350 Overheated, blew headgasket. Need resurfacing?

Discussion in 'Small Block Tech' started by MrSony, May 8, 2019.

  1. MrSony

    MrSony Well-Known Member

    A few weeks ago, my SP 350 overheated on the highway (crappy radiator), and got to 260 on the gauge. I pulled over, shut it off. Took a while but it settled down and didn't over heat again on the way home. About a week later, I started the car up and drove to the gas station to air up the back left tire. Started with 1 pump, ran perfectly fine and smooth. Started it back up afterwards, and the engine was shaking and stuttering. Thought it was just some bad gas, so I floored it while driving and it went Ba-WHAA (pause...) AAAAA (pause) POP POP AAAAA and it had no power at all. Took it home, gave it a compression test, #1 was 90 psi (was 170), and 3 and 5 were 0. I stopped testing after that. So, this leads me to believe the headgasket blew out between 3 and 5, and I guess partially 1. The engine still idles fine, save for a shimmy here and there (I guess when those affected cylinders fire), and if not flooring it, still drives "normal". it feels like it's running on, well I guess 6.5 cylinders.

    My question is, how easily to SBB deck surfaces and heads warp? It only got to 260 once, and it still idles ok and if just putting around is ok as well. No coolant in the oil. Any input is appreciated.
  2. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    Resurface and try new gaskets maybe get new bolts mine has studs in it, that will bump the compression a little.
  3. hugger

    hugger Well-Known Member

    I wouldn't even fool with checking it,..just pull both and have them cut .008
  4. MrSony

    MrSony Well-Known Member

    The heads, or the block? or both? why .008? that just the standard "surface"?
  5. Stevem

    Stevem Well-Known Member

    Mill only the heads !
    Wipe down each cylinder with a good amount of oil , pack them with paper towels or rags and then use 3 inch OD drill mounted spin on type scotch brite pads to clean off each block deck surface.
    Then clean all the grit and oil out of the cylinders and lifter valley.

    While things are down / apart check all of your push Rods at there ends for ware and roll them on glass to check there straightness.
    Also check each rocker are ware points at this time.

    When you get the heads back from milling set a head gasket on them and lightly roll over any part of the newly cut sharp deck that sticks out passed the head gasket fire ring and then your good go!

    PS, before you drop the heads back on Make sure that all of your needed threaded bolt holes work as needed!
    Last edited: May 9, 2019
  6. alec296

    alec296 i need another buick

    What gaskets are you using? Clean up on heads are a decent plan. 260 is lot of heat.
  7. Stevem

    Stevem Well-Known Member

    It's not so much how hot they got in terms of iron heads and related damage it's how fast the cooled down!

    A sure way to crack any overheated head is to refill the rad with room temp water and then start the motor up!
  8. alvareracing

    alvareracing Well-Known Member

    260* can peanut butter the rings, hopefully you got lucky and didn't get them, but I'll bet you won't have the same leak down as before!
  9. MrSony

    MrSony Well-Known Member

    Felpros. Same as whats on there.
  10. MrSony

    MrSony Well-Known Member

    The engine actually runs alright, starts fine. Just is very vibrate and shaky, like its missing on a few cylinders. No doubt its because 3 and 5 have no conpression.
  11. MrSony

    MrSony Well-Known Member

    Let it be known, I did rebuild this motor (stock bore, just ta cam bearings, crower cam, ringa bearingd and gaskets), in 2017. It has about 10,100 miles on that rebuild. Afaik it had about 75000 when I got it.
    Last edited: May 9, 2019
  12. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    I would mill the heads 8 or 10 thou and new head gaskets
  13. MrSony

    MrSony Well-Known Member

    Ythink the block would be fine?

    Any reccomendations on a good straightest for checking warpage? Whats the acceptable range? None?
  14. BuickV8Mike

    BuickV8Mike SD Buick Fan

    24" steel rule and a shim gage would be a good start. I would be mostly concerned with the bow in the long length. I think you might be over thinking it. I would just put new gaskets on it and go. Just me.
    MrSony likes this.
  15. MrSony

    MrSony Well-Known Member

    That's what I hope can be done.
  16. Schurkey

    Schurkey Silver Level contributor

    You've compression-tested three cylinders, they were all bad. And then you quit.

