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Old 08-23-2021, 06:33 AM   #1
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My 3126B Valve Adjustment

Yesterday I did the valve adjustment on my 3126B as it just went over 100k miles on our last trip. I had a feeling I would find them significant out of spec, and I was mostly right. Intake spec is 0.015" +/- 0.003" and they were all 0.005" or less. While none of them were at 0 lash, there were several that were very close, and it makes me wonder if they were running an actual 0 lash when hot.

The exhausts were closer. Spec there is 0.025" +/- 0.003". Three were at the tight end of that (0.022") so I adjusted those anyway. One at 0.030", I think one was tight out of spec and then one that didn't need any adjustment at all. So now everything is adjusted to +/- 0.001" of spec.

Reading up it seems Cat prescribes an initial valve lash check at 30k miles and then again at 100k. I'm betting the 30k mile one was never done by the original (or maybe 2nd) owner. It also seems like there are two groups of people who do the valve adjustments - those who they were fine and noticed no difference and those who seem to have noticed about a 1 MPG improvement afterwards. I don't track fuel economy but I do pay attention to boost and temperatures (including EGTs) so I'll be curious to note if there's any change there once I drive it. I bet it will sound happier at idle.

Mostly this is a reminder that if you don't know the status of your last valve lash check, it's worth getting done. The process itself is really quite simple to do. I wish I'd done it sooner on this engine. If you are replacing coolant hoses, that's an ideal time as on my coach the coolant hoses go over the #1 cylinder and make access up there harder.

Funny enough, when I pulled the valve cover the first thing I thought was "This valvetrain looks just like the valvetrain on my 1947 Cat D4 bulldozer". I guess in 50 years they didn't change much on the valvetrain and rocker arm design. If it ain't broke, don't fix it.
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Old 08-23-2021, 06:54 AM   #2
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good info - thanks. Iím running a Cummins but itís all generally applicable and a good reminder. If you took any pics.....
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Old 08-23-2021, 07:32 AM   #3
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good info - thanks. Iím running a Cummins but itís all generally applicable and a good reminder. If you took any pics.....
I don't know the valve adjustment requirements (if any) for the Cummins engines since I haven't had to do it, but basically anything that has adjustable valve lash it's a good idea to check since it is often off.

I might take a couple of pictures before throwing the valve cover back on. I'm going to put together a video at some point in the next week or two, right now I'm focusing on getting the bus ready for our next trip.
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Old 08-23-2021, 09:54 AM   #4
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Ted - I was wondering what method/tool you used to turn the engine for pinning?
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Old 08-23-2021, 10:02 AM   #5
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If (OK, big IF) the valve adjustment on your Caterpillar engine was done by a Caterpillar dealer AND he recorded it with Caterpillar Corp as he should, you can get that information along with any other service work that has been done on it by calling Caterpillar Corp with your engine serial number:


Caterpillar Corp: 877 777-3126


When I called, I was even able to get actual performance data from when my engine was run on a dyno before leaving Caterpillar.


For anyone who has ever adjusted valves on any engine with push rod/mechanical lifters, checking and adjusting valves is straight forward.


And, if taking it to a dealer for adjustment, I would recommend NOT asking for an estimate until they see access to the engine (if you have good access). In many cases (like rear closets, transverse beds, etc) getting to the valve cover takes most of the time. If you choose to do the "access part" you can likely save $$$.
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Old 08-23-2021, 02:14 PM   #6
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Ted - I was wondering what method/tool you used to turn the engine for pinning?
I used a breaker bar with a socket on the balancer. The first time was slow since I had to turn the engine a bit, see if it would go in, keep on doing that. Then I made a mark on the balancer and the second revolution was easy.

Well, "easy". It takes a lot of force to get past those compression strokes.

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Originally Posted by wolfe10 View Post
If (OK, big IF) the valve adjustment on your Caterpillar engine was done by a Caterpillar dealer AND he recorded it with Caterpillar Corp as he should, you can get that information along with any other service work that has been done on it by calling Caterpillar Corp with your engine serial number:


Caterpillar Corp: 877 777-3126


When I called, I was even able to get actual performance data from when my engine was run on a dyno before leaving Caterpillar.


For anyone who has ever adjusted valves on any engine with push rod/mechanical lifters, checking and adjusting valves is straight forward.


And, if taking it to a dealer for adjustment, I would recommend NOT asking for an estimate until they see access to the engine (if you have good access). In many cases (like rear closets, transverse beds, etc) getting to the valve cover takes most of the time. If you choose to do the "access part" you can likely save $$$.
Good point, I should check with them to see. It would be an interesting data point.
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Old 08-23-2021, 05:49 PM   #7
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I bought my coach with 33K on it and did not know history of the motor if they did this recommended service. So I did this myself also and only found a few that were slightly out of spec. Its really not that difficult of a job. What are you doing to monitor boost?
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Old 08-23-2021, 07:34 PM   #8
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I bought my coach with 33K on it and did not know history of the motor if they did this recommended service. So I did this myself also and only found a few that were slightly out of spec. Its really not that difficult of a job. What are you doing to monitor boost?
I monitor boost and a bunch of other engine parameters with BlueFire. I added Autometer independent gauges for EGT and oil temperature since neither of those go through the ECU on my bus.
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Old 08-24-2021, 05:41 AM   #9
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Quote:
Originally Posted by Ted DuPuis View Post
I don't know the valve adjustment requirements (if any) for the Cummins engines since I haven't had to do it, but basically anything that has adjustable valve lash it's a good idea to check since it is often off.

I might take a couple of pictures before throwing the valve cover back on. I'm going to put together a video at some point in the next week or two, right now I'm focusing on getting the bus ready for our next trip.
Itís a 150,000 mile service interval for the 2007-2018 6.7. 2019 and later donít require it per Cummins.
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Old 08-24-2021, 06:55 AM   #10
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Itís a 150,000 mile service interval for the 2007-2018 6.7. 2019 and later donít require it per Cummins.
That's a number I should know since I have a 2017 Ram with a 6.7.
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Old 08-24-2021, 09:30 PM   #11
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Ted ; was your valve cover gasket , the grey string type or did you use something different ( aftermarket ) ?
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Old 08-25-2021, 05:08 AM   #12
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Ted ; was your valve cover gasket , the grey string type or did you use something different ( aftermarket ) ?
I went with the factory Cat gasket - the grey string type like you mentioned. I was surprised when I first saw it, but it seemed to hold up well for 20+ years so hopefully the new one will too.
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Old 08-25-2021, 08:14 AM   #13
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I went with the factory Cat gasket - the grey string type like you mentioned. I was surprised when I first saw it, but it seemed to hold up well for 20+ years so hopefully the new one will too.
If it'll do 10 years that's all I'll need .

Service records indicate , initial adjustment was done at 19,000 , currently 93; so an item to add to the to do list .

Just replace heater hoses... that was fun ...NOT!
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Old 08-25-2021, 09:39 AM   #14
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Just replace heater hoses... that was fun ...NOT!
Thatís on my list, as well as replacing the bedroom coolant driven heater. Not looking forward to that. Iím planning on wrapping the hoses going to the heaters in foam to hopefully make the heater more effective, as itís seemed to do little more than a warm breeze.
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