Why to have your top end looked at!

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This is my second bus and my second top-end tune-up. On both buses, I’ve had to replace three roller rockers due to what appears to be surface failure. On this bus, one of the cam lobes also started to fail. In my opinion, the top end should be inspected somewhere between 100,000 to 120,000 miles. It would have cost a lot less if I hadn’t needed to replace the cam.

Ray Davis was kind enough to post these pictures.

[MyPrevost]

Were there any symptoms that made you check for something?

[MyPrevost]

Kevin,

I encountered something similar with a plane engine once.

I used to do oil analysis every oil change, which I performed at 35 hours. They always came back normal, and there were no trends indicating a rise in any of the elements.

The galling on the rollers can happen almost instantly and is usually attributed to a lack of lubrication. I’m not sure anyone could have detected any signs that it was about to occur until it happened.

That was certainly the case with the plane engine.

[MyPrevost]

Kevin, thanks for the post and for sharing the harsh reality—sorry to hear your cam got wiped out.

I believe the Detroit service manual states that the first valve adjustment should be done at 60K miles, and mine is about at that mileage, so the time has come. It looks like a pain to do in an XL. Most diesel mechanics I’ve talked to say the valve train in a Series 60 should be maintained every 100K.

I’ve even seen cams go flat in new engines still on a dyno; it can happen quickly!

[MyPrevost]

This is just my opinion, but having 2 for 2 means 100% failure—definitely not good odds. I think there’s an issue with these rollers, and if you don’t catch it soon enough, the pictures show what can happen next.

I did buy all my parts from United Engines, and they’ve been great!

[MyPrevost]

Kevin, the outside and bottom exterior of your engine looked slicker & cleaner than those parts. Sorry to see and hear of your problem-

What where the symptoms that prompted you to tear into it?.

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We just had the valves done at around 64,000 miles by Pacific Power. The tech said everything looked good, but he found a loose Jake brake connection and fixed that.

He also recommended checking the valves every 50K to 60K, which is a bit of a hassle since you have to take apart the closet and then put it back together.

Has anyone ever modified the closet step on an XLVII to allow for easier removal of the valve cover without having to disassemble the closet?

[MyPrevost]

There was no specific reason other than preventive maintenance to check and adjust the valves. I asked my mechanic what symptoms might indicate cam wear, and he said to look for rough idle, power loss, and lower fuel mileage. He also mentioned that with the computer, it can be tough to notice these issues at idle because it compensates for a failing cylinder by increasing the idle speed to maintain the preset level.

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Kevin, correct me if I’m wrong—feel free to use caps if I’m misreading this, as a lot of guys might rush to DD based on your post.

Your problem wasn’t caused by valves being out of adjustment; it was just noticed after having the valves adjusted.

Furthermore, an engine can have its valves adjusted, and the problem could still show up before the next oil change. This isn’t an adjustment issue but rather a lubrication issue.

Correct?????

[MyPrevost]

Jon,

I firmly believe this issue is not related to adjustments or lubrication. My inspection of the valves was purely a preventive measure, as it’s crucial to assess the internal components when possible. I’m not suggesting a complete teardown just for the sake of it.

From my observations, it seems that Detroit Diesel might have a recurring issue in this area of the engine—this is now two engines with similar problems. I’m uncertain how long the motor could operate before cam wear starts to affect its performance. I feel reassured knowing the inspection was done, and I plan to repeat this at 220,000 miles, assuming the economy remains favorable and I still have the bus!

 

[MyPrevost]

Kevin:

Did you get any kind of a response from United that they agree or disagree with your opinion on a Detroit issue?

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The issue you’re experiencing isn’t simply due to valve adjustments; it’s more likely related to lubrication problems that can arise independently. While valves can be adjusted and may highlight existing issues, a loss of lubrication or faulty rollers—potentially due to improper hardening—are more critical factors.

Additionally, the DDEC system likely monitors oil pressure and can log instances of low pressure over time, which could help pinpoint the problem before it leads to serious damage.

[MyPrevost]

The issue you’re facing wasn’t caused by valve adjustments; it merely became apparent after they were made. It’s important to note that an engine can have its valves adjusted and still develop problems before the next oil change—indicating a lubrication issue rather than an adjustment one.

Jon is right: this points to a loss of lubrication or faulty rollers due to improper heat treatment. It raises the question of whether the DDEC system tracks oil pressure drops over time.

[MyPrevost]

I think Ken is likely correct in identifying a hardening issue, but I maintain that lubrication plays a significant role. If this were a widespread problem, the trucking industry would certainly be addressing it, as their trucks operate for long periods, keeping a consistent film of lubrication between the rollers and the lobes.

In contrast, motorhome owners often let their vehicles sit for extended periods. When starting up after such inactivity, any protective lubrication has likely drained away. Once metal begins to gall, there’s no remedy—no amount of lubrication can reverse the damage, and the deterioration can actually accelerate.

If the components are properly hardened, their resistance to this kind of damage may help mitigate issues from dry startups. Kudos to Ken for highlighting that point.

 

[MyPrevost]

I agree with both Jon and Ken, but I lean towards Ken’s perspective that the hard face on the roller may not be ideal. Jon’s point about oil draining off after long periods of inactivity is crucial, as it exacerbates any issues related to the roller’s surface hardening.

Just to add, when I was working on my ’99, I found 110 roller rockers for that model engine within just 30 miles of two Detroit shops. This suggests there may be a broader issue with the part, not just a concern for RV owners.

 

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