    FIRST thing you need to do is compression-test the rest of the cylinders.
    "I" would do a leakdown test on all eight, also. Having two no-compression cylinders next to each other doesn't mean you couldn't have put holes in two pistons--or burnt the exhaust valves of two neighboring cylinders. This is--probably--a failed head gasket. Doesn't have to be, though.

    At least one cylinder head is coming off. Yeah, you might as well pull both, and get busy with the straightedge. Check both heads, check the block decks. Maybe you machine the block--maybe not. NO way to know until you check for flatness. Come to think of it...were these heads and the block decks checked for straightness when the engine was assembled?

    Something else to consider: The "HOT" light on the dashboard is triggered by a temp sensor that may not switch on until 245--260 degrees, depending on application. In some applications, GM considers 260 degrees "just" hot enough to warn the driver. DID THE COOLANT BOIL? Coolant boiling is the real measure of "overheating". That's where damage becomes fairly certain.

    DID YOU FIX THE OVERHEATING PROBLEM so this doesn't happen again?

    Unless the block needs it, too.

    The Automotive Engine Rebuilders Association, Ford, GM, have each issued notification warning against doing exactly that. The Scotchbrite abrasive gets into the engine, cannot be completely cleaned out, and then destroys the bearings. This has been well-known for years.

    Sample From General Motors: TSB 00-06-01-012D
    Do not use abrasive pad/bristle devices to clean the gasket surfaces of engine components.
    Abrasive pads should not be used for the following reasons:
    • Abrasive pads will produce fine grit that the oil filter will not be able to remove from the oil.
    Abrasive pads can easily remove enough material to round cylinder head surfaces. This has
    been known to affect the gasket’s ability to seal, especially in the narrow seal areas between
    the combustion chambers and coolant jackets.
    • Abrasive pads, wire and abrasive rubber finger wheels can also remove enough metal to
    affect cylinder head, block, oil pan rail, and intake manifold runner flatness, which can cause
    coolant and oil leaks and air leaks. It takes about 15 seconds to remove 0.203 mm (0.008 in)
    of metal with an abrasive pad.
    • Abrasive pads, Abrasive rubber fingers wheels & wire wheels with high speeds grinders
    produce air bourn debris that can travel throughout the shop contaminating other work
    being performed outside of the immediate work area.

    On top of that, some gorilla will decide to "clean" the gasket surface--and he gets so heavy-handed with it that he'll carve waves into what used to be a flat casting. Aluminum is easy to "clean" waves into, but a real doofus can destroy iron castings, too.

    Last edited: May 26, 2019
    MrSony likes this.
  17. MrSony

    MrSony Well-Known Member

    The engine is actually in a g body regal. The mechanical gauge read 260 before I shut it off. Coolant was boiling. The radiator is a piece of crap, and the belt was slipping. Both issues will be addressed. The engine was just a weekend garage rebuild to get my car ready before winter two years ago. Has 10k miles on the rebuild, stable oil pressure, stock bore (honed myself) with new rings, home valve job. It was pretty peppy and didn't burn much more than a pint every 3k miles. The front rope seal leaked (cut it too short. Whoops) as well so that attributed to it. NEVER smoked or anything. It was a nice engine. Crower lvl3, stock everything else save for Everyday Perf. M4mc and a TA Hei modded to the power timing thread specs. 211rwhp at 5k, 263rwftlbs at 2700.
  18. Schurkey

    Schurkey Silver Level contributor

    Coolant boiled? Add crack-testing to the list of things to be done by the machine shop.
  19. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    Do a leakdown test and you will then know for sure where your problems are, very easy to use just need an air comp that can push 100 lbs.
  20. MrSony

    MrSony Well-Known Member

    Let it be known, the coolant has always kinda percolated at least for a few seconds after I shut the car off. This was one of those times. Sitting there off it did get to 280 on the gauge. Once I let it cool down to 200, it was perfectly fine on the hour long ride home and for the next two weeks until the hg blew after I restarted the car after airing up my tire.

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