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Bore damage - how much is ok?

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how much scoring can a 4 smoke barrel handle?

my 2005 wr450 appeared to blow a head gasket on sunday and pump all the water out, it didn't seize but suddenly started sounding "hollow" as if the muffler had fallen off

there was steam and then air blowing in radiator - bugger all water left in radiator and none in overflow.

pulled it down and head gasket is definately blown

there are also some light vertical scores on the bore suggesting it went very close to seizing? (the scoring was not there when i put a new slug in 250km's ago)

you struggle to see the scoring but you can feel it when running a oily finger around the bore.

have to decide whether or not they are bad enough to stop rings sealing?

i haven't dropped all the oil yet but there is no water in it so hopefully no metal in it.

will also check out the water pump to see if that failed

Its been suggested that the aftermarket gaskets (MCAS) may have been arse? (a few people have suggested only OEM for WR's?)

i can obviously re-assemble and compression test/check for oil use but before i do i am after peoples thoughts on how much scoring can a 4 smoke barrel handle?



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You want to re nikasil that sunofabeotch. Any scoring you can feel will affect the ring seal.

Stick with OEM gaskets, its a safe bet.

The bike overheated. Its possible that the shaft and gear that drive the water pump impeller got too hot. That may compromise the integrity of the metal. I've seen that gear explode on a bike before...it ain't pretty. I'd take the w/p gear, shaft, and bearings to a machine shop and ask their opinion.

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If a 4" bottle brush hone will not remove the scratches in 3 quick passes through the bore, you should replace or replate the cylinder. Even if it does, you then need to check the clearance, and replace or replate if it's out of spec.

As to why the gasket blew, my guess is a failure to properly follow the torque procedure as laid out in the manual. It's a bit complicated, and a common source of trouble for the home tech. You will also want to check the flatness of the head and cylinder deck.

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thanks for the reponses - taking barrel and head to engine recon guy on sat to get the final verdict.

understand the home tech comment and will certainly be very carefull on re-assembley - that said all torque procedure as per destructions were done (snapperhead mechanical services)

also will pull water pump apart to check all that.

also sourced a 2nd hand barrel which might be used.

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took it to Japanese Motorcyles this morning (they recon'd the head).

scoring is minor and yes a ball hone would sort it

but - when he wiped the oil out (i put some in to feel the scoring) he spotted 2 small chips in the barrel - right through the coating and perfect for snagging a ring - pretty much at the top and bottom of the stroke.

so $440 for electrosil to recoat, or similar $'s for importing a new one or a 2nd hand one (someone on dbw has one which i am chasing up)

thanks for your help.

(thanks to Jap Motorcycles for taking the time to look)

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