Bolt only type conrods Fiat TC.

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Piotrek125p
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Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 12:16 pm

Hi.

GC, you wrote in Your article about conrods that a new type bolt only type conrods are weaker than old type bolt-nut type:
-new type hardness about 15-18HRC
-old type hardness about 19-20HRC

I done some simple test on my Vickers machine and get another than Yours results:
-new type hardness about 24,8-25,6HRC
-old type hardness about 23,1-23,8HRC

Test was done on well polished caps and small ends on rods from different sets. Vickers machine was of corse in excellent condition, about week before my tests it passed annual calibration test.

The new type rods were this type
5874152544.jpg
My new bolt only type TC rods
5874152544.jpg (62.85 KiB) Viewed 3817 times
GC, do You done a metallurgical test only on one set of rods ? Maybe some of rods were weaker and another were stronger and it is necessary to do a hardness test before fit it in mildly tuned TC with not a big budget ? Further, for bolt only type rods I can buy without problem a new set of great ARP rod bolts, for old type rods it is impossible.

Of corse I am talking about rods for road not race engines, about second type of powerplant I have the same point of view like You - if you race use race parts.

Sincerely
Piotrek.
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Guy Croft
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Sun Jan 10, 2016 1:05 pm

Hardness is only a guide, I don't doubt your results at all.

I had a full metallurgical examination made on the set you refer to many years ago, the lab advised inferior carburising treatment. Of course one set doesn't mean every set but that report enough for me to discontinue standard rods for race engines, as you say..

From that new set one snapped at the neck just below the pin, completely wrecked a 192bhp NHRA engine, after just three short-oval laps of practice with no more than 8000rpm. Polished and shot-peened - all a waste of time.

G
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Piotrek125p
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Re: Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 1:10 pm

Ok, in next week I want to do a hardness test on all of my new type rods (used and new) and share the results here. I will contact with my professor from Lodz University of Technology of which I am a graduate and ask him what metallurgical tests they can do for me. Maybe some of bolt only type rods can be used in tuned (not race) TC engines ?
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Sun Jan 10, 2016 2:14 pm

well yes you can use them but they don't come (unlike say VW) as balanced sets. I have seen variations of over 40gm. That is a huge imbalance to remove and frankly not worth my time.

It's the rpm that breaks them. You can run production rods in an Integrale at 260bhp no problem if you don't over-rev them.

G
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Piotrek125p
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Re: Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 2:17 pm

But they will be fully machined and balanced, I checked the weight of my rods and it was max 10g difference between the lightest and the heaviest. I will not use an unmodified and not balanced rod.
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Sun Jan 10, 2016 2:27 pm

The 40 gm I mentioned was in the big-end of one rod.

Just weighing the total mass of the rods does not mean the end-over-end weights are right. Balancing end-over-end puts the center of gravity of the rods in the same place.



G
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Piotrek125p
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Re: Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 2:34 pm

As rod balancing I understand the alignment of the masses of small end of all set, a big ends and overall.

I have a rig for it and done it for other engines.
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Sun Jan 10, 2016 7:05 pm

Feel free to post some pics of your rig,

G
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Piotrek125p
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Re: Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 7:37 pm

Ok, I will make some photos of my rig propably in next weekend, I want to do some tests with another set of rods.

GC, You wrote in Your first book about TC rod small end weight reduction by grinding it by 2mm to side. Could You explain why You suggest exacly 2mm ? I like to know it, because I want to know what I can do in rods from another engine (can I grind a small end and for which width). How to calculate it ? About big end everything is clear for me, but I am not 100% confident how to calculate it in small ends.

When I first time measured big end diameter in new type rod I noticed that cap is loose, this is not good dowelled and could set in vary positions. I thinking to fit a stainless steel dowell (something like flywheel dowell). I can do it accuretly, then I want to resize big end (I have a very reputable firm in Poland who can do it for me-I check on CMM rods resized by them and this was done excellent) and fit a new ARP bolts set. What are You thinking about this idea ?

Anticipating Your question, I want to modify and use OE rods simply because this is cheap and if it will pass my metallurgical test could be exceptionally safe. I bought a new OE set of rods for 200zl (about 35 pounds), all machining I could do personally (a good occasion to get new engineer experience).
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Sun Jan 10, 2016 9:08 pm

I won't give advice on production rods.

GC
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Piotrek125p
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Re: Bolt only type conrods Fiat TC.

Post by Piotrek125p » Sun Jan 10, 2016 9:15 pm

Ok, I guess that You wrote about dowell pins, but what about small ends question ?
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Re: Bolt only type conrods Fiat TC.

Post by Guy Croft » Mon Jan 11, 2016 2:36 pm

Sorry Piotr,

I'm not giving any advice on old OE rods ...

G
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