Bobs buggered engine thread

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pulsarboby

Guest
diesel weasel said:
the piston is wider at the skirt, not thinner, or do you mean the actual thickness of the skirts profile as you look down on it ?
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yes thats the widest point so will be the first point to make contact with heat expansion!
the gudgeon pin area because of the hole will be the first bit to melt as its on an edge and heat will be concentrated to that edge, if you know what i mean.
 
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azboy

New Member
if i was u boby i would measure a un scored parts of the bores and the bottom of the pistons normally the non thrust sides and just check the tolorances between them, as when i was youngger i saw this exact thing happen to a motor cross bike after a rebuild, not the person fault who built the engine but the machine shops mess up any 1 can make a mistake just check the tolorances they have boared the engine out too, as the way the pistons look the bores are too tight and as they got hot they have got too tight and cause this prob, it want do no harm checking.
 
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azboy

New Member
our garage use a machine shop often they shimmed a head for us then it melted a valve because the tolorance was way too tight keeping the valve when hot from fully closing, they have never made a mistake before in 4 years we have been using them but theres a first time for everything, im just glad they never made this mistake on my engine.
 
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pulsarboby

Guest
will take it all back to them arran, and get them to check it too but tbh cant see why the other engineers wouldnt have spotted it if it had been out of spec!
but as you say its worth a try.

it just seems funny that it ran fine with good comps up till that dreaded day then all compressions dropped on all cylinders from 170 to 125 and 75 on 3!
 
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ashills

Active Member
when u had it mapped would have been the first time it saw lots of boost though wasnt it bobby ?? so alot more heat / stress than it had been put under from running in or did you use my method and rag the tits of it to run it in lol
 
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pulsarboby

Guest
lol it was run in hard alan, i dont pussy foot around with them.
ideally the track is a good place to run it in, done that with my bikes in the past, but its a bit nerve racking none the less, as your never quite sure if somethings gonna let go, bike especially!
 
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youngsyp

New Member
pulsarboby said:
lol it was run in hard alan, i dont pussy foot around with them.
ideally the track is a good place to run it in, done that with my bikes in the past, but its a bit nerve racking none the less, as your never quite sure if somethings gonna let go, bike especially!
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Up until recently, I would have disagreed with that, as the best way to run a fresh engine in. Although, I wouldn't have been able to justify my stance as, it was all hearsay.
Having read into the subject though, through interest and seeing the differing views, it would seem, as you've pointed out, that a heavy run in period, with 'normal' loads is the best way to bed the rings in, to get and maintain a good seal. And of course, as long as the bearings are all lubed properly, it won't effect them.
A good quote I read was "if it doesn't hold together then, it's only a matter if time, until it lets go in the future !" Logically and mechanically, that makes perfect sense !
 
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jpward

Guest
pulsarboby said:
lol it was run in hard alan, i dont pussy foot around with them.
ideally the track is a good place to run it in, done that with my bikes in the past, but its a bit nerve racking none the less, as your never quite sure if somethings gonna let go, bike especially!
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The guy thats doing my engine work ran an engine in one night i was there, screwed it back together after new pistons, rods, couple gear cogs, topped up the coolant and oil and whacked in a new battery

Moments later first turn of the key and he was revving it like someone trying to intise a rack from the traffic lights, he laughed as i had a look on my face that probably said "Any moment now" so i can see how being on a track with the threat of lock up mid corner could make for a change of leathers :lol:

But few moments after that it was on the dyno quite surprised at how little he really gave it in terms of run in time but held together for a few power runs

He also said 500Mi is more than enough for the R and to drop the oil at 200Mi every one else i ask over here said 1k min whats your guys opinion?
 
stumo

stumo

Active Member
Run it hard but don't screw the bowels out of it is the way i run engines in. and don't use synthetic oil, just normal stuff.

you can't drop the oil enough times IMHO as it's cheap compared to the price of an engine.
 
