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Old October 28th, 2019, 09:10 PM   #1
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Valve won't loosen any more

One of my intake valves won't unscrew any more, and the valve is too tight for my liking. It's at exactly 0.08mm. What's happening here? How can I fix it?

The bikes at 43000 miles and it's been about a year and a half since I last did the valves. I'm unsure of the bike's service history before 30,000 miles.
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Old October 29th, 2019, 02:30 AM   #2
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If it’s a pregen it’s probably valve recession. 0.08 will buy you little a bit of time before pulling the head off for a valve job. There are a few bodgy things involving removing small amounts of metal from various parts of the valve train (you are only looking at couple of thou of an inch spread over two or three components) that can also buy more time and I must admit to having used them once or twice when the valve train concerned was almost completely shot to get another 10,000km or so out of a dodgy motor however not on a GPX.
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Old October 29th, 2019, 02:38 AM   #3
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If it’s a pregen it’s probably valve recession. 0.08 will buy you little a bit of time before pulling the head off for a valve job. There are a few bodgy things involving removing small amounts of metal from various parts of the valve train (you are only looking at couple of thou of an inch spread over two or three components) that can also buy more time and I must admit to having used them once or twice when the valve train concerned was almost completely shot to get another 10,000km or so out of a dodgy motor however not on a GPX.
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Old October 29th, 2019, 06:26 AM   #4
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Take a close look and see if you can tell exactly what the problem is, to be sure the problem is really that you've reached the end of the adjustment, rather than something being wrong with the threads, for example.
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Old October 29th, 2019, 07:30 AM   #5
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Just double checked. It's out of room to back out is all. Makes sense at nearing 50k miles.

What all does a valve job entail?
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Old October 29th, 2019, 08:21 AM   #6
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You're saying that the adjustment screw can't retract the "ball" end of the valve rocker arm any further because the base of the "ball" end is up against the underside of the rocker arm, right?

So you remove this rocker arm from the head, which is easy to do with just your fingers only, just rotate the engine until that particular valve is not under compression from the camshaft lobe.

Then remove adjuster screw from the rocker arm and gently grind/polish/sand off just a few thousandths from the underside of the lifter to give you a bit more room to adjust the lifter adjuster screw inward.

I've seen pictures of this work done to an EX250 rocker arm. I've just done a quick search for an image but couldn't find a picture to post here.
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Old October 29th, 2019, 08:38 AM   #7
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Then remove adjuster screw from the rocker arm and gently grind/polish/sand off just a few thousandths from the underside of the lifter to give you a bit more room to adjust the lifter adjuster screw inward.
Very good advice. Filing just ten thousandths of an inch off will give you several more valve adjustments. If you're not confident about doing this, I'm sure a machine shop would grind off ten or twenty thousandths for you cheaply. But it doesn't need to be precision work, since that surface doesn't actually contact anything.
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Old October 29th, 2019, 08:39 AM   #8
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Very good advice. Taking just ten thousandths of an inch off will give you several more valve adjustements. If you're not confident about doing this, I'm sure a machine shop would grind off ten or twenty thousandths for you cheaply.
I just found this (really old) thread on ninja250.org which contains a warning about how you would have to do the grinding of the rocker:

https://forums.ninja250.org/viewtopic.php?p=33384#33384
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Old October 29th, 2019, 10:59 AM   #9
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Just double checked. It's out of room to back out is all. Makes sense at nearing 50k miles.

What all does a valve job entail?
I would say you are looking at replacing the valve seats and not just regrinding them. Typically a valve job is resurfacing the valves and valve seats.

There was a thread here where an employee of APE was discussing the problem and solution.
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Old October 29th, 2019, 11:24 AM   #10
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Or... just locate and purchase an entire (low-miles) EX250 cylinder head assembly and fit it to the bike.

From a quick search on Ebay it appears there are more than a few complete cylinder head assemblies available (from 2005-2007 year-model bikes).

Yeah, some wrench-turning will be required, but your valve issues would be solved.
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Old October 29th, 2019, 03:04 PM   #11
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I'm not typing in the right keywords into eBay apparently. Can I get a link?
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Old October 29th, 2019, 03:26 PM   #12
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here's a nice looking complete cylinder head assembly off of a 2006:
https://www.ebay.com/itm/2006-88-07-...US!-1#viTabs_0

Although, here's a complete, low-miles 2005 engine for not a whole lot more:
https://www.ebay.com/itm/88-07-2005-...kAAOSwi5VdlN2L

If you live in a bigger-sized city it might be worth the effort to see if there's a motorcycle junkyard/part-out located there. This can get you a cheap whole engine or a complete cylinder head without the cost of shipping.
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Old October 29th, 2019, 04:34 PM   #13
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You have nothing to lose really by grinding a bit off the underside of the rocker to get a few thou more clearance. It cant hurt anything and will give you a bit more time to decide on a long term solution!
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Old October 29th, 2019, 05:19 PM   #14
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You have nothing to lose really by grinding a bit off the underside of the rocker to get a few thou more clearance. It cant hurt anything and will give you a bit more time to decide on a long term solution!
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Old October 29th, 2019, 07:11 PM   #15
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I bought that cylinder head assy and I'll pop it in when I get time. I like the suggestion of grinding the rocker, but my clearance is okay enough for a few months. I'd just do the valve job properly but I'm just so damn busy these days. Semester's almost over, though. Thank goodness. I'll probably play doctor with the valves on my engine when I have the new one buttoned up so the stakes are a bit lower.

Dog bless all of you on this forum. Thank you so much for helping me when my google-fu has failed me and giving a nice spectrum of solutions :-)
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Old October 29th, 2019, 08:55 PM   #16
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Unless you’re racer with needing to get trophies and points to put food on table, do ‘t bother with rebuilding head. There’s plenty of used good-condition heads on market for much, much cheaper than what it costs for proper rebuild. To fix valve-recession issue you need to:

- replace factory valve-seats with copper-beryllium seats for much better heat-transfer from valves

- replace intakes with stainless-steel valves
- replace exhausts with Inconel valves
- get fully-radiused valve-seat cut. Way, way better than 5 or 7-angle valve jobs

Now you’ve done upgrade/repairs to head that makes effort worthwhile to fix factory valve issues.
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Old October 29th, 2019, 09:34 PM   #17
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Unless you’re racer with needing to get trophies and points to put food on table, do ‘t bother with rebuilding head. There’s plenty of used good-condition heads on market for much, much cheaper than what it costs for proper rebuild.
See post immediately above yours. He bought a used head.
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