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Technical SBC untapped crankshaft

Discussion in 'The Hokey Ass Message Board' started by Gearhead Graphics, Mar 2, 2020.

  1. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,604

    Gearhead Graphics
    Member
    from Denver Co

    Working on my SBC for the bucket, and the crankshaft snout is untapped. Ive read around about it. Seems its about 50/50 for beat the balancer on vs drill and tap.
    The motor isnt apart, its on my stand. Id rather NOT take it apart and have a machine shop drill it.
    Can someone talk me into beating it on, or into drilling and tapping it as it sits on my engine stand?
     
  2. I drilled a 348 crank snout, worked out fine. Borrowed a mag base drill but couldn’t get it set up correctly so I just drilled it with a hand drill, started small and worked up to the proper size.
     
  3. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,221

    Jmountainjr
    ALLIANCE MEMBER

    If you want to drill it by hand, and want a job on par with most machine shops, make a drill guide. Track down a friend with a lathe and make a sleeve that will slide onto the crank snout that has a drill guide on the end. Then just be careful squaring up the tap, or use a tap guide.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 46,865

    squirrel
    Member

    What are you doing with this engine? If it's a mostly stock rebuild, you won't be racing, and the parts are in good condition...use a 2x4 and a BFH and install the damper, and don't worry about it.
     

  5. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,604

    Gearhead Graphics
    Member
    from Denver Co

    @squirrel, its a mostly stock 350. Big cam, its been apart before, probably bored but unsure how far. Its just my t bucket, no real racing. Everything with the pan and valve covers off looks to be fine. The balancer is off a different motor, unsure of condition, but visually looks OK.

    Leaning more towards BFH, just wanted some reassurance
     
  6. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,362

    56sedandelivery
    ALLIANCE MEMBER

    There is actually a guide, sold on that auction site we all know and love, that makes drilling and tapping an undrilled crank easier than eyeballing it. Years ago, I did the 327 in my FED by using a reverse fluted drill bit; I fired the engine up, and using an electric drill set on reverse, drilled the hole pretty quickly. Took a little longer to tap it. Course I also had the room to do it; had it been in a car, it would't have been possible. Look up 283209768214 on E-Bay for an example; this is't the one I've seen in the past, but it's also cheaper. Interesting that the number starts in "283", one of the engines it's designed for. I am Butch/56sedandelivery.
     
    Last edited: Mar 2, 2020
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  7. deuceman32
    Joined: Oct 23, 2007
    Posts: 314

    deuceman32
    Member

    I totally agree with Jim, especially if you are using an automatic trans.

    Now for you stick shift guys who like high RPM launches, I once made my own drill guide. I started with the cheapest crank turning socket I could find, and slid it onto a newer crank that was already drilled and tapped. Took a 7/16 fine bolt about 3 or 4 inches long, cut the head off and turned the top 2" or so down to 25/64" in diameter. Screwed this into the crank with the socket on it. Scrounged a thick wall steel bushing about an inch long with a 3/8 or smaller hole, ran a 25/64 bit through this, slid it onto my homemade pilot stub, and welded the bushing to the crank socket, which then becomes a slide-on drill guide for your undrilled cranks.
     
  8. X-cpe
    Joined: Mar 9, 2018
    Posts: 998

    X-cpe

    We pounded all of them on before they put a bolt hole in them. Using a 2x4 is best because if you hammer directly on them you risk peening over the edge of the center hole and then the pulley lip won't center up and the pulley won't lay flat. That leads to cracked pulleys.
     
  9. I’ve never heard of a 350 not being drilled. Are sure there’s not a broken bolt in the snout?
     
  10. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,604

    Gearhead Graphics
    Member
    from Denver Co

    Also not 100% sure its 350. Going by what I was told, but havent looked up any numbers.

    Im quite positive no broken bolt, Did the best degrease job I could, and flashlight, no visible difference, no threads, no bolt.
     
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 46,865

    squirrel
    Member

    Uh...yeah....that's what I was thinking. If it's a 283 or 327 and not drilled, then the damper is small, and it came with a short water pump, and would be fine. If it's really a 350 and getting a big damper and it might have a long water pump in it's future, then a bolt would be good.

    There are several variables here, you see....Chevy started using bolts around the time the 350 came into production. Which was just before the long water pump came along. Think about the loads on the crank snout, how far forward they are from where the damper meets the crankshaft, etc.
     
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  12. deuceman32
    Joined: Oct 23, 2007
    Posts: 314

    deuceman32
    Member

    Hey Butch, thanks for posting (while I was typing). The store bought jig looks really good and they sell it for less on their own site, 12bolt.com. Plus I just learned that the ideal drill bit is a W size, not 25/64. More thread bite. $40 for the jig, $55 includes W bit and tap. Thanks, man.
     
  13. squirrel
    Joined: Sep 23, 2004
    Posts: 46,865

    squirrel
    Member

    I bet if you had a lathe you could make your own drill jig, pretty easily.
     
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  14. PacaRacer50
    Joined: Oct 3, 2010
    Posts: 159

    PacaRacer50
    Member

    I will never understand why Chevrolet didn't drill, tap and use a bolt to retain the dampers on the small blocks from day one. I have spun off and destroyed three perfectly good small blocks because of this in my past. After the third one I made sure to have my machine shop drill and tap out every Chevy engine I did from there on out.
    Two of the engines were backed with automatics with stall converters that were above 2800 rpm so I would do it regardless of what trans is behind it.
    The stick shift engine was a 220hp 283 in a 64 Impala and when it came off it tore off the waterpump, fan shroud and the hood was totally destroyed. Hood actually bend up 8" all the way across from side to side. It sounded like a cannon went off under my hood. I was launching it at 6500rpm in a drag race against a Olds 442 that belonged to a friend of mine.
    After the Impala did that I never built another one without drilling the crank. I have done about 30 small blocks since then for myself and friends and never again have I had an issue with the dampners.
    Play it safe and drill & tap it..
     
