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Signature620 · 07-01-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

It either has excessive valve recession, incorrect cam timing (check that someone hasn't fitted the vibration damper incorrectly while you're at it) or the rocker shafts have not been fitted correctly (could be due to poor head casting or incorrect steps taken while fitting the shafts).

Not being able to get the 7mm feeler between the jake lever and top hat is cause to remove the head and measure valve recession in Cummins warranty guidelines.

Minich Truck Repair · 07-01-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

Thanks for the reply, after 2 heads and having the same results the place we bought them through decided to send one of there cummins certified guys to come look at it. He went through and checked all the gears on the front said they were all good, put the wedges in and pinned it to time the cams went through on the adjustments and got the intake and exhaust valves adjusted just like we did. Got to the jakes and had the same problem as us on them, he tried a few different things and couldn't get them to adjust. He had us pull the head off while he made a few phone calls, he wanted to check the liners to make sure they were within spec for clearance and not sticking up to far from the block and everything checked out. His recommendation was to send the head back and get an OE cummins head, said it has to be in the machining of the head. New cummins head will be here tomorrow.

Again thanks for all the input

Signature620 · 07-01-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

You'll be on the right track once the genuine one arrives. You might even be lucky enough to get a brand new one in a ReCon box. You'll know by the recent casting date stamped into the rear intake side and the lack of pitting around the exhaust ports.

Rawze · 07-01-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

(07-01-2019 )Signature620 Wrote: You'll be on the right track once the genuine one arrives. You might even be lucky enough to get a brand new one in a ReCon box. You'll know by the recent casting date stamped into the rear intake side and the lack of pitting around the exhaust ports.

You can also tell if it is recon or new by the box it comes in. -- New always comes in a box that is a several inches wider vs. a recon head that comes in a box that is barely more than the width of the head itself.

... at least, that is what Mr. hag said to me the other day anyways.

and like you said, intake rear side of head, it will be stamped with part# + recent date without the "RX" on it.

Personally though,.. even if i had to pay $1,000 more for guarantee of brand new head,,.. I would do so.

07-01-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

adjusting the jake running clearance by rotating the rocker shafts is a thing of the past and is a screwup on cummins part to include it in the manual. If your running clearance is that far out you have something wrong with the shafts/rockers, jakes, cam, head etc. you will not need to adjust them anymore.

DosGatos · 07-02-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

Well, that's not fun to read. I checked the quickserve page. It was just updated in April and the method is still there. I'll have to re-do the overhead from the beginning with the shaft in the flat-to-flat orientation and see what I've got.

Rawze · 07-02-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

(07-02-2019 )DosGatos Wrote: Well, that's not fun to read. I checked the quickserve page. It was just updated in April and the method is still there. I'll have to re-do the overhead from the beginning with the shaft in the flat-to-flat orientation and see what I've got.

I have seen something related happen a couple times. I think it even happened to hammerheads truck once, put him in a panic.

Sometimes, the rocker shaft will slip just a bit, or get twist in it when tightening it. detent clearance will be too low, making you think something is wrong. Only trouble, is that it will be messed up on only the front 3 (or rear 3 cylinders) consistently,.. or the problem will progressively get worse between cylinder 1 to cylinder 3, or 4 to 6.

If re-seating it a couple times and re-checking does not solve it,.. then head is problem.

Hammerhead · 07-04-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

(07-02-2019 )Rawze Wrote: I have seen something related happen a couple times. I think it even happened to hammerheads truck once, put him in a panic.

Sometimes, the rocker shaft will slip just a bit, or get twist in it when tightening it. detent clearance will be too low, making you think something is wrong. Only trouble, is that it will be messed up on only the front 3 (or rear 3 cylinders) consistently,.. or the problem will progressively get worse between cylinder 1 to cylinder 3, or 4 to 6.

If re-seating it a couple times and re-checking does not solve it,.. then head is problem.

Yeah, serious panic. Thought I had serious valve recession and was thinking I was replacing a head, unplanned and seriously early.
Don’t ask me how it happened, but the jake measurements progressed from good to worse front to back on the front rocker shaft. I pulled the front 3 injectors and looked at the valves and seats with my boroscope I shared the pics with Rawze, and he confirmed what I was seeing, that all valves and seats looked fine, no visible signs of excessive wear, so I pulled the front rocker assy and everything appeared fine. I also measured every valve stem and they were all measuring the same, so the difference didn’t make sense. I put it all back together and remeasured the valve clearance and all was “normal”.
The resulting theory is somehow the rocker shaft torsionally rotated slightly, caught by regular overhead adjustments and measurements. When these shafts were put in, I used straight torque, not torque plus angle and I used the “old” value. That is the only logical conclusion we could come to. If you’re going to use straight torque in place of cummins torque plus angle, use 90 ft/lbs. An old video suggests 74(?), and that was what I had used.

DosGatos · 07-13-2019, **(Subject: JAKE ADJUSTMENT ON ISX )**

Did the overhead from scratch; loosened up everything but didn't remove the shafts. I have about 60k on the new rocker shafts and had rotated the shafts. Don't keep notes so no clue what happened when I installed the replacement shafts.
Following the instructions starting with the flat ends set to the block and final torque to 90lb I have a consistent .090 +,- running clearance. Odometer is 835k so was expecting less. Looking over the head I see all the freeze plugs are unpainted. Can only guess the head was rebuilt but I have no service records from the original fleet or second owner.