Mixing 1116cc pistons with 1500 rods - not exactly sure what I've got

Discussion in 'Rear-Engine Fiats' started by myredracer, Nov 19, 2018.

  1. myredracer

    myredracer True Classic

    Just going through parts I have and need to put a 1608 crank into a 1438cc OHV block. This will be going to go into my Abarth 1300/124 project - the original motor was long gone when I got the car. I have a 1608 crank, 1500 rods and 1116cc pistons. The rods are bushed and I have new bushings for the small end. The pistons I have are Borgo (standard size) and they have the pins pressed into the pistons in the box. If I have it correct, the 128 pistons came in press-fit and free floating type? I can't push the pins out of the pistons by hand so does that mean they are press-fit? There's no retaining clips with the pistons. The old 1438 OHV piston pins in comparison are pressed into the rods.

    The 1438 motor I have is a brand new crate motor that I came across locally years ago. It's pretty cool to work on a motor that is entirely new, untouched and so clean inside and out. I'm hoping the 80 mm 1116cc pistons will drop right into the 80mm bores in the 1438 block (fingers crossed) and that the clearances are correct. Don't mind having to enlarge the bores a bit but hope I don't need a new set of 1st oversize pistons...
  2. Kent Baird

    Kent Baird Italian car collector.

    Lakewood Colorado
    Hi Gil, I have wanted to do the same 124 pushrod 1650cc reversed engine build. This is the info I have: The 1100cc 80.00mm 128 and 80.00mm 1438cc 124 OHV pistons I have are 22mm press pins (No clips). The measurement from the top of the piston to the top of the 22mm pin is about: 128=23.45mm and 124=26.82mm. The rod journals are about 3mm larger on the 80mm longer stroke 1608 crank than the 71.5mm 1200 & 1438 OHV crank. I also want to deck the block surface some to get the piston up and more compression. Abarth cut a lot off the 1300 cylinder head to up compression. I think the stock low lift 124 sedan camshaft was use. The stock cylinder head will get valve spring bind with a high lift cam. PBS told me that the spring base needs to be machined lower to allow taller springs. I have a set of PBS pistons that were for this stroked application. (See the photo). As sometimes PBS is known for the machine work is not perfect. The pin bore is not square with the shirts each piston is slightly different. They are 80.00mm with 20mm pins and have clips for bushed rods. The measurement from top of piston to top of the 20mm pin is 23.94mm.

    My questions. What size is 1500 x19 crank rod journal? Is it the same as the 1608 crank to use the same 124 1608 rod bearings? I was thinking the 1500 x19 Scat rods would be nice choice. Then use custom lighter weight pistons with small free floating pins.
    Does anyone know where to get a hot cam regrind for the pushrod camshaft? Maybe Delta, any reviews?

    Check out this video of this type of car: Abarth OT 1300 124, 1.38.545, Franciacorta - Silvio Pederzini

    Kent B.
    Lakewood, Co

  3. lookforjoe

    lookforjoe True Classic

    1608 crank uses same rod & mains as 1500cc motor. I used the 1500 scat rods in my 1600. Had Wiseco pistons made to spec (after I broke a ring land on the Mahle's from Steve), since stroke is altered.
  4. bruakeman

    bruakeman True Classic

    I had no idea that the 1500 SOC engine shared bearings (or anything) with the twincam. I have a 1438 OHV/1608/1100 engine with 80mm Borgo pistons. They are press fit pins. PBS built the short block about 15 years ago also using the stock 124b rods. I seem to remember having the head, a Seat (Siat?) I got from Gregg Schmidt, slightly worked so as my compression was not too high. I still have another untouched head and some 81mm pistons should I decide to go all out! More I think about it, it must have been closer to 20 years. Good lord time is flying by. From all I've read the stock cam is a pretty decent grind, but I'd be interested in what else you may find. I'm running a single 32 DCOF, runs great.
  5. myredracer

    myredracer True Classic

    Hi Kent, thanks for the comments/info. Here's what I can tell you after a week of investigating things. I've had the new 1438 motor and a bunch of parts for a long time and it's been a bit of a head scratcher to figure what the plan was.

    Interesting on the PBS pistons. I used to have a new PBS bellhousing adapter (1300/124) and it had a casting flaw in a run of them. Can't remember exactly what (IIRC, wrong position for bolt holes into transaxle) and it needed additional machining and maybe welding. The 1500 rods (as well as 1100 & 1300) and 1608 crank rod journals are the same diameter and width.

    Using the 1608 crank, I calculated that the stock 1438 compression would go from 9 to 10:1. I'm okay with that for myself and not sure if I'd want to deck the block or mill the head unless it was needed to clean or prep the surfaces.

    The 1438 crank stroke is 71.5mm and the 1608 is 80.0. Stock 1438 rod length by my measurement is 129.5mm (center to center), the 1500 rod is 128.5mm and the 1116 (and the 1300) is 120.0mm (way too short). The compression height (center of pin to top of piston) of the stock 1438 piston is 37.8mm and for the 1116 piston is 34.7mm. So that means the distance from the centerline of the crank to top of pistons for stock 1438 is 71.5/2 + 129.5 + 37.8 = 203.05mm. For the 1608 crank, 1500 rods and 1116 pistons it is 80.0/2 + 128.5 + 34.7 = 203.2mm. I don't think 0.15mm can be an issue. Note that the 1116cc pistons have very slight crown in them and the compression height figure would be to the top of the piston. Good info. on pistons in different Fiat models can be found here http://www.pistonespersan.com.ar/marcas/PERSAN_Fiat.pdf

    One nice thing about the 1500 rods is that they are quite a bit lighter compared to 1116 ones at 620 vs 665 grams. The 1608 crank is waay heavier than the 1438 at 13,130 gr (28lb 15oz) vs 9,635 gr (21lb 4 oz.). Have been thinking about lightening the flywheel a bit to compensate but have read a few too many warnings about doing this to stock steel ones to make me unsure. I don't think it would need much lightening because although the 1608 crank is heavier, the centrifugal/rotational mass of a crank is smaller compared to the much larger diameter of a flywheel. A 1438 crank & flywheel has 10 mm bolts same as the 1608. For racing, the flywheels are sometimes doweled to the crank which I think I may do. Later 124 spider engines with their higher HP have 12mm bolts.

