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czechalien

Valve leak check

20 posts in this topic

Quick question guys,

I'm using a grinding compound to polish the valves on my 06 YZ450F and the manual calls for pour solvent on to the intake and exhaust to see if there's a leak.

Now solvent is paint thinner, gasoline, mek etc. now do i have to use that, can't I just use water or something like that?

Thanks

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Solvents will flow through an opening that water will not. I would use rubbing alcohol, as it does the same thing and is much less toxic.

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Maybe im wrong but i though you could not resurface the valve faces as they are coated in titanium and if you wear through that the valve is toast?

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They've been titanium since '01, but that doesn't change anything. Under no circumstance should titanium valves be lapped, regardless of what the manual says. Lapping is unnecessary when the seats are refinished correctly.

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so my valves are ruined?
Potentially, but not necessarily. The problem is that the valves absolutely depend on the very thin layer of titanium nitride (or similar) coating applied to their faces, and there isn't a way to see the condition of the coating visually.

What were the valve clearances when you took it apart?

What are they currently? (You'll have to assemble the head to answer this one)

What made you decide that this needed to be done?

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I'm doing a top end and want replace the springs and stem seal too while I'm at it.

I saw the valves and seats have some corrosion on both specially on exhaust , so and because the manual says use lapping compound, I did and everytime I pour liquid in to check if it leaks, it does very very slowly and I don't see any corrosion any more, but it still leaks.

The clearance were fine on all valves.

Also, do i have to have the cylinder honed, before I install new rings?

THX

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What were the valve clearances when you took it apart?

What are they currently? (You'll have to assemble the head to answer this one)

What made you decide that this needed to be done?

intake - .010 all of them

exhaust - .015 both

I didn't assemble it yet, I'm still waiting for parts.

What can I do how will i know it's ok to install the valves?

When I test for leak, it leaks very very slowly, but it does.

THX

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It should be tested for leaks with the valve springs installed. Are they?

The first thing to note is whether you have lost any clearance in the process of lapping. If it's changed more than .02mm, I'd be concerned, but there still is no way to know how much the coating was degraded, if at all.

You really have only two choices. Replace the valves and get the seats refinished and don't worry about it, or install the valves, run the engine for a day, and recheck the clearance. If if hasn't moved, you could be safe, but you'll want to check them frequently for a while to be sure they are holding stable clearance numbers. If they start closing up suddenly, that would mean the coating has worn through, and the valves need replacement.

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I will buy new valves and have a shop to put them in and adjust the clearances with cam installed.

Even the second recommendation would make sence if you have time to check it often and always have it in the back of your mind, that something can go wrong.

This way I will know it's done properly and don't have worry about it for a long time.

Thanks guys for all your help

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Use stainless valves, lap them in, use petrol for leak test and just use your finger to hold the valve in place while you put 10 mills of petrol in.. If they are lapped correctly then you will see no petrol leak through.

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The seats need to be recut or reground regardless of whether stainless or titanium is used.

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I bought stainless steal valves and will have a mechanic cut the seats since the valves are new.

Next time I do top end I will lap them in and that should do it.

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If you are using SS valves, you MUST also use heavier valve springs to compensate. Stainless is nearly twice the weight of Ti, and the valves will float at high RPM unless the appropriate springs are used.

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So if I pulled the head and removed the valves on my 06YZ450 and wanted to get my seats recut by a shop they will not need lapping since they are Ti and I could assemble it at home? Is there any special steps I should be aware of or can I install the new valves, bench shim and install the head? Thanks!

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The shop will need the valves to center the seats on them. They will charge the same amount in most cases whether they assemble them into the head or not, so there's really no point in doing it yourself.

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