Cracked valves, what do I do now?

[Mishakol129]

Hey guys. While the engine was in the car still, I was pulling the intake and exhaust manifolds. (The exhaust manifold was cracked, you can see it here). Then finally the head. When I got it off, I noticed that some of the valves were cracked.

See picture:






This is kind of strange because this head has not even 40,000 miles on it and was a rebuilt one I got more than a year ago.

Anyways, what I want to know is what I can do to fix it, what tools I need (and if there is a guide, great) to fix these broken valves.... Should I replace all of them?


Thank you guys, I hope you like the pics.


Ps, should I get new head bolts?

[cb7attack66]

wow a machine shop will charge up to 300 for a job on it,but,by the looks of that i would question the cylinder head,not just the valves,resurface...i would try to find a low mileage head ,or yes replace all those valves

[danf20bcb7]

realistically replace all of them, when you change your front brake pads you dont just pop on pad on one side on right?. yeah some may still be good but your already there why not? and you might wanna investigate as to why it happend, whether running to lean or using crappy gas or other things. heres a lil help Replacing a broken valve, for example, won't fix the problem if he underlying cause is misalignment between the valve guide and seat. Unless the misalignment is corrected, the new valve will fail too as flexing causes it to fatigue and break.

Replacing a burned valve won't fix a compression problem if the underlying cause is a hot spot in the cylinder head. If the hot spot is not eliminated, the new valve will run hot and burn too.

Replacing a worn guide by installing a new one, a liner or a valve with an oversize stem won't fix an oil consumption problem if guide wear is the result of excessive side scrubbing of the valve stem due to rocker arm misalignment. Unless the stem height is corrected, the guide repair won't last.

That is why analyzing what caused a problem before you try to fix it is so important. Broken or burned valves as well as worn or loose guides, cracked or loose seats and similar valvetrain damage is often the end result of a chain reaction of events. One problem leads to another and eventually a valve failure. So replacing parts without understanding what made them fail is no fix at all.

To avoid valve related problems down the road, do the following:

1. Analyze the amount of wear as well as wear patterns in the head and valvetrain components when the head is disassembled. A careful inspection should reveal any abnormal conditions or wear patterns that would indicate additional problems.

2. Inspect each and every component in the valvetrain and head so all worn or damaged parts can be identified and replaced or reconditioned.

3. Keep a close watch over production quality so the parts that are being reconditioned are done so correctly.

4. Pay attention to specs, critical dimensions and rocker arm geometry to assure proper reassembly.



ENGINE VALVE DEFECTS

Many things can make a valve fail. Defective valves are one thing nobody talks much about, but it ranks as the number two cause of valve failures. Thermal and mechanical overstress is number one.

One study that was conducted by a leading valve manufacturer found that as many as 1 out of every 5 (20.7%) valve failures resulted from defects in the valves themselves!

This particular study was published over a decade ago, and even though the same basic alloys and manufacturing processes that were used then are still used today quality control has come a long ways. CNC (Computer Controlled Numeric) production machinery and statistical process control have done much to eliminate human error in the manufacturing process. But like any other mass produced component, defects occasionally slip through. So do not rule out bad valves as a possible cause of a premature valve failure.

Defects include the presence of metallurgical impurities and inclusions in the metal that weaken the valve, forging defects that leave microscopic cracks, pores or separations in the metal that lead to breakage, faulty welds between stems and heads in two-piece valves that can allow the head to separate, faulty welds in hollow stem valves that can lead to breakage, improper heat treatments that fail to fully harden or anneal a valve resulting in rapid wear, machining errors that produce the wrong dimensions or surface finish which can cause all kinds of problems if not detected prior to installation, and poor adhesion of chrome plating that allows the protective plating to flake off the stem.

The best way to make sure the new valves you are using are free from defects, therefore, is to (1) inspect the valves to make sure tolerances are within specs (stem diameter, stem taper, overall length, etc.) and there are no obvious defects (nicks, pits, hairline cracks, etc.), and (2) source your valves from a reliable supplier. One valve looks pretty much like another, so you cannot judge quality by appearances alone. A cheap price may be attractive, but if the valve does not hold up where is the savings? So don't take chances on poor quality valves from questionable suppliers that might end up costing you far more than what you saved on the valves themselves. Buy from a reputable supplier who stands behind their product.

WHY ENGINE VALVES FAIL

Any valve will eventually wear out if driven enough miles. But many valves call it quits long before they should because of burning or breakage.

Let's talk about burning first. Exhaust valves are the ones most likely to burn because they run hotter than the intakes. The intake valves are cooled by the incoming air and fuel, and consequently operate at about 800 degrees F. Exhaust valves, on the other hand, receive little such cooling and are blasted by the hot combustion gases as they exit through the exhaust port. Exhaust valves run at 1200 to 1350 degrees F. on average, which makes them much more vulnerable to erosion and burning than intakes. The higher operating temperature requires a tougher alloy, so exhaust valves are usually made of stainless steel or have stainless steel heads (typically 21-2N or 21-4N alloy with a high chromium and nickel content). For heavy-duty gasoline and diesel applications where heat is even more of a problem, a tough Stellite facing (cobalt alloy) may be needed on the exhaust valve face to control wear.

