they are just hidden under the other damage
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
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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.
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@NINJA Piston, small end and bore have already been fitted. Just a new piston and a bit of cross hatching :winking_face:
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.
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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@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 :grinning_face_with_smiling_eyes:
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So the head.....
They didn't do much by the looks of it, just a quick clean of the mating surfaces
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.
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@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.
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@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 :winking_face:
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@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.
!!! 