any one got any ideas or can they be heated under assembly disasembly the color of it

is this normal pls remember my piston seized for some reason oil good water good no worn parts all new well 2 weeks ago


its heated during assy to make it easier to press it together

the rod/big end eye would be discloured if the rod had seized

many thanks guy one of my list regards peter uk big thanks

just seen your pic of the piston - not good

is there an oil jet, to spray the underside of the pistion/cylinder wall on the 400?

this maybe blocked and hence lack of oil resulting in the seize

what clearance was the cylinder/piston?

thanks guy

youve hit the nail wi the hanmmer

the squish if too close the heat will damage the piston many thanks for the reply

err.... I think I've confused you

I was asking about pistion to cylinder clearance ie usually about 0.04mm, not the squish, in case the clearance was wrong and was the cuase of the seize

Squish is different

The smaller the squish the better (as long as compression ratio doesn't cause detonation)

Static squish will be larger then when the engine is running as the rod will stretch, esp at max engine speed

thats what some one thought heppend guy detonation to do that to my piston the bike was running great smooth etc mmy friend from a bike garage says i would have valve issues b4 detonation problems if they were to close together aftera recent skim thanks regards peter

if i can find out the orriginal height of a barrel and head i can work out how much has been skimmed machined off does any one no pls

thanks peter

thats what some one thought heppend guy detonation to do that to my piston the bike was running great smooth etc mmy friend from a bike garage says i would have valve issues b4 detonation problems if they were to close together aftera recent skim thanks regards peter

dentonation leave the crown of the piston melted or pocked marked where the ally has melted

unlikley to cause a 4 stroke to seize unless very servere

post a pic of the piston crown please

sorry about the late reply heres the top


Can't see any sign of detonation or pinking

As the exhaust side skirt is facing, that means the seize/damage shown in your other thread is on the intake side - very unusual. Its usually the exhaust side skirt that takes the beating, but it looks unmarked from what I can see

I think you gotta doing some measuring or take it to some one who can

At the moment its just a guessing game without the facts

hi mate searched for the old piston today,,,this was run in the engine with no head barrel skimming been done standard

now the marks are simmilar to the new piston in a skimmed set up not as bad but simmilar, the barrel was honed for the new piston and i cant vouch for a honing b4 that but im hearing yes you can hone a nickel sealed barrel and no you cant heres a few pics of the old piston,,this one never seized was just replaced on first build regards peter



That original piston ain't looking good either

Its been trying to seize as indicated by the drag marks down the skirt and on the ring land between the rings

you can see where the squish is working around the edge, becuase no carbon black has formed there

Have to ask what oil you are using

You really do need a good motorcycle specific oil, as these engines are in a fairly high state of tune

You really need a synthetic or at very least a semi-synt - plain old mineral oil is asking for trouble

Remember, that once the clearance between the piston and cylinder reaches 0.10mm (0.004") its worn out

I've heard of cases of the piston tilting in the bore and being punched out the front of the cylinder

Yes you can hone a Nikasil coated cylinder, but honing is done with stones, which removes metal, where as for a new piston & rings you just want to break the glaze

You run the risk of having too much piston cylinder clearance if its been honed

thanks for the time guy

the oil was a 14 40 semi not the cheap butt not the most expensive

will be using yam lube on next build

at least as you say the squish is looking ok

regards peter

will post soon on rebuild when my bits arrive

ok lads just waiting on piston and gaskets coming ordered a genuine piston this time barrel has been re nikosealed

checking over every thing b4 the build can any one tell me how to get down to this pipe just to check it a for been there and b for clean regards peter is it a n engine split again to find out


no 13

DSCN1444.jpg Edited by bluesbiker

You should be able to get to the #17 bolt under the clutch cover. That pipe connects the center cases.

thanks vince its the only thing i can think of i am asuming this pipe feeds :thumbsup: the piston area oil there 3 holes in it seemingly,,i thought it was a splash feed could i be wrong,,sorry to go on and on but when i get the piston and gaskets back its cost me now since december 1400 in repairs

That pipe takes the oil to the transmission I believe

guy when i look down the space behind crank and con rod are i can see some transmission gears etc etc all one oil wonder how to find out how piston is supplies

my mate said if it were spray fed and not working my little end would have suffered first i honestly give up

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