Ezrider Posted March 4, 2017 Share Posted March 4, 2017 so today i finnally got around to setting the overhead on my mack, as much as i hate to admit it i have never had the overhead done on this truck, of course when i bought it had very few miles on a rebuild but now with about 300k on the rebuild and my fuel millage has seemed to be worse lately. i figured i better get it done. now i have also never done the rack on a semi back when i had my freightliner i had it done by a shop. i don't really use any shops for anything anymore and have done valve lash adjustments on auto's many times and have the literature that includes the procedure for my engine for setting the valve lash so not something i felt uncomfortable with in the least. took me probably 4 hours start to Finnish.i wanted to share something i found very odd when i did the overhead on this engine that does not seem quite right to me, but having never done it myself i thought i would ask if its normal to find this when running the rack or was the rack was never properly set when the engine was inframed?i checked the valve lash on each valve prior to adjusting them and here are some things i found oddmost intake valves were vary tight the tightest one i could feel a tinny bit of lash my pushing on the rocker arm but i could not get a .001 feeler gauge in there. spec is .016 with the exception of #3 witch was dead on .016 and #6 witch was .014 all the rest of the intakes had less than .003 lash.exhaust valves all sloppy loose. with the acceptation of #3 again witch was only .025 (spec is .024) and #6 witch was .22 (too tight) all the rest were .028-..30now for the jake breaks old spec is .015 new spec for updated jakes witch i have are .021? anyway i chose to set them at .015 but here is what i found for pre adjustment lash on the jakes #1 couldn't get a .001 feeler gauge in there it was so tight #2 .027 #3 .018 #4 .021 #5 .010 #6 .016anyone else find it odd how far allover the place the lash was before adjustments? i haven't drove the truck sense running the rack but it does seem to idle smoother now. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted March 5, 2017 Share Posted March 5, 2017 its not old at all because when you let the overhead go that long the valves and seats start to burn and one can not say how even the valves will wear from one cyl to another, Quote glenn akers Link to comment Share on other sites More sharing options...
gearhead204 Posted March 5, 2017 Share Posted March 5, 2017 the other variable is how consistence the valve seat width is, the rebuilder may of had some fat seats which will wear in slower than narrow seats, the other thing is if the rebuilder reused push rods and put them in different places than their original locations the wear patterns will give a false reading when the overhead was first done then as the scrambled parts" lap " into their new counter parts the adjustments can be erratic . 1 Quote Link to comment Share on other sites More sharing options...
Ezrider Posted March 5, 2017 Author Share Posted March 5, 2017 letting it go too long/ valve wear would explain tight intake valves but it doesn't explain loose exhaust valves. nor the inconsistency in valve lash push rod mix up theory makes sense. cyl heads were replaced during the in frame. i wan't to say they were new heads but they very well could have been re-mack heads, id have to look it up to be sure. but i know for sure they were not the old heads sent out to a outside machine shop, was done at a Mack dealer and heads were replaced. i wouldn't think they would use a bunch of mix matched valve seats. but i suppose even that could be possible. i know i am certainly glad i didn't wait any longer before getting around to doing the overhead 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.