2001? Yzf 426 stroked complete resto

Valve clearance is as follows - intake 1=0.15mm intake 2=0.19mm intake 3=0.16mm

Exhaust 1=0.25mm exhaust 2=.30mm

I am beginning to run out of ideas.Tried running a snake cam through the spark plug hole but there is not enough light so the only way to check the piston is going to be pulling the head and if I do that I might as well pull the cylinder as well so I can check the connecting rod.

Ok so finally had a chance to tear down the top end. Problem found. The piston has gouged the cylinder with two hours on the motor. The Pistons compression rings had their end gaps in line with each other as well. Connecting rod has 0 up and down play.Grayracer any ideas on what could have caused this?ImageUploadedByThumper Talk1434861926.272533.jpgImageUploadedByThumper Talk1434861939.454111.jpg

Edited by Nick H

What it looks like is either the piston was fit too tight, or it picked up something and wedged it between the piston and cylinder wall.  The cylinder looks to me to have a little more than two hours on it, though.  Hard to tell.

What's the other side of the piston look like? 2 marks also? If so I'd say the piston to bore clearance was to tight.

I don't know if the cylinder was a fresh replate or not. The story behind the engine is that gt thunder did the stroker kit + bottom end rebuild. The previous owner did the top end and the shop I bought it off of supposedly make a custom timing chain (I call b.s. On that at this point) and did some head work plus the hot cams. I built the rest of the bike. So now I guess I'm looking for a reputable company to replate the cylinder plus a new piston and rings. After just doing the clutch and clutch basket this stings.The piston that's in it was supposedly a hi-comp piston.Not sure if I should go home-comp again or stock compression ratio.

Edited by Nick H

The other comment that I withheld was that the cylinder looks like it has more than two hours on it, frankly.  If it was used enough, it could have had a worn spot in the plating where the aluminum showed through. 

I am in agreement with you grayracer.So the only place I have found in BC to replate the cylinder is mongoose and they quoted me just over $400 for a replate.The yammi dealer quoted 530$ plus tax for a new cylinder. Looks like I got hosed on this one.

Send it to US Chrome it will be about $200. Call them first.

Or tgere is one on ebay right now for $180 canadian used but excellent shape, comes with piston and rings. Also a brand new ine on tgere for 300 check em out

I don't know if the cylinder was a fresh replate or not. The story behind the engine is that gt thunder did the stroker kit + bottom end rebuild. The previous owner did the top end and the shop I bought it off of supposedly make a custom timing chain (I call b.s. On that at this point) and did some head work plus the hot cams. I built the rest of the bike. So now I guess I'm looking for a reputable company to replate the cylinder plus a new piston and rings. After just doing the clutch and clutch basket this stings.The piston that's in it was supposedly a hi-comp piston.Not sure if I should go home-comp again or stock compression ratio.

anymore updates? did you get it back together?

Cylinder was sent to Mongoose cylinder works for replating. Original shop paid for that and sold me a new high compression forged wiesco piston + top end kit. My parts are in transit back to me as we speak.It sure will be a nice feeling getting this motor back together.

Cylinder was sent to Mongoose cylinder works for replating. Original shop paid for that and sold me a new high compression forged wiesco piston + top end kit. My parts are in transit back to me as we speak.It sure will be a nice feeling getting this motor back together.

Cylinder was sent to Mongoose cylinder works for replating. Original shop paid for that and sold me a new high compression forged wiesco piston + top end kit. My parts are in transit back to me as we speak.It sure will be a nice feeling getting this motor back together.

Good deal. I stumbled across the thread this morning and read through it, got to the end and wondered if you got it back together. The 426 is a great bike, fun as heck to ride and quick.

Good luck and update us when you can.

ImageUploadedByThumper Talk1440216816.009217.jpgImageUploadedByThumper Talk1440216835.740789.jpgImageUploadedByThumper Talk1440216855.325495.jpgImageUploadedByThumper Talk1440216879.944110.jpgImageUploadedByThumper Talk1440216900.129101.jpgImageUploadedByThumper Talk1440216913.930137.jpgImageUploadedByThumper Talk1440216925.631050.jpgImageUploadedByThumper Talk1440216937.780535.jpg

Ok so the replated cylinder, new piston and rings plus a top end gasket kit finally showed up today.installed all parts and fired the bike up. There is a very loud rpm dependant noise! The bike starts and idles easily. I have double checked cam timing. The only parts I still have on order is a primary drive (crank) retaining nut + washer + associated case gasket and a header to muffler gasket. I am at a loss at this point. Have a faint hope of curing it with the crank nut but who knows. Parts will be here Wednesday.

Edited by Nick H

Used a mechanics stethoscope today and it seems like the noise is coming from the crank nut. So I have finished throwing the plastics back on and buttoned up the top end. Fingers crossed! Also have finally drilled out the last of the broken bolts in the frame that were preventing me from mounting the last of the skidplates so those will be going on soon as well.ImageUploadedByThumper Talk1440281529.073554.jpg

Edited by Nick H

The noise that is caused by the crank nut loosening almost always comes from the deformation of the square key that locates the balancer gear on the crank behind the main drive gear.  If the new Yamaha key fits loose in the crank, that indicates that the crank key way has also been beat up, and you should but a generic square key and file it to fit snugly.  If it's just a little loose, Loc-Tite bearing mount may be helpful as an alternative.

 

BTW, If it has such a key on the balancer gear, it's a 2000 model, or an earlier YZ400F.  Starting in '01, the balancer gear was splined.

Wrapped the tank today.Thought I would post a pic. Still waiting on bottom end parts.ImageUploadedByThumper Talk1440451221.929660.jpg

ImageUploadedByThumper Talk1440568670.901750.jpg

So the bottom end parts showed up a day early. The old crank nut and crank showed damage to the threads upon removal. Going to get a die tomorrow that's the correct size for the crank as my set doesn't go quite large enough.Both gears on the crank are splined and did not have much play at all so I am concerned this might not be the cause of the noise I am hearing.however the gear lash between the crank gear and the counterbalancer gear seems to be quite large.Does anyone have a spec for this?Also the manual I have refers to using the woodruff key on the counter balancer drive gear as part of the gear timing process. I want to make sure my counterbalancer weights are aligned properly however my crank is of the later splined variety. Can someone post on how to properly time this gear set? Thank you in advance.

Edited by Nick H

So, with splines, it is in fact a 2001 or newer crank.  There are timing marks on the crank balancer drive and driven gears, and each gear has a "key spline" so that it goes onto its shaft only one way.

 

There is no spec listed for the drive gear backlash, although in '08, they did take steps to reduce it.

 

The big YZF has a rep for being generally noisy.

Thank you grayracer for the information. Repair of the crank + installation of the crank nut went smoothly. However the terrible noise is still making itself heard. So at this point I have exactly 0 idea how I am going to move forward. I am at the point where I am almost ready to take it to the dealer. Counterbalancer timing was correct as well. So to recap brand new top end.Crank only has a few hours on it and turns smoothly. Connecting Rod has zero up and down play. Everything under the outer clutch cover is in excellent shape. If anyone has any other ideas on where to go with this (grayracer) I am 100% open to suggestions.

Edit : After the new nut was installed I checked for excessive play between the counterbalancer driven and slave gears and play was minimal.

Edited by Nick H

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