The intake and exhaust valves rely on physical contact with the valve seat and guide for cooling. About 75% of the combustion heat that is conducted away from the valve passes through the seat, so good seat contact is essential to prevent burning. The remaining 25% of the heat is dissipated up through the valve stem and out through the guides. Sodium filled hollow valve stems in heavy-duty applications are sometimes used to draw even more heat up through the stems to aid cooling. If the valve does not receive adequate cooling, it can overheat, burn and fail
Anything that interferes with valve cooling or creates extra heat in the valve or head can lead to premature valve failure. A buildup of deposits on the valve face and seat can have an insulating effect that slows cooling and makes the valve run hot. So too can poor contact between the valve and seat if the seat is too narrow, nonconcentric or off-square. If deposits build up in one spot or flake off in another, it can allow leaks that create hot spots on the valve and result in "channeling" (grooves eroded or burned into the valve).

Weak springs or insufficient valve lash can also prevent good valve-to-seat contact and allow excessive heat to build up in the valves. A loose seat or poorly fitting guide can also hinder heat transfer to the head and contribute to burning.

Not paying attention to the installed valve height when doing a valve job can lead to burning. When valves and seats are ground or cut, the valves sit deeper in the head than before. This causes the stems to stick up higher which changes the rocker arm geometry and may lead to a loss of valvelash when the engine gets hot. Two engines where this particular problem has been turning up are the Ford 2300 OHC engine and the rear-wheel drive version of the Mitsubishi 2.6L (which has hydraulic lash adjusters). If the proper geometry cannot be restored by grinding the tips of the valve stems (no more than about .010 maximum or you run the risk of grinding through the case hardened layer), the seats should be replaced to correct installed height (an expensive fix but cheaper than a comeback). Another option is to install valves with slightly oversized heads (.030 in.) that ride higher on the seat to compensate for seat machining.

Valve recession can cause the same kind of problem. As the seats wear away and the valves recede into the head, valvelash is lost. Eventually there is little or no lash left and the valve makes poor contact with the seat, overheats and burns. Valve recession tends to be more of a problem on older engines that lack hard valve seats and are used in heavy-duty truck, marine, agricultural or industrial applications. The cure here is to install hard seats. Stellite or hard faced valves may also be necessary if the valves show evidence of erosion.

Cooling problems in the engine itself can lead to valve sticking and burning if the operating temperature gets too high. Low coolant, a defective thermostat, a weak water pump, a radiator obstruction, a defective cooling fan or fan switch, etc. can all make an engine run hot. This, in turn, makes the valve stems swell which may cause them to gall or stick in their guides if there is not enough clearance. If the valve sticks open, it can burn or be destroyed if it smacks the piston.

Blockages caused by casting flash inside the head or a head gasket that does not have the correct coolant holes can allow hot spots to form that can cause valve and guide problems. So too can a buildup of scale inside the head the interferes with good heat transfer.

Valves can also run hot because of elevated combustion temperatures. Factors such as retarded ignition timing, lean fuel mixtures (often due to vacuum leaks), detonation (from too much compression or low octane fuel) or preignition (from hot spots caused by deposits in the combustion chamber or too hot a spark plug) can all play a role here. Likewise, exhaust restrictions such as a clogged catalytic converter or crushed pipe can make the valves run hot.

Anything that interferes with valve cooling or creates extra heat in the valve or head can lead to premature valve failure. A buildup of deposits on the valve face and seat can have an insulating effect that slows cooling and makes the valve run hot. So too can poor contact between the valve and seat if the seat is too narrow, nonconcentric or off-square. If deposits build up in one spot or flake off in another, it can allow leaks that create hot spots on the valve and result in "channeling" (grooves eroded or burned into the valve). good luck man

[GhostAccord]

Not to be the content police here however, that text that you copied and pasted is from AA1Car.com / Engine Valve Failures: Causes & Cures and it is Copyright material.

If you are going to copy and paste some copy written tech info from another website. You have to give credit where credit is due.

http://www.aa1car.com/library/ar1192.htm

Very good info though, good find for sure!

[Mishakol129]

realistically replace all of them, when you change your front brake pads you dont just pop on pad on one side on right?. yeah some may still be good but your already there why not? and you might wanna investigate as to why it happend, whether running to lean or using crappy gas or other things.

That sounds like a plan but I don't know how to do a valve job and what tools are required of it. Also, it seems that I may have a slightly bent spring.


I think the cause of the bad valves is simply bad quality. I got that one as a remanufactured from Japanengine.com and they sell them for only 385$. So what i'll do now is put high quality valves in it instead of crappy quality... b/c I am pretty sure I have sufficient cooling in my car.


Thanks for the resouce. 1AAuto is a nice company.

[Tabor]

I think the cause of the bad valves is simply bad quality. I got that one as a remanufactured from Japanengine.com and they sell them for only 385$. So what i'll do now is put high quality valves in it instead of crappy quality... b/c I am pretty sure I have sufficient cooling in my car.

