Bent valves in a Honda CRV engine

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Guys, pls give your inputs/opinions on this one: My Honda CRV 1998 on 53,000 miles with 2.0 liter ("B" engine, I believe) suddenly made loud ticking noises 2 months ago. The engine vibrated a lot and I'm surprised it did not illuminate the check engine light. My favorite auto repair was only a few blocks away, brought the car to him and he pulled the cylinder head. He found one exhaust valve on #2 cylinder to be bent. The timing belt had been changed a year earlier but valve and spark timing were dead on. (We made sure we checked that.) The timing belt was an original Honda part, didn't have any missing teeth and it surely couldn't have jumped a sprocket or two without being obvious on inspection now. The tops of the pistons of course had some carbon on them, so a rotary wire brush was used to get 'em cleaned. I looked very carefully, but there were no marks on the piston tops . After scratching our heads on what could have caused the valve to bend, the valve and its valve guide were changed. After everything was back together, I personally observed that the correct valve lash was adjusted (.006" for intakes and .009" for the exhausts)and I myself used the timing light to make sure spark timing was right as per the manual. Firing her up, everything was sweet. Today, less than 500 miles later after the above scenario, I noticed a slight vibration of the engine at idle, but not at speed. Opening the hood, I heard a perceptible ticking sound that warned me loose valve clearance. There's no power loss or engine miss. I brought her back to the same mechanic and we found an intake valve on #4 cylinder that wasn't closing as we turned the engine crankshaft nut. Looks like another bent valve! I, he, nor the machine shop that did the head has ever seen anything like this. The car's an automatic, never overheated, has never been used for towing, and is babied - hardly ever sees anything higher than 3500 RPM. I use the correct oil and gas, and observe correct and timely maintenance schedules. The only thing I can think of right now is bad valve metallurgy, however far fetched it may be. My plan is to replace all 15 remaining valves and possibly their valve guides as well. Comments?
 
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B20 engines are Honda's "step child" and are known to have issues with burnt valves and other valve issues. Search some CR-V forums and you'll see others have had similar issues. My suggestion is a complete valve job including replacing all the valve seats in the head.
 
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 Originally Posted By: StevieC
My future inlaws have a '99 CRV that is approaching 200K KM (120K miles) and it runs like a clock.
Half-humorously, half-seriously -- as it it "ticks" constantly, or runs very nicely??? I think I know what you mean, but I'm going to have to find you guilty of the offense of "famously ambiguous posting."
 
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Several questions for you: (1) is the replaced timing belt OE ? (2) do you still have the original timing belt with you? (3)is the replacement valve (and guide) OE? This time around, I would perform a thorough check by pulling the cylinder head off and get some clearance readings using a dial gauge. Also: have you/someone touched on the cam/crank shaft (altered it, changed it to something non-factory spec., etc.) and/or deck has been plane-ed (skimmed) down or something? Judging by all your descriptions so far, it sounds like your engine block is running so close in clearance (between valves and piston tops) that you have very very little margin of error (maybe a couple of thou inches?!?), which is unheard of in the world of Honda engines. My take is the timing belt first and then have someone (with serious experiences in HOnda engines) to perform a crank to piston top check (to ensure that the TDC marking does corresponds to the crank marking and then check the cam shaft part and re-do the timing belt. (*Timing belt is of suspicion still) Q.
 
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 Originally Posted By: ekpolk
 Originally Posted By: StevieC
My future inlaws have a '99 CRV that is approaching 200K KM (120K miles) and it runs like a clock.
Half-humorously, half-seriously -- as it it "ticks" constantly, or runs very nicely??? I think I know what you mean, but I'm going to have to find you guilty of the offense of "famously ambiguous posting."
Could have picked better words... It runs like a "fine Swiss watch" and is very quiet when at operating temperature.
 
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 Originally Posted By: Quest
Several questions for you: (1) is the replaced timing belt OE ?
No it's an aftermarket Dayco replaced by me...
 Originally Posted By: Quest
(2) do you still have the original timing belt with you?
No I threw it out, but it was in new like conditon, very flexible, no worn or cracked teeth, couldn't tell it had over 100K KM (60K miles) on it at the time of change.
 Originally Posted By: Quest
(3)is the replacement valve (and guide) OE?
Not sure what you mean here... Didn't replace anything but the belt.
 
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What Chris said or a worn valve spring (my wild a** guess). If the spring was worn out or incorrect (mixed up with another customer, or missing a shim/washer) then the spring rate would be wrong, and at higher (not yet red line) rpm the valve could float and bent when come in contact with the piston.
 
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What was the clearance on that valve before disassembly? I think the valve burned/warped rather than some fluke timing belt issue or foreign object that only effected one one valve.
 
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Assuming that the head hasn't been "skimmed" and not timing issues, then I cannot see any reason why/how the valve would bend, no matter how "weak" the springs are. I still suspect that it's a timing belt issue, valve float may still be of suspect but not high on my list. I would double-check /ref against factory manuals RE: t-belt installation and markings and such. Afterall: Honda doesn't have a clear/concise markings for T-belt installations to begin with, so skipping a notch or 2 is not uncommon. Q.
 

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 Originally Posted By: tom slick
Why would a timing belt issue only affect one valve then disappear?
It wouldn't. It sounds like this engine has some defective valves that are bending perhaps due to heat. I echo the sentiment on replacing them all.
 
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 Originally Posted By: Pablo
Some kind of valve guide seizure.
 Quote:
It sounds like this engine has some defective valves that are bending perhaps due to heat. I echo the sentiment on replacing them all.
That's the only time I've heard of a valve bending outside of valve train mismatch (in the wrong place at the wrong time). Friend lent out his motor for a stock car race (clay track- Grandview). The braided ss water line leaked. It got hot. That was the only damage. A bent valve.
 
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In 99 or there-abouts Honda changed the spec on the valves to a less durable,softer metal. The adjustment should be checked every 30k miles. My son's GF's 99 CRV was throwing a code for a misfire. Had the valves been checked at the 1st instance, it prolly would have been OK. But nothing was done until a noticeable miss happened. I ran a compression check and #4 was low. I replaced the 2 exhaust valves in #4 and so far so good. It is a neat engine, but for geting the manifold on and off.
 
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