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+--- Thread: Jake brake adjustment (/showthread.php?tid=1106)
Jake brake adjustment - joed2323 - 11-15-2016
Ok, ive adjusted jakes before on series 60s and its cake walk, its simple.
Please give me the run down on why the adjustment of the Jake brake is odd to me on these cm2250s/871s/cm2350s?
Ive watched rawze video on the injector swap, and he ran thru the overhead, (the overhead makes sense to me) but the jakes on how you have a toleance of +/- such a min/max is odd, especially coming from a series 60 were you adjust the Jake brake and your done...
With these cummins motors if jakes are for example over spec,you have to loosen the rocker shaft bolts and "push or rotate the shaft towards where it needs to be then retighten down the rocker shaft stud bolts and recheck the tolerances for the jakes. .
Ive adjusted valves on two motors now and, yes I had the rocker shafts off and installed them. Yes I understand either the front rocker shaft or rear rocker shafts have to be installed and tightend down when the rocker shaft is down not bolted down when the valves are pushing it up... I ran thru these motors and checked the given min/max tolerances and thankfully the were perfect. But it just didnt make total sense. If it was off for example I would think just to loosen the adjuster nut on the given jake that was out of adjustment and adjust it. Walla done...
I just dont necessarily understand the engine brake adjustment procedure and why on these motors.
I know you guys are gonna use caution towards me and be shocked that I ran two overheads but just didnt grasp why the engine brake has "any" given tolerance to be within spec...
Well I dont like that. I want my engine brake to be spot on and "great" engine brake.
Their is a adjustment screw for the Jakes... Do I have the procedure backwards, and I only need to adjust the screw/nut adjuster in the "detent position" which to me makes sense to me! If its off you adjust this. Not loosen up the rocker shaft bolts and adjust accordingly???
Thanks guys for being patient.
I really just want to understand this jake brake adjustment procedure, and what throws me off is with it being within spec from a min to a max spec, not just a specifed spec of say 7mm
I even used a dial indicator like rawze did on the jakes, they were all within spec but I just still didnt understand why these jakes are allowed such a wide tolerance that is sufficient to work, not just a .027" for example. Woops its off, let me loosen the Jake brake nut and turn it towards the correct direction to make it exactly .027"
Again the # I stated is wrong, just a # used in this example
RE: Jake brake adjustment - Wiseman - 11-16-2016
I hope this will help you to understand why this small clearance needs to be adjusted by rotation of the rocker shaft .
When the rocker is held by the detent you have to be sure the roller doesn't ride on the camshaft lobe and you have enough clearance. And this have nothing to do with the 7mm which is adjusted with rocker out of detent position.
Now about the +/- . Even from the factory not all valves have absolutely identical height due to factory tolerances when valve seats are grind . There's small differences from valve to valve and from cylinder to cylinder. With time valves tend to sink into the valve seats and that's why we need to make valve adjustments because they are getting tight. Some more some less . Here's where turning the rocker shaft comes to play and you make all 3 rockers when in detent position to have enough clearance for the rollers not to ride on the camshaft lobes. The 7mm have nothing to do with . First you do the 7 on all 3 , then check clearance and rotate if necessary. 7 will still 7 .
If impossible to make all 3 within speck your engine head is shot because the valve/s have sunken already enough irregularly from cylinder to cylinder into the valve seat/s and ready to brake do to seating on its very edge .
If Rawze wake up in a good mood and responds with manufacturer cover up don't be surprised.
Either way keep the fire extinguisher as close as possible.
He wrote about this . It's somewhere in the treasure chest.
RE: Jake brake adjustment - Signature620 - 11-16-2016
When the engine brakes are energised, a piston in the jake lever extends to take up the clearance and then it acts like an ordinary rocker. The purpose of the clearance is to ensure that the lever does not contact the valve or the cam when not in use.
