Blue smoke on a cold start. Forged pistons

[GreddyMR2]

He checked and did bigger gaps, because it's forged pistons. I didnt ask the numbers. He said I can even hear a bit of knocking when engine is cold, but I don't.

[GreddyMR2]

My engine rebuilder told that blue smoke on cold start can also be related with rich mixture.
Also he mentioned that I should be gently for first 300-400km, because bearing should bed in properly. And also advised that I should do at least 2000km for proper engine brake in.

[ashley]

Blue smoke is normally oil being burnt, a rich mix would normally give you black smoke.

Just to check:

- You are getting blue or grey smoke
- It is only when the engine is cold

If you get the engine hot, then leave it off for 15 minutes, then start it again (so still warm)- does it smoke at all?

[GreddyMR2]

Well, today I think it was blue smoke. When I started it after work, it was more like grey smoke.

When I start it after 15mins or so, I can't notice any smoke.

But today I noticed that sometimes on throttle it throws a black smoke. However can't see very clearly when I'm driving. I need somebody to ask to go behind me to check what is the smoke.

My ecu is standard, I have exhaust cam gear retarded by 5 degrees. Also I use 3SGE cams. And walbro fuel pump. Maybe it's too high fuel pressure?

[ashley]

Sounds like your main problem is blue smoke- so burning oil. And it sounds like it only does it when the engine is cold.

To my simple mind that suggests that as something is warming up in the engine it is stopping the oil ingress into the cylinders...so could it be that your ring gaps are a bit too big, but closing up as they get warm?

Maybe a cold/ luke-warm compression test (while it is smoking) and then a hot compression test when it is not smoking, and compare the results?

It doesn't sound like stem seals- I'd expect you to get a bit of smoke with the engine warm, after it's been left sat for a while; and you'd expect some smoking on over run I guess. It only takes a little bit of oil to make a fair bit of smoke.

It does sound odd...what head gasket did you use, and was the block deck surface ground, and the cylinder head face surface prepared?

[GreddyMR2]

My engine rebuiler also told that it could be because of bigger than standard piston/rings gaps.

I will do a compression test and will see.

I use cometic head gasket. I think every surface was prepared, but have to clarify about this.

P.S. There was no smoking at all when I started it for a first time. How to explain this?

[ashley]

Ask him to give you the following information:

Ring gaps
Piston to bore clearance (he should have specified this when he gave the block and pistons to the machine shop to rebore)

report back and we can see if that's your problem

[GreddyMR2]

Ask him to give you the following information:

Ring gaps
Piston to bore clearance (he should have specified this when he gave the block and pistons to the machine shop to rebore)

report back and we can see if that's your problem

I will ask him tomorrow If that's the problem, I suppose I will have to live with it, right?

[ashley]

Depends what the clearances and gaps are mate, if they are way out then the only way to fix it is to pull the engine apart...fingers crossed that's not the problem

[GreddyMR2]

I hope.... Do you think I burn a lot of oil, if thats the problem?

[ashley]

It can't be that much if it stops smoking once it's up to temperature mate, it really doesn't take much oil to produce a lot of smoke!

[bobhatton]

My full gasket kit is Cometic including valve stems. Maybe they are poor quality?
But hopefully it will stop making smoke after brake in.

You should only use Toyota valve stem seals

[bobhatton]

He checked and did bigger gaps, because it's forged pistons. I didnt ask the numbers. He said I can even hear a bit of knocking when engine is cold, but I don't.

You do not use bigger ring gaps because of forged pistons.
You also do not have any running in for the bearings.
Your builder does not know what he is doing.

[ashley]

Your builder does not know what he is doing.

Ever the diplomat Bob!

[bobhatton]

Your builder does not know what he is doing.

Ever the diplomat Bob!

I try my best

[GreddyMR2]

Unfortunately he doesnt remember the gaps.

What's more, the pistons and rings I bought are not new and the engine they were in was overheated. So builder says that I need to drive some more km to get them bedded in well, because the rings could be scratched a bit from overheating.

Also, this morning I saw less smoke than previously. But it was warmer outside.

[bobhatton]

Unfortunately he doesnt remember the gaps.

What's more, the pistons and rings I bought are not new and the engine they were in was overheated. So builder says that I need to drive some more km to get them bedded in well, because the rings could be scratched a bit from overheating.

Also, this morning I saw less smoke than previously. But it was warmer outside.

Ok, now I can see the problem.
If the engine was over heated the rings will have lost their tension, they will never seal against the bores. New rings should have been fitted, never reuse old rings.

So strip the engine, hone the bores and fit new piston rings with the correct gaps.

[rev3turbo]

wow that was a silly choice on an engine rebuild

[GreddyMR2]

I am now thinking why I did so... Again, stupid choice to save some money.

Anyway, I think I will run this now and maybe I will fit new rings at winter

[ashley]

Re-using rings in a new engine?!!

Oh dear- I think you were right afterall Bob