blowen headgasket, il6 165hp

[ziggy]

hi, well, i started workin on my ol skow. decided i had a blowed head gasket between 1 and 2 on my 72 il6, 165hp 250cid chevrolt engine. decided that with a air leak down test. tested cyl. 1 and 2, both those cyl.s had low compression, 90psi. cyl. 3-6 @ abouts 140psi which is spec. air leakdown indicated no air passing out of carb, exhust, and minimal air passed through the holes in the head leading to the crankcase. had much air passing between 1 and 2 at the sparkplug holes. <br />so now i got my head off. question is what to do now. the suspision for the blown headgasket is the engine overheated a min. of two times. the engine and valve train have been gone through in 98. rebuilt truck engine is what i have with a mecrusier head. can i get away with just checking the head for flatness and if it is, just put me a new headgasket ontoit and be done with it? <br />any special areas i need to be looking at while the head is off. i havn't yet, but intend on looking closely at the area between 1 and 2 of corse. as of right now intital inspection shows blackness between 1 and 2 on the headgasket. aslo the metal bewtween these two cyl.s is a bit blackened and blue. i assume i've found the problem. one quik good note. a quik run of my fingernail up the cyl. wall of #1 and i couldn't catch me any ring wear. just a little charcole at the top above the rings. should i be coating the deck with soome oil? the piston walls too. talked to the head guy today and if i go for a whole head rebuild that it'd be 3 weeks. ...i'm thinking of not doing anything other than checking for flatness of the head, if thats ok, put it back where i found it. any comments on what i should be checkin for???

 

[KaGee]

Re: blowen headgasket, il6 165hp

You can do a quick check of the head and the block if you have a good straight edge.

 

[ziggy]

Re: blowen headgasket, il6 165hp

thanks kagee, i have nothing that would quilify as a straight egde. the min. i am hopeing to do is to take the head to a headshop and have them check the head for flatness. if flat, i plan to put it back where i found it. w/o a valve job. is it nesseasary to check the block deck for flatness too? that i don't have a plan for..do i need one?

 

[Silvertip]

Re: blowen headgasket, il6 165hp

As long as you are at the shop, have them take a skim cut to "true" it. If the engine has been overheated a minimum of two times, that's what compromised the head gasket. The head has very likely warped and needs to be trued. Doesn't have to be disassembled for that and the cost is minimal. Don't use an automotive head gasket. It won't last. Chances are the block received no damage from overheating unless it was really "cooked". If you had good compression on cylinders 3-6 chances are also good that 1 & 2 are ok. The only way to be sure however is to disassemble it and take a look. As they say "pay now or pay later".

 

[Bondo]

Re: blowen headgasket, il6 165hp

An old Trick that must be done with care,.....<br />Is to run a Flat File over the surface,.... Lightly,+ Evenly..........<br /><br />It'll Show the Highs or Lows as you clean the surface.............<br /><br />I'd Start with a Wire Wheel or Rol-loc Disc to clean the bulk of the gasket,+ debris out of the way..........<br /><br />You'll want to Look Extremely Closely where the Burn-thru occurred,.... Cracks might be hiding there......<br />The Head is a candidate for Cracks in the same place.......<br />Around the Valve Seats Too,.... That motor took a Pretty Good Thermal Shock......

 

[ziggy]

Re: blowen headgasket, il6 165hp

thanks folks, upinsmoke, i've got a buddy that says the same thing about the skim cut. i wondered about the disassembly of the valves to do that, incurageing that ya don't have to remove them to do the skim cut. gonna talk to the head (marchineist)guy tomorrow. only gonna use oem gaskets, least that's the the mercrusier store better sell me.. . and yeah, i'm hopein the 1 and 2 are similar to 4-6 too. and i am willin to take the chance at this point going on my air leakdown test that revealed not much air passin from the crankcase. bondo, thanks for the tip for lookin close for cracks, will do, when it's light out, tomorrow. so just grind the top of the block off with a wire wheel ay? ok. the file trick, i've used that in my trade, though with much smaller parts. will contemplate that idea as a file is pretty flat,i got me a dull single ******* cut that might be a start for that. where will the metal dust go though, can i put enough rags into the cyl. to keep that dust out? thanks guys, yer helpin me out for sure..

 

[ziggy]

Re: blowen headgasket, il6 165hp

wow, i got me a word cut out of my statement up above. geee, and i used a proper tool name too. about the file that is....censorship on proper tool names???

 

[Reel Poor]

Re: blowen headgasket, il6 165hp

If your not going to disassemble the valves and have them checked at least check them with some liquid. Block the head up some way (maybe 2x4's) so the combustion chambers are facing up and fairly level. Then pour some alcohol or miniral spirits into the combustion chambers to see if the valves are sealing enough to keep the liquid in the chamber areas. If the alcohol leaks from the chamber area and into the intake or exhaust runners you may as well have the valves worked. If it holds the alcohol the valves are probably seating good enough. Let the alcohol stand in the chambers for a while to see if it leaks past the valve seats.<br /><br />Don't use water, the water has to much surface tension to prove a problem.

 

[ziggy]

Re: blowen headgasket, il6 165hp

another good idea, thanks reel poor. sounds like i should be doing that before i go to the see the machinist. perhaps that test and the clean up and inspection for cracks between 1 & 2 prior to seein the machinist even...it will be interesting to see if i can block it up, upside down with the valves and rockers still attached...like plain ol rubbin alcohol? i might have minearl spirits around the house too....

 

[Reel Poor]

Re: blowen headgasket, il6 165hp

Yea rubbing alcohol will work as well as anything with low surface tension. And yes I would do that before you take it to the machine shop.<br /><br />Some machine shops have a tool that they can use to check the ability of the combustion chambers to hold vacuum. This one is made by Sioux.<br /><br />

<br /><br />

 

[ziggy]

Re: blowen headgasket, il6 165hp

thanks for the pic reel poor. gonna have to have the machine shop use a tool like that on my head as i did yer fill up the combustion chamber trick, used brakekleen and #1 & #2 intakes both appear to leak.... good news so far is the metal between 1 & 2 aint melted away...