Leppi

Short Story:
The front balance shaft of my 95 Odyssey broke and punched through my timing belt cover. The mechanic to whom I had been bringing it is unwilling to take the engine apart to find out where and how it broke.

Do you guys have any theories about what could have caused this?


Long Story:
History
About 4 months ago I bought a 1995 Honda Odyssey. From what I understand it is essentially a '95 Accord under the hood. I have repair and maintenance records going back to 1997 and about 16,000 mi. It got all of the recommended servicing and was never late on an oil change.

It has belonged to my family or friends of the family since it was bought in 97. I am sure the records are comprehensive and exhaustive.

This is my first car, and I don't know that much about them. Most of the technical information is copied off of repair receipts, based on what the various mechanics told me, or stuff that I have worked out retroactively.

When I bought it, I had it inspected by the mechanics who had worked on it before. They found an oil leak under the timing cover and replaced:

-Valve cover gasket
-Timing belt
-Oil pump
-Oil pan

This was 4 months / 1000 Miles before the balance shaft broke.

It ran fine after that, I don't have enough experience to tell if it was louder or rougher than it should have been at that point. 3 weeks ago I noticed it was leaking oil and brought it in to the same mechanic.

The oil cooler had broken, and was replaced. The check oil light never came on, which is worrying considering it was quite obviously low on oil.


Symptoms
After that I started paying much more attention to how the engine sounded. I noticed that it tended to rev higher than it should have before shifting and that the shifts were a little clunky. The previous owner confirmed this. I was not too worried as the transmission did have 140,000 miles on it. I did not expect it to last much more than a year or two at that point.

I also noticed a reverberating low frequency buzz coming from the engine. It started out fairly quiet and always got better as the engine heated up. Up until the balance shaft went it was getting progressively louder. Sometimes it would be randomly a little better or worse, but the trend was towards worse.

This was a very low frequency, somewhere between 5-20 Hz. I suspected one of the belts was slipping. If a belt somewhere in the engine had gotten oil on it when the cooler went, it could have slipped intermittently and caused that sound.

In hindsight, if the balance shaft had gotten out of tune with the camshaft, that could have caused a beat frequency to develop.

This leads me to the second, and possibly related issue that I noticed. In addition to the high revs before shifting, the engine's power output seemed to drop as its RPMs increased, and would improve markedly when it up shifted.

I do not know much about transmissions, but I think an increase in power after an upshift is not what is supposed to happen.

This led me to suspect that something was leeching power from the engine proportionally to its RPMs. At the time I thought that a belt losing friction with a pully and sliding across it rather than rolling would cause both the sound and the power loss. This would also explain the high revs before shifting as the transmission controller thingy (Transmissions are complicated!) was registering the resistance as external load and delaying the shift.

In hindsight again, both of these could be explained by the balance shaft running on worn bearings, or having something else obstructing it.

That is all the background information that I can think of at the moment. Which brings us to the description of the breakdown and my theories as to what could have caused it.

The Breakdown
On my last two trips on Friday morning and afternoon, the engine had actually sounded better than usual. Because of this I figured I could probably drive it for a few more weeks before I really needed to take it in. I had had a look at the drive belts that were exposed and they were in good condition. At the time I thought that some oil had gotten on the belts and had been causing them to slip. I figured that if the oil was rubbed or burned off on its own, the engine would quiet down on its own and I would not be out a couple of hundred at the mechanics.

On Monday morning it ran very well. It felt better then it had in several weeks. Then, on Monday evening, when I started it I noticed a clattering sound coming from the engine. I figured I could get it home, and take it to the mechanic in the morning. The clatter got loud as I drove, then became a very loud high pitched scream as I accelerated from a stop. I was worried that I would not make it through the intersection. I did, and was able to pull over about 50m after it started screaming.

At that point I turned off the engine and popped the hood to have a look. I saw what I know now is the head of the balance shaft poking through the plastic timing belt cover (I had no idea what was what at the time). I have a picture of it and I will try to find a way to upload it.

