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I have an '07 V6 with 133k, auto that knocks on cold start.

Timing belt done at service interval. Knocking can best be heard from the intake manifold.

Engine only knocks on cold start, used to only be when it was very cold out (20-30 degrees F) but now does it much more often.

Knocking always goes away once engine is fully warmed up, and always runs fantastic.

Valves adjusted at dealer 2 weeks ago. Tapping has gone away for the most part, but knocking is still present and loud (was making a few different engine noises). Dealer gave up on trying to diagnose, told me to take the car for now and bring back if needed..

Car still has an extended warranty from Carmax.

The knocking will only start about 3-5 seconds after start up, not before..

Any input on the severity of the knocking and what your experience is? Is the only solution to replace the rings? It really bugs me but does not seem to be causing issues yet. Would really like to fix it under warranty if I can show that there is a fault.

View My Video
View My Video
 

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If it's really knocking, i.e., pre-ignition, have you tried higher grade gas?

If it's piston slap, that's a different problem. And probably not anything to worry about.

Can you tell the difference?
 

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Discussion Starter · #4 ·
If it's really knocking, i.e., pre-ignition, have you tried higher grade gas?

If it's piston slap, that's a different problem. And probably not anything to worry about.

Can you tell the difference?
Can you hear it in the video clip? I'm not sure which it is...have not tried higher grade gas yet.

what weight oil you runnin', bro?
5w20 honda full synthetic.
 

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Discussion Starter · #5 ·
Thanks for the replies, I'm planning to run the tank pretty empty today and fill it with premium to see if the sound changes at all.


Any other ideas?
 

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It has nothing to do with gas type. That's just a noisy valve train. I have the same thing on cold start at 220000 miles, almost double your mileage, nothing wrong with that. Turn up the music, LOUD. If you are anal about it, check the valve clearance again.
 

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Discussion Starter · #7 ·
It has nothing to do with gas type. That's just a noisy valve train. I have the same thing on cold start at 220000 miles, almost double your mileage, nothing wrong with that. Turn up the music, LOUD. If you are anal about it, check the valve clearance again.
The valves were adjusted but did not seem to help the noise from the video. It did help reduce some tapping but that's about it.

It seems to me like my pistons are slapping around for some reason. Worn rings? Wrist pins?

I've seen a lot of questions about this noise with other owners but haven't found a conclusive answer. The bottom line usually ends up being "don't worry about it", "it's normal for these engines", but it is annoying to me and doesn't sound healthy for the engine. Also seems to be getting worse, in that it happens during any cold start condition, not just extreme cold conditions as it had in the past. It's made noise for about two winters now.
 

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I'm wondering if they changed the hydraulic tensioner when the timing belt was changed?
 

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Mine knocks like that only when it's very cold. If the valves are slapping the top of the pistons, then you have a whole other set of problems. If the valves are slapping, then the timing belt might might have missed a tooth during the install on one of the cam sprockets, and the timing is off. Chance is, the valves are bent already and the problem is much more serious, not just slapping sounds. But that knock would be very loud and does not go away even after the engine is warm. You can check this by turning the crank pulley manually clockwise 6 times with a wrench + 19mm socket and match up the marks on the lower cover and through the inspection holes on the top covers covering the front and rear cam sprockets. So check this first before worrying about anything. If nothing is amiss timing wise, then the valve adjustment job was done wrong or not done at all.

I have never done a valve adjustment on my V6 engine by the way, 220k miles.
 

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The interesting thing is you say the noise starts 3-5 seconds after the engine starts. I suspect the belt tensioner OR possibly the A/C compressor and or clutch. I would wait for a cold start and be watching specifically at the tensioner and see if it is bouncing around and making the noise or if the A/C compressor comes on at that time.
 

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Discussion Starter · #12 ·
Mine knocks like that only when it's very cold. If the valves are slapping the top of the pistons, then you have a whole other set of problems. If the valves are slapping, then the timing belt might might have missed a tooth during the install on one of the cam sprockets, and the timing is off. Chance is, the valves are bent already and the problem is much more serious, not just slapping sounds. But that knock would be very loud and does not go away even after the engine is warm. You can check this by turning the crank pulley manually clockwise 6 times with a wrench + 19mm socket and match up the marks on the lower cover and through the inspection holes on the top covers covering the front and rear cam sprockets. So check this first before worrying about anything. If nothing is amiss timing wise, then the valve adjustment job was done wrong or not done at all.

