Hello all, I am very new to the Fiat twin cam engine, but decided to use this forum as I have obtained one and a half engines and a gearbox, one of which I believe may have originally come from a Spider. The princely sum I paid for this was a box of beer and a promise they'd be gone by the end of the day!
I thought I would have a go at making one good engine from the two, and the gearbox appears serviceable enough but I haven't looked too much at it. I am doing this solely for the fun of it, and don't even have a recipient car for it. I did some initial searching around and saw some good knowledge come from threads on this forum so I am here to learn as I go, if you please...
Both my engines are 1608cc (fairly sure), one block was cracked through where the oil pump pickup bolts on, nobody seemed to be able to repair it so it was scrapped. Is it typical for them to crack in this location? The crank from the good block is nominal sized but scored. The crank from the cracked block has been ground .010" undersize on both mains and big ends, and looks to be in good shape, the bearings appear OK but they're cheap enough, might as well replace them and run the machined crank. I saw somewhere that the cranks are nitrided and shouldn't be machined without re-treating but is this true for the 1608 engine?
I have a set of pistons from both engines. The bores of the good block (which I will now simply call "the block") are factory 80mm and unworn, although will need a hone. (this block is marked 125A000 - so not a spider block?) The piston set looks to have less of an aggressive dome (I did read a very good thread on here where someone went into great detail about the different pistons, but alas could not see any pictures - no doubt someone will post and tell me to do a search for that very thread!), however the tangs that protrude from the bottom of the skirt (is the correct terminology a "slipper skirt"?) are cracked in some places. Is this a common occurrence and is it an indication of some other fault? some even look to have been trimmed or filed in the past
The other set of pistons *look* significantly more aggressive and came from the cracked block. They are .04mm oversize. One of the crowns has a sizeable corrosion pit in it (the block was living in a field!). Can corrosion like this be ground out and welded back up? in saying that, given the oversize I won't be using them anyway but it'd be nice to have a full set. The slipper tangs on this set are practically nonexistent, I don't know if this is factory or if they have been trimmed down to nothing. I cannot see any part numbers or markings on any of the pistons, although I haven't had them properly cleaned. Where should I be looking?
I can't remember the exact measurements of the pistons but they were both about 37mm from wrist pin centre to the top of the crown, with domes of 4mm and 6mm respectively, or thereabouts
The gudgeon pins look to be semi-floating, both piston sets appear to have snap-ring grooves in the bosses but none of them have snap rings installed, is this normal?
The rods all have different part numbers and markings, I am guessing the markings are weight categories? Are there any specific rods which are stronger/lighter/otherwise more desirable? mine are marked 4156938 and 4225915
That's enough for now, I have two heads and a few boxes of bits to comb through, perhaps I'll be back with more questions, thanks!
bottom end rebuild questions
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gibbon
- Posts: 2
- Joined: Sun Sep 05, 2021 12:56 am
- Your car is a: engine only project - 1608
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18Fiatsandcounting
- Posts: 3798
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: bottom end rebuild questions
See Private Message.
-Bryan
-Bryan
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18Fiatsandcounting
- Posts: 3798
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: bottom end rebuild questions
That's quite the project there, but you definitely got the items for the right price!
OK, where to begin...? First off, my knowledge is almost entirely about engines sold in the US, and there are almost certainly variations in other markets.
One very helpful piece of information will be the engine code. This is not the raised numbers on the side of the block (those are the casting numbers), but I series of letters and numbers stamped into a flat surface on the block right above the oil filter. For a 1608 engine, it should be something like 125BC.040 followed by 7 digits. The first part is the engine code, and the 7 digits is the individual block serial number. The engine codes would be very helpful for our discussion. The "125A000" you noted is probably the casting number.
I don't know how common it is for the oil pump mounting flange to crack, but I had one block that did this. I had it "fixed" by drilling a hole way up in the block so that a long threaded rod could be used as the 2nd mounting bolt, with nuts on each end. The hole in the block (with the threaded rod going through) was sealed with thread sealant. This actually did work just fine, but it is very crude. Yes, cast iron is very hard to weld because of the high carbon content, and the tendency to crack further upon heating/cooling, but there are very specialized people who can do this work. I imagine it would be very expensive even if you could find someone.