RE: Jake brake adjustment - Rawze - 11-16-2016
THE DETENT CLEARANCE CHECK/SET PROCEDURE FOR THE ENGINE BRAKE ROCKERS IN THE BOOK IS ABSOLUTELY INCORRECT!!!!!!!!!
MY VIEW ON IT IS THAT THE PROCEDURE FROM CUMMINS IS ABSOLUTELY WRONG AND IS FOR THE OLD STYLE ROCKER SHAFTS!!!!!!!! -- AND ROTATING THE ROCKER SHAFT IS A VERY VERY VERY VERY VERY VERY BAD THING!!!!!
IF THERE IS TOO LITTLE CLEARANCE BETWEEN THE DETENT POSITION AND THE TOP OF THE VALVE --- REPLACE THE HEAD!!!!!!!! -- THE VALVE SEAT IS WORN OUT AND THE VALVE RIDING THE EDGE OF ITS SEAT AND IT HAS VERY HIGH RISK OF SNAPPING OFF!!!!!
NEVER ROTATE THE ROCKER SHAFT!!!!---- KEEP IT ALIGNED WITH THE FLAT AT ITS END AND THE LOCK-DOWN SCREW/SPACER!!!!!
===================
IF YOU ARE INSTALLING THE SHAFTS AND ASSEMBLY! -- ITS RADIAL ALIGNMENT IS SET WITH A FLAT AT ITS END!!! -- THERE IS NO F##KING ADJUSTMENT AT ALL IN THE NEWER CM870,871,2250,2350 ENGINES! -- THE PROCEDURE IS SIMPLY OF OF DATE IN THE BOOK!!!
I HAVE NEVER SEEN A SINGLE HEAD WHERE YOU HAVE TOO LITTLE CLEARANCE AT DETENT POSITION TO THE VALVE AND THE HEAD WAS STILL ANY DAMN GOOD AT ALL!. --- THEY ALWAYS FAIL!!!
You are only fooling yourself and taking huge risk on ALLOWING YOUR, OR OR SOMEONE ELSE'S ENGINE TO LATER SNAP A VALVE OR BURN THROUGH ONE BECAUSE YOU LET IT GO KNOWING THE VALVE(S) WERE TOO HIGH IN THEIR SEAT!!! --
(if it is adjusted right and nothing wrong with the rocker) -- AND THERE IS TOO LITTLE DETENT CLEARANCE ==== THE VALVE IS TOO HIGH IN ITS SEAT!!! SIMPLE AS THAT AND THE HEAD IS SHOT!!!
If you ignore this problem and mask it by rotating the rocker shaft and leaving the alignment screw at its end under-torqued (because that is what you would have to do)!. -- YOU ARE ONLY FOOLING YOURSELF OR SETTING UP YOUR OR YOUR CUSTOMERS ENGINE FOR UNEXPECTED HEAD FAILURE!!! -- INSTEAD -- You should point out the problem clearly and the fact the head is SLAP WORN OUT or machined incorrectly! and can take the rest of the engine with it when it goes.
NOT ONLY THAT, BUT if it is only one cylinder or 2 like this -- THERE IS A COMPRESSION IMBALANCE IN THE ENGINE NOW AND IT WILL ALWAYS HAVE ENGINE BALANCE ISSUES that lead to uneven bearing wear, and possibly of a snapped crank shaft under long term stresses combined with high enigne load on the cylinder(s) that the valves are NOT worn up into the head. Problems that can shorten its life with possible catastrophic failures as it ages later on!.
IF YOU ARE INSTALLING A ROCKER ASSEMBLY, align the shaft properly and squarely to the flat and its lock-down screw spacer a its end as you tighten it up. ---- DONE! -- MAKE SURE THE FLAT IS SQUARE TO THE LOCK DOWN SCREW AND SPACER!. Do NOT mis-align it, OR Align/ tilt/ or adjust it AWAY from this position FOR ANY REASON!
Checking for worn out / incorrect valve seats...
