General Possible? Remove speedo gear from Fiat 850 pinion gear...

[mzerega]

Greeting technically-minded Fiat enthusiasts. An 850 Spider out here in California will soon run on a 9/35 (3.89:1) crown (ring) and pinion gear set -- thanks to Middle Barton Garage, in Bicester. Unfortunately, the new pinion is not equipped with the little speedometer gear that fits into the threaded end of the pinion shaft...which leads us to the question: How does one remove this little gear without damaging anything? Is this possible? Would love to hear from someone who's successfully performed this operation

 

[timmycm850]

Hi Mzegera.

I lucky found an original 60s abarth one 9/37( now in my Lombardi) with the small gear fitted but knew the modern ones come without. I thought the small gear and shaft were an interference fit into the end of the shaft so I guess the trick would be to find a damaged ring and pinion and grind it to remove the little gear from the damaged shaft.

Alternatively tap a thread down the middle of the small gear and use a puller to pull it out whilst heating the longer gear.

Must admit I've never tried it though.

Tim

 

[mzerega]

Hi Mzegera.

I lucky found an original 60s abarth one 9/37( now in my Lombardi) with the small gear fitted but knew the modern ones come without. I thought the small gear and shaft were an interference fit into the end of the shaft so I guess the trick would be to find a damaged ring and pinion and grind it to remove the little gear from the damaged shaft.

Alternatively tap a thread down the middle of the small gear and use a puller to pull it out whilst heating the longer gear.

Must admit I've never tried it though.

Tim

Thanks for your suggestion, Tim. Interesting idea, to drill, tap and pull/extract the speedo gear. If I had a lathe, I'd try it After ruminating on this little problem and considering the secondary market value for an old 8/39 pinion (near zero), I may just implement your first suggestion i.e., "surgical" extraction of the speedo gear. Thanks again, Tim.

 

[timmycm850]

I guess in real terms a replacement standard ring/pinion is about £250. So if you needed to go back thats the base costs. Whats the cost of a dare gearbox(if you can find one).

Tim

 

[mzerega]

I guess in real terms a replacement standard ring/pinion is about £250. So if you needed to go back thats the base costs. Whats the cost of a dare gearbox(if you can find one).

Tim

Well... I paid £1100 for the 9/35 ring/pinion alone Fortunately, the gearbox that was in the car (a 1969 Spider) is in excellent condition internally. I'm replacing the 8/39 to reduce 113 KPH cruise RPM by ~1000...due to typical California freeway speeds and a 903-to-954cc turbo engine build; the incremental power and torque should be sufficient and I expect a much quieter, more efficient ride at higher speeds.

Another bit of fortunate, late news is: I managed to find a new speedo gear, and the washer that's underneath, on a popular Italian auction site With a bit a good fortune, the parts will be here within a month or so. I'll just press in the new one...and see if I can't find somebody who needs to old 8/39 set...complete with its speedo gear.

All the best to you, Tim. Thank goodness, there will be no hacking of good, used parts

 

[timmycm850]

Oohh. Good find. Its likely the dppedo will be slightly out but if it makes you legal then you can learn the speed of set with use.

Interesting 954cc turbo. That will help with the torque figure very well

Tim

 

[mzerega]

Amen, Tim. In case you're interested, here's how I'm getting to 954cc and 100+ HP
66.5MM hypereutectic pistons from a motorcycle
- Significantly shorter and lighter than Fiat factory pistons
To make up for lost compression height on the pistons, and to achieve desired static compression:
2.0mm longer connecting rods (219.5mm) also from a motorcycle
68.00mm factory crankshaft stroked to 68.75
to achieve 9.2:1 static compression
With 0.83 bar of boost from GT12-copy turbo adapted to Zastava 750 exahuast manifold, for 12.4:1 effective compression
Fuel and spark controlled by Speedunio NO2C

 

[timmycm850]

Interesting mix. I do like the fact that the turbo flange seems a perfect fit with the 750 manifold