Occasional smoke on start up.

[Stanglover]

In a previous post by Superbond, I mentioned that my engine had started to smoke on start up and I would post separately on my engine.
I don't intend this to be a long drawn out thread, but I would like to get an idea of why before I start spending money on pulling the heads and redoing them.......... again.
I know my way around my 71 M code 351C, but I have never done an engine rebuild myself other than replace head gaskets many years ago. The basics are fine.
Here's what I know. Last summer, I saw the first signs of blue smoke on start up and was told there was some signs of smoke on hard acceleration.
This year after winter's hibernation, there was noticeably more smoke. This only seems to be after the car has sat for a while and not so much after that.
What I know about this motor; It was redone in 2016 after an earlier build when the builder chose to put in a HV oil pump that eventually took out the #1 cam lobes and lifters as well as the main bearings. The latter build saw KB13cc dish top pistons instead of the KB flat top, a new Melling MTF 2 cam and the valve seals changed to a type with a spring like coil around the stem. Not sure what they are called! I do NOT know if the guides were done, but I do know the exhaust valves were change to SS one piece.
A couple of days ago, I did a cylinder pressure test and change the plugs back to Autolite 24's. I had been using Autolite 25's, one step hotter. This was to see if there was any significant change in plug color under the same engine conditions. Just me being curious I guess!
These are the numbers 1-8; 185, 190,195,195 190,195,192,195. # 1 cylinder also showed a slightly darker plug color, but no sign of oil. All other plugs were light brown with some variation. This is telling me that the rings are not the problem, so it has to be the valve stems or seals, but how do I know which without pulling the heads? Right now, I'm not overly worried, it's not belching smoke yet. If and when it gets to be worse, I'll have to consider a top end rebuild.
Oil; Castrol Edge 10W30, pressure; 70 psi hot running, 35-40 hot idle.
Thoughts?

 

[71ProjectJunk]

Do you know what type of valve seals were used when the engine was rebuilt in 2016? Are those the original heads or did you change to aluminum heads? If they are original heads what was done to the valve guides? It seems to me that the issue is not the piston rings, oil is either coming in from the valve guides or from the intake manifold. The question is from which of those 2? Only other place would be from the PCV valve. The issue is how to figure out exactly from where.

 

[Stanglover]

Do you know what type of valve seals were used when the engine was rebuilt in 2016? Are those the original heads or did you change to aluminum heads? If they are original heads what was done to the valve guides? It seems to me that the issue is not the piston rings, oil is either coming in from the valve guides or from the intake manifold. The question is from which of those 2? Only other place would be from the PCV valve. The issue is how to figure out exactly from where.

To answer your question ( ought to have mentioned that in the first place), The heads are original. I do NOT know what type or name of the seals used other than what I mentioned. I do not know if the guides had anything done to them. Part of the reason this motor was redone in 16 was for excessive oil usage, probably due to the use of umbrella type seals. It has been fine up to last summer. As for the intake, it too is original and yes, I've had that off and on a couple of times. The last time was after the rebuild and they installed the rubber end seals that leaked badly. I have had no problem with that and do not suspect the intake as a problem......... yet.
I checked the PCV and it is working as it should, but worth double checking and yes, there is a baffle under it.
I'm 99% sure it's seals and they can be changed without taking the heads off, but.......
Like I said, It's not a big issue yet, but people notice and that bothers me more than the start up puff of smoke.

 

[boilermaster]

Stanglover,
The next time you go for a drive (drive like you NORMALLY do, when you are done remove your PCV valve and hose at the carb, hang the assembly so it can hang and drain from the carb end into a clean container and see what you collect overnight.
When you re-install, look for that occasional smoke on start up.
Too much pcv flow could be laying in the bottom of the hose causing the smoke on start up.
your engine may not like the brand or part number of the pcv valve you have.

 

[Hemikiller]

Smoking temporarily on startup is likely to be a valve stem seal issue. There's also a chance you're getting fuel percolation and dumping gas into the intake.

