Question about breaking in my rebuilt engine

DennisMo · 2026-05-16T15:03:19-0600

My 1973 850 has new pistons and rings and the cylinders are newly bored oversize.
The piston to bore clearance is 4 thou as per piston spec.
The machine shop's final hone was very fine as they said the top piston ring is chrome.
(I have never seen a hone so fine)

The shop told me to ride it hard, replace the break in oil at 50 miles with new break in oil, then replace with regular oil
at 300 miles. They said that the rings should be bedded in within the first 100 miles.

Love to get your comments

Thanks

Dennis

ashman · 2026-05-16T17:04:44-0600

Just ride it normally, don't labor it and don't over rev it, just ride it and don't over think it, just take it easy for the first few hundred miles, do an oil change at 500 miles or sooner with whatever oil you normally use, as they say rings bed in pretty quick.

Dedubyah · 2026-05-16T17:13:58-0600

If it's just pistons and rings, I usually start it and run it for a few minutes until warm, shut it off until cold and repeat. I then ride it, giving it a good pull from 3-3500rpm to 5000 rpm in third gear then shut the throttle and coast down to 3-3500rpm. I do that for 5 minutes or so and consider it broken in,

dobba99 · 2026-05-16T17:22:07-0600

Don't forget to retorque the head, after the first thermal cycle. Then after 50 miles, 100, 500

DennisMo · 2026-05-16T17:40:54-0600

Thanks
I have not yet checked compression but it feels good. Although I use electric starter I did stand on the kickstarter yesterday and it would not go down with just my weight.

DennisMo · 2026-05-16T17:42:20-0600

I have about 100 miles on it. Will retorque on next rainy day!

velo54 · 2026-05-16T17:53:18-0600

Sounds like good advice from the engine shop.

ashman · 2026-05-16T19:01:37-0600

dobba99 said:
Don't forget to retorque the head, after the first thermal cycle. Then after 50 miles, 100, 500

Depends on what head gasket was used, copper or fiber seems the fiber ones need a lot of retorquing, copper torque down then retorque at 500 miles.

Torontonian · 2026-05-16T19:18:55-0600

Wish I had your machine shop ( If I lived in Van. ) , not a fine crosshatch , looks good though . . But I'm happy with Gord Bush , here in Toronto ( Etobicoke ) .
That said , I'm about to fire up the new J.S. motor ( outside now ) , with long rods , short pistons , the same rebore , oversized for them .
Will report back soon , a cold snowy winter over .

Question about breaking in my rebuilt engine

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