Technical THe crank nut on a 1608.

[Randiego]

Hi fellow Fiat enthuiasts,

Several years ago (2015), I started on the build of my 73 Spider. I took a 1608 engine to JRS Machine in LA and they did all kinds of improvements and I had the head ported polished and oversized (1MM) valves installed. Mark Allison got me some performance cams and I am putting on Italian Weber 40 IDFs on his mainifold.

When I got the engine and components back, I assumed that all was in the parts that were in the box. NO CRANKSHAFT NUT ! ! :-( I had another engine (the original 1500? out of the 73 sitting here and I pulled the nut and the front pulley off. The pulley fits fine but the nut will not thread on. Is the nut a different size of thread pitch for the 1608 vs. the 1500? Before I have to order one, I was hoping that one of you could help me with this question. The nut that I got off of the 1500 doesn't thread on.

 

[bugsymike]

Hi fellow Fiat enthuiasts,

Several years ago (2015), I started on the build of my 73 Spider. I took a 1608 engine to JRS Machine in LA and they did all kinds of improvements and I had the head ported polished and oversized (1MM) valves installed. Mark Allison got me some performance cams and I am putting on Italian Weber 40 IDFs on his mainifold.

When I got the engine and components back, I assumed that all was in the parts that were in the box. NO CRANKSHAFT NUT ! ! :-( I had another engine (the original 1500? out of the 73 sitting here and I pulled the nut and the front pulley off. The pulley fits fine but the nut will not thread on. Is the nut a different size of thread pitch for the 1608 vs. the 1500? Before I have to order one, I was hoping that one of you could help me with this question. The nut that I got off of the 1500 doesn't thread on.

No specific knowledge, but 50 years in motor trade. Lovely looking car, in 1978 I had a 1971 Alfa Romeo 1750 GTV . My first wife got it along with half my house, I bet she wished she hadn't part exchanged it for a Morris Marina!
No chance of them finding your correct crank nut?
No chance of damage to crank thread stopping nut go on?
Can you get a vernier gauge and compare both crank thread diameters , then get a thread gauge to check in case of different thread.
Assuming they are different, it should be possible once you know the thread type and size plus the exact diameter.
Just in case you haven't seen a thread gauge , it looks like a set of feeler gauges but with saw type teeth that should just drop into the crank threads a perfect fit and then written on them will be the detail, metric , imperial, whitworth, fine, etc plus a number to correspond with the nut size you need to identify. Sorry if I am "teaching you to suck eggs" I never know what level of knowledge people have.
I assume this is the engine type. with the lower one the original engine? If this is wrong please correct in case anyone else tries to give further help

1608

125BC.040

1438	124 AC.040

 

[Randiego]

Bugsymike,

Thank you for your response. I was panicking because it is the only nut that I have. Well, that nut is the same for all 124 engines up through the latter engines (2000?) I could not see the bottom of the crank threads. I got the engine on a lift and raised it up to inspect the lower threads. Sure enough, the machine shop "bumped" the crank and the first two rows were "flattened". I got my small needle file (triangular) and carefully dressed the threads, restoring them. I lightly oiled the nut and VOILA ! it went on without a hitch. So the lesson here is to really inspect the problem and know all facets and issues before you panic ! Had I taken the time to raise the engine up for a good look at the bottom of the crank, I would have seen the issue. Lesson learned. Thanks again Mike.

Randy

 

[bugsymike]

Bugsymike,

Thank you for your response. I was panicking because it is the only nut that I have. Well, that nut is the same for all 124 engines up through the latter engines (2000?) I could not see the bottom of the crank threads. I got the engine on a lift and raised it up to inspect the lower threads. Sure enough, the machine shop "bumped" the crank and the first two rows were "flattened". I got my small needle file (triangular) and carefully dressed the threads, restoring them. I lightly oiled the nut and VOILA ! it went on without a hitch. So the lesson here is to really inspect the problem and know all facets and issues before you panic ! Had I taken the time to raise the engine up for a good look at the bottom of the crank, I would have seen the issue. Lesson learned. Thanks again Mike.

Randy

Hopefully the only lack of care the machine shop have exhibited, I have seen a few over the years. Good luck with the rebuild.
It may sound a bit "kinky" but I used to rub my hands over the surfaces of engine parts and often even with my thick skinned engineers hands I could feel a little knick were a machine shop had skimmed a cylinder head and then been careless putting it down on the bench, potentially causing gasket failure etc.