I have never done a valve adjustment on my V6 engine by the way, 220k miles.
Timing belt was done correctly and is not off. Valves are not hitting the pistons because the engine runs smooth as can be once warm. Even when cold, the engine runs great, it is just very noisy..

No loss of power on warm motor and I baby it when cold and don't push it at all.

It is possible the valve adjustment was done wrong, but I am thinking this is a very slim chance. After the valves were adjusted, the tapping quieted down, but the knocking (or slapping) was still present as before the work was done.


The interesting thing is you say the noise starts 3-5 seconds after the engine starts. I suspect the belt tensioner OR possibly the A/C compressor and or clutch. I would wait for a cold start and be watching specifically at the tensioner and see if it is bouncing around and making the noise or if the A/C compressor comes on at that time.
This is the part that I don't understand...to me, it seems like I'm getting oil starvation. I had the dealer check on this possibility while doing the valve adjustment and they did not see anything obvious. No discoloration or other signs.

A/C is always off when I shut the car off, so it is not the compressor kicking on.

I will check on the tensioner bouncing around, but the sound would REALLY have to be traveling through the block if this was the problem. I can hear the sound equally from the front and rear of the block, coming from inside and/or under the intake manifold..
 

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Discussion Starter · #13 ·
Ok so a little more information...

It was warmer today, and the noise started closer to 20-25 seconds after a cold start now.
 

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It sounds like normal noisy valves to me- not piston slap.

All I can think of is wrong weight of oil or bad oil filter not flowing like it should. Did you change your spark plugs at 110K miles? Check for proper plugs AND tightness?
 

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Car still has an extended warranty from Carmax.

The knocking will only start about 3-5 seconds after start up, not before..

Any input on the severity of the knocking and what your experience is? Is the only solution to replace the rings? It really bugs me but does not seem to be causing issues yet. Would really like to fix it under warranty if I can show that there is a fault.
Which dealer has been looking at it, CarMax? You'll likely have to take it elsewhere if you want it diagnosed as an issue. Was this sound present when you first test drove? I wouldn't call that normal even with 220K. It might be weak oil pressure that builds slowly, which would explain why it eventually goes away. I would put a mechanical oil pressure gauge on it and check the pressure. How long does the oil light stay on when you cold start? Maybe you could film that and another member with V6 can tell you how long it takes theirs to go off? Either way, check the pressure.

I would also run some motor flush through it, such as Motor Medic, just in case something is clogging the oil pickup in the sump. If you do this, remember to change the oil filter, even if new.

That knocking is not a tensioner issue
Agreed.
 

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I suggest checking the timing first. This is easy to do yourself. There were reports on acurazine.net for those who installed the timing belt that missed a tooth, getting a knock immediately after. It's very easy to miss a tooth on the rear cam sprocket on this engine if the old belt wasn't marked and marks transferred to the new belt. Car still runs, but noticeably noisy. I'd like to take back my previous statements. I started up the car this morning at 32 degree and it does not sound loud like OP's engine. It's noisier than when it's warm, but no loud knocking sound.
 

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I suggest checking the timing first. This is easy to do yourself. There were reports on acurazine.net for those who installed the timing belt that missed a tooth, getting a knock immediately after.
But how would a timing knock go away when warm?
 

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Unless oil pressure is going to 0 I do not see how the crankshaft bearings or rod bearings could make a noise after running for 3 to 30 seconds. The timing belt is either lined up or not. It does not change with temperature.
 

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I think you might have a loose timing belt, and the adjuster is rattling against the tensioner. I had that same sound at first cold start of the day. The rattle would fade away as the engine warmed up. I did the timing belt, water pump, tensioner, idler pulley, adjuster pulley, and the noise was gone. I'll try to post the video.

OK it doesn't sound exactly the same, mine sounds more rapid, but here it is. Click the pic.

 
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