Installing LT1 aluminum heads procedure
04-14-2014, 11:26 AM
#1
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Installing LT1 aluminum heads procedure
Compared to standard iron heads is there any unique procedure required to install LT1 aluminum heads on an iron block? I see a lot of head gasket kits include new headbolts...is that an absolute or is it common to reuse the bolts with thread sealer?
04-14-2014, 12:15 PM
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Re: Installing LT1 aluminum heads procedure
It depends on the year of the car as far as the head bolts go. 96 and up (and some late 95s) are TTY and cannot be reused. If you want to take the safe route, buy some ARP bolts and don't worry about it.
04-14-2014, 12:19 PM
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Re: Installing LT1 aluminum heads procedure
04-14-2014, 12:36 PM
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Re: Installing LT1 aluminum heads procedure
04-14-2014, 01:53 PM
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Re: Installing LT1 aluminum heads procedure
Non TTY bolts look like the old SBC head bolts. The TTY ones tend to be a little more slender and silver looking.
While all bolts stretch, TTY bolts are made to stretch to a certain degree to create a uniform clamping force. That is why the tightening sequence is different. Once they stretch, they don't return to the original length (as much as a non TTY bolt would). Reusing them could result in breakage or loss of proper clamping strength. As suggested, I would buy some ARP bolts. Cheap price to pay for something as important as the head seal on an LT1.
While all bolts stretch, TTY bolts are made to stretch to a certain degree to create a uniform clamping force. That is why the tightening sequence is different. Once they stretch, they don't return to the original length (as much as a non TTY bolt would). Reusing them could result in breakage or loss of proper clamping strength. As suggested, I would buy some ARP bolts. Cheap price to pay for something as important as the head seal on an LT1.
04-14-2014, 02:20 PM
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Re: Installing LT1 aluminum heads procedure
He's asking about the difference between an "early" and "late" 95. No 95's have a CKP sensor.
04-15-2014, 08:09 AM
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Re: Installing LT1 aluminum heads procedure
Change the bolts, unless you have a detailed knowledge of their history. Here's a good article on head bolt tightening technology.
http://www.sbintl.com/tech_library/a...e_to_angle.pdf
The important part is at the end:
If the bolts are conventional, they were installed to a torque spec. If the factory did it, the thread prep, lubricant and the tightening process were carefully controlled. If at some point in it's life the head were removed and reinstalled, the process falls apart. 90% of the torque value is due to friction. The rest has to do with bolt stretch. The process is subject to limitations on block thread prep (were the threads properly chased?), the lubricant uses, cleanliness, accuracy of the torque wrench, skills of the installer, etc. The bolt could be installed to the proper degree of stretch, or it could be over-tightened or under-tightened. If marginally over-tightened, what happens when the aluminum heads get a bit too hot, and the aluminum expands more than the steel bolt, due to the significant difference in the coefficient of thermal expansion of steel vs. aluminum? The bolt could have been stretched beyond it's elastic limit.
http://www.sbintl.com/tech_library/a...e_to_angle.pdf
The important part is at the end:
A final subject is the relative merits to re-using critical fasteners. If I had a dollar for every head bolt I’ve wire brushed and reused I could afford a pretty nice vacation next year. There are very few of us in this industry that haven’t reused critical fasteners!
However, times change, engines change, technology changes, I’ve changed. My policy is that if new critical fasteners – especially head bolts – are readily available, old ones are replaced. Understanding much more about fasteners and engine operating conditions today, I’m reluctant to reuse them.
A well-respected OE engineer specializing in engines tells me that critical fasteners have about six rundowns in their useful life. They use four of those at the OE manufacturing operations, leaving rebuilders just two. One rundown for checking sizes puts us on the last rundown during final assembly. My thinking is: why take the chance? Replace the fasteners! The relative cost compared to the total engine job is small and the peace of mind is great.
Reprinted by permission of Engine Builder magazine
However, times change, engines change, technology changes, I’ve changed. My policy is that if new critical fasteners – especially head bolts – are readily available, old ones are replaced. Understanding much more about fasteners and engine operating conditions today, I’m reluctant to reuse them.
A well-respected OE engineer specializing in engines tells me that critical fasteners have about six rundowns in their useful life. They use four of those at the OE manufacturing operations, leaving rebuilders just two. One rundown for checking sizes puts us on the last rundown during final assembly. My thinking is: why take the chance? Replace the fasteners! The relative cost compared to the total engine job is small and the peace of mind is great.
Reprinted by permission of Engine Builder magazine
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