Blue/grey smoke after idle

[sunsetR33]

On 31/03/2025 at 12:02 AM, Duncan said:

Aside from the fact it is likely fuel related if it is black, the symptoms otherwise sound like worn valve stem seals. Oil gets past the worn seals when the engine is off and burns when the engine starts. If it happens on deceleration while driving (puffs of white smoke) that is another valve stem seal symptom because oil gets sucked form the head into the combustion chamber under vacuum with the throttle closed.

They can be replaced in the car if you have some way to keep the valves closed while working (eg compressed air into cylinders) but is much easier with head off.

Can't you put the pistons to TDC and then do the valve seals? Or will the drop down too far to pull them back up?

[GTSBoy]

34 minutes ago, sunsetR33 said:

Can't you put the pistons to TDC and then do the valve seals? Or will the drop down too far to pull them back up?

The old approach was to fill the cylinder/chamber with a length of rope pushed in through the sparkplug hole. The new approach is to connect compressed air to the sparkplug hole and fill it with enough pressure to push the valves up.

Doing either of these things with the head on and the engine in the car is a lot less pleasant than doing it properly.

[sunsetR33]

I get that taking off the head is best but that's a bit much for "just" valve seals. I was just under the impression that one would be able to rotate to TDC and be able to temporarily drop the valve without losing it and effectively having to remove the head to then recover it. I never knew people actually pushed rope into the cylinder to do valve seals hahaha

So just to confirm, just going to TDC will not work? In that case I know when I do valve seals I'll maybe just remove the head and do some other things while I'm there, or just wait until I do an engine build.

[Duncan]

I don't know, I've never done it that way, but

1. While it is an interference engine, there is still clearance between the valves and the piston at all points in the regular timing cycle

2. There is not a lot of distance before you can't catch the top of the valve stem any more

I don't know if 2 is greater or less than 1. But

3. If it doesn't work out you are f**ked, engine is coming out to disassemble so it is a big bet.

[pacman_1219]

9 hours ago, sunsetR33 said:

I get that taking off the head is best but that's a bit much for "just" valve seals. I was just under the impression that one would be able to rotate to TDC and be able to temporarily drop the valve without losing it and effectively having to remove the head to then recover it. I never knew people actually pushed rope into the cylinder to do valve seals hahaha

So just to confirm, just going to TDC will not work? In that case I know when I do valve seals I'll maybe just remove the head and do some other things while I'm there, or just wait until I do an engine build.

Even with the piston at TDC there was room for it to drop, but I don't think it can drop fully into the cylinder, the problem you have is that you need something pushing against the valve to hold it up so you have enough room to put the new stem seal on and the spring etc. 

I used compressed air only because putting rope in the cylinder seemed a bit risky to me, I know people have done it countless times before like this.

Overall it's a pain in the ass job. Honestly you'd probably be better off taking the head off because the risk of dropping something in the engine and the finicky-ness of it all is very stressful.

If you are going to attempt it though i 10000% recommend a 36050 valve spring/keeper tool. I had both the traditional lever type and after doing 1 cylinder it was absolute pain to get those valve keepers in place, even with 2 people.

That 36050 is amazing, you do have to push hard to get them in place but it works perfectly almost every time.

Back to my actual issue I think my engine is just tired and old and the rings have gone bad. The comp numbers (cold, no oil) were:

Cyl 1 -129psi

Cyl 2 - 133psi

Cyl 3 - 138psi

Cyl 4 - 137psi

Cyl 5 - 157psi

Cyl 6 - 142psi

 

Cylinder 5 and 6 having the most carbon on them.