Hi All, I'm looking for help with setting the timing on a cummins engine. Where should the piston on cylinder 1 and 6 be when the auxiliary drive pulley is on A.
If I remember correctly they should be a couple inches below top dead center. There should be a 1+6 TDC mark on the accessory or auxiliary drive pulley that you can use to verify it is installed correctly. Terry
When my auxiliary drive pulley is on A, the 1 and 6 piston is at the bottom and the 3 and 4 is just below deck
Is there a 1+6 TDC mark on the pulley? Terry
You say setting timing? Did you change the camshaft and need to time the followers or are you adjusting the valves and injectors? And what model of 855? Truck Shop
@ Terry - yes there is, I'm unsure if it is in the correct order as it has been worked on before (not by me). @ Truck Shop - I'm adjusting the valves and injectors. Had broken push rods. Someone else worked on truck previously. NT855 Big Cam
With the 1+6 TDC mark aligned with the pointer the 1 and 6 pistons should be at the top. I have seen auxiliary drives installed out of time. It's not a problem until you try to set the valves and injectors. Terry
@ Terry - what would cause the pistons 1 and 6 to be at the bottom when Aux drive is on A and when I am setting on valves on cylinder 1 or 6.
When aux. drive is on C, pistons 1 and 6 is up. And when cylinder 1 valves are closed - I tried to to set cylinder 1 injector , the engine locks.
Someone may have installed the auxiliary drive out of time. You need to roll it over till the 1+6 TDC mark lines up with the pointer and make sure the 1 and 6 pistons are at top center. If they are not the auxiliary drive will have to come out and be put back in time. Terry
With #1 at tdc the valves for #6 will be just opening or closing. You can tell this by just baring it back and fourth, the exhaust valves will be just closing and the intakes just opening on #6. Depending on the direction your turning the engine. With that said look at the marks on the accessory drive and see where A is at according to the pointer on the case. To properly time the accessory drive you will need to remove that pulley and there is a allen socket pipe plug on the cover you remove to see the timing marks on the cam. When lined up properly the two marks on the cam gear will line up with two dots on the accessory drive gear. Truck Shop
Fixed time or STC? CPL? This makes all the difference as there is a different procedure and settings for both.
If it's a BC-I-II-III use the outer base circle method and set injector Valves lash ex .014 int .027 injector 72 in lbs valves and injector on same cylinder. A 1 1 B 5 5 C 3 3 A 6 6 B 2 2 C 4 4 If it's a New Big Cam IV use the same OBC method but injectors are set at 105 in lbs This covers CPL #s 821,833,903,904,806 If it's a 88BCIV use OBC method and injectors are set at 90 in lbs This covers CPL #s 827,910,1185,1188,1210,1211,1256,1280 If it's a N14 use OBC method and injectors set at 125 in lbs This covers CPL #s 1374, 1380,1395,1405,1507, Truck Shop
I just finished dinner and realized I quoted the valve lash wrong, BC I-II-III Exhaust .023 and intake .011 injector 72 in lbs jakes .018 The BC IV, the 88BCIV and the N-14 are Exhaust .027 intake .014. Jakes on the NBCIV and 88BCIV are .018 N-14 Jakes .023 Truck Shop
The valves and injectors on Cummins engines with a PT fuel system are not set with the cylinder on top center as is done with most engines. When the PT injector is finished delivering fuel the plunger seats in the cup to stop combustion gasses from entering the nozzle tip. There is an additional approximately .010" extra lift on the cam lobe to seal the plunger tip to the cup during peak pressure of combustion. Once the piston moves downward and the cylinder pressure drops this extra force in no longer needed and the cam lobe is ground accordingly. Well after top center is where the injector and valves are set using the torque method on the injector. If I remember correctly 60 to 90 degrees after top center. Terry
Thank you for correcting me on that. By some old notes I have it was 65 degrees. Truck Shop
I learned that lesson the hard way on a 504 Cummins, replaced the injectors and adjusted to top center and BENT every injector push rod in it. Did get them straight with mallet and an oak stump and it continued to run for several years, but taught a good lesson.
Hi All - thank you. I was able to fix the issue. Now I'm having a problem with the injector.
Problem with the injector???