273 commando Build

-
246385562_311722616983203_7214626194564188517_n.jpg
 
UPDATE UPDATE UPDATE !

SAD NEWS AGAIN ! Blew another head gasket again .. same pass side , different location now on #8 and blew into the valley again . this last build i installed arp bolts torqued to there spec #100 .with there lube , chased all the threads agin blew out the bolt holes, head were milled straight, .003 off head and retorqued after a few heat cycles.
I have noticed where the gasket blows is where it hasn't enough material clamping surface on the gasket between the bore and the edge of the valley approx 3/8/-1/2" width.. because the head gasket has such a big bore . I used 318 head gasket on this build. still too big for the stock 273 bore... the 273 has 150 psi when doing compression check .

this last build was impressive ! reason being the engine screamed with endless power.. eveerytime the engine blew a head gasket was when pushed the gas pedal down just enough to open the secondaries 3/4 way .
this engine revved like it was on nitrous .. It was that fast of a rev. no BS !
stock 920 heads with just alittle clean up on casting ports that's it. isky cam .. If you need more info just look back at previous posts here.
the the question now is what should I do.. o ring the heads stud it ? up for suggestions maybe that block is warped or the bolt holes are all pulled up stretched upward now after the 3 times of messing with this issue..
I'm tired of messing with this same issue all the time .
 
stroker402 said:
UPDATE UPDATE UPDATE !

SAD NEWS AGAIN ! Blew another head gasket again .. same pass side , different location now on #8 and blew into the valley again . this last build i installed arp bolts torqued to there spec #100 .with there lube , chased all the threads agin blew out the bolt holes, head were milled straight, .003 off head and retorqued after a few heat cycles.
I have noticed where the gasket blows is where it hasn't enough material clamping surface on the gasket between the bore and the edge of the valley approx 3/8/-1/2" width.. because the head gasket has such a big bore . I used 318 head gasket on this build. still too big for the stock 273 bore... the 273 has 150 psi when doing compression check .

this last build was impressive ! reason being the engine screamed with endless power.. eveerytime the engine blew a head gasket was when pushed the gas pedal down just enough to open the secondaries 3/4 way .
this engine revved like it was on nitrous .. It was that fast of a rev. no BS !
stock 920 heads with just alittle clean up on casting ports that's it. isky cam .. If you need more info just look back at previous posts here.
the the question now is what should I do.. o ring the heads stud it ? up for suggestions maybe that block is warped or the bolt holes are all pulled up stretched upward now after the 3 times of messing with this issue..
I'm tired of messing with this same issue all the time .
Click to expand...
Dang, where's it blowing out at?

100_4806.JPG
 
I used composite 318 head gaskets installed dry .. Arp bolts I used there moly lube on the bolt threads torqued #100 to there spec and I re torqued after a few heat cycles
 
stroker402 said:
I used composite 318 head gaskets installed dry .. Arp bolts I used there moly lube on the bolt threads torqued #100 to there spec and I re torqued after a few heat cycles
Click to expand...
Ah ok…my bad….misread your post…thought there was some kind of lube on the gaskets…
 
I stopped checking decks for flatness with a straight edge a long time ago. That's heads and blocks.

The block needs to be decked and then you need to look at your tune up. When you are blowing gaskets like you are it's two things. The decks are not flat and you are getting detonation.

The gaskets don't lie.
 
I agree ! I have another original stock bore 273 block to rebuild. .. electronic dist curved with fabo plate 34* total 16* inital 18* in the plate
 
I'd bet that deck is most of the issue. This one looked flat with a straight edge also. This is a "touch off" pass with my CBN surfacer. See the grooves? That's the factory surfacer marks, and its shitty. Your block is 60 some years old, should have been surfaced during the build.

20241022_135117.jpg
 
stroker402 said:
I appreciate that !
ok when I deck the block that will change the intake manifold angle then ? right ?
Click to expand...
Mill it just enough to equalize and square the block. The intake gaskets should work fine. Has to be the block. I've run std Fel-Pro head gaskets with 920 heads with more compression and full throttle TQ. I've even run "J" heads with never a head gasket failure.
 
Now, if you have to cut a large amount to correct slope and twist (common problem) you MAY have to mill the gasket surface to allow the intake to set far enough down that the intake ports align properly.
 
here is a pic of a stock oem 273 commando 10:5 compression steele shim head gasket.... you can see the gasket is egg shaped toward the top near the valley ... could this be an issue with the way the chamber is shaped and the gasket I used. just say n . the composite gaskets I have been using are perfectly round.

273 commando head gasket.jpg
 
stroker402 said:
here is a pic of a stock oem 273 commando 10:5 compression steele shim head gasket.... you can see the gasket is egg shaped toward the top near the valley ... could this be an issue with the way the chamber is shaped and the gasket I used. just say n . the composite gaskets I have been using are perfectly round.

View attachment 1716318884
Click to expand...
Because no one makes 273 specific gaskets, you may need to contact Cometic and have them make you a pair with the 273 sized bore. . A few here have done that. Double check the deck and head flatness when you have those heads off.
 
You must log in or register to reply here.
-

Back
Top