Some of you might be familiar with my happenings recently.

In Aug I had no.4 piston melt due to det, bad fuelling, fcuked timing etc. Engine had a complete rebuild, rebored to house over-sized forged pistons, forged rods, uprated bearings, oil pump, fuel pump ScoobyECU mapped to UK fuel etc. Since the rebuild car has covered 1600 miles. 1st 1000 covered with wastegate actuator dis-connected and rev's kept below 4k.

Now, not all the time but I'd say on a ratio of around 12:1 when I start the car from cold, I get a puff of blue smoke (rich smelling in oil) 5 seconds after engine has been started. This lasts for about 1-2 seconds then clears leaving normal exhaust gases out the back box. Car is using a little oil (I'd say around 1 litre in 1600 miles).

What could it be ? The fact its not all the time has me baffled. Can any tech heads give possible causes ?

Either the bores are gaining more oil residue than they should, possibly one bore has all the rings "gaps" lined up and causing the oil to get into the combustion space.Plus being as the bores lie on their "side" it does allow oil to settle there.
the oil useage you are noting does seem consistent with a rebuild "run in", but would not like it to continue much longer, Perhaps a return visit to the engine builders may give peace of mind, plus they will of seen the car if anything else happens a bit leter on if they give it the "all clear" now for example.

piston rings rotate in piston, but oil burning is largely due to oil control ring.

would possibly be because of incorrectly gapped rings, pistons cold during initial startup combined with too large a clearance, or poorly bedded in pistons, or piston rings upside down, or cracked ring land, or just a breather issue etc etc etc.

Any rattles on start up?

Smoke on full power after warm up?

More info required!

paul

Valve stem seals ??

David API Engines

I've had this on me motor. MY02 with 30k and tuned to 1.45 bar with APS turbo, etc. It's only appeared about 3 times and isn't consistant. The car is off the road now and only gets the engine turned over every 2 to 3 weeks till warm, but during this time no smoke....and thats from a very cold engine. It doesn't seem to use much oil also.

The oil consuption sounds about right for the new build Derek.

If your forged pistons are Omega or Cosworth with slipper sides then this amount of oil consumption etc is quite normal for this style of piston and unless there is a significant noise increase I wouldn't be too concerned about it.

David API

Turbo?

I think you can sometimes expect this. Do you park/leave the car on a slope? My 911, flat 6 etc will do this EVERY start-up when left for a few days/weeks. The oil rests in the bores and fires on start-up. Well known 911 traite, no worries.
It is worse if you over fill a 911 (dry sump)oil system also.
Graham.

Graham you mean that your 911 suffer also from oil consumption? New age WRXs are very prone to this phenomenon due to "lazy" piston rings may be!
JIM

thx for your replies Guys.

I can dismiss the piston ring positions as these were fitted as per manufacturer's spec. No need to return the engine to rebuilder as it was us that done the rebuild :D;)

I've just carried out the car's oil change since the rebuild using MOBIL1 15w/50 replacing Castrol 10w/40 magnatec. Will monitor usage & exhaust for any more signs of blue smoke.

My golden oldie 911 uses about 1/2 litre per 3000 miles including full on hill climbing competition. I use, as I do for the Scooby, Shell Gemini semi synthetic. Runs great, stays fresh looking for all year!!
Old 911's are just perfect, but the STi is better!!!!!!!!!!!
Graham.

I wasn't reffering to how were the rings were fitted, but how they were bedded in during the running in process. You need some sharp blasts under moderate power at the start to bed the rings in, cruising at light load for a length of time will glaze the rings and not allow them to bed into the bores properly.

paul

Paul,

The car was given decent right boot upto 4k and through the gear as the engine certainly wasn't tickled at the beginning.

Started car this morning and alas a blast of smoke, smelling of nice new Mobil 1 :(

Forgot to add, there's no rattles just the sound of forged pistons with the smaller skirts (so I've been told anyway)

Is Mobil 1 part of your run in schedule or you preferred choice??

After trying that and then Motul 300V Comp.. Mobil 1 seemed like Pish..

Simon

I bought a box of 4 x 4litre Mobil 1 during the rebuild for future oil changes. I've never had Mobil 1 before in any car but thought I'd put fully synthetic in.