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  15. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,781

    DDDenny
    Member
    from oregon

    My NOS small journal crank came out of the GM box drilled/tapped, make sure to use the correct style thick washer and lockwasher.

    20190828_162529.jpg

    Average Joes have been doing them for years without a jig, would I try it, nope.
    Somehow, come up with something to establish a straight hole, don't do a " it's good enough for what it's for" kind of job.
     
    Deuces likes this.
  16. I had a new, over-the counter 327/365 back in 1965.....the crank was drilled/tapped from the factory. My 327/375 HP motor in my '40 has a drilled crank also. The only non-drilled cranks I have seen were early 283 motors......with the small dampers.

    Let us know what it really is.....
     
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  17. I still remember the first SBC I encountered without a drilled and tapped crank. I was 19 and it was a homemade 302 with a 283 crank in it. Someone told me to just smack the balancer on with a BFH and it would be fine. It had been together for a while in a running car. But, pretty sure I drilled and tapped it knowing it would soon see more than 9000 rpm in a 3300 lb car. I just didn’t trust not having it attached a little better. That one never came apart, but I did lose a balancer on a Pontiac that was bolted on but got lose a few years later which thankfully just broke and stopped the engine, yanking the timing chain apart. No other damage to that one.
     
  18. oldolds
    Joined: Oct 18, 2010
    Posts: 3,029

    oldolds
    Member

    I think I would bolt all replacement dampers on. I am not sure the clearance is the same for a press on compared to bolt on. If you are using a random used one who knows what held it on.
     
    onetrickpony likes this.
  19. jaracer
    Joined: Oct 4, 2008
    Posts: 497

    jaracer
    Member

    Before attempting to install the damper, set it engine side down on a hot plate. I've used a coffee cup hot plate, but a larger one is better. Let it set there for at least 10 minutes, then install it quickly. You will still have to tap it on, but you'll be surprised at how easy it goes.
     
  20. If it was mine, I would drill and tap it. Install the proper bolt and washer so I could sleep at night.;)
     
  21. tiredford
    Joined: Apr 6, 2009
    Posts: 493

    tiredford
    Member
    from Mo.

    When I was a kid, I had a balancer come off a 283 @ 70mph. I pulled the radiator and drilled a hole by sight. The indent in the crank was kinda tapered, so I let that guide the bit. I used a 3/8 or what ever tap I had and called it good. Found a big washer with a small hole and bolted it down. I beat the balancer back on then the bolt and washer. I had no idea you had to have lathes and machine shops to do this simple little thing...lol
     
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  22. Jokester
    Joined: Jan 29, 2005
    Posts: 440

    Jokester
    Member

    I had a 283 with a thick 350 type dampener/balancer (4 speed car). Threw it off while leaving a stop sign at a non-aggressive speed. Fortunately missed the radiator.

    Also had a 327 with the same type thick balancer on it (TH350 trans). It came loose on a road trip (300 miles) and it ate up the keyway in the crank. Had to replace the crank.

    Now both cars have them bolted on.

    my 2 cents.

    .bjb
     
  23. birdman1
    Joined: Dec 6, 2012
    Posts: 994

    birdman1

    I remember Chevy getting sued by the government after some of the dampeners flew off and killed people. Just kidding lol
     
  24. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,536

    junkyardjeff
    Member

    I used that kit from 12bolt.com to drill the crank in my 235 and worked just fine,ended up getting the tap and drill bit since I did not have a W bit in my tap and die set.
     
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  25. saltracer219
    Joined: Sep 23, 2006
    Posts: 764

    saltracer219
    Member

    I have machined a lot of S.B. Chevs and I have never seen a 350 without a tapped crank snout either!
     
  26. Toner283
    Joined: Feb 13, 2008
    Posts: 1,326

    Toner283
    Member

    Tman and Blues4U like this.
  27. southcross2631
    Joined: Jan 20, 2013
    Posts: 4,004

    southcross2631
    Member

    When you beat the balancer on try to support the rear of the crank because the thrust bearing is taking the force of the blows if the balancer gets stuck. you can cut a block of wood to slide between the engine stand and the back of your crank.
    Have pounded the balancer on lots of times. If it was me I would drill it after seeing a guy lose one on his front motor dragster. It came off hit the track and took out one the frame rails. Luckily he 2 on each side.
    Heating them up makes it much easier.
     
    bobss396 likes this.
  28. Take your time if you want to go the BFH and 2 x 4 method, it only gets worse if it gets a crooked start. Make sure everything is squeaky clean and a scant use of Lubriplate never hurts.
     
  29. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,604

    Gearhead Graphics
    Member
    from Denver Co

    Ordered the setup from 12bolt. Im curious enough now I'll get the casting #s off the motor tonight or tomorrow and post them to see what it is in reality.
    Friend took it out of a 55 chevy he was building for a gasser, it has side mounts so its not the original motor for that, and then i bought it from the guy that bought it from him, so a lot of forgotten information on it. Either way I'm sure itll motivate my glass bucket plenty well enough
     
    scotty t likes this.
  30. squirrel
    Joined: Sep 23, 2004
    Posts: 46,865

    squirrel
    Member

    take a picture of the back of the crankshaft too, where the flywheel bolts on. The shape of it will tell us what the stroke is, most likely.
     

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