Engine "rattle"

[AndyCapp]

I've had my 1980 SSD from new. I did a full engine rebuild when it had around 22k miles on. The crank
had a very small, but measurable amount of play, so I had new rods, bearings, washers and pin installed. That
was many years ago. The bike had been stored for a long time. I've recently had it going again (we were not
in the same countries, or even continents for many years and that's my lame excuse). When I had it
out at the end of last year, I noticed an engine rattle on light throttles, but I convinced myself that due to
manufacturing sloppiness, it probably always made that noise. It now has 25k on the clock.
I've had it out this year and the noise is much worse. It's load related, but not a low-down 'knock' - is that
what cranks do when they are on their way out? More of a higher-pitched, something a bit loose type of thing.
I've had both casings off and can find nothing loose (Generator, Primary drive, clutch etc). If it had tappets & rockers,
I'd say it was a tappet type noise.
The noise is not there at tickover, or very light throttle (in any gear), but is there at low-mid RPM on a light throttle,
but seems to go sway on mid-high throttle and mid-high RPMs. It seems related to engine speed, not clutch/gearbox speed.
I'm running on monograde 40 oil.

Please, please, please don't say it's the crank - meaning engine out and a full rebuild ......

[rwhc80]

G'day Andy,

I'd be dissapointed if it turned out to be crank with only 25K on it ! so my question is, How long has it been since you did the shims on the heads for valve clearances ??

Cheers
Rick

[AndyCapp]

I did both heads (off the bike) over winter, so it cannot be that. New guides, valve & rocker shims. Anyway, it's load related, so I think that would rule out
anything valvetrain related ?
It's not very noticeable when cold, but gets louder the hotter the engine is.

[BevHevSteve]

Andy - time to re check what you did on the valves.

[wdietz186]

After you check the valves and look for loose parts on the bike,have a look at the exhaust system. It is possible the center tube [Conti] or a baffle[LaFranconi or aftermarket] has rusted and come loose and is rattling when the harmonics are right. A check of the ign. timing might be in order too as todays gas is not like it used to be. And the view from far left field could include piston slap or pin wear too.

[AndyCapp]

I've just taken the engine out. The l/h side crank (primary drive) shaft had play. I split the cases.
The L/H shims on the crank output shaft were eaten up. I also found the remains of at least one more in
the sump. The main bearings look fine.

Just to be clear - I am talking about the shims inside the cases, on the crank - for the L/H main bearing

So, questions ...
1. What on earth would cause those big shims to get destroyed (I can see nothing wrong with the main bearings)
2. If I re-shim it up - could this happen again ?
3. The main bearings rotate freely and smoothly - maybe I should replace them anyway ?

Historical note. I've had the bike form new. Many, many years ago I did a full engine rebuild. I'm confident I
shimmed the crank correctly. And it ran for some years after without a problem. It was then in storage for
over 10 years. It's been back on the road a couple of years now - but with limited mileage. The noise
appeared last year.

I hope the excess free-play hasn't had an adverse effect on the big ends....

[Craig in France]

Just to be clear - I am talking about the shims inside the cases, on the crank - for the L/H main bearing

These ones, Andy?



Ciao

Craig

[wdietz186]

Andy, Do you remember if you preloaded the crank when you set it up the last time? If set up to just zero end float when it gets hot you will have play and the banging back and forth due to the helical gears can eat the shims up. I shoot for .004" preload when I do mine. This is noticable drag but falls on its own when the heavy side of the crank is up. It is doubtful it has done anything to the rod bearings by being loose. Do check the piston/cyl. clearance while you are in there and have a look at the pins too.

[AndyCapp]

To Craig in France, yes those are the ones.

To wdietz186. When I set the crank up all those years ago, I don't think it mentioned preload in the Hayes manual I was using,
so I probably went for zero free-play. I also remember going to my local dealer and looking at his Ducati workshop manual.
You could be onto something. I noticed that in the several years of storage and being transported around from
country to country, several engine bolts which had been tight for years, were now not tight at all. Could it be the
cases had swollen slightly over the years - allowing for too much free-play ?

I was thinking the big-ends may have worn unevenly as, under load, the crank will not have been running true.

Thanks

[Craig in France]

To Craig in France, yes those are the ones.

Ok Andy. The reason I asked is that those aren't really shims. They're thrust washers and, as Bill has indicated, you adjust them to get the correct end float. (And yes, wear in the thrust washers has been cited as a cause of big-end failure).

As to the amount of end-float, Bill is right (again): factory spec is zero, but general wisdom is to go further and pre-load a little. Go here, for example:
viewtopic.php?f=50&t=1959
viewtopic.php?f=9&t=2902

HTH

Craig

[wdietz186]

Craig,Stop it my head is getting big!
Andy, How much end play did the crank have? I think it would have to be over about a millimeter to cause any undue big end wear. You could inspect the side play on the rods to get an idea. The thrust washers on the crankpin would probably show some signs of wear. They are probably fine.
As for the cases expanding,only heat will make them grow.Which bolts were loose?

[AndyCapp]

There was quite a bit of free play. With the primary gear & clutch still in place I could easily move the crank by hand. I could see and hear the
movement. I did check side-to-side clearance between the con rods and con rods to crank webs. It was only 0.10 - I think this is well
inside the service limit ?

Several of the small crankcase allen bolts were loose, but several were still fully tight - sometimes next to each other. Strange.

Update. Since the rebuild, I took the clutch cover off again to make sure all was still ok. I could detect a very small amount of
up and down movement when I used a lever between case & flywheel. Perhaps 1 to 2mm or so at the end of the crank. I'm guessing
this is ok, as if there was no movement at all, then that would mean the main bearing is too heavily loaded ?

(PS. http://en.wikipedia.org/wiki/Andy_Capp)

[jockduck]

Hi, yes its true that if the shims are not preloaded they can spin and wear, is it possible the main bearing inner has been spinning on the mainshaft? also a shim wearing mechanisim, There are some pretty flimsy shims out there, I believe Ducati used narrower (smaller outside diameter) shims on later bevels, I always use a single shim of the correct thickness instead of multiple skinny ones in areas of stress, in stationary areas multiple is OK. I even cut my own shims from steel stock to get what I want.
Jock

[wdietz186]

Andy, If you preloaded the crank and everything is assembled correctly [trans shafts,shift drum end float] you should not have any up/down play at the end of the crank. Unless the bearing is bad or the case is cracked. When the crank is preloaded there will be a noticable drag when turned with the cases torqued. The crank should fall of its own accord when the heavy side of the crank wheel is at 90deg. from vertical. Did you by any chance set the preload up without the case gasket in place?

[Craig in France]

The reason I asked is that those aren't really shims. They're thrust washers and, as Bill has indicated, you adjust them to get the correct end float. (And yes, wear in the thrust washers has been cited as a cause of big-end failure). As to the amount of end-float, Bill is right (again): factory spec is zero, but general wisdom is to go further and pre-load a little.

Have just been reading Ian Falloon's "Book of the Ducati 750 SS" in which he writes:

"If the (drive-side) thrust washer broke, oil supply was lost to the big-end assembly."

And:
"It was also important to preload the angular thrust bearings when assembling the crankcases to allow for expansion of the aluminium (of the cases) in relation to the steel crank. A correctly shimmed cranksahft will turn quite stiffly in the crankcases when cold."

So, just like wot Bill said (... again )

When the crank is preloaded there will be a noticable drag when turned with the cases torqued.

Ciao

Craig