Cam journal scouring seized cam, what can I get away with?

Hello,

The cam on my YZ426F seized not long ago, causing the timing to go out and the valves to hit the top of the piston.

I am replacing most of the top end (valves, cam chain, seals). One journal on the intake cam side shows scour marks on the cap and head. Can I get away with just sanding back the one journal with very fine wet n dry paper? A new head would cost more than the bike is worth.

Did anyone here get away with just smoothing off the offending journal area?

if anything in the head is damaged at all, get a new head.

ifthe valves did in fact hit the top of the piston, that means they might have bent something in the head, like a valve guide...

get a new head..

a whole new head equals a whole new bike for me, I don't want any further problems, just want to get out there and ride a bike instead of waiting for parts

if anything that involves any kind of movement in an engine is damaged, you should replace it. something can cause damage if it is 1/10 millimeter off

I don't want any further problems, just want to get out there and ride a bike instead of waiting for parts

Classic mistake :thumbsup:

Yeh you are right and I agree. If I was head of Ducati engineering I would replace the whole motor, but I'm got limited funds.

Couldn't I say that worn piston and rings still work fine, just not efficiently and that means worn but smooth cam journals still work fine, just not 100%, maybe 80% will that make mean my bike won't blow up if I only ride it once every few weeks?

Millennium technologies can fix it for you http://www.mt-llc.com/. If you want to risk it, you could try sanding out any burs and what not and just running it, but I wouldn't recommend it.

If ya really don't like the bike...go ahead, give it a try. From your description of the problem, I don't think it'll work....but like I said, ya don't care about the bike. When it dies, part it out on ebay, and buy another.

...ya might go ahead and get your sellers account now.

If ya care to keep the bike, get it checked out by someone knowledgeable, and go with their recommendation.

yeh I don't care about the bike, I will ride it for a while, check it out after a few rides (if it gets that far), if it dies soon I will sell it off, if it takes a little longer I will sell it off later in a whole piece. Maybe I could buy another YZ426 and keep this as a parts bike, hmmmm. I miss my 2-stroke a hell of a lot now

yeh I don't care about the bike, I will ride it for a while, check it out after a few rides (if it gets that far), if it dies soon I will sell it off, if it takes a little longer I will sell it off later in a whole piece. Maybe I could buy another YZ426 and keep this as a parts bike, hmmmm. I miss my 2-stroke a hell of a lot now

This is not meant to be negative...but I'll be surprised if it starts.

If it doesn't start, I'll have a lot of untouched new parts for sale on eBay :-)

Knowing my luck it'll start and run fine for months, then BOOM gone forever.

I like the 4-stroke power delivery but not their high maintenance, just like my taste for women I like them easy to make happy :-)

If it doesn't start, I'll have a lot of untouched new parts for sale on eBay :-)

Knowing my luck it'll start and run fine for months, then BOOM gone forever.

I like the 4-stroke power delivery but not their high maintenance, just like my taste for women I like them easy to make happy :-)

I understand your plight, I've put together some things that a house built of lincoln logs has tighter tolerances...and they surprised the heck out me. Used to work at Crower when I was 18...we slapped together some real clunkers that for unknown reasons, wouldn't blow on the dyno. Just revved the P out of them. Funny how things work sometimes.

I'll see this mainly as a learning experience, I'll check the cam/head condition frequently and if I can catch things starting to go very bad I'll take action. If it blows then back to a 2-stroke until the engineers work out a more reliable 4-stroke machine, like a light, powerful, motocross Honda CT110 standard of reliability 450 - thats what I want :-). Dream land maybe but good to dream while at work

Are your valves currently sealing? Usually when a piston contacts valves, bad things happen.

nah valves bent so replacing piston, rings, seals, valves, springs (everything except head) on the top end

Instead of parting it out on Ebay, why not look for a new top end on Ebay?:thumbsup:

By the way, do you have any idea how the top seized up in the 1st place? The reason I'm asking is that Yamaha has had some issues with people installing oil filters for the YZ (2stroke) in the 4stroke engines causing the top ends to seize up. The filters were mislabeled from the MFG. They're exactly the same shape and size so if you're not looking for the extra oiling holes designed into the 4stroke filters there's a good chance you installed a YZ filter!:p Just a thought.

Instead of parting it out on Ebay, why not look for a new top end on Ebay?:thumbsup:

By the way, do you have any idea how the top seized up in the 1st place? The reason I'm asking is that Yamaha has had some issues with people installing oil filters for the YZ (2stroke) in the 4stroke engines causing the top ends to seize up. The filters were mislabeled from the MFG. They're exactly the same shape and size so if you're not looking for the extra oiling holes designed into the 4stroke filters there's a good chance you installed a YZ filter!:p Just a thought.

Which two strokes have oil filters? I haven't heard of this issue before.

Seized cams are most often caused by over torquing the cam cap bolts, or some sort of lubrication issue.

Looking for a whole top end on ebay isn't a bad idea since you don't care about the engine anyways. It would be a lot cheaper than investing all those new parts into a head that has issues.

Yamaha has had some issues with people installing oil filters for the YZ (2stroke) in the 4stroke engines causing the top ends to seize up. The filters were mislabeled from the MFG. They're exactly the same shape and size so if you're not looking for the extra oiling holes designed into the 4stroke filters there's a good chance you installed a YZ filter!

That's hysterical. :p:moon::lol::thumbsup:

The filters probably came from the same place that makes radiators for the Volkswagen flat 4's, left handed metric Crescent wrenches, and sky hooks.

I haven't heard of 2-stroke oil filters but I suppose I am only young :-)

Think the over tightening cam caps + not so good oil flow were the culprits.

Thing about being in Australia, these heads on eBay are hard to find. The cheapest (brand new) is about $450 US.

OK, HaHa!! This is the way I understand it. The Yamaha 2stroke uses a filter for the gearbox only. It is the same shape and size as the 4stroke filters used to oil the gearbox and the head.

Have a look at these pics. Both are Yamaha oil filters. The filter on the left is for a 4stroke Yamaha. The filter on the right is for a 2stroke Yamaha gearbox(gearbox only). If you put the filter on the right in certain Yamaha 4strokes it will absolutely, completely waste the top end!

DSC09438_2.jpg

Look real close to the filter in this pic. See those 4 small holes along with the 2 large holes? The 4 small holes are what oil the top end!

TW20oil20filter.jpg

Now I've never owned a YZF and I have no idea what the newer filters look like so do your own research.

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