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ducks13
New User
Sep 27, 2008, 4:55 PM
Post #1 of 5
(3172 views)
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I have a 97 honda passport with a 3.2 V6, it is the same as an Izuzu. I have never worked on an engine with highly stressed head bolts before and am a little confused by what I have observed.
The bolts seem to be extremly tight although the torque spec for the new bolts is only 47 ft-lbs. I would guess that it is taking 125+ ft-lbs to break them loose. One of the bolts actually broke when I loosened it and one of the bolts was already broken when I got to it. The shop manuals say these bolts should be replaced, not reused, when you change the head gaskets. I believe they are 12mm bolts.
I have the hayes shop manual and got alldata's online shop manual too and they both have the same torque spec. I think hayes says they should be lubricated while alldata's said dry.
So, my questions is, does 47 ft-lbs sound like the right torque spec and if so why were the bolts so tight when I removed the old ones? Also, why do they have to be replaced if they only get torqued to 47 ft-lbs?
Thanks
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 27, 2008, 7:29 PM
Post #2 of 5
(3167 views)
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Guess you'll have your plate full with just the broken ones first. The bolts have to be replaced with the exact right ones. They are "one" time only. Many use a bolt that stretches to just right and doesn't repeat that.
http://www.autozone.com/...eId=0900c152800214f5 << That link agrees with the 47 for final torque after a round of lower as you'll see.
Not sure what to say on the contradictory suggestion as to lube or leave dry. The link above didn't bring it up at all.
Arggh! By the time you get the broken ones out I'd question how well the block threads are after that and want to feel even a used bolt (cleaned up) not resist too much as far as it needs to go in each hole.
See if others disagree or their suggestion on that. I'd be inclined to use at least a drop of oil for assembly unless there's a specific reason not to. New bolts might have a coating that would be defeated by any lube. This busting them off thing is not helping anything - that's for sure
T
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Guest
Anonymous Poster
Sep 27, 2008, 10:48 PM
Post #3 of 5
(3162 views)
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Definately replace the bolts with new......no question.
Lube or dry no diff.....just don't fill the bolt holes with oil...bad idea...
Of course the bolts are going to come out hard, they are bolting down the heads, that where the combustion happens..... wouldn't be a bad idea to run a tap down those holes to clean em out..... Then you'll definately see why they came out hard......
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ducks13
New User
Sep 28, 2008, 4:42 AM
Post #4 of 5
(3155 views)
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You can spin them out with you fingers once they have been loosened about a half turn. I have one of the broken ones out already and expect the second one to come out easy once I get an ezout in it. They break off about and inch or so down into the block so you half to drill em. My LH drill never moved it but when I put the ezout in I spun it out with my fingers.
It is pretty hard to keep threads in an engine dry so they will difinetly be oiled. I am replacing all of the bolts.
I still don't understand them being so tight, when I was breaking the loose they would make noise like they were highly stretch, like guitar strings.
I haven't worked professionally on production cars in 20 years and these bolts and torque specs just seem surprising to me.
Thanks for the thoughts.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 28, 2008, 5:27 AM
Post #5 of 5
(3154 views)
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Added Comments on these bolts and more:
This way of securing a head to block with magical bolts that behave as a spring with stretch action must have come about over the ions of problems with alloys for engine use and especially engines that use the alloy head on a cast iron block as the expansion and contraction expected with dissimilar metals needs to be overcome.
As said, I would put something to prevent these bolts from locking in so hard as to break getting them removed. As said with overdoing that and oil in a blind hole will get you in trouble so don't allow that or any dirt or filing from drilling out old broken ones to remain - blow out with air or whatever it takes to be sure.
Noted with cooling system and other sealing items throughout a vehicle that lots of thought has gone into gasketing and sealing items such that they will not need "retorquing" as did even hose clamps now about all spring loaded to adjust to changes with the rubber to metal changes with heat and cooldowns.
It used to be "Dealer Prep" to re tighten a zillion things on a vehicle after just a short time of operation time before delivery new.
There's no consumer tolerance for having a list of things to do when you buy something new as was the case back in the stone age when I started with the automotive stuff....
T
(This post was edited by Tom Greenleaf on Sep 28, 2008, 5:30 AM)
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