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unkle_george

Intake wearing into head? What now?

32 posts in this topic

IMG_0289.jpg

I think I figured out why all of my intake valves are tight. Check out how the cam has worn down into the head and it's mushrooming over the buckets. I can't get them out now.

One of a few causes I can think of. First, I recently had someone rebuild the top end and put in a 13.5:1 piston - which blew the head gasket and it got a little hot. I've been having problems with it since then.

Second, I just recently sucked in a bit of sand after the plastic decompression plug blew out. (Thanks Yamaha ). It wasn't very much though, 1/2 cc at most, and the exhaust valves are perfect.

So do I:

1. Whip out the trusty dremel and try to clean up the mushrooming so I can at least get the bucket off, put smaller shims in and go from there? With as much wear as I see, it's going to be off more than the thinnest shim.

:applause:

Order a new head from the TT store and figure out how to swap that out?

The shop that did the origional work went under and the best shop in town wants _Way_ too much money for something I'm sure I can do myself.

Has anyone seen cams do this before and is my head toast?

- Ryan

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you will never get the cams to ride true in that head again....

new head.....which stinks...

also, new valves/springs and everything else...

i wonder if head "assembly" includes the valves and everything else?

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They all had seperate part numbers, so I doubt it.

I saw someone parting out a YZ here a couple weeks ago. Does anybody remember who?

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Looks to me like it must have been oil starved at one time for some reason. Or maybe it happened when it got hot due to head gasket problems. Could have been the sand ingestation, there are lots of causes, and many of them from what you have told us were experienced by this engine. I would look for a parting out, or maybe even a whole new/used engine off of ebay? Sorry to hear about your luck, hope you can find the least expensive fix. I know I have seen 426 engines go for arouns 500-800 on ebay. Maybe time to upgrade!!

Josh

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It costs about US$400 for new copper valve seats. That looks like a bin job to me.

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Any idea what the cause is?

That kind of damage is often caused by several problems or a combination of two or more. Oil starvation to the cam journals is the most obvious as is oil contamination. Either problem coupled with the cam caps being overtightened could lead to this result. Since you mentioned overheating, that coupled with any one of the other conditions I noted could be catastrophic. When oil overheats the microscopic film between surfaces disappears causing metal to metal contact. Add in an overtorqued cam cap bolt or two and voila! A seized cam journal, which is what I see in the photo. As someone else said, once the damage is done head replacement is the only alternative. Unlike a car that has replaceable cam bearings, the Yamaha head does not. Minor galling can be cleaned up, but your pic shows distortion of the metal. Time for a new head. :applause:

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That type of damage can usually be fixed by cleaning it up and line boring the cam journal. (Where they take a skim off the cap and head surfaces then bore the standard size journal through. You end up with only a slightly shorter distance between the cam and valve buckets, plus your cam sprockets and drive sprocket. I'd try a good machine shop first before buying a new head.

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That type of damage can usually be fixed by cleaning it up and line boring the cam journal. (Where they take a skim off the cap and head surfaces then bore the standard size journal through. You end up with only a slightly shorter distance between the cam and valve buckets, plus your cam sprockets and drive sprocket. I'd try a good machine shop first before buying a new head.

With a true OHC engine there is only so much material that can be removed before the head is junk. Once the journal support has been damaged to the point of mushrooming, it's toast.

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That's what I figured. I ordered a new head from the TT store... ~$450, along with new valves & all.

The Exhaust valves haven't moved at all ... It only has 3k miles on it so I'm going to just rebuild the intake side.

- Ryan

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That's what I figured. I ordered a new head from the TT store... ~$450, along with new valves & all.

That's cheap, actually. I had to replace a TTR250 head and it cost more than that for a BARE head. Make sure you find out the cause of the damage before you toast another head. :applause:

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That can also be caused by overtorquing the caps.

They only want about 70-75 ft/lbs or so... that spec is critical.

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Hey Unk, thats not normal wear. It was either starved for oil or when it became heated, it disfigured the head and the cam bore is no aligned or "inline". That is "galled" and the only options are "have inserts installed" this would be like engine bearings, or replace the head. Replacing the head isnt as tough as it sounds. I suspect the head will come with new guides already in place, maybe stem seals, but likely, not.. Technically, you will need to grind the valves with the new head, UNLESS you replace the valves with new, then just install them and set clearances. Set them a little wide, they will settle in and remain steady. Yes, use a dremel to clean up the galling to get the buckets out. If you align bore the cam bores, you should grind the seats. When the head overheats, it "twist" and the valve face is usually mis aligned from the guide and wont seat properly, even though, it may run OK.

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That type of damage can usually be fixed by cleaning it up and line boring the cam journal. (Where they take a skim off the cap and head surfaces then bore the standard size journal through. You end up with only a slightly shorter distance between the cam and valve buckets, plus your cam sprockets and drive sprocket...

The other drawback to this is it reduces clearance and the shims only come "so thin" so if this is done, you will need to have the valve stem tips knocked down a smidge with a valve grinder.

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