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Discussion Starter #1
sentence in manual:
"The crankshafts for this engine are nitrided and therefore cannot be reground."

does it mean, that it cannot be polished?
if so, then its bad news for me, but has someone tried to do it?
or maybe i can fit some 8V crankshaft into this engine? 16V crankshafts are very hard to find in estonia.

please help!

thank you,

mags.trendkill
 

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I have heard of people re grinding cranks. If you were worried about using a reground crank you could just get it re-nitrided.
 

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machining technology of today means that you can re grind a nitrided crank and you most certainly can have it polished / linished...we just had one done for a 16V. Once it is ground it can be re-nitrided and will be as good as new. I wouldnt use a 1.7L 8V crank, as its not quite as durable.
Make sure you search for a good reputable machine shop to do the work.
 

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When I took the crank out of my 16v engine recently, it was a bit scored on the journals. I took it to a decent machine shop machine and they just linished it, but they actually said they could machine it and renitride it if that was necessary. The Alfa manual just probably wants you to purchase a new crank - assuming you were reading the manual in 1993 when cranks were probably readily available through Alfa Romeo :)

~Benjamin
 

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machining technology of today means that you can re grind a nitrided crank and you most certainly can have it polished / linished...we just had one done for a 16V. Once it is ground it can be re-nitrided and will be as good as new. I wouldnt use a 1.7L 8V crank, as its not quite as durable.
I am interested to hear your reason for making the comment regarding the durability of the 1.7L 8V crank as opposed to the 1.7L 16V crank. I am running a 1.7L 16v crank in my race engine, which is 1800cc, and I am looking to build another motor but only have a 1.7L 8V crank for this engine.
Do you know if the forging details, ie strength of material, of the cranks are different? There doesn't appear to be any other differences that I can determine.
 

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I am interested to hear your reason for making the comment regarding the durability of the 1.7L 8V crank as opposed to the 1.7L 16V crank. I am running a 1.7L 16v crank in my race engine, which is 1800cc, and I am looking to build another motor but only have a 1.7L 8V crank for this engine.
Do you know if the forging details, ie strength of material, of the cranks are different? There doesn't appear to be any other differences that I can determine.
Well since the 1.7L 16V crank is nitrided, the first 0.010in of metal on the surface is significantly harder than that of a non nitrided crank, therefore it will be more resiliant to wear and can resist fatigue, especially at higher rpms. Since the 8V crank is not nitrided it can be more susceptible to these factors, but is still a strong and very good crank.
I would imagine that both the 8V and 16V cranks are identical, only one is nitrided. The strength of material for the two should be the same, they would have both gone through the same processes except the 16V got nitrided at the end of finishing.
It may be worth asking at your machine shop if you can have the 8V crank nitrided (some offer this) then you could make it just the same as the 16V one - not sure if thats a possibility, but ask anyway.

But I think the key to a good engine is not the fact that the crank is nitrided or not, but whether all the parts are balanced together - this is how stresses are kept to a minimum.
 

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sprint#37

Did you ever determine the reason for the crank to fail? Was there a bearing failure? I notice from the photo you posted that one of the main bearing shells looks pretty ugly, or is that just a light reflection? Do you have any close-up photos of the combustion chamber on your head?
 

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B.t.w. I had a broken crank in my 1700 8v race engine in spring this year. All parts were well balanced..
was the crank from another engine that was damaged in anyway? ie bearing failure? Before a crank is machined I always have it crack tested (X-rayed) to see if there are any small hairline cracks, if there are its thrown away. Often cranks that have had bearing failure develop these cracks and over time they grow resulting in what happened to you. Have you got a close up of the break? Perhaps you can see where it propagated from, I'll show my metallurgist friend and see what he says.
 

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sprint#37

Did you ever determine the reason for the crank to fail? Was there a bearing failure? I notice from the photo you posted that one of the main bearing shells looks pretty ugly, or is that just a light reflection? Do you have any close-up photos of the combustion chamber on your head?
There was no bearing failure before. I opened the engine in winter and checked all bearings. Then I drove 2 races without any problems, in the 3rd race the crank broke while accelerating in 4th gear.
The crank broke at the rod bearing for the 2. cylinder, as a result the first main bearing was badly damaged, the front part of the crank gets loose, the timing belts went off and all valves in both heads were damaged.
The heads I use are from a 1500 engine with modified combustion chamber and big valves, now with 7 mm stems..
 

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was the crank from another engine that was damaged in anyway? ie bearing failure? Before a crank is machined I always have it crack tested (X-rayed) to see if there are any small hairline cracks, if there are its thrown away. Often cranks that have had bearing failure develop these cracks and over time they grow resulting in what happened to you. Have you got a close up of the break? Perhaps you can see where it propagated from, I'll show my metallurgist friend and see what he says.

No, it was the standard crank with standard bearings, not machined before. There was no bearing failure before..
Sorry, but there´s no close up, the crank is used now by a friend as candle holder..;)
 

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No, it was the standard crank with standard bearings, not machined before. There was no bearing failure before..
Sorry, but there´s no close up, the crank is used now by a friend as candle holder..;)
Haha, what a great use for a broken crank...your 7mm valve stems must look mean...I want a set too now!
 

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One more thing to be aware of if you grind 16v crank: thicker main journal bearings from 8v should be fit with modification. 16v has injectors to cool pistons so 16v bearings have ports to supply oil to these injectors. Bearings from 8v lack these ports but there's no problem drilling a 2 holes.
 
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