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Discussion Starter · #1 ·
I have a 900ssie that I'm swapping the pistons and having the heads worked on a little bit, and I'm really apprehensive about the best way to run it in when it's all back together. I did a search but couldn't find anything about breaking in a "used" motor, only discussions on new engine break-in.

I'm worried that I won't be able to seat the rings properly and will ruin my motor the first time I ride it. I didn't have the cylinders honed because I was under the impression that you didn't need to (or actually are unable to) hone the nikasil cylinders due to their hardness. Hell, they look absolutely brand new to me.

Should I try to break it in on a dyno, or will a country road suffice? I don't know how expensive it will be to do it on a dyno, and I don't know if I can afford it, so I'm hoping the backroads will be good enough.

Any tips or advice for piston and cylinder reassembly are also very welcome in addition to advice for the break-in. I guess I'm just paranoid that something will go horribly wrong and I'm afraid of turning my motor into an incredibly expensive paperweight

Oh, one last question, when I took it all apart, the tops of the pistons and the combustion chambers in the heads were caked with carbon buildup. I know that's not normal, but I had no oil consumption before I pulled the motor and I've always used good gas, so I'm wondering what the cause is. Running too rich maybe? Anyways, thanks for the advice!

Discussion Starter · #2 ·
Re: Rebuild break-in procedure? (blueSS)

The answer to how to break-in an engine, and whether to use a synthetic oil during break-in, is different for new engines and rebuilt engines. What the engine manufacturers do and recommend for a new engine break-in should not be construed as the best solution for a rebuilt engine. Here’s why.

The manufacturer controls the complete quality assurance and quality control process: design, fabrication, build, inspection and testing. The overall result is not necessarily better than can be achieved by a custom engine builder, just more consistent.

So when a manufacturer first fires-up a new engine on a test stand, they know from experience (and monitoring each engine’s exhaust oil combustion products) that the piston rings will seat properly before the engine leaves the factory. Every Ducati is run-in for ten minutes or more on the dyno using a prescribed rpm and temperature sequence. Many manufacturers including Ducati, Porsche, Mercedes-Benz, Corvette, Viper and Aston Martin do their initial fill with a synthetic oil, and piston wall glazing is simply not a problem for them.

The piston rings seal is mostly complete after this initial test run. The follow-up part of the break-in (that you read in your Owners Manual) has little to do with piston ring sealing. It’s meant to accommodate the time it takes for normal wear to occur to thousands of mating parts like bearings and gears, that will happen regardless of the type lubricant used. It’s particularly important to change any lubricant early, and often, to remove the resultant wear debris.

However, when you rebuild an engine you can introduce a number of variables (that affect glazing) that are different from a new engine such as piston ring material, clearances (that affects ring pressure on the wall) and cylinder wall surface finish. Also, not all engine rebuilders have complete, accurate control over their cylinder-wall finish and ring type like the manufacturers.

Cylinder wall glazing occurs when the engine is run at power levels too low to produce temperatures high enough to expand the piston rings sufficiently to prevent a film of oil being left on the cylinder walls. The high temperatures in the combustion chamber will oxidize this oil film so that it creates a condition commonly called glazing. When this happens, the ring break-in process stops, and excessive oil consumption can occur. Excessive glazing can only be corrected by removing the cylinders and re-honing the walls.

The build quality of engines 25 years ago probably contributed to the controversy that somehow synthetic oils are too slippery for break-in and that than conventional oils should be used.

So what do the oil manufacturers say?

According to a Road & Track article a few years ago regarding the use of synthetic oil during break-in, Mobil’s position was that engines break-in just fine on synthetics, and that any wear point in the engine significant enough to be an interference, and thus susceptible to rapid wear, would be a wear point no matter what lubricant is used. Redline on the other hand, recommended a mineral oil for break-in. They say that in their experience, occasionally a rebuilt engine will glaze its cylinder walls when initially run on Redline synthetic, so by using a mineral oil for 2,000 miles, verifying there is no oil consumption, and then switching to the synthetic, glazing is eliminated.

In any event, as a rebuild, you shouldn’t use an Owners Manual-style break-in period. You need to reproduce the Ducati factory dyno runs to avoid cylinder glazing. One way is to monitor tailpipe hydrocarbons to see when they drop during dyno runs.

The other way is to ride it like you stole it.

Discussion Starter · #3 ·
Re: Rebuild break-in procedure? (blueSS)

Well, it's certainly hard to follow any technical post that Shaz makes, but I pulled my 900SS engine and made it a 944 with ported heads so I think I have some insight on the subject.

The shop I sourced the 944 kit from suggested I ride the bike normally but keeping RPMs under 6,500 for the first 500 miles using conventional oil, then switch to synthetic and feel free to explore the upper ends of things. With about 500 miles on the clock I brought the bike to the shop to have the fuel map tweaked which was done on the dyno. The bike runs strong and great and doesn't use any oil.

As far as the been-there-done-that advice, I would be careful with the piston circlips and make sure they are carefully seated before buttoning things up. Make sure to oil the cylinders, pistons, wrist pins, etc before reassembly. Check the squish. Check piston to valve clearance although I don't expect there to be any worries with stock cams and valves with drop-in pistons. Check ring gap. Check piston to cylinder gap. Might as well check valve clearance while the heads are on the bench. The rest is really the reverse of removal. Buy the Haynes manual for pics of what you need to do.

BTW, that same shop saw the accumulated carbon on my heads when I dropped them off for porting and said it was due to a combination of light loads on the motor and emissions fuel.

Discussion Starter · #4 ·
if it's just getting pistons i'd run it till hot on the bench at least once, maybe twice (totally cool between) then go out and give it lots of throttle up to maybe 2/3 max revs. you need cylinder pressure to bed rings in. do that for a little while then go nuts. i get re-pistoned engines on the dyno pretty quick. rebuilt bottom end i try to get 500 - 800km on before i get into them.

as the rest of it's been there before you don't need to worry about that. the only plain bearings are the big ends anyway - i'm not aware of anyone recommending break in periods for normal ball bearings.

Discussion Starter · #7 ·
Re: (Old Baldy)

Awesome info, thanks guys! I took the cylinders down to the local machine shop and he said he couldn't truly rehone the cylinders because he didn't have the diamond-tipped hone necessary to cut the nikasil sleeve. But he cleaned them up a bit and hopefully got the glaze off. I'm still waiting on my heads to be finished, so nothing is put back together yet.

There is a small concern I have about the hc pistons going in, however, in that I don't have the original directions that came with them, and I have no idea which side is intake or exhaust. There are no markings on the pistons, and the valve reliefs aren't symmetrical. One is larger and shallower while the other is smaller and deeper. But they actually seem to be approximately the same size. maybe it's just the angle of the valve? I guess I'll just line them up with the heads when they come back and see which way 'round they fit.

Thanks again for the help!
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