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spun bearings with pictures rebuilding 08 spec??

7K views 5 replies 5 participants last post by  tones160 
#1 · (Edited)
so this is my new engine which i brought used its a 2006 put about 30 miles on it and the infamous knock appeared luckly happened just as i was on my road . knew what is was straight away as i had blew a rod less then 3 weeks before this.

so i dropped the motor checked the pan had couple bronze specs dotted all around not as bad as i thought it would be.

so i dropped the motor out just finish stripping it down last night and only one of my bearings had spun it didnt even have the tabs on it nor was it attached to the rod cap. this is for my cylinder 4 all other bearings seemed alright and i could actually see what colour code they were. the spun ones got wiped clean but since am in am going to replace all the bearings since am in and the rings.

now hes my question for this rebuilding 2006-2007 motor business where you -1 and use that as your new size is this just four the journal bearings are dose this apply to rod bearings.

and also as you can see from the pics my crank is pretty much perfect accept for where rod 4 was it is deeply scratched. sine only one bearing spun and the scratches are not that deep because it didnt get to run for long. can i just sand and polish my crank myself just to make that one bit smooth again . all my journals are all good i can run my nails through the journals and crank and no scratches .


So my main question is do i -1 for all bearings our just journals?

can i still get away with this crank?

if i dont minus -1 for the rod bearings should i order the same colours again since i can see them except rod 4?
or plastiguage them first

and rod cap for cylinder 4 was pretty hard to get of compared to the rest it didnt want to budge should i replace cylinder 4s rod. rod seems good condition.

ps am not looking to spend 890 pound on a new crank cheapest methods
 

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#2 ·
I can only recommend a you let a machine shop regrind the journal and use a different bearing. it may be best to replace the crank depending how much material they need to remove.

if you are replacing rings the cylinders are nikasil coated. which means you'd have to pay for this as well. so might as well do it all right. don't try to sand and polish the crank yourself. it will probably fail and you wasted all that time and money.
 
#3 ·
Usually to save time and money... my machine shop charges me $160 to polish the mains/recon-rods... then
assemble the rods to the crank. Obviously the bearings cost extra. You might want to look into running it on a
balance machine, if possible. (it is a stock crank)
At the very least you're going to need new rod hardware and a whole lotta fine measuring/weighing.

Bores look good from the pic... so long as the pistons are in good shape, throw new rings in.
Yamaha did have a TSB on sizing the rod bearings down (or upping the clearance)
 
#4 ·
i decided that since only one cylinder spun a rod bearing and bike was pretty much stopped straight away. and the rest of the crank is is perfect condition decided and just going to give a try and polish it myself seen a couple vids on youtube, then measure up the new bearing size for rod four. and since i know the rest of my bearing colors am just going -1 and order the sizes i need so basically to 08 spec.
tbh rod 4 and piston looks good but am just going to order a new rod just incase
 
#5 ·
I would suggest taking all four connecting rods and crankshaft to have them sized at a machine shop by a professional. These connecting rods are notorious for becoming out of round and often need honed to correct size. Do not simply just go by color code. I would also advise pressing in new rod bolts. Rod bearing clearance should be about .002 inch. I strongly advise you not to just throw it back together in your garage as it WILL break again if bearing clearance is not correct. Best of luck.

Regards,
Joe
 
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