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Break-in period?

Discussion in 'The Garage' started by NewHavenMike, Nov 5, 2017.

  1. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    This is for those of you that have rebuilt their engines by either just the top end or entire assembly.

    I rebuilt my 360 with a new rebore/honed jug to the first overbore size. I believe its +.25mm. I was able to find NOS pistons and NOS rings. My machinist who rebuilds primarily harleys, spec'd the bores to within .003" The manual says the limit is .002". I did not know this at the time but he didnt seem too worried about it as this is something he does all the time with his own in-house machines...

    Aside from getting the carbs and exhaust just right, which took a couple months, the engine has run beautifully so far. Right out of the box, I was running the engine somewhat hard, and overjetted. I wanted to get a good seating so I made sure to put the engine under stress throughout the RPM range. I did that the first couple hundred miles and then slowed it down some. When I passed 500 miles, I had done my oil changes and then started running at sustained highway speeds on my 40 mile one-way commute.

    I recorded an oil loss of about a quart throughout the first change and an additional 1/2+ quart for the second change. Im about 2500 miles since the rebuild and Im about to Winterize my bike within a month or so. Ive noticed that oil loss this time around has dropped considerably to where it would be considered normal.

    Has it taken anyone else this long for the rings to seat? I was thinking because the rings are the original old iron type, that it takes much longer than the recommended 500 miles for a full break-in?

  2. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    When I took apart my 100k km (62k mi) engine, there was virtually no ring ridge and cross hatching was still seen in the bores up to within 1cm (3/8") of the top of the ring travel. Oil consumption was less than 500ml (1/2 qt) every 10k km (6k mi) oil change, despite being beaten on most every day. If it wasn't for a broken plastic chain guide and a leaking intake valve, that engine could have gone another 100k km.

    So yes, they can take a while to break in.

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