Follow along as I build a 79 Spider

The forum for all of your technical questions on your classic FIAT autos
fp55scca
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Re: Follow along as I build a 79 Spider

Post by fp55scca » Thu Jan 10, 2019 11:00 pm

--Tim, with respect to the ridge at the top of your cylinders, that is common, and the severity is usually directly proportional to mileage. The ridge should be removed, or you will risk ring flutter at high rpm. When the compression ring contacts the ridge, it forces the ring inward, which reduces the pressure behind the ring that provides the sealing force for the compression ring. The result is a loss of torque at high rpm.

--My recommendation would be to start your rebuild with a fresh bore. There is no spec in Guy Croft's books as to a limit on this ridge, which dictates when a motor must be re-bored, because Croft does not rebuild a motor without re-boring it.

--There is, of course, a limit on the side clearance of the piston skirt, so regardless, you will need to measure your bores and compare to piston diameters. For cast pistons, the piston skirt-to-bore clearance should be 0.04 - 0.06mm. You could go as much as 0.075mm, but then with any wear you will experience piston slap which in turn will wear your piston skirts.

--From the appearance of your block, it looks like you will need to deck this block for a reliable head gasket seal. About 0.010" should do it, but you can take as much as 0.040" without creating a clearance issues. Decking the block will also give you a small compression bump.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
whitehause
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Re: Follow along as I build a 79 Spider

Post by whitehause » Thu Jan 10, 2019 11:09 pm

I'm going to run a holley 5200. I have a brand new Airtex electric pump I was going to run as a booster pump for the fuel side of the nitrous set up on my Corvette. It's a 5 to 6 psi fixed output pump, so it would work for the fiat. That would eliminate having to time the aux shaft and I could just cut the end off the shaft and tap it for an npt fitting like you posted earlier.

The deck is actually in very good shape, there was a lot of junk on it I hadn't cleaned off so in the pics it looks kinda crappy.
whitehause
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Re: Follow along as I build a 79 Spider

Post by whitehause » Fri Jan 11, 2019 12:49 pm

So I just got back from a machine shop that I never even realized is 1/2 mile from my house. It's a small place that was passed from father to son ( who is now 50 ) and is in a large garage behind the house. I'd seen the small sign out front with simply "Rams Engines" on it, but never stopped in since I wasn't sure what they even did.
Well, after talking to the very nice and knowledgeable owner for over an hour he will inspect the block and let me know what diameter will clean up the block so I can order the pistons because he wants the pistons in hand before he starts, hot tank and clean the block, bore the cylinders, finish hone and match each new piston to each bore and number the pistons to the bores for.......$140.00.
Needless to say I'll be dropping the block off on Monday so he can inspect it and I can get the pistons ordered 8-)
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davedecker4
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Re: Follow along as I build a 79 Spider

Post by davedecker4 » Fri Jan 11, 2019 2:36 pm

Perfect!
Machine work isn't always as costly as people imagine.
Its nice to start off with things right sometimes.
He can also look at your aux. shaft if you like. Btw its better to grind down the eccentric lobe than lop off the end of the shaft. I once had a spider modded that way, which caused excess wear to the auxiliary shaft bearings from torque on the front belts. Something to keep in mind.
Dave Decker
a 'couple' Fiats and Lancia's
whitehause
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Re: Follow along as I build a 79 Spider

Post by whitehause » Fri Jan 11, 2019 4:12 pm

My shaft doesn't have a separate lobe, the whole end of the shaft past the bearing surface is off-set to create the lobe. cutting seems to be the only real recourse on this one.
bnam2
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Re: Follow along as I build a 79 Spider

Post by bnam2 » Fri Jan 11, 2019 11:48 pm

whitehause wrote:
Fri Jan 11, 2019 4:12 pm
My shaft doesn't have a separate lobe... cutting seems to be the only real recourse on this one.
Gee, sounds painful! Good luck.

:D
Byas
1965 Fiat 1500 Cabriolet with 1600twin-cam
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fiatmac
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Re: Follow along as I build a 79 Spider

Post by fiatmac » Sun Jan 13, 2019 1:47 pm

fp55scca wrote:
Thu Jan 10, 2019 8:55 pm
whitehause wrote:
Thu Jan 10, 2019 8:41 pm
What's strange is there is no definitive lobe on my shaft, the entire far end is the same diameter, just off set from the center line. I plan to keep the mechanical fuel pump since I have a new one already. I just need to make sure the timing is right with this one.
----------------------------------------------------------
--Tim, that's interesting. That was my first impression, because the aux shaft (on the left) in my pic is the same, and I figured it was factory. I would not try to run a mechanical pump with it. I don't think the offset is sufficient, otherwise why would Fiat bother to put a lobe on it? I can send you one with a lobe if you need it, but really I don't recommend a mechanical pump. What carb are you running?
Apparently the design of the aux shaft was changed to the offset rear section “lobe”starting with the ‘77 1800 engine and continued to the end of production on the 2000 engine. See Midwest Bayless listing for the aux shaft. My 2000 engine has this design.
Stan McConnell
Retired engineer
Salisbury, NC
82 2000 Spider
78 124 Spider on the rotisserie
whitehause
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Re: Follow along as I build a 79 Spider

Post by whitehause » Sun Jan 13, 2019 2:29 pm

Yep, mine's got a date with the air saw soon.
fp55scca
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Re: Follow along as I build a 79 Spider

Post by fp55scca » Sun Jan 13, 2019 4:00 pm

davedecker4 wrote:
Fri Jan 11, 2019 2:36 pm
......Btw its better to grind down the eccentric lobe than lop off the end of the shaft. I once had a spider modded that way, which caused excess wear to the auxiliary shaft bearings from torque on the front belts.....
---------------------------------------------
--Dave, I've been cutting these lobes for 20 years, including race motors which see a lot of rpm and torque. I've never seen wear to the aux shaft bearings from cutting the rear lobe.

--Before refitting any aux shaft, you have to determine that your aux bearings are not worn. Then when cutting the lobe, don't cut any closer than about 4mm to the rear journal; and then, don't put a plug in too deep. Doing so can block oil feed to the rear journal, which of course would be a disaster for that bearing. When you look at the aux shaft in this context, it's pretty apparent.

--I have also noted also that the oil journals in various aux shafts are not a standard size. Tim, you will probably have to cut your aux shaft first to determine the diameter of a suitable pipe plug. Be sure to include Loctite when inserting the plug.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
whitehause
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Re: Follow along as I build a 79 Spider

Post by whitehause » Sun Jan 13, 2019 10:31 pm

I have 2 Harleys which basically means I have stock in Loc Tite......I Loc Tite everything
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