Big blue smoke burst

[richard1]

Well...it seems that after 117K I will need to do something on this engine and I am not very comfortable with it in Las Vegas. The engine doesn't burn any oil at all between oil change (2K) and runs smoothly.

- No smoke at cold start

- No smoke at idling when at normal temperature

- Burst of blue smoke at pick-up after deceleration as at a stop sign.

- Problem has increased since I put Rislone Ring Seal Additive today.

After all my research on the archives of this site, it seems that I have to expect valve seals problems.

I will perform a compression check during the weekend but I have some questions:

1- My engine was without any problem and the car is driven on a daily basis and meticulously maintained. Is this problem can happen suddenly?

2- Is the load of the A/C running could have been part of more stress on the engine since the A/C has been rebuilt?

3- It is a 72 240Z full stock and original, never rebuilt.

4- Clean coolant in the radiator.

5- Clean oil in crankcase.

Thanks for any comments you may provide.

[Nissanman]

A1

Yes.

A2

Perhaps.

A3

Find that hard to believe but, WOW:surprised:surprised

A4 & A5

Good signs both.

Your diagnosis of valve seals is one that I concur with.

The high vacuum generated on coast and at idle can suck in quite a bit of oil through worn intake valve guides and/or deteriorating seals.

The increase of the smoke after the piston ring treatment is reasonable proof that the rings are now sealing a lot better than before, thus increasing the vacuum the engine can pull.

You could probably live with the valve seal issue for some time, I wouldn't call it an urgent repair or an impending disaster:nervous:

Bear in mind that even though the seals are now becoming ineffective, you must expect to re-condition the entire engine when you decide to repair it.

It is false economy to do the bare minimum.

[Carl Beck]

Check/change the PCV valve - first. See what happens...

Bad valve stem seals usually cause smoke on start-up, when oil left in the head drains down the valve stems into the cylinders.

FWIW,

Carl B.

[richard1]

I installed a new PCV valve two weeks ago. The old one was good but very dirty.

[sblake01]

I was more leaning toward rings when I read this the other day. You said 'no smoke at cold start, no smoke at idling when at normal temperature, and burst of blue smoke at pick-up after deceleration as at a stop sign'. That leads me more torward rings than vavle guides. I was waitning to see the compression test results but, no matter. Rings or valve seals, you still need to do them both as Nissanman said.

[beandip]

117K and just a little smoke like you have described is not at all unusual. If you are using a good Quality oil I can see no need to use Rislone. I have used this product with good results years back with sticking hydraulic lifters. A used car I bought. Changing the oil as you have the engine should be vary clean indeed. I agree with Carl Beck on the seals. Gary

[richard1]

The results of my compression test show that my engine is showing its age no matter how much I cared over the years with good maintenance and regular oil change every 2K.

#1: 135

#2: 117

#3: 120

#4: 90

#5: 100

#6: 117

The Rislone additive seems to have help a lot There is no more big blue smoke burst now at pick up after deceleration. I am surprised that there is no more smoke at all.

Just a very small puff when I pull out of the drive way after the engine has idled for a long time.

What do you think guys?

[Nissanman]

I think you have answered your own question, it is showing its' age:rolleyes:

Unless it develops a major problem, you could keep driving it for a while yet.

However, with those numbers in the compression test, it will certainly benefit from a complete overhaul.

My reference says that on a '72 in good condition the compression should be ~180psi.

More importantly, the lowest reading should be at least 75% of the highest.

0.75 x 135 = 97.5.

Your lowest is 90psi:ermm:

#4 cylinder may also have a valve sealing issue which a Leakdown test should verify.

However, it is probably academic considering the low readings across all the other cylinders.

Your attention to regular and frequent oil changes almost guarantees an engine that will not require a great deal of machining to it.

My guess is a fresh set of main and big end bearings, new rings with cylinder hone, and a reconditioned head.

The last bit will probably be the most labour intensive and possibly the most costly if you have a Shop do it.

Just make sure you do it all at the same time, it is too important to do by 1/2 measures.

When done it will be a quantum leap in engine performance, it will be better than new:D:D

[richard1]

Nissanman, what kind of major problem could arise?

The one that happened yesterday is not related to the engine but major.....the automatic transmission is slipping.

I went to a transmission specialist yesterday. The converter is bad and the entire transmission needs to be redone.

I will have the car back tomorrow after a $1,600.00 expense. I am impressed that the parts are so easily available for a complete transmission rebuilt.

Anybody can tell me what could be the cost of a stock engine rebuilt or could I find a rebuilt one and just swap?

[Nissanman]

I guess the worse case is for the head to corrode or the head gasket to blow.

The former depends a lot on the quality of the coolant you have used over the years.

The latter may just happen due to age and brittleness of the gasket.

It may never happen:paranoid:

Can't quote you any $.

In your position I would rebuild the matching number engine.

The car will retain a lot of value that way.

You might be able to find a 1/2 reasonable used L6 engine to use temporarily but bear in mind they are all getting old now.

[cunniwj]

$2,000-3,000 in my area. Your tranny probably would have been less if you did it all at one time.

[richard1]

I am told by a hobbyist that the engine must be warmed-up at normal temperature to do a compression reading on all cylinders.

Maybe I am dumb but when I reported mine above in this thread, the engine was cold and never started.

Sorry if I look stupid. It seems that I am missing something or????

The other thing he told me is the carburetors needs to be at full throttle......I don't understand this one.