Break (in) Dancin' a 6-71

[spartonboat1]

So if I bite the bullet and do a re-kit/re-build on a 6-71N (no, won't be an out of boat re-build- on a tight budget), what is the break-in recommendation?

 

[REBrueckner]

I was told by my (very experienced) mechanic: "no break in required."

I would not go out and run WOT for extended periods but apparently part of the "run it normal" approach is so that rings and piston liners wear in over a normal operating range.

Be interesting to see what other advice is given here.

 

[spcoolin]

50 Years on the Great Lakes...http://www.samsmarine.com/forums/images/smilies/biggrin.gif

Sorry...I couldn't resist...

Steve~

 

[rsmith]

Improper break in will result in cyl glazing and excessive oil use. FTFD

 

[Boatsb]

can you run a DD for break in when installed in a MY?

I have never heard of that being done before

Run it like a sport fish for 30- 50 hours and it should be OK.

 

[saltshaker]

When I had my 6V92 done I was told to keep it under 2000rpm for the first 4-5 hrs except for very short periods. Run it at varying RPMS for the next 4-5hrs but try to avoid extended low rpm cruising. After that try to run her in cruise range 1800-2100rpm for the next 5-10hrs. Change the oil and use it as you normally would. With a 671N I would think that would be 200rpm off of top end or at least fast enough to keep the temps up.

 

[Jaxfishgyd]

Both of my 6-71N's were rebuilt (only the blocks didn't leave the boat) in 2000 when we bought the boat.... I was told to run her 'normal' but not to use WOT for any extended time for the first 20 hrs, then to change the oil and filters.

 

[krush]

Make sure it is all good, then run the hell out of it to seat the rings. Don't idle too long. Maybe not WOT, but definitely run in the higher output range to build good cylinder pressure to push hard against the rings.

 

[spartonboat1]

My normal run, which is start up, 10 mins idling to prep and cast off, then a 20-35mins (longer time if wait on drawbridge) 900rpm no-wake run out the river to the big water, then 1,400rpm to get out of the channel, finally cruise at 2,150-2,180 (about 250rpm off max), for couple hours.

So the advice sounds like 'run very normally'. I never run WOT, or at least very seldom.

I appreciate the responses!

 

[saltshaker]

My normal run, which is start up, 10 mins idling to prep and cast off, then a 20-35mins (longer time if wait on drawbridge) 900rpm no-wake run out the river to the big water, then 1,400rpm to get out of the channel, finally cruise at 2,150-2,180 (about 250rpm off max), for couple hours.

So the advice sounds like 'run very normally'. I never run WOT, or at least very seldom.

I appreciate the responses!

Sounds perfect. You should run them WOT just to make sure all is well. Those 671N's can run all day at WOT. My 46C had 8V71N's when I bought her. When running in heavy seas she needed more HP. Best way to run her was WOT. Never hurt a thing.

 

[Fanfare]

I had my 8-71N diesels rebuilt by the DD distributor, Western Diesel Services, in Jacksonville, FL, in 1980. After they got them back together they took them outside and hitched them up to a water dynamometer and a fire hydrant. They started them up, one at a time, checked for obvious leaks and examined fluids for water. All OK, they started throttling them up, a few hundred rpm at a time. Shortly they were at full throttle. The dynos were throwing a stream water far in the air. The engines were not in any kind of frame, just sitting on their pans on railroad ties. They would twich a little with rapid acceleration but otherwise just sat there. The mechanics gradually slowed them down and shut down. I asked about break in. No need after this, they said.

Nevertheless, I varied speed and load for the first 25 hours or so. At about 50 hours I changed the oil in engines and transmissions. Got another 23 years out of them.

 

[spartonboat1]

I did hear that WOT is needed to ensure that the rings do not leave a lip on the upper cyl walls, which can later damage or degrade the rings, when running at WOT. So no doubt a period of WOT is indicated after 5 or 10 hours of normal use.

 

[Canuck Dennis]

A little off subject but similar, I had a pair of high performance Merc inboards put in to my previous 36 ft boat, had # 3 merc offshore legs when we took it to sea trial the new mains one of them threw the dipstick and most of the oil...

Two days later the factory rep came for the second go around, the only thing found to that time was a little rattling noise every so often at idle, so the word was...lets take out and either make it or break it, this time the dipstick stayed in\and we ran 5200 rpm for 15 mins, all ok said the rep, and we will warranty it for 12 mos..have fun.....and I did...was a great boat with those big legs but sure sucked fuel.

 

[spartonboat1]

Going to have a tech come by this July 4th weekend and pull the inspection port covers. If he finds any through and through cracked rings, then some type of re-build it is; i.e. not cracked on the surface, although that can't be good either.