It's funny, I myself have been tracking down information on 1438 and 1608 pistons in the past week, and it is a frustrating experience. There is some information online, but sometimes it is contradictory and sometimes flat out wrong. If you can find some piston casting numbers (inside the piston) or some part numbers stamped on top, that would be helpful. Although 1438 and 1608 pistons can be almost identical in appearance (both 80mm), there is one significant difference and that is that 1438 has the piston pin (gudgeon pin) firmly pressed into the small end of the connecting rod, and so there are no clips on the outside of the piston pin bore to hold the pin in place. The 1608 has those clips, and the connecting rod small end has a bushing so that the piston pin rotates both in the piston and in the connecting rod. It's called a "full floating pin" and seemed to be what most manufacturers adopted after 1970 or so.
But what you have seems very unusual in terms of cutouts for the piston pin clips but no actual clips. Someone may have tried to mix and match some parts. Does the pin rotate in the end of the connecting rod, and does the end have a bushing? If not, then you have a "locked" piston pin that is held to the connecting rod but can rotate in the pin bore in the piston.
Let's see, what else...? I have not heard of the tangs on the bottom of the piston breaking off, but given that you see evidence of "alteration", someone may have tried to use pistons that were not original to this block and thus hit the crankshaft lobes or the like. I've heard of stories where someone took any old 80mm piston (like from a Honda) and tried to make it work in a Fiat block. Sigh...
37mm is about right for the distance from the centerline (ooops, centreline) of the piston pin to the top of the crown, and in fact I believe it is exactly 37.75mm for 1438 and 1608 pistons. Domes came in heights of 4mm or so for normal compression (US markets) and 6mm or so for high compression for Europe and other markets. Sounds like you might have a set of both.
I don't know much about connecting rods, but you could Google those part numbers and see what you come up with.
So it kinda sounds like you have a non-US engine that I'm not very familiar with, or you have a combination of parts from various engines, which may not have worked and thus the engine was scrapped. In a nutshell, the crankshaft/con rods/pistons must all be specific for the particular engine, and there are only a few instances where swaps will work.
Hope this helps, and I'd be happy to provide more info but this should help you get started.
-Bryan
OK, where to begin...? First off, my knowledge is almost entirely about engines sold in the US, and there are almost certainly variations in other markets.
One very helpful piece of information will be the engine code. This is not the raised numbers on the side of the block (those are the casting numbers), but I series of letters and numbers stamped into a flat surface on the block right above the oil filter. For a 1608 engine, it should be something like 125BC.040 followed by 7 digits. The first part is the engine code, and the 7 digits is the individual block serial number. The engine codes would be very helpful for our discussion. The "125A000" you noted is probably the casting number.
I don't know how common it is for the oil pump mounting flange to crack, but I had one block that did this. I had it "fixed" by drilling a hole way up in the block so that a long threaded rod could be used as the 2nd mounting bolt, with nuts on each end. The hole in the block (with the threaded rod going through) was sealed with thread sealant. This actually did work just fine, but it is very crude. Yes, cast iron is very hard to weld because of the high carbon content, and the tendency to crack further upon heating/cooling, but there are very specialized people who can do this work. I imagine it would be very expensive even if you could find someone.
It's funny, I myself have been tracking down information on 1438 and 1608 pistons in the past week, and it is a frustrating experience. There is some information online, but sometimes it is contradictory and sometimes flat out wrong. If you can find some piston casting numbers (inside the piston) or some part numbers stamped on top, that would be helpful. Although 1438 and 1608 pistons can be almost identical in appearance (both 80mm), there is one significant difference and that is that 1438 has the piston pin (gudgeon pin) firmly pressed into the small end of the connecting rod, and so there are no clips on the outside of the piston pin bore to hold the pin in place. The 1608 has those clips, and the connecting rod small end has a bushing so that the piston pin rotates both in the piston and in the connecting rod. It's called a "full floating pin" and seemed to be what most manufacturers adopted after 1970 or so.
But what you have seems very unusual in terms of cutouts for the piston pin clips but no actual clips. Someone may have tried to mix and match some parts. Does the pin rotate in the end of the connecting rod, and does the end have a bushing? If not, then you have a "locked" piston pin that is held to the connecting rod but can rotate in the pin bore in the piston.
Let's see, what else...? I have not heard of the tangs on the bottom of the piston breaking off, but given that you see evidence of "alteration", someone may have tried to use pistons that were not original to this block and thus hit the crankshaft lobes or the like. I've heard of stories where someone took any old 80mm piston (like from a Honda) and tried to make it work in a Fiat block. Sigh...
37mm is about right for the distance from the centerline (ooops, centreline) of the piston pin to the top of the crown, and in fact I believe it is exactly 37.75mm for 1438 and 1608 pistons. Domes came in heights of 4mm or so for normal compression (US markets) and 6mm or so for high compression for Europe and other markets. Sounds like you might have a set of both.
