Engine Valve Adjustment ( Motorhome )

[Dave Atherton]

First of all ( All Engines Run And Test Before Being Shipped From Factory ), after second oil
change it is practice to check valve lash. If valves do not fall within range adjustment is necessary.
What needs to be done first Pin lock flywheel at number one cylinder ( you can tell when pin lock is correct on number one cylinder because both intake and exhaust rocker arms are loose and can move
by hand.    Engine Valve Lash Setting C- 12  Valve Lash Setting ( Intake Valves 0.015 + - 0.003 )(Exhaust Valve Setting ( 0.025 +- 0.003 ) At TC Compression Stroke set inlet valves 1-2-4 and
exhaust valves 1-3-5.      TC Exhaust Stroke  set intake valves 3-5-6 and exhaust valves 2-4-6.
Firing Order 1-5-3-6-2-4  note: after setting valves on the TC Compression Stroke, remove
flywheel locking pin and turn engine in direction of rotation CCW from rear of engine 360 and reset
flywheel lock pin, check valve rocker arms on number 6 both should be loose. Set rest of valves on
TC Exhaust Stroke. Again remember if valves fall within above specs adjustment is not necessary
which means there is a window of 0.006.
Before checking valve lash begins if engine is equipped with engine compression brake, loosen the
adjusting screw on the piston for the compression brake prior to adjusting engine valve lash if
needed. Place feeler ggauge between rocker arm and valve bridge and turn adjustment screw in
clockwise direction untill slight drag is felt on feeler gauge. Remove Feeler gauge and tighten locknut
to 22+- 5 ft.lb.  Valve adjustment is the same for other engines C-9 etc. except there is not a compression brake so omit that step. Again other engines all valves lash checking the same and
adjustment is the same. Before a person thinks about doing this job ( Valves ) size up the task
before. Can you get at valve cover and remove, now much dirt is going into engine when removing
valve cover. Now that valve cover is removed, can you check adjustment or adjust valve and
torque locking nuts ( room to work and see what your doing ). Pass along another thought at top
of page Engine has been run and tested at factory, check valve lash after first or second oil change.
Than Cat says you can go 300,000 before setting valves again ( remember the 0.006 +- on
checking valve lash. In many cases over again setting valves often adjustments will change and a chance of having a adjustment lock come loose has happened. a person needs room to work on
all six cylinders and in many cases with a motorhome that cannot happen very easy.
Dave Atherton Retired Cat Mechanic

[Mike Groves]

Dave,

I've considered having the valves on my C12 adjusted, but given that it appears to start/run very well with expected fuel economy, and the fact that the original owner SHOULD HAVE had the valve adjustments done, I've not done it because it was my information that assuming the adjustment had been done the engine was good for a long time (I believe you're saying until 300,000 miles if the original valve adjustment was done).

Some owners here have told me that better safe than sorry, but I just have a hard time with letting a shop do anything on the engine at all when it appears to be operating very well.  According to Petersen/CAT here in Portland, they couldn't fine the serial number of my engine having had this valve service, but would that definitely mean it wasn't done by someone else?  No, right?  Could have been done by any competent shop right?  For example, I have my maintenance (oil change etc) done by Pape' Kenworth.  They also offered to do the valve adjustment, and if they had would they have access to CAT database to enter the work into the CAT system?

Mike

[Dave Atherton]

Mike, my above post spells out if valve lash falls within specs I posted no adjustment is needed.
I have my mixed views on setting valves like the earlier days. Remember engine was tested before
shipping which means the valves were seated and ring setby running under load which
also set all operations of engine. After second oil change it says to remove valve cover and check valve lash, if valve lash falls into the above specs I posted no adjustment is needed. After this check
you can go as high as 300,000 miles than check again. Many service shop Cat , freightliner etc
say you have to adjust valves and more times this is done more money outlay. At this point have
service shop show you off Cat SIS where this says is required. What you will find if vlave lash
falls into window on above setting no adjustment is not needed, if adjustment is needed than the
adjustment is needed. With electronic engines the window of 0.006 is rear to exceed this measurement. My thoughts alone if it is not broke and someone cannot come up with something
to over ride Cat SIS tech info give some thought to subject. Over the years there has been problems with different people
setting valves and incorrect setting on just one valve or locknut for valve not to spec will cause
many problems if a person did nothing. Again my own thoughts but have seen the other side of
valve adjustment gone south. Dave Atherton Retired Cat Mechanic

[Dave Atherton]

Marty, good piece of information pertaining motorhome valve adjustment. If
some of our member that plan on doing this ( very good Idea ) You have control
of what going on with your engine and money being spent. If some members
plan on checking valve lash on your engine remember after valve cover is removed
first step is to loosen the compression brake piston. Than after checking and or
adjustment there is a correct adjustment to reset the compression brake. I did
not go into depth on the above because we are getting involved. If someone would
like information on setting compression brake I can provide tech information on
correct settings. Dave Atherton Retired Cat Mechanic