I had it towed to the mechanic who had last worked on it to see what was wrong and if anything was covered under their warranty on parts and labor. They had a look at it and told me that the front balance shaft had broken. They said it was probably a freak manufacturing defect.

Theories
I did not like the act of god explanation. I asked some other mechanics and the local Honda dealer if they knew anything about balance shafts breaking. None of them had ever heard of the balance shaft breaking without some sort of external cause. I also trawled the Internet for everything that I could find, this forum was one of the most informative that I found, but I could not turn up anything that directly related to what I experienced.

I found out about the balance shaft seal on that engine model being subject to a recall, so I went through the records and found that it had been replaced in 2001 at 60,000 mi.

The mechanic would charge me around $1000 to take apart the engine to see where and how the balance shaft broke.

Questions
My questions to you guys are:

1) What could have caused a balance shaft to break?
2) Could a screwed up timing belt replacement have put stress on the balance shaft causing it to break?

If you have gotten all the way to here in the post, I salute you good sir!

MAD_MIKE

Leppi First I would like to thank you for such a well written post.

Seriously can a Mod take a screen shot of this post with the '1' under Leppi screen name and title it 'THIS IS HOW YOU WRITE A POST' and cram it in the FAQ.

Leppi Until you post a picture of the balance shaft, and the front of the engine...


It can be hard to speculate as to why it failed.

If you look at How-To: Replace Timing Belt, Timing Balancer Belt and Water Pump on a F22B1 there are several large pictures showing the front of the engine and the timing belts. If you could pin point which shaft broke that would be helpful.

As for the hard shifting of the automatic, click on the link in my sig H4A and scroll down to the NM/NC section. There are two magnetic sensors that can become covered in ferrous material and will need to be cleaned, these are shaft speeds sensors and tell the TCU when to shift, hard shifting will occur if they are covered in material.

Leppi

I have a picture, but I don't know how to upload it. All I see is the link to picture button. Do I have to host the picture somewhere and link to it?

I don't know where the balance shaft broke, the break point is probably somewhere in the block. However, the mechanic is unwilling to disassemble the engine without being paid, and I do not have the tools or experience to do it myself.

MAD_MIKE

Where you write your post is the 'Reply to Thread' box. Directly below this is the 'Additional Options' box, in it will be a 'Manage Attachments' button. Click on it. You can upload pictures from your computer or a url. Keep in mind that there are size limitations, although H-T is very generous with sizes. The size attachment key is on the 'manage attachments' screen.

But the attachments box does not show up if you only use the 'Quick Reply' box at the bottom of the thread. You need to click on the 'Go Advanced' button.
There are two balance shafts.
Looking at the above pic I posted the large sprocket in the center is the crank, the smaller belt is for the balance shafts. The two pulleys left and right of the crank are each balance shafts. The left one is the front balance shaft. The right domed sprocket is part of a gear drive system, used to offset the sprocket, allowing clearance of the tensioner pulley and water pump. If that failed or broke it may be an easy fix if it did not damage the oil pump housing or the gear on the end of the rear balance shaft.
Part #44 in the diagram.
http://www.hondaautomotiveparts.com/...3sx001_e13.png

But if there is more extensive damage to the actual balance shafts, bearings and block, it may be cheaper to just replace the engine.

Leppi

It was the front balance shaft. I cannot upload the picture because I am still a trial user.

Sadly it will never get fixed and we will never know what went wrong. The Odyssey is getting scrapped on Tuesday.

Thanks for the insights, if my next car is a Honda, I will be spending a lot more time on this forum.

Hidenplanvew

you can give it to me.. free of charge

MAD_MIKE

If you contact a mod they should be able to help you get over that hurdle.
That's unfortunate. 90-97 Hondas are probably some of the best vehicles on the road. I'm surprised the balance shaft failed. At the moment I cannot recall how the front balance shaft is retained into the block. Is it still in one piece?

As for scrapping, these year Hondas hold their value fairly well. Even a dead engined one can still be sold for a decent price.