Need help with small cam timing

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by campwells, Jan 13, 2025.

  1. campwells

    campwells Bobtail Member

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    I recently got really deep into a 1973 international Paystar 5000 with what I believe is a 855 290hp small cam Cummins engine. It had bad fuel so I rebuilt the fuel pump and injectors- replaced plunger & barrel assemblies with NOS as well as new injector cups. I had to rebuild the accessory drive assembly as it was walking in and out- all went well. While I’m here I decided to re seal some leaks, rocker boxes valve covers water pump , everything I can easily get to….. well this included the cam follower assemblies.
    While removing the pushrods all exhaust rods were badly bent one was broke in half, Intake rods weren’t happy but not bent so bad really just 2 bent ends and others had damaged ends. One follower assembly was beat to hell and we found a nos replacement. Now I know injector timing is set by the shims on these followers and the settings depend on the engine serial # and CPL #. However our tags are missing, nothing on the timing cover- it’s been physically removed, and the pad on the cooler side is rotted away so I don’t have any way that I’m aware of to find what I need to get this set up. Is there a somewhat generic settings that would work decent? I understand there are a few variables which together make the desired setting, I know what injectors we have, I can hopefully identify which cam we have if they are stamped. What else would I need? Or again is there a generic range that will work okay for a 80,000lb 10 wheel dump truck that we’ll definitely be overloading on flat ground. I do have a manual for the same model truck we also have, it’s a 1975, the block where the serial stamp should be is different and again no visible marking I can find there, no data plate or markings on its timing cover either. I’m not sure if it’s a big cam being a 75 but the follower boxes are the same physical size as far as footprint as the 73 we have -I understand the big cam has a slightly larger in height follower box because the gasket kit we got has follower box gasket /shims that are taller than not this 73 and 75. Now that manual does have procedure for finding this timing/ shims thickness, I am buying the tool and understand the process but what is the actual setting?
     
    Last edited: Jan 13, 2025
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    We usually just measured the old ones and installed new ones the same thickness.
     
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  4. campwells

    campwells Bobtail Member

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    I’ve never worked on one of these but from what I have been told, read and understand that was common, however it’s not the correct way to do it. Now if I was just resealing it I would do the same but I am changing one set of followers and not sure if what was there was even correct to begin with. I was planning on using the original to start with and check, I was also thinking I could put my used follower rollers on the new follower lever arms and use my original cover plate. I’m not sure how much my original is worn but the rollers look nice and turn nice, it’s the cup side of the lever arm that’s best to ####. My thought is if I put new roller in with its new assembly it may be off enough for those 2 cylinders to be pissed off and out of sync. Now all that aside I can figure out what shims I need if I knew the CORRECT INJECTOR TIMING HEIGHT SETTING. That’s what I’m missing, I don’t have the spec because I don’t have the ESN or CPL numbers.
     
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  5. SmallPackage

    SmallPackage Road Train Member

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    Rocker box shims are steel. Way early ones in 1950’s were brass. The best way to seal them is with a gasket shellac. Like Indian Head or an aircraft gasket sealer. Do not use rtv. They will seep over time that is normal. Rear one always seems to be the worst for seepage. If engine was happy with the timing it already has, leave it be. Replace any shims that may be torn with same thickness and paint on a coat of shellac. Keep in mind that one cam follower may have more or less shims than the others, If timed by a true old hand Cummins tuning expert. I’ve seen 6 on one next to the other that has two. Machine tolarances and wear doesn’t make them all equal.
     
  6. SmallPackage

    SmallPackage Road Train Member

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    If that engine still has the compression release it may be the reason the push tubes are bent. Some newbies don’t really understand how to use that thing. It is for opening the exhaust valves to lower the compression during cranking to allow the starter to spin engine over faster. It’s rod rolls up like a cam and pulls the tubes away from the followers. Once starter rolls at top speed and begins to fire push the handle in and lets the tubes go back to normal position. Leave it pulled and it could damage tubes. Also some folks and I have been guilty of this in a situation or two have used it to shut down an engine that has a stuck on fuel solenoid. Not recommended as a normal thing but out of desperation.
     
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  7. campwells

    campwells Bobtail Member

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    We just recently got the truck in non running condition from an auction so we have no information on it as far as if it was set up correctly to begin with and can only speculate as to why it’s damaged but it’s sounds plausible that someone grabbed it when it was running but hasn’t been touched since we have got it and it was sprung to the passenger side. The exhaust collars on the pushrods were wiped out and there was also damage on the injector push rods at the same height location although they are not ment to interact with the compression release. I was told sometimes they were used to as a compression release like a Jake brake during operation but our engine does have Jake brakes so I’m not sure about it. Our trucks were also military trucks, built for the army so they may differ slightly or have other “options” as standard equipment. I would assume the engine was originally set up correctly as the shim packs on the follower boxes are .010” .007” and .010” front to back. I understand not everyone is familiar with these and just assume a gasket is a gasket and sometimes you’ll find all 3 are the same and it’s almost guaranteed to be wrong, having them be different may be good indicator that it was set up correctly at one time. This is not a problem I can figure out what shims I need if I knew what setting I need. I need to identify my cpl and esn and my tag is missing- this is my problem-
     
    Last edited: Jan 13, 2025
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  8. SmallPackage

    SmallPackage Road Train Member

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    If the compression release was used as a compression brake “Jake” that is devastatingly wrong. It doesn’t work in the same way. It is not meant to be used at any rpm higher than starter cranking speed. If it was Used like that will be the source of all that damage for sure. I wouldn’t want to know what would happen if that handle under the dash was pulled out while at cruising speed. Yikes.
     
  9. campwells

    campwells Bobtail Member

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    Not aware of any handle under the dash, and nothing is physically connected to this arm front of engine other than the spring holding it in place. I was told by a supposed Cummins mechanic…… I take everything with a grain of salt other than a factory manual. I figured it would be used as a starting aid, possibly to help prime fuel or oil. So I imagine the comp release arm is moved it rolls that linear shaft and forks or something maybe a flat of that shaft grabs and lifts the exhaust a bit to release the compression, if this is correct wouldn’t it lift it just enough, but not enough to contact the piston? So even at rpm other than the follower jumping around what would happen? I’m a experienced mechanic but I’ve never worked on a big Cummins- I have worked on 6bts and tons of small truck diesels, built engines and know quite a bit about older detroits/gm 2 strokes some cats- not these so I’m able to follow what makes sense. Appreciate your time and input but what do I do about the missing id tag for setting it up correctly?
     
  10. BoxCarKidd

    BoxCarKidd Road Train Member

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    Google: Cummins small cam serial number location. Then go down to Truckers Report . Com. AUG 8 2020. Tag on injection pump?
     
  11. BoxCarKidd

    BoxCarKidd Road Train Member

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    I would not be concerned about the levers or rollers being different but the housings. It could have even been resurfaced. I would put them on your old housing and shim as removed. But that is just my opinion.
    Injectors can also be adjusted on the outer base circle torqued to 70 inch Lbs if I recall correctly.
    Thought on inner base circle they all adjusted to 0.170 with aluminum housings.
     
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