M600 Front piston swap

Hey all, I'm new here so I thought I'd start at the deep/stupid end.

I'm currently rebuilding my little 600, and one of the myriad of things I want to fix is the front piston slap/ringing that is so common on this bike.

From what I understand the only real way to fix it is to swap the piston. Does anyone know of anything that would stop me swapping a piston from a rear cylinder and using it in my front one? Because they are a hell of a lot easier a cheaper to get hold of. Basically are the two pistons different in any way I haven't noticed?

Or even simply skimming a tiny (and I mean tiny) bit off the piston skirt of the current piston? Haha. That would be fun.

Thanks in advance!

[slob]

The pistons should be identical. The barrels are not interchangeable, since the fins run at 90degrees to each other.

Yes. I appreciate the cylinders are (very) different but I couldn't see any reason for the pistons to be. I was wondering if I had missed anything.

I can't lie, I secretly want to put my current piston in a lathe. Hehe. Would be fun.

What would you do to your piston once you have it in your lathe. You do realise that piston slap occurs due to piston wear, putting it in your lathe won't replace the metal that has worn away. Why not replace the piston with an unworn one, then put your worn piston in your lathe and "turn" it into something useful, like an ashtray or something, that would be fun wouldn,t it?

Well, from my (admittedly limited) knowledge the problem on the 600 comes from some sort of vibration mode caused by the unique combination of the bore, stroke, engine speed, weight of the piston and orientation. And probably the casting of the piston originally plays a part. I say this because the 750, 900, 620 etc aren't affected.

The damage is clearly visible on the outer surface of the lower (as the piston is oriented to ground when fitted in the bike) side piston skirt. It happens as the aluminium piston slides home into the cylinder, the skirt hit the bottom edge of the steel cylinder liner.

The lower face is the one affected simply due to gravity.

The fact that the ONLY damage on the pistons is in that area seems to imply some sort of flaring of the piston skirt (although as I type this I have thought of another possibility). From this I was wondering if I could simply shave the damaged area (a tiny bit) to remove the material that is interfering.

This obviously only makes any sense as an idea if the skirt is flared in the first place. I was planning to jig it up and take a clock to the surface to check this anyway

Oh - and don't worry; when I replace the piston (as is the 99% probable outcome) I have some (even more ridiculous) plans for the old piston.

Thanks for both of your quick replies though!

PS: this post wasn't supposed to be stating fact, more like me just thinking out loud.

I take your point about " thinking out loud " but just one more point , if you mic up your piston to check the dimension of the skirt, do bear in mind ( assuming you don't already know this ) that a brand new piston is not a uniform size when it is cold, it is slightly smaller in the piston ring area. The widest part of a new piston is at the bottom of the skirt at 90 degrees from the gudgeon pin holes, this could mislead your line of thought if you measure it. The theory of this is that there is more metal in the ring area than in the skirt , hence more expansion when hot.
I have owned and restored 12 Ducatis , most of them carb models, only one of those suffered from piston slap, that was a 600SS with 25K miles on it, a new piston cured it. So " they all do it" is a myth used by people who are in the process of selling their bikes.
Let us know how you get on with that.

[utopia]

Checking in my manual, I notice that the pistons are marked in the area of the valve cutouts, A for inlet, S for exhaust......but presumably (?) its just a matter of fitting them the right way round for each cylinder, rather than any dimensional difference between front and rear.
I also notice that both the piston crown and the top face of the barrel are marked with a "size" code, A or B, so you'd need to match that.
The manual (both Haynes 2V and my genuine Ducati for M750) makes no mention of any difference between front and rear, as far as I can see.
One has to wonder though, if the front and rear pistons are identical, why are they differentiated at all ? (I presume you're talking about brand new pistons). Surely the extra part number is just unnecessary parts dept complication .

Just out of interest, has this bike had a big bellypan on it during its life ?
I only ask because in my experience, the big ones which encase the front header tend to make the engine overheat, particularly when the bike is stationary, and I'm wondering whether there's a link to accelerated front cyl piston wear/slap.

[Dukedesmo]

Originally Posted by utopia

Checking in my manual, I notice that the pistons are marked in the area of the valve cutouts, A for inlet, S for exhaust......but presumably (?) its just a matter of fitting them the right way round for each cylinder, rather than any dimensional difference between front and rear.

(A = Aspirazione, S = Scarico) but yes they are indeed interchangeable.

On the watercooled engines, not only the pistons but also the cylinders and heads are identical - you just assemble the pulleys etc. on the opposite side and fit blanks on the side you don't use.

[Kato]

The "early" pre 98? 600’s, had forged pistons that make the horrible slappy noise when cold, not that it gets much better when they warm up. Sounds like the insides are trying to get out, most will tell you "they’re all like that". If you pull it apart, chances are there will be not a lot wrong with it, Just very short pistons, the issue can be almost cured by replacing the piston on that cylinder with the cast piston from a later model ( which supersede from the early ones anyway ) pistons are not different front / rear, either will fit into either barrel

So no reason you couldn't swap front to rear but you'll prob need a set of rings and after a few miles it will be noisy again

Pistons still available from Ducati Part No 120.2.042.4A but not cheap £248 each

Maybe JE or somebody will do a set

Dookbob,

I did not know that point you made about the skirt being larger than the face, but I can see why now you've said it. Every day's a school day. Might make those measurements kinda hard...I'll see what comes up.

Utopia,

You are basically walking down my thought process.The bike has had a baby belly pan on it for a good while, but it doesn't do much in the way of blocking air flow to the header.

Kato,

The point about the forged vs casting makes a hell of a lot of sense. I was actually talking about buying a second hand rear piston (since they are dirt cheap) and sticking that in, but I do realise that if it is of the same era then it will get noisy again after a while.


At the end of the day, I don't exactly give the poor wee bike an easy life. I bought 18 months ago with 19k on it, now it has 37.

Again, thanks for everyone's input!

[slob]

Originally Posted by Blacksheep

... I bought 18 months ago with 19k on it, now it has 37...

Good work!

[Kato]

At 37k on the clock I'd suggest re nicosil the barrels use late cast pistons (a few on flebay) and a new set of rings job done

Kato,
When you have a barrel re nicosiled, does the process involve boring the cylinder before the new nicosil is applied, or does the re nicosil bring it back to the original size without boring?

[Kato]

Originally Posted by Dookbob

Kato,
When you have a barrel re nicosiled, does the process involve boring the cylinder before the new nicosil is applied, or does the re nicosil bring it back to the original size without boring?

The process dose not involve a re bore if you don't want it they will re-plate and hone to original size if thats what you want
I always use http://www.langcourt.com/index.html

Originally Posted by Kato

The process dose not involve a re bore if you don't want it they will re-plate and hone to original size if thats what you want
I always use http://www.langcourt.com/index.html

Thanks for that Kato