Strange head bolts

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friedman
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Strange head bolts

Post by friedman » Sat Dec 08, 2018 12:45 pm

Getting set to install the head on the 85.5 spider motor and note the head bolts are different than what I'm used to seeing for spider motors. Two big differences, not sure you can actually see them in the pics:

The thread on the 85.5 bolts go up most of the shank whereas the earlier bolts are only threaded for a short portion.
The shank of the 85.5 bolts are smaller in diameter between the threaded portion and the area near the hex head, 0.393" for an early bolt shank and 0.359 for the 85.5 head bolt. Threads are the same for both and the 85.5 bolt flares out near the hex to 0.393" where the washer sits.

Older bolt says SBE and 10.9 on the top of the head and the 85.5 bolt says FA and 10R on the head.

Anyone else seen these headbolts?

I'm working on the assumption that the torque is the same for both style bolts.
Carl in Virginia
75 spider
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77 X1/9
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Re: Strange head bolts

Post by fp55scca » Sat Dec 08, 2018 1:00 pm

--Carl, you didn't post pics? But it sounds like you may have Fiat "stretch bolts". You'll need to confirm, to be sure, before doing torque, because the torque value and method of doing the torque are very different.

--According to the same GC reference, p. 187, if they are stretch bolts, the procedure appears to be 15-30 ft/lbs at two steps of 90 degree rotation each.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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Re: Strange head bolts

Post by friedman » Sat Dec 08, 2018 1:34 pm

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Great, Maybe I'll just use some used, good condition old style bolts.
Carl in Virginia
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Re: Strange head bolts

Post by fp55scca » Sat Dec 08, 2018 7:48 pm

--Carl, personally I would not re-use them. I think the general rule for stretch to torque, or torque to yield bolts is that they are not re-used. Get some good used ones and be sure to check thread stretch on those. General rule there is 4 re-torque uses. (Again, that's GC, p. 187).
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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Re: Strange head bolts

Post by friedman » Sun Dec 09, 2018 9:03 am

I agree Jim. I have at least one set of used head bolts and I'll install those and throw these away. GC indicates in his book (I found the page) that early spiders used these and very late spiders (which had splined heads, never seen these).

Just goes to show that any old Fiat motor may have a very interesting history, none of which have a narrative. I had assume, stupidly, that this motor had never had major work and yet the evidence (machined crank) clearly shows otherwise.

I was looking at a 1438 TC that came out of a 124 coupe (severely blown head gasket) and it had a sleeve in one cylinder!
Carl in Virginia
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Re: Strange head bolts

Post by rridge » Sun Dec 09, 2018 9:16 am

According to Matt Brannon the '83-85 Spider factory head bolts were torque to yield. the first picture below is from the Midwest Bayless website. And as long as we're posting head bolt pictures. The pictures beyond are four sets in my inventory. Left to right are an old factory bolt, a newer factory bolt, an SBE aftermarket bolt, and an FF bolt that was sourced through IAP. The FF bolts are uninstalled and available.
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Richard
'81 Turbo Spider
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Re: Strange head bolts

Post by fp55scca » Sun Dec 09, 2018 9:59 am

--Richard, that's pretty interesting! I'm not real familiar with the SBE and LF bolts. Were these aftermarket bolts sold by IAP?

--It's also interesting to see the different approach to the fillet radius under the head of each bolt. New factory and SBE use a similar design, while old factory and LF use the more shallow radius.

--Like Carl discovered, it's often difficult to determine the history of a motor, thus knowing how many re-uses the bolts may have seen. As a general rule for head bolts, after thoroughly cleaning (including wire wheel on threads), and oiling, for a street motor you can run a good condition nut onto the thread by hand. If any binding, reject that bolt. For racing, or very high performance, a quality stretch gauge is prudent to check the threads.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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Re: Strange head bolts

Post by friedman » Sun Dec 09, 2018 3:31 pm

Thanks Richard, my alter ego as an X head always goes to the MWB website to look up which years had what parts but never occurred to me to do this for spider parts. My spare set of used head bolts have a different pattern on the bolt head, take a pic in a bit. I cleaned them, checked the threads, oil the threads and underside of the head (also chased the threads in the block with is extremely critical) and the bolts torqued up to 30 and then 61 lb/ft just delightfully.
Carl in Virginia
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Re: Strange head bolts

Post by friedman » Sun Dec 09, 2018 3:38 pm

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Second pic shows the head bolt from my stash of used parts that I used on the motor, the top pic is the motor so far because everyone likes to see nice clean TC motors...even if the TC part hasn't been bolted on yet.
Carl in Virginia
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Re: Strange head bolts

Post by rridge » Sun Dec 09, 2018 5:00 pm

Jim wrote:
--Richard, that's pretty interesting! I'm not real familiar with the SBE and LF bolts. Were these aftermarket bolts sold by IAP
The FF or LF bolts came from IAP in 2013 when things were winding down there. They were a special order. The SBE and old Fiat Bolts were from a parts stash I bought. I think the newer Fiat bolts were my '81's originals. From the 1920's well into the 1950's and perhaps beyond the Fiat Engineering Dept was one of the best in Europe and firmly in control of things like head bolt design so I tend to think older is better from the factory.
--It's also interesting to see the different approach to the fillet radius under the head of each bolt. New factory and SBE use a similar design, while old factory and LF use the more shallow radius.
Yes, quite a range on head details. I also took a look at the 12.9 YFS head bolts that Croft sells. They have no radius under the cap screw head.

Carl,
That's a great looking X in your garage. Is it available for a test drive? The engine isn't bad looking either.
Richard
'81 Turbo Spider
Rockville, MD
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