Broken main cap bolts on a 455

Discussion in 'Street/strip 400/430/455' started by 69SkylarkGS, Dec 14, 2019.

  1. 69SkylarkGS

    69SkylarkGS Well-Known Member

    Pulled the 1970 455 apart today to inspect it, put a new timing set and some new gaskets on. The engine is extremely clean inside and appears to be very low mileage. The strange thing is, we found two broken main cap bolts. One was broken at the head and the other was broken down on the stem. The stem bolt was the one that goes into the block. My friend who has been a master mechanic for many years looked at the bottom end and said everything else appeared to look great. The bearings showed no signs of wear and he said the engine literally looks like it barely has any miles on it. We recovered the top of the bolt and were able to remove both broken bolts with no issues. Anyone ran into this issue before? My friend couldn’t believe how clean the rest of the engine was for the age of it. The engine was removed from a wrecked low mileage Lesabre in the 70s and sat in the owners garage until I bought it. Any thoughts?
     

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  2. 69SkylarkGS

    69SkylarkGS Well-Known Member

  3. 69SkylarkGS

    69SkylarkGS Well-Known Member

    The bolt that was broken at the stem was still in its bolt hole and had not came out.

    5B0CD0A9-2C0A-42E2-AAB8-63C50E375D3D.jpeg F1329A17-9308-4397-A120-5BEC82C339B5.jpeg DDBCF4AD-0458-4642-8FC6-9ECF62C2887A.jpeg 16149870-9BF2-4A07-A6C1-B5AEC01F037A.jpeg E011B1BC-3582-4F6C-A1C4-5607FDF59E88.jpeg D1893313-C621-42EE-A1C2-A5223024CCFE.jpeg 87F522F3-23DA-48BB-B9BF-D4009720AA59.jpeg ED31B5E1-4747-4582-A2F4-CD356A4DE7F7.jpeg 63BE352E-A840-4696-B9D0-69A56A4911B0.jpeg
     
  4. johnriv67

    johnriv67 Well-Known Member

    That’s very strange, and just about the most beautiful engine I have seen. ITS SO CLEAN!
     
  5. 69SkylarkGS

    69SkylarkGS Well-Known Member

    We both were scratching our heads trying to figure it out. He suggested I check here. A friend of his who builds performance engines for a living said if all bearings check good it should be fine but suggested studs as replacements.
     
    Bill Nuttle and DasRottweiler like this.
  6. Freakazoid

    Freakazoid Gold Level Contributor

    I concur, either extremely low miles, with excellent maintenance. Can't believe there was no main failure. That's unreal.
     
    69SkylarkGS likes this.
  7. TrunkMonkey

    TrunkMonkey Well-Known Member

    I have seen things like that when an engine is suddenly/forcibly "stopped" in a collision.

    Often the crank will twist.

    If everything measures correctly and no cracks are found during NDI, press on with a rebuild.

    Make sure anything that could have been involved in a "high thrust" event, also be checked.
     
    Mark Demko and 69SkylarkGS like this.
  8. 69SkylarkGS

    69SkylarkGS Well-Known Member

    You think it needs a complete rebuild? With it being such a low mileage motor I was planning on running it. Obviously the 2 broken main cap bolts that we found today are a concern. I was hoping to replace the main cap bolts and roll, as a complete rebuild is probably not in my budget at the moment. I would replace them all with studs.

    My buddy said the same thing about the wreck possibly being the cause.
     
  9. Philip66

    Philip66 Well-Known Member

    That thing is super clean!
    Any sign of oil pan damage, like maybe it was dropped??

    I would replace the bearings just to be safe. You had planned on just replacing gaskets and timing set, right? While you're in there do the rods and mains.
     
    69SkylarkGS likes this.
  10. 69SkylarkGS

    69SkylarkGS Well-Known Member

    No pan damage. There was a little bit of sludgy oil in the bottom of the pan but I expected that from sitting for 40 years lol. That was the plan. Timing set is on we did that today. I’m now going to replace the water pump too. It’s off and I have to wait on parts anyway. I’ll probably do a flowkool with our hot weather here in SC.
     
    Philip66 likes this.
  11. telriv

    telriv Founders Club Member

    I just had that on a '65 Riv. GS 425/2x4 had one rear cap main bolt broken in the block. Original numbers matching block with a little over 100K. Engine appears to have NEVER been taken apart. Also two top rings were also broken. The bolt & rings that were broken were all black at the break points so they have been broken for a while & who knows for how long???
     
  12. TrunkMonkey

    TrunkMonkey Well-Known Member

    When it comes to mechanical and unknown conditions that are not expected, I would pull it, inspect it and verify.

    I come from aviation maintenance and chewed on dragster parts as a toddler in the 50s, and "overkill" is my call sign.

    However, if you do bare minimum and if goes badly, it is not like it is going to fall out of the sky and squoosh a busload of children taking puppies to the park.

    It is possible, it being a low mile engine, that the bolts were over-torqued on factory assembly, broke sometime later and that the engine never saw high RPM. If it had, it would have been another engine "back in the day", that went "boom" and got repaired or replaced.

