Break-in questions

[Aurel]

Hi all,

My top-end rebuilt motor (3.0SC) is still in its break-in period, and I have noticed some changes: gas mileage went from 12.2 mpg on the first tank to 18.8 mpg on the second. The motor seems to have more power at higher rpms, and rev more freely now. I suppose those are normal changes with the rings sitting and making better compression. What was your experience with your rebuild? Did you notice those changes, or was the power the same from begining? I have about 400 miles since rebuilt now.
Also, when did you do the second oil change?

Aurel

[cgarr]

I noticed a change in mine, The parts are starting to get happy with each other! Second oil change was about 3k but thats when I always change it anyhow.

[MBEngineering]

HI Aurel
I would have 500-1000 miles and then; oil and filter, valve clearances, clutch adjustment, check for leaks, check the igniting timing/fuel Co% and drive to the next 6000 service, good to see another one safely back on the road.

regards mike

[Aurel]

Originally Posted by MBEngineering

HI Aurel
I would have 500-1000 miles and then; oil and filter, valve clearances, clutch adjustment, check for leaks, check the igniting timing/fuel Co% and drive to the next 6000 service, good to see another one safely back on the road.

regards mike

In his book, Wayne says change oil after first 20 min (which I did), then change again after first drive (which I haven`t done yet), then change at 1000 miles when doing valve adjustment. Does it sound like too much?

Aurel

[MBEngineering]

HI Aurel
I would put 2-300 more miles on the moter and then give it a check over, as you have changed the oil already, poss' change it again then it then, depends on the $$ as 3 oil changes is $$$$$$$ with top oil, if you have had running in oil and then reasonably $$ oil to your choice to run the engine on I would just do the 2 oil changes, you are closer to the crude than we are so 3 oil changes is £££ for us is a bit OTT, my collage tutor always told me "if any thing was going to happen, it will be in the first 5 Min of the engine running"

regards mike

[Aurel]

Thanks Mike, that was more or less my plan, I am glad you recommend that too.
Not so much because of cost, but because the time under car allowed by my wife has run very thin .

Regards,

Aurel

[Rot 911]

On my rebuild I changed the oil after the 20 minute bedding in period and then after the first 500 miles when I rechecked my valves. Then back to a normal oil change schedule.

[Aurel]

Update: My car started to develop a misfire under load at higher rpms. It sounds to be coming from the passenger side. I beleive this may be related to the motor breaking in. I have passed 500 miles now, but not the 1,000 mark yet. Here are my guesses:

1- The pistons make more compression, so the ignition timing needs to be advanced a bit more.
2- What I hear could be cylinder-head leak if the headstuds need to be retorqued.
3- Valves too tight?
4- Worst case scenario: the cam timing changed...I had the overlap set at 2.0 mm, that is the most advanced with these cams. Obviously, I`ll check the other suspects first.

Any other suggestions?

Aurel

[otto in norway]

I thought the overlap was supposed to be 1,1mm..? Or 1,4 for later models? ('81->)
Hmmm... I'm no expert, but 2 mm seems to be a bit much, so perhaps what you are experiancing, is backfire..?

[Aurel]

Otto,

My cams are not SC, but DC15, aka sportSC. They are supposed to be set at 1.8-2.0 mm.

Aurel