8 replies to this topic

[Edington]

I have a very good friend who used to rally mini's and he has just rebuilt his Cooper S engine. Rebored, new pistons with twin inch and half SUs. It starts and runs well just around the village at no more than 40mph as a run in speed. However, after about 10 minutes a puff of blue smoke appears out the exhaust. This has repeated on a number of short runs. He's checked the oil level and that is ok and its clear although he noticed that checking the oil at the bottom of the sump it is black in colour. Anyone any thoughts on why this puff of blue smoke happens?

[cal844]

Valve stem oil seals sound worn, but best to do a leak down test and go from there.

It may be worth getting the carb cleaned and then reset the CO as needed

Edit: I should really read threads better...

I agree with Steve that you need to get load the engine to bed the rings in, if you don't itll either glaze the bores or always smoke....

Set the CO to 3.0% at idle and do 1000 miles on a cheap oil, then replace the oil and filter with valvoline VR1 (there are others out there but I've had good success on this)

Edited by cal844, 21 October 2021 - 04:17 PM.

[sonscar]

I would probably worked it harder than 40 mph,rings and or bores glazed if you are unlucky.Rings need on/ off throttle and load to seal properly,Steve..

[absx2]

It needs a few short sharp bursts to bed the rings in.

Mollycoddling around will glaze the bores, the black oil is caused be the combustion gases escaping past the rings. 

An engine builder once told me to run them in how you want them to go.

[Dusky]

Never ever ever ever use a cheap oil to run in. Oil quality is the most important at that stage. A proper break in oil is worth it's weight in gold. Although running an engine in on millers or valvoline is almost just as easy. Load the engine, and let the engine braking do it's work.

[cal844]

I personally use Comma Classic in my own cars (I've done 8000 miles between oil changes when I daily drove minis) and didn't see any wear issues on a 80k mile 998 in 10 years. What I use and what I recommend others to use is from experience.

I've previously rebuilt 3 motors, 2 of them still survive on the comma classic that we used when we built them, using the proper assembly lube that the cam supplier recommended (on the one that didn't the owner didn't check the oil for a month 😣)

I'm currently 1000 miles into running in new rings and bottom end bearings on a 998 using the comma classic oil....
Its went well so far in 10 years BUT if I personally could afford to I'd use the Valvoline VR1.

Just putting what I've found in black and white, as I say if you can afford a £20 (5L) use that but the 5L Valvoline is better...

Hopefully I've cleared that up a little 🤔😣

[timmy850]

Maybe check the oil level inside the rocker cover when it happens again. If you put in the cam bearing wrong it’ll fill the rocker cover with oil and could cause more to get past the valve stem seals

[Edington]

Many thanks guys I'll pass all the comments on and hopefully get it sorted.

[slidehammer]

I am wondering if it could be a breather issue and pressure is building up and then the puff of smoke and that releases pressure until it has built up again. Always worth checking the more simple fixes before you go in deep! I would check all breathers are in place and clean along with any of the associated pipework