I don't know much about connecting rods, but you could Google those part numbers and see what you come up with.
So it kinda sounds like you have a non-US engine that I'm not very familiar with, or you have a combination of parts from various engines, which may not have worked and thus the engine was scrapped. In a nutshell, the crankshaft/con rods/pistons must all be specific for the particular engine, and there are only a few instances where swaps will work.
Hope this helps, and I'd be happy to provide more info but this should help you get started.
-Bryan
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Nut124
- Posts: 748
- Joined: Wed Oct 25, 2017 6:39 pm
- Your car is a: 1978 124 Spider 1800
Re: bottom end rebuild questions
Hello Gibbon,
Reading your post leaves me a bit puzzled. Why would anyone rebuild engines for no particular purpose. I rebuilt mine recently and it cost me $$$$.
Is this engine expected to run and perform? Perhaps for sale? Or is this a training exercise of some sorts?
If a serious rebuild:
- Cracked pistons must be replaced.
- The piston pins must have the retaining clips in place.
- Factory rods are considered good unless there is evidence of overheating or impact damage.
- Rod bolts can be weak if used more than one time or over torqued. Fiat went to a beefier bolt in -79(?) and a lot of books only quote the torque spec for the bigger bolt, which will destroy the earlier bolt.
Reading your post leaves me a bit puzzled. Why would anyone rebuild engines for no particular purpose. I rebuilt mine recently and it cost me $$$$.
Is this engine expected to run and perform? Perhaps for sale? Or is this a training exercise of some sorts?
If a serious rebuild:
- Cracked pistons must be replaced.
- The piston pins must have the retaining clips in place.
- Factory rods are considered good unless there is evidence of overheating or impact damage.
- Rod bolts can be weak if used more than one time or over torqued. Fiat went to a beefier bolt in -79(?) and a lot of books only quote the torque spec for the bigger bolt, which will destroy the earlier bolt.
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gibbon
- Posts: 2
- Joined: Sun Sep 05, 2021 12:56 am
- Your car is a: engine only project - 1608
Re: bottom end rebuild questions
Thanks for the replies fellas
As mentioned in my PM to Bryan, I am in New Zealand where we have had open slather to import cars since forever, so we have a really eclectic mix of NZ new and "grey import" vehicles from all over the place, so I wouldn't be surprised to find that the engines are all mixed and matched
Nut124; it's literally just a hobby and something to do. I am an aircraft mechanic by trade so have access to all the tooling needed to do the job, so for me it's just the price of parts. I am also rebuilding a mazda 12a rotary, yes I do it for the fun of it, I intend for it to be a running engine, but I am not going to go above and beyond with anything too high-end. Thanks for the heads-up regarding the rod bolts! Can you recall the diameter of either the large or small bolts?
Bryan; the 125A 000 number is stamped, not cast.. it has a stamped serial number below it 0125446, both on a machined square in the block. (I'm looking at some photos here so don't have any more useful information about it's location right now) I have a pic of a cast number here too (below a frost plug somewhere) that says 4180231
I was able to pull some numbers off the pistons, the higher domed ones with the very short tangs are marked MONDIAL PISTON 2457(?). The shorter domed ones with the longer tangs are marked FIAT 132AB 263872 from what I can tell. I can confirm both sets have the gudgeon pin attached in the small end bearing, and floating freely in the piston. Going off what you are saying, is it possible perhaps that I actually have 1438 engines which have been refitted with 1608 pistons? One of the two cranks had a casting number on it, but I haven't got that in front of me. What is it about the 1438 rod that captures the gudgeon pin, is it just a press fit "bearing"?
The seller didn't know much about the parts, they were a deceased estate. The one engine was supposedly pulled down for a refresh so was apparently operable prior. The other one had the cracked block and the oil pump pickup was actually loose in it - I'd say someone had a low pressure indication and the engine was pulled as a result.
Looking forwards to hearing back, I'm just trying to get some consolidated shipping sorted at the moment as it's looking like a set of pistons is in order now. Looking forwards to comparing the two heads!
As mentioned in my PM to Bryan, I am in New Zealand where we have had open slather to import cars since forever, so we have a really eclectic mix of NZ new and "grey import" vehicles from all over the place, so I wouldn't be surprised to find that the engines are all mixed and matched
Nut124; it's literally just a hobby and something to do. I am an aircraft mechanic by trade so have access to all the tooling needed to do the job, so for me it's just the price of parts. I am also rebuilding a mazda 12a rotary, yes I do it for the fun of it, I intend for it to be a running engine, but I am not going to go above and beyond with anything too high-end. Thanks for the heads-up regarding the rod bolts! Can you recall the diameter of either the large or small bolts?
