860 GT Rod Big End Float lateral Spec???

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Tinkerbell
Mariana
Posts: 45
Joined: Sat Sep 05, 2020 3:57 am

860 GT Rod Big End Float lateral Spec???

Post by Tinkerbell »

Hi Everybody,
I decided to visit my pistons and barrels and also look at the con rods. The rods have approximately .033" lateral float between them. That is to say if I push them to one side of the crank , I can get a .033" feeler gauge in between the rod sides. The Haynes says a little clearance is OK. There appear to be shims on the outside of each rod, although they do not appear in the parts manual.
Anybody know the significance of all this ???
Sincerely,
Kara
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Craig in France
Paso 750
Posts: 928
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: 860 GT Rod Big End Float lateral Spec???

Post by Craig in France »

Hi Kara,

1. Put the Haynes manual on the back of the shelf. Good for pictures, pretty much useless for anything else.

2. Get yourself a copy of the factory workshop manual. This has all the assembly specifications as originally conceived by Ducati. (However, do not be surprised to hear that over the years some of these have been challenged by some people ...)

3. Buy yerself a set of metric feeler gauges :) .

So:
a) On a new or rebuilt engine, the factory tolerance for the gap between the con rods is: min. 0.43mm, max. 0.914mm.
On a used engine, the maximum allowable wear is: 1.2mm.
So at 0.033" = 0.8382mm, you is OK!

b) The shims you refer are, in fact, thrust washers and you should be aware that their health is critical to the life of the big end bearings. (They stop the conrods 'tipping over' which would otherwise lead to all sorts of bad things happening ...)

The factory assembly tolerances for the thrust washers are: min 0.81mm, max 0.9mm.

c) Equally important is the built-up length of the whole shebang: min 46.1mm, max. 46.3mm.

And we haven't even started with radial clearances, balancing, alignment ...

HTH

Craig
Tinkerbell
Mariana
Posts: 45
Joined: Sat Sep 05, 2020 3:57 am

Re: 860 GT Rod Big End Float lateral Spec???

Post by Tinkerbell »

Hi craig
Good news! I have metric feelers, but I convert to inches to understand their significance!
Thanks!
Kara
User avatar
Craig in France
Paso 750
Posts: 928
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: 860 GT Rod Big End Float lateral Spec???

Post by Craig in France »

Tinkerbell wrote: Tue Apr 13, 2021 12:15 pm <snip> I have metric feelers, but I convert to inches to understand their significance!
:-D :-D
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