The cheapest thing to do now is probably to pull a junkyard head and take it to a machine shop. They will replace any valves that need it or just re-grind them if they don't.

[Mishakol129]

wow a machine shop will charge up to 300 for a job on it,but,by the looks of that i would question the cylinder head,not just the valves,resurface...i would try to find a low mileage head ,or yes replace all those valves

Replace all of them? That's rather a waste if only it was these two valves that were defective. But, maybe it should be done, I dunno. I should at least replace the two that broke and probably also replace their stem seals, but I don't know about the springs, if I should get those new as well.


Maybe i'll just take it to a machine shop to get their opinion about it.

[Mishakol129]

The cheapest thing to do now is probably to pull a junkyard head and take it to a machine shop. They will replace any valves that need it or just re-grind them if they don't.

Junkyard head, what's wrong with the head I have now? Its a remanufactured one, not much is wrong with it except those two valves.

But what is your opinion / knowledge on this, why do you think I need an entire new head?

[Tabor]

But what is your opinion / knowledge on this, why do you think I need an entire new head?

Because I wouldn't trust any of the valves in that head. It would most likely be cheaper to grab a head from some you-pull-it type yard and take it to a machine shop than taking *that* head to a machine shop and asking them to replace all 16 valves. That is just my opinion (having taken heads to machine shops before).

EDIT:

Maybe i'll just take it to a machine shop to get their opinion about it.

This is a good idea, worth the time at least.

[Mishakol129]

Because I wouldn't trust any of the valves in that head. It would most likely be cheaper to grab a head from some you-pull-it type yard and take it to a machine shop than taking *that* head to a machine shop and asking them to replace all 16 valves. That is just my opinion (having taken heads to machine shops before).

EDIT:



This is a good idea, worth the time at least.

I wouldn't have a shop do the work, since i'm rebuilding the lower half I may as well do the upper half as well. It seems easy with the right tools. Gonna take the pistons and block to a machine shop to inspect them, and now I'm gonna take the head with me to get his advice on it.

[deevergote]

I would take it to a machine shop and see what the machinist suggests. It would be pointless to replace only the damaged valves if the currently undamaged ones could end up the same way very soon. Replacing all the valves might end up being cheaper in the long run.

My question is, WHY did this happen? Were the valves cheap quality parts made with inferior metal? Or was something happening inside your engine that did damage? If the engine was running incorrectly, and detonation is what damaged your valves, then you'll need to correct that before you drive that car again.

[oyajicool]

Color of cracked valve suggests over heating.
Tear down and close inspection should reveal what went wrong there.

[toycar]

Color of cracked valve suggests over heating.
Tear down and close inspection should reveal what went wrong there.

^^^^


What he said


Tear down and inspect. I would probably just source a better condition head(personally) since a complete motor from my JY is $100 bux.

I would imagine if the head is not ruined at a minimum it'll require a hot tank bath, milled, new seals and a number of new valves.


I would just start over. Maybe have the machine shop check the head and see if its good, but from there I woudl replace everything and be happy about it.

New valves, guides, seals, springs, retainers, the whole nine yards.

why? because even if its not all ruined, all of the parts are old as fuck and you may as well fix it right the first time.


Do you want to do this again in 10,000 miles?

[Mishakol129]

^^^^


What he said


Tear down and inspect. I would probably just source a better condition head(personally) since a complete motor from my JY is $100 bux.

I would imagine if the head is not ruined at a minimum it'll require a hot tank bath, milled, new seals and a number of new valves.


I would just start over. Maybe have the machine shop check the head and see if its good, but from there I woudl replace everything and be happy about it.

New valves, guides, seals, springs, retainers, the whole nine yards.

why? because even if its not all ruined, all of the parts are old as fuck and you may as well fix it right the first time.


Do you want to do this again in 10,000 miles?

All this talk is making me just want to get a whole new rebuilt one. I can't do all that work, i've just got too much work to do already overhauling the engine, its gonna take me forever. Ebay has this seller who specializes in heads and has been in business "since 1968". They say they have "Viton" valves installed on them. They look like the real deal and have top seller rating.

Check them out: http://www.ebay.com/itm/HONDA-ACCORD...-/160352707543

Only 350$, same price I paid for the one I have now. I got that one from JapanEngine.com. They seem much more professional and legitimate than Japanengine.

But on another note, could it be that it was not my head that caused the break but something else like an overheat? Never once did my car overheat though (my thermostat could have malfunctioned though). Maybe the ignition or something similar caused this. I was knocking cylinders really hard for like 4 months. I had extremely low compression in 2 of the cylinders when I did my compression test. Weird thing was is that I lost compression only after I put on the new cylinder head. (I had put the newly rebuild head on my old block which had like 290,000 miles on it, and some people were saying that doing that causes too much compression and blows out the bottom end of the motor). And indeed my motor did blow out after that.

[oyajicool]

Your broken head was installed 40000 miles ago on a block that had 290000 miles already. That makes your block have 330000 miles now.

I wouldn't just replace the head. I would take out the block for rebuild as well at this time if I were you.