Bryan; the 125A 000 number is stamped, not cast.. it has a stamped serial number below it 0125446, both on a machined square in the block. (I'm looking at some photos here so don't have any more useful information about it's location right now) I have a pic of a cast number here too (below a frost plug somewhere) that says 4180231
I was able to pull some numbers off the pistons, the higher domed ones with the very short tangs are marked MONDIAL PISTON 2457(?). The shorter domed ones with the longer tangs are marked FIAT 132AB 263872 from what I can tell. I can confirm both sets have the gudgeon pin attached in the small end bearing, and floating freely in the piston. Going off what you are saying, is it possible perhaps that I actually have 1438 engines which have been refitted with 1608 pistons? One of the two cranks had a casting number on it, but I haven't got that in front of me. What is it about the 1438 rod that captures the gudgeon pin, is it just a press fit "bearing"?
The seller didn't know much about the parts, they were a deceased estate. The one engine was supposedly pulled down for a refresh so was apparently operable prior. The other one had the cracked block and the oil pump pickup was actually loose in it - I'd say someone had a low pressure indication and the engine was pulled as a result.
Looking forwards to hearing back, I'm just trying to get some consolidated shipping sorted at the moment as it's looking like a set of pistons is in order now. Looking forwards to comparing the two heads!
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18Fiatsandcounting
- Posts: 3798
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: bottom end rebuild questions
Well, as far as I can tell, your engine is from a Fiat 125 model sedan, produced from the late 60s to early 70s, and it was imported to NZ, so that would make sense.
There were several different connecting rod bolts used, M9 of various lengths, and M10. M10 was used on 1979 and beyond, so for the 2L. Basically, the different bolts were to accommodate the different journal diameters (and stresses).
You asked earlier about nitriding: I have heard that the cranks were nitriding, but that's all I know.
You do have a strange mix of pistons and rods, but maybe that's just because they are non-US so I'm just not familiar with it. The 1438 had a press fit piston pin where the rod was heated up in an oven and the pin was quickly pressed in. All while centering the piston/rod on the pin. Probably required some practice to get it right. The 1438 pin was thus held very tight in the rod, so the rotation was between the piston pin boss and the pin. 1608 engines and beyond used the full floating pin arrangement, which required a circlip to keep the pin from sliding out. If the circlip is not there, the pin will rapidly start working its way towards the cylinder wall, causing all sorts of sadness.
You might have a 1438 block with 1608 pistons. I believe that can be made to work, although you'd have to convert the rods to floating instead of pressed in pins. 1608 pistons do have a shorter "tang" on the skirt. Actually, my understanding is that the tang is the same, but the cutout on the rest of the skirt is less. My understanding is that the cutouts were there to avoid clearance issues down in the bottom of the block or with the crankshaft lobes.
OK, a lot of conjecture on my part, but that's because I'm not familiar with non-US engines! Good luck with it, happy to answer any other questions, and my wife and I love NZ. We had our honeymoon there. Auckland, Rotorua, Hawke Bay, and Queenstown.
-Bryan
There were several different connecting rod bolts used, M9 of various lengths, and M10. M10 was used on 1979 and beyond, so for the 2L. Basically, the different bolts were to accommodate the different journal diameters (and stresses).
You asked earlier about nitriding: I have heard that the cranks were nitriding, but that's all I know.
You do have a strange mix of pistons and rods, but maybe that's just because they are non-US so I'm just not familiar with it. The 1438 had a press fit piston pin where the rod was heated up in an oven and the pin was quickly pressed in. All while centering the piston/rod on the pin. Probably required some practice to get it right. The 1438 pin was thus held very tight in the rod, so the rotation was between the piston pin boss and the pin. 1608 engines and beyond used the full floating pin arrangement, which required a circlip to keep the pin from sliding out. If the circlip is not there, the pin will rapidly start working its way towards the cylinder wall, causing all sorts of sadness.
You might have a 1438 block with 1608 pistons. I believe that can be made to work, although you'd have to convert the rods to floating instead of pressed in pins. 1608 pistons do have a shorter "tang" on the skirt. Actually, my understanding is that the tang is the same, but the cutout on the rest of the skirt is less. My understanding is that the cutouts were there to avoid clearance issues down in the bottom of the block or with the crankshaft lobes.
OK, a lot of conjecture on my part, but that's because I'm not familiar with non-US engines! Good luck with it, happy to answer any other questions, and my wife and I love NZ. We had our honeymoon there. Auckland, Rotorua, Hawke Bay, and Queenstown.
-Bryan