    That happened more than a few times.

    But, as I stated, I have seen similar damage from engines coming to an instant stop in a collision, so I offered that information.

    And if you are going to pull the crank, have it checked for runnout and make sure all the crank-pins are in phase (see if the crank has any twist from along its length). And when you inspect, look for any impact evidence on the thrust sides of the crank journals and the sides of the bearing saddles, and both sides of the number three journals where the thrust bearing saddles the journal.

    That should only cost a few dollars to have it checked out, but it is easy for one to spend another's time and money.

    :)
     
    Mark Demko likes this.
  13. Schurkey

    Schurkey Silver Level contributor

    Not common, but I've heard of broken main bolts and broken main caps; and the bearings looked "wonderful" despite the breakage.

    "I" would slap a couple of bolts in there, look at the oil pump, disassemble a couple of lifters* cross my fingers, and run the thing.


    *The thing that scares me about how clean it is inside, is that it may be that clean because someone ran high-detergent oil additive to "flush" the engine. Hydraulic lifters are like sixteen tiny oil filters--crap gets in, but the clearances are so small that it can't get back out again. The lifter "guts" fill up with the most hateful sludgy crap you've ever seen. If I pulled a lifter or two apart--and they're as clean as the rest of the engine--I'd do the happy-dance and reassemble everything.
     
    69SkylarkGS, BuickV8Mike and 69GS400s like this.
  14. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Being that it has sat dry for 40 years it would probably be a good idea to do a re-ring and throw a set of new bearings in there while you're at it. There is a possibility that some of the rings are collapsed from sitting dry that long and have lost their spring?

    If you're already replacing all the gaskets, adding a set of rings and bearings would be cheap insurance that it will run well after the install. This is the least I would personally do anyway, would hate to do all that work to install it in a car to find out its a boat anchor and I had to take it back out!:mad:

    Would be a good time to do some oil mods as well while its apart if in you want?

    While its apart have the block and heads checked for cracks(first before spending $$ on parts), the car it was in had to be hit pretty hard to break those bolts. Makes me wonder if anyone died in that accident to be hit so hard that a couple of main bolts broke!:eek:

    Also don't swap to main studs without having the block line honed with the studs installed.
     
  15. sean Buick 76

    sean Buick 76 Buick Nut

    I’ve seen this a few times. Broken main bolts, and the bearings were fine. I would just replace the bolts and move on. This is another reason I use ARP studs in all my rebuilds but you also need to align hone the mains if you swap to studs.
     
    DasRottweiler likes this.
  16. 69SkylarkGS

    69SkylarkGS Well-Known Member

    It actually did not sit dry. It had plenty of oil in it, I wouldn’t say it was completely filled but definitely a good amount of oil. I went to roll the motor over on the stand, forgot about it and blessed my garage floor with plenty of oil lol. The PO told me the engine was stored properly but obviously I can’t verify that. The oil looked fine, other then the little bit of sludge in the bottom of the pan. I’ve only seen the inside of a few motors as I’m not nearly as experienced as many here but I’ve never seen one so old but clean inside.

    I was told the wreck totaled the 70 lesabre and it was hit in the rear, so I’d imagine it must have been bad if that is true.

    I appreciate the heads up about the studs, I’ll just get TA’s bolts then.
     
    Last edited: Dec 15, 2019
  17. 69SkylarkGS

    69SkylarkGS Well-Known Member

    I’m glad someone has seen it before, it makes me feel a little better about it. I’ll stick with the bolts as well. My hope was to basically do the new bolts and roll. As long as everything else checks good anyway. Other then headers, exhaust and an Edelbrock intake it will be basically a stock engine that doesn’t see north of 5k. The car will be used for cruising on a weekend etc. The only reason for the intake is I already have it and it weighs so much less for ease if it needs to be pulled again down the road.
     
  18. BQUICK

    BQUICK Gold Level Contributor

    Yeah, I wouldn't disturb that factory build.
    Never seen that but I did have a low mileage 455 that had a long head bolt where a short one was supposed to be. Put a short one in and ran it a long time. Head gasket never leaked....
     
  19. 69SkylarkGS

    69SkylarkGS Well-Known Member

    That’s interesting about the short bolt. I’m sure there were factory errors over the years. My buddy also said one of the broken bolts looked like it may have had a casting flaw in it when we inspected it.

    This is one of the things that concerns me, disturbing the factory build. I don’t have any machine shops anywhere near me that do Buicks. They all mostly do Chevys. I’m in Myrtle Beach, SC so I’d be rolling the dice having it rebuilt anyway.
     
  20. BQUICK

    BQUICK Gold Level Contributor

    "...so I’d be rolling the dice having it rebuilt anyway."
    The shortest lived motor I had was one that was fresh with new bearings. They might have been new but not set up right was the problem. As was breakin procedure....
    The factory didn't do a bad job....except for some built on certain days....:rolleyes:
     

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