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jpward

Guest
stumo said:
Run it hard but don't screw the bowels out of it is the way i run engines in. and don't use synthetic oil, just normal stuff.

you can't drop the oil enough times IMHO as it's cheap compared to the price of an engine.
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Aye I had already got Full Syn oil and he just opened the box of bits I had when i left the engine down and nicely handed it back to me £80 wasted well for now anyway

Dont intend setting boost above .8 until I know its holding together probably about 1k to rule out any building work and to get used to not leaning in the corners and cr@p brakes when I return to car driving after a few months off :lol:
 
gtirx2

gtirx2

Member
azboy said:
if i was u boby i would measure a un scored parts of the bores and the bottom of the pistons normally the non thrust sides and just check the tolorances between them, as when i was youngger i saw this exact thing happen to a motor cross bike after a rebuild, not the person fault who built the engine but the machine shops mess up any 1 can make a mistake just check the tolorances they have boared the engine out too, as the way the pistons look the bores are too tight and as they got hot they have got too tight and cause this prob, it want do no harm checking.
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I was going to say the same thing about a moto cross bike but what i was going to say is this guy was running it with neat petrol with no oil and it did pretty much the same as bobs motor but the bike seized soild with me on the back:shock:and only ran for about 10 mins:lol:
Like i say i am no expert but i would of thought if the clearences were that tight it would of happen alot sooner,like when he ran it in.
But saying that it does take a lot of fuel to bore wash a motor so who knows?
Another option would be that the oil squirters under the piston stop working or got blocked and the piston got hotter and started to seize but the odds of that are very slim indeed on more than one piston?
As for pic's the only thing i can find of a bore washed cylinder and piston is here http://www.crawfordperformance.com/news/article_16.shtml
and admitedly the scores are on the other side of the piston but it does look rather the same i think, if not quite as bad.
 
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pulsarboby

Guest
just when i thought things could get no worse:doh:

removed the crank the from my engine yesterday and the main bearing shells are scored to boogery too, and on close inspection the crank is now badly marked so now im gonna need a crank aswell.
what a nightmare, this has also obviously been contaminated with petrol in the oil which has thinned it right down and broke down the oil film between running surfaces:roll:
so now i need to completely rebuild the bottom end again!
 
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pulsarboby

Guest
nope your right there jim, looks like ive been well and truly hit with the sh1tstick:sad:
 
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pulsarboby

Guest
yeah but thats just helped me to become more at peace with myself, and my feminine side:lol:
 
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pulsarboby

Guest
ok a little update on my boogered engine!

my new set of cp pistons arrived yesterday so i took them the old and new block, crankshafts etc down to gards engineering, who have done a few 200sx's and have a lot of experience with the sr20det engine.

i showed him the old wiseco pistons, block and crank, and his words were..........ive never ever come across anything like it in all my years of engineering:shock:
he truly did not know what had happened!
he said that the melted piston had elongated towards the gudgeon pin side 1.5mm which had caused it to melt on that side.
the block clearances (rebore) were fine. he just couldnt understand why a piston would elongate on the non thrust side:?
the crank has also mullered every single main bearing shell, which again is most unusual.
he said that the two things that should never happen to an engine, have happened in my case.
anyway he wanted me to leave all the parts with him and there going to get there head man down from up north this week to examine all the parts and try and find out exactly what had happened to my engine, so that piston could become a celebrity:lol:

gonna be around a week before i get my newly bored block back with pistons fitted, so come to a bit of a grinding halt at the moment.

but its got me more curious than ever now to know exactly what went wrong with that engine, i still say the massive overfuelling had caused it, but the engineer guy isnt so sure, as he cant work out why its melted on the non thrust side, and why all the main bearings are scored to fcuk.

will wait and see what the big chief has to say, all will be revealed at some stage.
 
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pulsarboby

Guest
in all fairness the guy did actually say that, as he just couldnt explain it!
suppose it is possible
but the compressions had also dropped on the other 3 pistons from 170 to 125 psi so they may have followed and gone the same way as no3 in time.

very baffling to say the least!
 
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