273 commando cylinder head bolt torque specs ? same as 340 ?

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stroker402

stroker402

1968 dart GTS convertible
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chilton 273 318 head torque spec says 85 ft lbs in low compression engines but does not mention what it would be for the commando ....just says 273 318 .. it says the 340 is 95 ft lbs. wouldn't you think the commando with 10.5 compression will be torqued at 95 ft lbs also like the 340 ?.
getting read to install my commando head back on the 273 .. It blew the pass side head gaskets 3 times already.. last time I had the heads milled make them flat.. they were not that bad only too off .002 ".
block appears to be flat . I check with a few different straight edges. used mr gasket 1121 head gaskets .. these suck the ring is so big in the bore, there is not enough meat to even clamp too. the fire ring is almost in the valley. that's where it blew last time .
arp bolts will be used this time.
I had the 1121 head gasket torqued to 95 ft lbs like a 340 with high compression.
opinions ?
 
stroker402 said:
chilton 273 318 head torque spec says 85 ft lbs in low compression engines but does not mention what it would be for the commando ....just says 273 318 .. it says the 340 is 95 ft lbs. wouldn't you think the commando with 10.5 compression will be torqued at 95 ft lbs also like the 340 ?.
getting read to install my commando head back on the 273 .. It blew the pass side head gaskets 3 times already.. last time I had the heads milled make them flat.. they were not that bad only too off .002 ".
block appears to be flat . I check with a few different straight edges. used mr gasket 1121 head gaskets .. these suck the ring is so big in the bore, there is not enough meat to even clamp too. the fire ring is almost in the valley. that's where it blew last time .
arp bolts will be used this time.
I had the 1121 head gasket torqued to 95 ft lbs like a 340 with high compression.
opinions ?
Click to expand...

I torque 1/2 head bolts and studs to 110.
 
67 273 2bbl and 273 4bbl use the same engine parts, except pistons and cam.

Torque specks would be the same.
 
Dana67Dart said:
67 273 2bbl and 273 4bbl use the same engine parts, except pistons and cam.

Torque specks would be the same.
Click to expand...
two different compression engines.. do you really think 85ft lbs is going to hold back a 10.5 compression engine that spins 6000 rpms ? 340's were 10 to one compression and they have 95 ft lbs torque. what gives? can't believe everything you read .
 
Bolt torque is based on bolt size, type of bolt thread pitch, metallurgy of the bolt and block, and the amount of allowable stretch.

If you over torque the bolts they are more likely to break.

To me the engineers who designed the parts would be a better source of info.
Screenshot_20240510-203428.png


10 more lbft may be allowed due to better head bolts?
 
Compression ratio has not one darn thing to do with bolt torque.
 
stroker402 said:
two different compression engines.. do you really think 85ft lbs is going to hold back a 10.5 compression engine that spins 6000 rpms ? 340's were 10 to one compression and they have 95 ft lbs torque. what gives? can't believe everything you read .
Click to expand...
The torque spec is a essentially a measure of how much a bolt is being stretched as it is tightened. There is a particular amount which is ideal, and all other amounts which are not. The torque spec for a bolt therefore has nothing to do with what the bolt is holding and everything to do with the nature of the bolt itself. If you want to hold something on harder, bigger bolts must be used, not more torque on the same bolt.
 
i'd order up a set from cometic.

they're not cheap, but it beats the pants off doing that job three more times
 
On my HP 273 the heads were machined and the block checked. I used similar head gaskets to the 1121's and torqued to 85. No issues in 14 years. I wonder what you have going on that you keep blowing that gasket?
 
My 1121s @11.3 Scr, were almost into the valley by the end of the first summer. IMO
the 1121s need a rougher deck finish to hang on to them harder.

I caught the slide on the First of 6 teardowns. and that was with ARP Bolts, torqued to 105.
I swapped to the bulletproof 039 FelPros, and ran 10.7Scr for the next couple of years. I reused the FelPros every time at Q= 039.
When that cam dropped lobes, the next bigger cam had a soft bottom end, so I took it apart and re-decked it for a Q of 032, Scr of 10.95 (that wasn't enough to satisfy my hunger for a bottom end, but was a good start.)
At the next teardown, the gaskets were still looking good, so I reused them. At the last inspection, in 2004/05, everything inside the engine was surviving, so I gave her a treat with brand new 039 FelPros.
Your results may vary
 
