Engine/Transmission (1998.5 - 2002) A warning to all who do their own valve adjusments.

[chuckwilson]

My Cummins engine manual says NOT to turn the engine backwords (12V) it may cause fuel pump damage. The key word here is MAY!!!!

 

[obert]

I do recall somthing from way back when i got to play with more engines than now-- "If turning the engine backwards, go past TDC mark, and return to it on normal rotation. "

 

[MCummings]

You have MULITPLE gears that not only are set and designed to run in one direction, but they are helical cut(as I recall).

There is only one gear between the crank and the cam. Crank, connected to cam, then IP.



If we can take Piers' words, and open 'em up, we could assume that each gear represents 2* of variance from forwards to backwards. So your cam is 2* off when you rotate it backwards.



Easy solution, rotate the crank 2* passed TDC...



If you really want to get pickey, rotating the engine also makes the oil pump loose prime, oh no. The humanity.





Now why is it bad to rotate the motor from the belt? The A/C, Alternator, and fan can suck up to 50HP from the motor. That power is transmitted directly through the belt.



If you try to turn the motor forwards, the tensioner will "adjust" and let the belt slip. The motor will only turn backwards because the alternator pulley pulls the belt tighter around the balancer.



ANyway. My $. 02



Merrick

 

[Forrest Nearing]

I just watch the valves and adjust whichever one is on the base circle of the cam... I make a little checklist and mark off the ones I've done, rotate the engine over some more till other valves get on the base circle, set those, etc. untill they're all done.



no problems in 200k of combined Cummins driving, and no problems on any of my old gasser hotrods using this method.



you guys are WAY overthinking this... taking up lash in the cam gear? you guys realize that production tolerances probably account for a wider difference in cam orientation between one truck and another than lash in the gears...



take a look at a camshaft... I'm guessing our lobes have something like 180* seat-to-seat duration... that leaves another 180* of BASE CIRCLE... and you guys are splitting hairs over maybe a degree or two?



as long as it's on the base circle of the cam when you set the valve, it's set correctly.

 

[2broke2smoke]

I just watch the valves and adjust whichever one is on the base circle of the cam... you guys are WAY overthinking this... taking up lash in the cam gear? you guys realize that production tolerances probably account for a wider difference in cam orientation between one truck and another than lash in the gears... take a look at a camshaft... I'm guessing our lobes have something like 180* seat-to-seat duration... that leaves another 180* of BASE CIRCLE... and you guys are splitting hairs over maybe a degree or two?

as long as it's on the base circle of the cam when you set the valve, it's set correctly.

EXACTLY !!!

drink a beer ... take a pill ... something!!!

 

[MKeener]

BILLVO,

I have adjusted many top ends on CTD and C-12 and C-13 ACERTS by using the alt nut never had a problem with doing it that way. As long as you pay attention and pin the engine you will fine on your adjustment. Pin the eninge on that CAT's that is, i watch the valves on the CTD to set them.

 

[obert]

Very well put

... you guys are splitting hairs over maybe a degree or two?



as long as it's on the base circle of the cam when you set the valve, it's set correctly.

That part is entirely correct. You could make your procedure more simple, the lil' engine in our trucks only needs to be at two positons for overhead. at #1 TDC set 1I 1E 2I 3E 4I 5E. Turn to #6 TDC; 6E 6I 5I 4E 3I 2E.



Perhaps the argument for position accuracy is due to one of the middle cyl's being so close to the cam lift that a few degrees could move the lifter.



I think the "service manual" method itself might prove forrest's (and others') pont that as long as the valve is fully closed, ie: off the cam lobe, a propper adjustment can be achieved.



I like to run my valves a little tight, too. There is a diference in noise, but i doubt we'd see it on a dyno. I've been frowned on for that... . tighter valves are supposed to cause accelerated wear on the keepers. I say my lash is set within check spec, so its ok. I just check it more often.

 

[MKeener]

obert,

do you set your valves tight with the engine hot or cold? On a hot eninge i will set mine on the tight side of the spec becuase that is where the eninge runs. on a cold engine will will set them on the loose side of the spec becuase the einge is cold on the lash will decrese when the eninge get hot.

 

[BigPapa]

do you set your valves tight with the engine hot or cold?

Valves are to be set at the . 010" and . 020" clearances COLD. I've never seen clearance specs for hot or warm engine.



Scott

 

[obert]

Most valve lash specs are for a clod engine, so I took it for granted as fact for the ISB. So I make it a point to ste the overhead on as cold an engine as possible. Who wants to lay over that hot radiator anyway?

Really, though, with a . 010" window for checking "OK", how much does it matter if your setting in the middle? Youre totaly right on MKeener, but even if you use cold spec on a hot engine, it will still "check" ok. It is a good method, though, and perhaps a mark of finesse from the hand of a skilled mechanic.



No matter where the valves are set, or how you prefer the feeler gauge to "feel", make shure they are all the same. I think exh. espesially. Clatter is one thing, like billvo says most wont notice. But alot of us have limited or no muffleing device in the exh system, and diff's in ex lash as little as . 001" can easily be heard. Noticed or not, it annoys me, I like the smooth exh tone of the I6 block

I usually go for . 007 or . 008 IN, . 018 EX, BTW. There is no diff from stock setting for real, but I can put that on the MOD list and pretend there is!









