Cm870 Jake detent worn

[Pete379]

On Friday I heard a strange intermittent clanging noise from the passenger side of my cm870 when I parked the truck. Over the weekend I pulled the valve cover and noticed that the jake detent was worn on #6 and the noise was from it not sitting in detent while not engaged. The jake wiring harness also is in pretty bad shape so I plan on replacing that as well.

I was wondering if anyone had any experience replacing the rocker lever shafts and could give and tips or information that might help me when getting into this repair...

[Rawze]

(04-10-2017 )Pete379 Wrote:  On Friday I heard a strange intermittent clanging noise from the passenger side of my cm870 when I parked the truck. Over the weekend I pulled the valve cover and noticed that the jake detent was worn on #6 and the noise was from it not sitting in detent while not engaged. The jake wiring harness also is in pretty bad shape so I plan on replacing that as well.

I was wondering if anyone had any experience replacing the rocker lever shafts and could give and tips or information that might help me when getting into this repair...

MY injector leak-down test series shows the upper end being pulled apart and re-installed.






In this series, I said 70 ft-lbs on the bolts in one of them. It has been found that it is better to torque the rocker shaft retaining bolts to 105 - 110 ft-lbs. I now set them to 95 ft-lbs these days, especially if they have been off a couple times.

reference: http://rawze.com/forums/showthread.php?t...2#pid10802



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and I also discuss them in detail in my re-build series...





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I disagree with the book for setting the rocker shaft positions. It tells that the rocker shaft(s) can be rotated to get the correct clearance between the detent position of the rocker and the top of the valve stem. This is old out-dated information and is not correct. Here is a discussion about rocker detent clearance, wear and getting the rocker shafts in place correctly...

http://rawze.com/forums/showthread.php?t...66#pid9466



Maybe that helps.

[Pete379]

Thank you Rawze... That's exactly what I needed.. I feel much more comfortable after seeing it done and getting your input

[Hammerhead]

I have done this procedure a few times. As advised by Mr Hagg the first time I did mine, I advise everyone to also change Part # 3413129 Control Valve Assy Detent and Part # 2892986 Compression Spring in each Jake rocker arm. Shaft part #'s are 2882570 (front) & 2882571 (rear), do both while you're at it and be done. If one is worn out, the other is getting close and the downtime is just not worth the hassle.
The Control Valves are tapered, and wear round or ball shaped as the rocker shafts wear. Not replacing them means you will have a round contact area on a tapered surface. This coupled with Compression Springs which have been compressed over their lifespan & are weakened, will lead to prematurely wearing out your fancy new rocker shafts.
6 valves and 6 springs are less than 25% of the cost of one of the rocker shafts, making not changing them senseless. The only items required to do this part of the job is assembly lube (Vaseline or oil) & small snap ring pliers. This adds 1/2hr to the job and once completed, you will be absolutely amazed at how much your jakes have weakened over the years!
Oh yeah, and I second Rawze's advise, don't attempt to rotate the rocker shafts to locate the detent position. The new procedure with the new style shafts is to finger tighten the shaft bolts and torque the front bolt of each shaft FIRST to properly align the shafts, then torque the remaining shaft bolts. I also do not like the torque plus angle on these bolts, and torque to 95 ft/lbs.

[Pete379]

Hammerhead I just placed a call in to cummins they make a tune up kit for the engine brake which has the parts that you listed.. It was P/N 2882081... I had them throw that in with the updated jake harness for my engine and both rocker shafts. thank you for you help