stroker402 said:
chilton 273 318 head torque spec says 85 ft lbs in low compression engines but does not mention what it would be for the commando ....just says 273 318 .. it says the 340 is 95 ft lbs. wouldn't you think the commando with 10.5 compression will be torqued at 95 ft lbs also like the 340 ?.
getting read to install my commando head back on the 273 .. It blew the pass side head gaskets 3 times already.. last time I had the heads milled make them flat.. they were not that bad only too off .002 ".
block appears to be flat . I check with a few different straight edges. used mr gasket 1121 head gaskets .. these suck the ring is so big in the bore, there is not enough meat to even clamp too. the fire ring is almost in the valley. that's where it blew last time .
arp bolts will be used this time.
I had the 1121 head gasket torqued to 95 ft lbs like a 340 with high compression.
opinions ?
Click to expand...
I have new arp bolts to use this time around ... arp recommends 100 ft lbs and there special lube. I'll be using a composite gasket 318 with a small fire ring also . that mr gasket 1121 has such a large bore ... it's almost to the edge of the valley ... with a 3/8" gap all the way around the fire ring to the edge of bore. also I noticed when removing the head that black coating on the 1121 gaskets released a film that had plugged a few of the water jackets. 1121 suck.
 
273 calls for 85 pnds torque, i found if you torque above that, it distorts the block deck. my 340 i use 80 # torque , also i use moly lube on bolts, also i torque in steps, 40, 50 50 70, 80. i ran into this issue long time ago.. i have customer, runs a 340 @ 10.65 cr, i torque heads at 85, with moly lube, never has had a gasket problem, also i use felpro 1008 gasket. just food for thought.
 
perfacar said:
273 calls for 85 pnds torque, i found if you torque above that, it distorts the block deck. my 340 i use 80 # torque , also i use moly lube on bolts, also i torque in steps, 40, 50 50 70, 80. i ran into this issue long time ago.. i have customer, runs a 340 @ 10.65 cr, i torque heads at 85, with moly lube, never has had a gasket problem, also i use felpro 1008 gasket. just food for thought.
Click to expand...

Do you use Moly lube when torquing the 273 head bolts @ 85 Ft Lb?
 
perfacar said:
273 calls for 85 pnds torque, i found if you torque above that, it distorts the block deck. my 340 i use 80 # torque , also i use moly lube on bolts, also i torque in steps, 40, 50 50 70, 80. i ran into this issue long time ago.. i have customer, runs a 340 @ 10.65 cr, i torque heads at 85, with moly lube, never has had a gasket problem, also i use felpro 1008 gasket. just food for thought.
Click to expand...
arp bolts says to torque there bolts to 100 ft lbs.. Is that ok to do ?
 
shop manual says to torque 340's to 95 ft lbs.. why is it it doesn't warp 340 blocks with no issues with gaskets, heads or blocks? 273 is basically same block with smaller bore.
 
all i wrote, i in regards of torque is from personal experience, i have always used moly lube on my head bolts and main bolts, by using moly lube , you will have more clamping pressure without distortion. i used on my 273 and my 340,.i know arp wants 100, lbs, you will pull block deck up creating a deck with low places and high places. also gasket seal problems. first time i torqued my 340 block at 95, it bell mouthed the top of the bores, by .006 i retorqued it at 85 had no bell mouthing of bores. my 273 was 11.1 cr, my 340 is 9 to 1, cr. i run stock eliminator with it. just food for thought,
 
stroker402 said:
shop manual says to torque 340's to 95 ft lbs.. why is it it doesn't warp 340 blocks with no issues with gaskets, heads or blocks? 273 is basically same block with smaller bore
Click to expand...
Same design but not the same block
 
perfacar said:
using moly lube , you will have more clamping pressure without distortion
Click to expand...
It is my understanding that the drag that a dry bolt thread provides is calculated I to the torque spec.

The luse allows the bolt to spin easier and now the same amount of torque is over tightening the bolt


Somewhere I recall seeing lubed spec at 50 (just a number) and dry is 75 ( just a number)
 
Torque on a fastener cannot be calculated. It is an attempt to get a desired stretch on a blind fastener. It is found by trial and error, and is also dependent on the lubrication. See posts #14 and #19 and take it to the bank. Perfacar also is giving you which head gasket to use. The most accurate way to "stretch" a fastener, say a rod bolt is to measure before and after torquing to achieve the desired range of stretch.
 
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