Rebuild on 300 Cummins

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by 85COE, Feb 27, 2021.

  1. 85COE

    85COE Light Load Member

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    I'm looking at getting the engine on the Cabover rebuilt before I put it on the road. I found an old school mechanic who quoted me $4k with a 1 year guarantee. I just need to supply the parts.

    I know the crankshaft is something needed, but beyond that, I'm not sure. Would anyone care to enlighten me?

    Not a gearhead, learning this as I go along.

    Thanks!
     
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  3. AModelCat

    AModelCat Road Train Member

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    What's wrong with the crankshaft? Unless its broken or a bearing has spun it's probably fine.

    If its just worn past re-use spec, send it to a machine shop and have it ground undersize and get the appropriate undersize bearings to match.
     
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  4. AModelCat

    AModelCat Road Train Member

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    I've got a 42 year old CAT and the crank has not had 1 journal ground undersize yet. Just put new bearings in it and the bearing clearance is still within the spec range for new bearing clearance.
     
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  5. 85COE

    85COE Light Load Member

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    The engine has 809,xxx miles on it. The heads were replaced at some point, but no idea when. A rebuild seems reasonable so that way I can ensure it'll last another 800k miles. The reason for the crankshaft is for safety. Don't need the old one failing with a fresh rebuild
     
  6. AModelCat

    AModelCat Road Train Member

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    You're looking way too far into it. I wouldn't waste a cent on a new crankshaft if the old one is not worn or cracked. Huge waste of money IMO.
     
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  7. 85COE

    85COE Light Load Member

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    While I appreciate the feedback, I was advised to replace the crankshaft during a rebuild by an owner operator since 1975.
     
  8. Coal Region Deplorable

    Coal Region Deplorable Light Load Member

    Sorry to say this but that guy's giving you crap advice. I never cut crankshaft unless they're worn out of spec, and never replace them unless they're cracked or broken.

    Hell even the factory remanufactured engines from cat Cummins Detroit or whoever don't have new crankshafts in them
     
  9. AModelCat

    AModelCat Road Train Member

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    I did some reman work for CAT for a while. If you think a CAT reman is 100% new, you'd be quite shocked. If the parts meet reuse and salvage criteria, they go back in. I've rebuilt dozer transmissions where clutch packs were reused, as well as bevel/pinion gears.
     
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  10. Coal Region Deplorable

    Coal Region Deplorable Light Load Member

    You must be reading my mind I was just thinking about caterpillar. They clean that stuff good and then they have some fancy measuring device that uses lasers. Nothing that meets specs for rebuild gets trashed there.

    That's why cat wants cores back on just about everything
     
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  11. AModelCat

    AModelCat Road Train Member

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    You'd be suprised at what CAT considers ok for reuse too. Learned a lot there for sure.
     
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