    The 1608 crank counterweights his the bottom of the cylinder bores on #1 & #4 cylinders by a very tiny amount. A little work with a grinder will fix that easily. This was standard practice on 850 903cc blocks when installing 74mm cranks. The crank also slightly kisses the block at the oil pump and a little grinding will easily fix that too.

    The piston pin diameter in the 1438 & 1116 pistons is the same at 22mm. Main journal size of the 1438 & 1608 crank is the same. The rod journal size and rod big end size are the same and bearings are interchangeable. Note that there are two oil feed holes in the 1500 rods and for bearings you want the ones with 3 holes in them.

    I have a recollection that the stock oil pump could do with an upgrade to increase flow. It's possible that one from a Euro 131 with OHV has better flow and I have one in my parts pile which is why I might have bought it. An oil cooler might be a good idea and is easy to do. I have an alloy Abarth sump to put on the motor but the oil pump hits it and will need to remove some metal on the sump (it's pretty thick).

    I'm planning to do a little porting and polishing of the cylinder head, nothing too serious. I assume larger valves would be possible but not sure if there'd be a worthwhile gain in HP. I have an intake manifold for single Weber DCOE (came with the car) and another for dual DCOEs. The plan is to use the dual carbs. Not the original setup on a 1300/124 but the engine isn't the original Abarth one. Also have the correct carb, manifold & air cleaner if ever wanted for originality. I have a new Delta cam with performance spec (a regrind of course), another ebay find that came from Richard Radford. It's marked "D-9 623" and I've lost the specs on it. Maybe Delta could regrind another to that spec? Another nice piece I have is a Marelli electronic distributor that I got from Italy. The 1st one I got from the seller was for a twin-cam motor and had to get him to swap it with the correct one. Not easy because he didn't know a word of english and I had to struggle with google translate, plus returning something to Italy is not an easy process through Customs. I have a set of Alquati outer valve springs that I got from Midwest Bayless and have a 1" bind height and 210 lb spring rate. I have a set of new Abarth 124/131 OHV valve springs that I won't need now.

    Something I've just found and am unclear on is the clutches. The engine in my 1300/124 came with a stock 124 flywheel and the clutch is 180mm dia., the transaxle input shaft appears to be standard 850 (overall length could be different when I pull it out) and the pilot bearing in the crank is 850 dia. I have a 1300/124 200mm clutch disc, pressure plate and input shaft all of which are PBS. I also have a new 1300/124 disc that is 180 mm. Maybe the very early 1300/124s had a 180mm clutch and 850 input shaft? Greg Schmidt refers to the PBS shafts as being "850 at one end and 124 at the other". I like the 200mm clutch setup and will use that which will be good for higher HP anyway. The PBS pressure plate I have has reversed straps (also mentioned by Greg Schmidt) and has the straps re-attached with bolts and nyloc nuts which I am not sure is a good thing - may see if I can find a clutch shop to rivet them on. The clutch on my 1300/124 could be stock 124, I just don't know. I came across a reduction drive starter for the 1300/124 bellhousings some years ago on ebay. Just re-discovered it in the closet... Means I won't have to worry about using or restoring the original Scaglia one.

    One fun thing about the 124 1438cc OHV engines is that they are very similar in design to 850 engines so many modification procedures & methods are common to both. Just need to get some bearings for the crank & rods and then I can take the block into the machine shop. Also need to get some non-rotational crank seals.

    Besides the 1438 motor that I'll be stroking, I have a 1585CC Euro 131 OHV motor that I got from someone in New Zealand. Providing the 1438 motor works out, and I see no reason why, I'll be selling it. I have an NOS head, two sets of pistons and a few other new parts for it and also a cam & distributor out of a Fiat 242 van that are needed to reverse rotation. This is an alternative to stroking a 124 1438 pushrod motor but will not look quite as original to a 1300/124 due to having a belt drive arrangement for the cam.
    Last edited: Nov 20, 2018
  6. myredracer

    myredracer True Classic

    OMG, that is so true! Waaay more time has flown by than I have left on the planet. I'm trying to get 2 Fiat projects finished before I end up in a nursing home and have Alzheimers and can no longer remember that I even owned a Fiat... :(

    Many of the people who really know the intracacies of Fiats and especially anything Abarth related, are disappearing. Ordinary parts that used to be easy to find are now getting rare and often very pricey. Finding a shop that can do specialty work on Fiat motors, transmissions, etc. is also getting harder and harder. If I could only turn back the clock and stay there.
  7. bruakeman

    bruakeman True Classic

    FWIW I still have an original 124a Abarth 1300/124 sourced block and crank. It needs a serious overbore but for originality it is available.
  8. myredracer

    myredracer True Classic

    Definitely interested. Need to figure out how to do a PM on this forum.
    Last edited: Nov 21, 2018
  9. Achilleas Leousis

    Achilleas Leousis New Member

    Pbs also did tge same thing. Its a really good idea . Keeping the same engine and have 1608 cc. Is it possible for someone who has it to let me know the crankshaft number in order to try to find this crankshaft locally?

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