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Thread: cummins big cam/small cam balancing differences, and clutch/flywheel/pp swapping

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    Sergeant msgjd's Avatar
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    Default cummins big cam/small cam balancing differences, and clutch/flywheel/pp swapping

    I'm re-motoring a former army commercial truck that had a big-cam NTC-230, by installing a NTC-290 big-cam series-1 that was in a privately-owned M818 wreck I purchased for parts for my other M809's etc. The 230 had a pot-style flywheel for dual-disk clutch, and the 290 had a flat flywheel for single-disk clutch. The 290's flywheel/clutch/tranny/bellhousing were not with truck when I purchased it.

    1: Are any models of the SC or BC 855ci family of a different crank balance type? I'm thinking they are all internally balanced, but we all know what sarge would say if we think. I do know the 230 had an external harmonic balancer, as it was a taper-shaft crank, which failed at the usual spot.

    2: Does anyone know if I will have to change the clutch linkage or bell housing to accomodate the differences between a pot flywheel type and a flat type, because the pressure plate on a pot-type sits several inches closer to the tranny? Maybe is enough adjustment in the stock setup to accomodate different TO-bearing locations?

    3: I also want to ensure I get the proper clutch/pp for the torque, the engine tag does not list torque and I cannot find online a freely-disclosed torque output for a NTC290bc. (unrelated to my issue, but out of curiosity I wonder if the stock M809-series flywheel/clutch/pp would be able to handle a 290's output) . Not a lot of HP difference between the 230, 250, 270, and 290's, however, turning up fuel makes everything have a boundary somewhere and I would think an NTC has more torque than a NHC. The fuller roadranger the 290 will be mating to has a 2" input shaft. ------- update: I found a sales brochure (generator) listing the NTC290 at 840'# @ 1500rpm. I already knew the NTC230bc is rated at 805'# @ 1500rpm, and just a recap for some out there, the NHC250sc is around 685'#.

    I have not been able to find any heavy truck mechanics around here who have swapped pot-style and flat-style flywheels, so lets see what we can find here on this great site. TY
    Last edited by msgjd; 10-08-2019 at 13:24.

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    4 Star General 74M35A2's Avatar
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    Will on here has more various Cummins experience than the rest of us combined. He can take care of your #1/2 question (same question).

    For #3, is the pressure plate/trans input shaft of an 809 series 2"?

    I converted a smaller ISL from auto flexplate to pot type dual disc, and there were no external balancing on the removed flexplate or install pot flywheel. I had to use pot type due to need it all to fit within an SAE #2 clutch and flywheel housings, and the 13 speed Roadranger I mated it to has a 2" input shaft as well as you mentioned. Irrelevant to what you are doing, but I did not notice any external balancing efforts, and the engine seems to run smooth without vibration on the pallet at idle and full speed. Only pot type dual disc was rated to the 1250ft-lbs needed to fit within SAE #2 componentry. Went hydraulic clutch master and slave from late model Freightliner Cascadia. Low cost, simple, easy install (?). Not installed into truck yet. The slave cylinder I bought has an air-assist option on it to adjust pedal pressure. Pretty slick.

    I would simply judge it by observing for any counter-weights on the unwanted flywheel that came on the engine originally.
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    Last edited by msgjd; 10-08-2019 at 14:07.

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    "" For #3, is the pressure plate/trans input shaft of an 809 series 2"? ""

    Good call. In the complication of the matter and time running out on getting too many other things done before winter, I missed the obvious.

    "" I would simply judge it by observing for any counter-weights on the unwanted flywheel that came on the engine originally.""

    That is one of the problems, the original flywheel/clutch/pp/bellhousing/tranny for the Shiny-290 was long gone before I bought the donor truck
    Last edited by msgjd; 10-08-2019 at 15:48.
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    Flywheels are balanced individually. The Damper takes care of balance as the engine runs. Flywheel can go on any position. If you use a FW hsg from a small cam on a big cam, you will need to enlarge one mounting hole, it is the one above the cam, when the engine went to a larger dia cam, that hole was moved up/outward a bit. No need to use the cork seal ring.

    You need to use the correct flywheel housing for the clutch, flywheel, trans you are using. Being older, it will be next to impossible to tell you what that was.

    To find out what torque the engine makes, post up the info off of the fuel pump data tag, it will be something like, 021 3312A on the first line and then 3003324 on the bottom line.

    It is the silver tag in the pic on the pump housing where the front cover bolts on to the body. If it is painted, use gasket remover or paint stripper to remove the paint, rubbing it will destroy the info, it scratches VERY easily
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    There
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