Author Topic: Frame and engine  (Read 240 times)

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Online DC Concours

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Frame and engine
« on: April 29, 2019, 02:54:50 am »
I went for a short ride with a friend who just got his dad's ducati 900ss. He told me that his bike had a frame crack. He also told me that my bike had a weird design where the engine hung off the frame in a way that stressed those points and engine bolts are known to break!!! WTF.


What is he talking about? Can someone explain please...



Offline Nosmo

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Re: Frame and engine
« Reply #1 on: April 29, 2019, 04:31:55 am »
The engine does indeed "hang off the frame".  It IS the bottom of the frame in a way.  The engine is a stressed member, and takes the load that the lower tubes would in a cradle-type frame  It isn't really "weird", lots of bikes use it, and it works well.  The crankcase is very strong, and it saves weight by lightening up the frame.  The engine mount bolts do break sometimes due to loss of torque, vibration, and improper shimming.  Bolts properly torqued, with the frame/engine fit properly shimmed at the forward bolts, should last the life of the bike, i.e., 200,000 miles +.

Do a duckduckgo search:

https://en.wikipedia.org/wiki/Stressed_member_engine

https://en.wikipedia.org/wiki/Motorcycle_frame#Stressed_member

https://answers.yahoo.com/question/index?qid=20140206180153AAXG0o2

« Last Edit: April 29, 2019, 04:35:10 am by Nosmo »
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Offline mnbikeguy

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Re: Frame and engine
« Reply #2 on: April 29, 2019, 10:52:29 am »
IMO Ducati riders can be rather pretentious and given to a belief they have superior knowledge. He might be surprised to learn that every manufacturer including Ducati has been using engine as stress member frame design since the 80's. Here's a nice picture of what it looks like:



Offline Bob_C_CT

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Re: Frame and engine
« Reply #3 on: April 29, 2019, 11:09:49 am »
Just so you know there are multiple bolts and although the engine is part of the frame you would need multiple bolts to fail before there would be a chance of the engine being able to move enough out of its place to become critical.

You never hear of anyone’s engine falling out. 
What you do hear about is the bike feels like I am riding on marbles, not tracking well when at speed and usually when I’m dirty air.

That was my C10s symptoms after I bought her. Put up with it for a couple of months thinking that the large windscreen and the fairing was acting as a sail. Low and behold after examining what I thought I saw as the threaded end of a screw that had a thru hole tapped on the bottom engine was really the rear lower motor mount screw that had the hex head sheared off clean.
That is why it is important to keep up with at least a visual examination of the engine mount bolts. 2 upper forward on each side of the engine., one upper and one lower rear the goes all the way thru the engine left to right.
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Offline works4me

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Re: Frame and engine
« Reply #4 on: April 29, 2019, 11:38:43 am »
To me, Ducatis look like they were assembled using parts from the plumbing aisle at Lowes.
« Last Edit: April 29, 2019, 02:09:55 pm by works4me »

Offline david

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Re: Frame and engine
« Reply #5 on: April 29, 2019, 11:43:32 am »
Was that before or after he dropped the duck off at the dealer to be worked on for the 4th time of the month

Offline Bud

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Re: Frame and engine
« Reply #6 on: April 29, 2019, 11:52:46 am »
My 05 had a broken upper engine mount bolt on the right side.  When accelerating hard, it would feel like the frame was twisting, which I guess it was.
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Online DC Concours

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Re: Frame and engine
« Reply #7 on: April 29, 2019, 07:22:17 pm »
Thanks guys. I'll be checking my bolts from now on.


His Duc was fixed by the manufacturer in the late 90s. I think his is a 1995 900SS. Nice looking full fairing bike but a very uncomfortable bike.

« Last Edit: April 30, 2019, 05:35:43 pm by DC Concours »