... took too long gettin that up Answered that for me papa!

 

[BEvens]

My Cummins engine manual says NOT to turn the engine backwords (12V) it may cause fuel pump damage. The key word here is MAY!!!!

It has been 20 years since I was in diesel school but I was taught never to turn an engine over reverse rotation so I woul have to agree with chuckwilson. I was taught that if you went past your mark to continue rotation till you come back on mark. Injection pumps at least at that time did not like being turned reverse rotation.

Just my 2 cents.

 

[ChrisOlson]

OK i have to chime in here.



I have posted what I do for a living before A engineer on a large ship. I do many valve adjustments. on large bore engines up to 7000 HP I just did a complete rebuild on a 3512 from the crank up. a month ago I know a thing or to about diesels. If one of my engineers who work for me rotated an engine against its normal rotation they would be severly repremanded. The cat 3512 manual states to rotate the engine in normal rotation when adjusting valves. The cat 3512 has a pin to pin it in position to do

the valve lash adjustments. this makes TDC very easy. on our big engines "Enterprise" we have timing marks on the flywheel for each of the 16 pistons. Now as for the alternator method I would not do that because you would be putting a very adverse pressure on the shaft the pully adds a uniform pressure to the internals of the alternator. if ctd owners want to do it that way great I would not do it that way. .



I think billvo gave some sound advice



my 2 cents worth

 

[CFast]

The base lobe on the camshaft doesn't care which way it's rotated. A Series 60 camshaft is over head cam design. It's right there staring you in the face as you do the tuneup. As long as you put the roller on the base of the cam lobe it doesn't matter which way you turn the engine. The roller or lifter rides on the base of the cam for more than enough degrees to take up any slack by the geartrain. Base lobe is base lobe.

 

[obert]

Wether or not you can reverse an engine probly has alot more to do other internals and design than the cam itself. In the "small" world, some engines have timing belts. Turn those bakward and you likely 'un'time the engine, causing major damage. On the other end, 2-cycle detroits can run in reverse. To do it right a few outside changes need to be made, of course.

I think alot of the cases, reletive to me anyway, reverse rotaiton might be like going 58mph in a 55 zone. technicly it is wrong, but it wont get you in trouble.



Chris, that 16 cyl-- is that like some EMD engines I've seen? There is a main rod and piston and a "slave" rod/ piston v'd off the main rod, sort of makes another bank of cyls only one rod is tied to the crank. I know there is a word for that configuration, but sadly I'm not overly familiar with those beasts. I could see that being very critical of direction.

 

[CKelley1]

genosgarage.com has the barring tool for $42 it does not make any difference in direction of rotation the lifter is setting on the circular portion of the cam, there will not be even one ten thousandth of an inch difference. you do not even need to know where top dead center is or the firing order to perfectly adjust the valves. i learned this trick 30 years ago when we were trying to adjust valves on a engine the harmonic balancer had sliped on. just loosen all and set to speck. in this case 0. 010 and 0. 020 from this point on do not loosen any, just tighten. turn the engine about half turn and check gap, tighten any loose and turn another half turn adjust one more time and if you want turn another half turn and check.

 

[obert]

... you do not even need to know where top dead center is or the firing order to perfectly adjust the valves...

Care to elaborate on that part? OK, firing order, not so much, but TDC? Shure you can get by with not being dead nuts on, but you gotta be very well in the neighborhood of TDC on #1 and #6 during the procedure... .

 

[AEdelheit]

Care to elaborate on that part? OK, firing order, not so much, but TDC? Shure you can get by with not being dead nuts on, but you gotta be very well in the neighborhood of TDC on #1 and #6 during the procedure... .

Well Ive seen it done where you turn the engine over untill a given cylinder is on overlap, both valves open, then you can adjust both valves on its sister cylinder since it will be at TDC on the compression/power stroke. Ive used this method many times and as long as you can see the valves while turning the engine it works well.

 

[Teich]

Done this for long time always turned the way it ran, get in that habit and nothing will go wrong. That way everthing you read in the manual will make sense and will work right Laurie

 

[Joe Mc]

The only thing I can offer that actually happened to me is: we were installing new heavier valve springs and injectors in a buddies truck and I figured since we had to remove the rockers it would be best to set them since we were "right there". After all was said and done it rocked but sounded a "little" different. My buddy being the perfectionist he is had to pull the cover as the "little different sound" was not sitting well with him. He found the #6 rockers to be a bit loose maybe like 0. 030 and 0. 050 instead of 0. 010 and 0. 020 as they should be. Apparently, the cam lobes were off a tad when I thought they were dead on. So, if I ever have to do valve springs again I'll install "all" the springs and then follow the valve lash sequence as stated in the manual afterwards.

 

[CKelley1]

obert most of the cam is concentric only the lobe lowers the lash, by loosening the valves to start with you make sure none are to tight. now by adjusting all at this point and rotating any valves adjusted on a lobe will be loose adjust and rotate and adjust again. this way all valve are adjusted on the concentric part of the cam. try this and mark them with nail polish then do it your way and you can see it is exact