Ducati Monster Forum

I have a set of 92mm drop-in pistons I put in my '95 900 motor.  I set the top ring gaps to .020", the second ring to .016".  The oil rings came in around .017".  Pistons went into the bores without issue, put it all back together, and everything is running well. 

Flash forward a week, and I finally sort some carbourator issues I had been having, and go off for a quick 'break in run'.  Running straight 10W40 dino oil, with a fresh filter.  Ran it up to around 5-6K rpm's.  Felt really strong, the HC pistons really make the motor spool up quicker. 

Long story longer, I parked the bike after the 2 mile test run, next day I try to start it up, and its only running on one cylinder.  Check the plugs, and one of them is oily.  Peer down into the cylinder with a flashlight, and I'm surprised to see the sides of the cylinder scored up quite nicely.

Going back over everything I did, I can only recall one area where I may have made a crucial mistake.  I bought a set of used 900 bores off ebay for this project, de-glazed them, and dropped in the pistons (with the proper end gap).  The builders I've talked to have said 'Always, always mic your bore and your pistons'.  Crap.

My question is this: With a 92mm bore, and 'drop-in' pistons, is it still necessary to check?  And if it is, how do you match the cylinders to the pistons if the bore is too big?  Does the replating process actually add material to the bore?  I'm a little confused as to my error, and before I buy any more parts, I need to know what my options are, and what I need to check to make sure it doesn't happen again.

Thanks!

you just fit them, not much else you can do.  20 thou is a bit big for a top gap - i'd run 14 from memory.  but i doubt it'd oil up the cylinder.  maybe the cylinder is damaged?

The bores looked really good after the deglazing, I didn't see (visually) any reason not to continue.  But I suppose if the bores had been distorted, it might cause a problem.  Still, the scoring has me confused.  Thanks for your input Brad.

I usually check the bores but since I haven't found a round one yet, it gets a little depressing. Most people do what you did & never have a problem. How clean was the motor before you fired it? I usuall warm the motor up & then dump the oil just to be sure. There is always crap floating in the air. Do a compression test or a leakdown & that'll tell you how bad of a problem you're dealing with. I have a good 92mm just that is in the "ready" pile for a 944 bore. If it's the same one you need, I'll be happy to swap you (n/c).

Norm,

I had thought about maybe some sludge in the oil lines.  Before I throw yet another set in, I think I'm going to try and clean out the oil passages as best I can.  I'm not sure if its possible to rig the oil pump to a drill to run some oil through the system or not, or if its even worth it.   

If you have a set of 92mm bores, I'd gladly trade with you, and kick you some extra $$ your way for it.  I'm thinking I may be able to clean up the pistons, and just grab a new set of rings.  Otherwise, it would seem a 944 kit is really the only way to get some use out of these cylinders. 

The piston may have been a little tight, and siezed/scuffed in a couple spots.

You may be able to save it.

First, you've got to open it up and see what went wrong.

Just wondering what you "deglazed" the cylinders with. Make sure it is compatable with the nikasil that was used.

Some re-platers do not want anything very abrasive used because the coating is pretty thin.

My mistake, the one I thought was a 92mm ended up being 94mm. It's painted & set apart fro the 94mm sandblasted jugs so I thought it was different.

Sorry, that last post was from me, my son logs on to my computer & then forgets to log off.

Norm, I figured.  'canes' is a dead giveaway to Hurricane Motorcycles. :)

I deglazed it with a set of stones specifically for nikasil cylinders.  Nikasil is MUCH harder than stones, and its only really to take the light metal transfer off the cylinders and restore the hone. 

Thanks for all the input folks.  Much appreciated.