Ducati conrod bearing sizes - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 14 (permalink) Old May 10th, 2017, 9:48 am Thread Starter
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Ducati conrod bearing sizes

Hi

I'm rebuild a 999S engine with new bearings and so on
I also checked the conrod bearing shells with plastigauge.
Clearance between crank and shell is around 0,05mm (0,058mm is max).
Seems good to me so I want to replace them for the same size. Or should I get the clearance tighter?

The conrods have an A mark on them
But I can't find a mark on the crank?

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post #2 of 14 (permalink) Old May 16th, 2017, 11:57 am Thread Starter
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Nobody knows?
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post #3 of 14 (permalink) Old May 16th, 2017, 12:22 pm
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Probably the reason why no-one has replied is that it is an odd question. Apparently you have decided to replace the bearings. You don't state why. Anyway, unless you are having the crankshaft and rods reconditioned, you don't want to change sizes.

I try to be thorough. I rarely return to a thread. If you have a question for me, PM me.
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post #4 of 14 (permalink) Old May 16th, 2017, 3:21 pm Thread Starter
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I don't think it's a very odd question?
I disassembled the complete engine to replace bearings and so on. Because its an engine with no history and I want it to be reliable for track/race usage. I measured the clearance to be sure! it's within specs. The bearing shells don't look like new and need to be replaced.
Problem is...which shells do I need to order...original spec...yes..because measurement showed the clearance with stock specs are fine.

Conrods are class A
But I don't know which class the crankshaft is (A or B).
I can see something written on it with an A. But I don't know if this is the marking for class A crankshaft. So I'm looking for someone who can confirm the white paint on the crank shows the class type.
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post #5 of 14 (permalink) Old May 16th, 2017, 3:44 pm
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Originally Posted by D52R View Post
I don't think it's a very odd question?
I didn't say it was a "very" odd question or intend to insult you. The reason it seems odd to me is that anyone that would undertake an overhaul would not have a basic understanding of how the crankshaft and connecting rods are machined to take a specific bearing size, or conversely, in some case, how a particular size bearing is used when the rods and crank are sized after machining.

I'm all in for you taking on the project, even if it is your first. Getting some basics down before you attempt an overhaul can prevent a catastrophic failure. For example, never trust anyone, not a machinist, not the markings on a box, sometimes not even the markings on a part. Now that you have commented that you see visible wear and are replacing them for that reason, I would simply advise that if you do not have all the measuring equipment that an engine rebuilder has, you can still plastic gauge the replacement bearings during assembly. Make sure you torque or rod stretch the assembly to spec for your plastic gauge test.

As far as determine the bearing size, if you can't determine what the factory put in them with either markings or measuring equipment, take the crank and rods to a shop to have them measured so you buy the correct size(s).

I try to be thorough. I rarely return to a thread. If you have a question for me, PM me.
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post #6 of 14 (permalink) Old May 16th, 2017, 4:27 pm Thread Starter
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It's the first Ducati engine I rebuild. Not the first engine.
I have all the tools laying around, that's not a problem.
And I measure before I replace/install parts, like I already told. I only need to know where to find the class spec of the crankshaft. Is it the white paint, or the stamped in marking with some letters/numbers (not specified in the manual). Well yes you could measure the bearing shell/conrod bore but there is no list in the manual that specifies the color bearing shell you need with a specific measurement. That's the reason why I ask how to identify the crankshaft class.
I could buy 2x RED/Blue set and 2x Blue/Blue set spec shells. But you understand that doesn't make sense.
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post #7 of 14 (permalink) Old May 17th, 2017, 1:51 am
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i usually default to 4 blue shells. it's pretty rare for that not to be right, i don't think i've ever used reds. i think you might be able to get a lot more colours from say the 1098r catalogue with tighter ranges, but given it's been out of production for 4 or so years they might have dropped all the others by now.

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post #8 of 14 (permalink) Old May 17th, 2017, 2:01 am Thread Starter
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Thanks bradblack for your information
Any idea how much tighter a blue shell is compared to a red?
I will need one red shell. But the clearance is almost at the top of the spec limit. So maybe i could swap it also for a blue one.
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post #9 of 14 (permalink) Old May 17th, 2017, 2:31 am
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as for posts, use the sbk forum. this tech one gets little traffic.

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post #10 of 14 (permalink) Old May 18th, 2017, 2:18 pm
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Ill be doing a crank myself soon, and find this threa interesting. I talked t a friend whos been responsible for Volvo cranks and conrods for years an years; he recommended using clearances in the upper tolerance range to increase flow through the bearing and thereby increase the cooling of the bearing. Sounds logical to me ...?
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