Fiat TC block and engine numbers

[thommy124]

Hey, great forum! Will for sure be my favorite one!
I have a quetion regarding the identification of engine blocks and cylinder heads:
1) the different engine blocks are identified by their type numbers (e.g. 125A etc) which allows to determine bore and stroke by that number.
I could not find a corresponding number for the cylinder heads in any literature I looked through (including the Fiat Spider&Abarth and Fiat&Lancia Twin Cam books by John Tipler, Phil Ward and of course Guy Croft). Does such a number key exist that characterizes which head belongs to which block and in case yes, where can such a list be found? Looking on different heads, that I believe belong to different engines I find that the distance between the combustion chambers on the heads is the same, whereas on the blocks the distance between the bore centerpoints is different dependent on the bore. Also the pattern of cylinder head bolts is identic so that you can assemble any head to any engine. Is this true or do I have all the same heads, even though they wear different numbers and were sold as coming from different engines?
2) what is the nominal of the con-rod bearings on the crankshaft of a 1608 ccm engine? My old manual (Bucheli-Verlag, unfortunately just has data for 1400 ccm engine) indicates 45,518‚±0,01 mm, however I am measuring 48,25 mm and I am quite certain that the shaft has been revised at least once (or did someone grind on material?? :roll: ). Now I need to know which stage of undersize it is to order new bearings accordingly.ufgedreht?
Any help will be highly appreciated.
Thanks in advance,
Thomas

[Guy Croft]

Hi Thomas

you wrote:

I have a question regarding the identification of engine blocks and cylinder heads:
1) The different engine blocks are identified by their type numbers (e.g. 125A etc) which allows to determine bore and stroke by that number.
I could not find a corresponding number for the cylinder heads in any literature I looked through (including the Fiat Spider & Abarth and Fiat & Lancia Twin Cam books by John Tipler, Phil Ward and of course Guy Croft). Does such a number key exist that characterizes which head belongs to which block and in case yes, where can such a list be found? Looking on different heads, that I believe belong to different engines I find that the distance between the combustion chambers on the heads is the same, whereas on the blocks the distance between the bore centerpoints is different dependent on the bore. Also the pattern of cylinder head bolts is identical so that you can assemble any head to any engine. Is this true or do I have all the same heads, even though they wear different numbers and were sold as coming from different engines?
2) what is the nominal of the con-rod bearings on the crankshaft of a 1608 cc engine? My old manual (Bucheli -Verlag, unfortunately just has data for 1400 cc engine) indicates 45,518‚±0,01 mm, however I am measuring 48,25 mm and I am quite certain that the shaft has been revised at least once (or did someone grind on material?? ). Now I need to know which stage of undersize it is to order new bearings accordingly?

There is no list that ids heads to blocks.
The same basic head casting was retained when the 132 series with 84mm bores was introduced (also the 80mm bore Fiat 132 1592cc TC). The particular way Fiat redesigned the new block, using the old head casting left the valves on no1 and 4 cylinders offset 3mm relative to the bore centres, so they just enlarged the valve reliefs (on all cylinders, to make them interchangeable), you will see on the early 80mm bore units 124/125 that the valve reliefs are much smaller because the all valves fall on bore centreline. This was quite a cost effective solution - it is hugely expensive to tool up for a brand new head casting. It is important to note that with the later block the front coolant gallery is different to those used on the 1698, 1498 series, so check if swapping, the early head would need welding up and machining to use, never been worth it in my view. Get the later head!

Here is the grinding data for 1608 engines, there are two types, which I did not know when I wrote the GC book, the difference is in the crankpin only (rod journal), the mains are the same. Fortunately the Fiat 125A/B and 125B.000 crankpin is markedly bigger than the others so the difference is fairly obvious to crank grinders (as I found out when once specifying the wrong grinding size!). Always keep old bearings and compare size and features, like lug, oil holes when the new bearings arrive, never just throw them away. The same goes for thrust washers. Always check thrust washers for wear, and check the crank thrust region and block locating region too.

Before specifying any crank grinding or ordering bearings double check my data with your supplier and measure and record crank sizes with a micrometer.

If you work in inches multiply the metric data by 25.4 and use 4 decimal places eg: 1.9994 ¢‚¬Å“ 2.0002, but it is more accurate to work in metric, unless you have a digital Imperial micrometer that can measure to 0.0001‚ All the TC cranks have cross-drilled oil galleries and MUST be unplugged and cleaned out before refitting, in addition the grinding can leave the oilways very sharp and they MUST be radiused very carefully. (See also my post in GC V/W) about ‹Å“minimising power loss¢ž¢.



All stated sizes are millimetres
A after bearing code means aluminium/tin, the old B type trimetal bearings are very hard to get (meaning even I cannot get them)

A. Twin-cam engine type and vehicle:

125BC (1608cc) 124 Sport Coupe and Spider
124 AC (1438cc) 124 Sport Coupe
124AC3 (1438cc) - 124 Special T

Crank journal standard sizes
Mains 50.785 ¢‚¬Å“ 50.805
Rod 45.508 ¢‚¬Å“ 45.528

Rod housing diameter 48.629 ¢‚¬Å“ 48.646

Vandervell part nos:

Mains VPM91220A
Rods VPR91219A
Thrusts VPW21A


B. Twin-cam engine type and vehicle:

125B.000 (1608cc) 124 Coupe
125A/B (1608cc) 125 and 125 Special (incl Fiat Samantha)

Crank journal standard sizes
Mains 50.785 ¢‚¬Å“ 50.805
Rod 48.218 ¢‚¬Å“ 48.238

Rod housing diameter 51.330 ¢‚¬Å“ 51.346

Vandervell part nos:

Mains VPM91220A
Rods VPR91239A
Thrusts VPW21A

If you have anything different from above, let me know. Check availability of bearings before grinding. The regrind sizes are - 0.010", 0.020", bearings being quoted as part numbers above with oversize, eg +0.010". Sorry to mix up metric/imp units but being number-blind that's just how I do it with cranks. You are unlikely to be able to get +0.030" bearings these days for those old motors. Thrust washers are available in oversize but you never grind the crank thrust faces unless the bearings are badly beaten up, crank too. A light polish with Scotchbrite (fine) is all the crank thrust faces need, to get rid of any tiny high spots and varnish.

I should point out that when grinding a crank, the quality of grind and subsequent final polish are just one part of the job. If the crank is polished in the wrong direction, it will tear the bearings to pieces. This op must flatten the surface not raise it in direction of rotation - the effect is a bit like brushing an animal's coat the wrong way - it all stands up. AND - the care with which the main and rod journal radii are reproduced is vital to maintain the strength of the crank. AND - if the crank is slightly bent, say, having run a bearing, the flywheel flange will run out of true - get the crank/fw assembly balanced.

GC

[thommy124]

Thank you very much for the detailed information, Guy!
You put an awful lot of work and time in this site, answering all questions in high quality and maximum detail. I'm really impressed!

Best wishes,
Thomas

[Alex Marelli]

Hi all, hope this can help...

LINK DELETED BY GC

You can find here a list of engines code and head codes.

thank you,
Alex