AFTER the rocker shaft is in place PROPERLY, AND SQUARELY to the flat,... And now your doing the overhead valve adjustment correctly -- As you adjust the engine brake rocker via its set screw to the correct gap ("0.276") with it all the way back, its roller against the cam,... Then put it back into its detent position.
MAKE SURE the detent is strong and there is no free-play, or that it is weak. This will make for a bad day in someones engine. Weak detents or worn out detents on a rocker shafts can and will kill an engine. After inspection of this,... MEASURE the travel range between the rocker detent position and the top of the valve if it feels like there is not much clearance or if you aren't sure what it is. Measure the travel with a dial indicator placed at the center of the set screw.
[attachment=2676]
The travel it has between the DETENT position and the top of the valve, where it touches, should NEVER be less than 0.028" or so (cummins says 0.025" min but that is beyond way risky). IF it is LESS THAN 0.030" or so,.. EITHER the rocker is still out of adjustment and you didn't do something right,... OR the piston/set screw or something else wrong with the rocker itself is broken (still very very bad!) but MOST LIKELY --- ESPECIALLY AS AN ENGINE AGES!!!! -- The exhaust valves are riding TOO HIGH in their seats!
--- Here is a resulting picrture of what I am referring too ---
[attachment=2191]
It is JUST A MATTER Of TIME before it snaps and DESTROYS A CYLINDER -- and The Pieces go through the TURBO AS WELL! --- THE HEAD IS BAD!!!! PERIOD!
BTW: The one in this picture,.. I ran this guys overhead not 3 weeks BEFORE IT FAILED! - and pointed out to him that there was only 0.027" clearance from the detent to the top of the valve,.. and told him that HIS HEAD WAS BAD AND NEEDED REPLACEMENT!!!--- And he took it in stride and said he would save money up for a new one over the next several weeks.---
HE LOST THE WHOLE ENGINE AND THE TURBO TOO! -- Head would have been HALF THE COST!. And the sad thing is that the bottom end of his engine was still in good shape and would have gone another 600-800k likely, but the pieces of the valve scored the piston and liner,..and the guy drove it a couple hundred miles himself and washed out the cylinder completely because he was too damn stubborn to do things right.
SAD SAD SAD --- GUY DIDN'T LISTEN! -- TRIED TO JUMP OVER $3600 HEAD just to get a few more loads in -- BAD MOVE! -- And I WARNED HIM HEAVILY ABOUT It BEFORE HE LEFT!.
I don't scream this stuff because I am a maniac,.. I do so to educate people, and to HELP THEM MAKE WISE DECISIONS! and let them know that there is sometimes a LOT more to what you are doing.
====
more references: http://rawze.com/forums/showthread.php?tid=1632&pid=18718#pid18718
RE: Jake brake adjustment - joed2323 - 11-16-2016
Excellent info rawze. Thank you for clearing this procedure up.
I did exactly what you said here
Rawze Wrote:IF YOU ARE INSTALLING A ROCKER ASSEMBLY, align the shaft properly and squarely to the flat and its lock-down screw spacer a its end as you tighten it up. ---- DONE! -- MAKE SURE THE FLAT IS SQUARE TO THE LOCK DOWN SCREW AND SPACER!. Do NOT mis-align it, OR Align/ tilt/ or adjust it AWAY from this position FOR ANY REASON!
AFTER the rocker shaft is in place PROPERLY, AND SQUARELY to the flat,... And now your doing the overhead valve adjustment correctly -- As you adjust the engine brake rocker via its set screw to the correct gap ("0.276") with it all the way back, its roller against the cam,... Then put it back into its detent position.
In my short time on the two overheads I did, I checked them with the dial indicator like you did in your "injector replacement video" and they were spot on.
Now I know for next time exactly what I'm checking for. Again thanks
RE: Jake brake adjustment - Starlight - 12-30-2016
Post #4
Why can i only give 1 thanks to this post. Id add at least 100 if i could