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Sufficient Break-In Mileage For Synthetic Oil??? 28 May 2012 16:10 #525402

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pig9r wrote:

bountyhunter wrote:

Choosing a Break-In Oil for Your Motorcycle

There's a lot of mythology surrounding break-in oil. It's simply not the case that synthetic oils are more "slippery" than conventional oils. Also, break-in of a modern engine is completely different than break-in of an engine made before about 1980. Modern engines, by comparison to something made in the '60s, are pretty much already broken in from the factory due to the fact that today we hold much tighter machining tolerances. The exception, of course, would be the Ural, a motorcycle made on a production line unmodified since about 1935.


This contradicts what you posted earlier about the OP using syn after a rebuild. The OP has a '79 MKII, which according to this quote should be treated differently than a modern engine.

I don't believe it. Maybe it's true, I doubt it. I did a full bore on my 1979 750 twin and then did the first 30 minutes of running with dino oil which I immediately dumped, then switched to synthetic which I have run continuusly since. The ring seat was perfect and have never had a problem since (about 8k miles on rebuild now). Only reason I ran dino oil for the initial start up is I am too cheap to run $50 worth of synthetic oil for thirty minutes and then dump it.

I just don't believe a motor won't break in with syn oil in it. I suspect if a motor won't seat the rings, then the machine shop did not do something right.
1979 KZ-750 Twin

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Last edit: by bountyhunter.

Sufficient Break-In Mileage For Synthetic Oil??? 28 May 2012 16:19 #525405

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LarryC wrote: The bottom line with oil is........there is no bottom line, only opinions and a mix bag of experiences ;) Many of the bad experiences can be attributed to items 1 & 2 below.

Several things can and will affect the rings / cylinders:

1]hone grit
2]block preparation prior to assembly
3]ring material

MYTH: Spraying the bores out with carb cleaner or brake cleaner will get them properly clean for final assembly.

MYTH: dumping extra oil into the cylinders is a good idea on a fresh motor.

Yeah. On mine, I was using a 50-50 mix of Castrol and STP as "assembly lube" and I wiped the cylinder walls and pistons/rings with a thick coat. Also coated all bearing surfaces during assembly and filled the "cam reservoirs" on top with it. I wanted to make sure there was plenty of ZDDP on the surfaces while the oil pump came to life. Worked fine, but did blow a little smoke for a few minutes out the pipe while it cleared out all the extra lube.

After about 100 miles I checked compression bone dry/cold (sat overnight) and got about 150 psi, compared to 155 psi hot so I believe the ring seat is about as tight as it gets. Stock compression is 152. Have never seen even a hint of oil puff in the exhaust and the engine uses zero oil between changes.
1979 KZ-750 Twin

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Sufficient Break-In Mileage For Synthetic Oil??? 28 May 2012 16:23 #525408

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T_Dub wrote: I put conventional in for break in, because its too expensive to use syn for only 500 miles like others have said. I have semi syn to go in her after that. But thats only because i thought it was syn and just bought it. It's Motul 5100 bike oil. Should work fine. As long as you have 10W40 or similar, motorcycle oil, it will work for anything you want to do with it. All this debate is pointless. Go stick some oil in your bike. Synthetic will run cooler and last longer than conventional oil. I put it in because it wont break down as much in the heat. So I can go longer between changes. Everything else is moot really. Synthetic is only better because its more uniform and doesn't break down as easily.

Main advantages of syn are that it holds up well under hi temp and has very stable viscosity since it uses little or no VI's. If you have a high performance engine that runs hot and stresses the oil, it's definitely worth it. If not, probably don't need it.
1979 KZ-750 Twin

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