Factory type umbrella seals only last so long. It's simple enough to pull a valve cover and inspect the seals with a probe and flashlight. If they feel hard, or you're finding pieces of them inside the spring or lying in the head, it's time to change them out. If you have the performance oriented positive stop valve stem seals, they're supposed to last a very long time.

 

[Don C]

It sounds like they installed Viton valve seals, but they either need the top of the valve guides machined or have new guides installed. Even if the valve guides weren't replaced the Viton seals will seal with some looseness in the valve stems. It's possible one or more of the seals have slipped up off the valve guide. Another possibility is pulling oil out of the valley through an intake manifold gasket or porous intake manifold. A coworker, many years ago, rebuilt the 428 in his pickup and installed an Edelbrock intake that had a porous spot in it, drove him nuts trying to find why it was burning oil.

 

[Stanglover]

Stanglover,
The next time you go for a drive (drive like you NORMALLY do, when you are done remove your PCV valve and hose at the carb, hang the assembly so it can hang and drain from the carb end into a clean container and see what you collect overnight.
When you re-install, look for that occasional smoke on start up.
Too much pcv flow could be laying in the bottom of the hose causing the smoke on start up.
your engine may not like the brand or part number of the pcv valve you have.

Boilermaster, that's a good thought. I custom made my PCV tube to route around the back of the carb, so yes, it possibly is overloaded with oil. I'll check that for sure. Wouldn't it be nice if it were that simple!! Here's a pic of my concoction.

 

[Stanglover]

It sounds like they installed Viton valve seals, but they either need the top of the valve guides machined or have new guides installed. Even if the valve guides weren't replaced the Viton seals will seal with some looseness in the valve stems. It's possible one or more of the seals have slipped up off the valve guide. Another possibility is pulling oil out of the valley through an intake manifold gasket or porous intake manifold. A coworker, many years ago, rebuilt the 428 in his pickup and installed an Edelbrock intake that had a porous spot in it, drove him nuts trying to find why it was burning oil.

I can check the seals as you suggest. If it's not the PCV system, it is 99.9% likely to be seals and not the intake, but all will be checked as I go through it all.
As said, this is more annoying than an issue that needs to be fixed right now.
Thanks for your input Don.

 

[Stanglover]

Smoking temporarily on startup is likely to be a valve stem seal issue. There's also a chance you're getting fuel percolation and dumping gas into the intake.

Factory type umbrella seals only last so long. It's simple enough to pull a valve cover and inspect the seals with a probe and flashlight. If they feel hard, or you're finding pieces of them inside the spring or lying in the head, it's time to change them out. If you have the performance oriented positive stop valve stem seals, they're supposed to last a very long time.

Hemikiller, thanks for your input also. When this motor was first rebuilt, 2012, I was handed a complete set of umbrella seal that I guess came with the gasket and seal set and were not used. So, I don't know exactly what they used. However I know those were replaced in 2016.
As for fuel percolation, with the cross overs blocked off and a 1" fiber spacer, that problem was hopefully fixed several years ago. I have not noticed any of the symptoms I was getting before hand. I'll rule that out for now.

 

[71ProjectJunk]

They could have knurled the valve guides instead of putting new guides in, knurling does not last too long. As you have the unused umbrella seals, they probably installed some type of seal that sits on the valve guide and should stay there and not move. It is possible that one or more of them have gotten loose, and are now just flopping on the valve stem and not sealing well. I would take the valve covers off and take a look at all the seals, one or more may have gotten loose from the valve guides and are letting oil through.

 

[Stanglover]

They could have knurled the valve guides instead of putting new guides in, knurling does not last too long. As you have the unused umbrella seals, they probably installed some type of seal that sits on the valve guide and should stay there and not move. It is possible that one or more of them have gotten loose, and are now just flopping on the valve stem and not sealing well. I would take the valve covers off and take a look at all the seals, one or more may have gotten loose from the valve guides and are letting oil through.

To be clear, the umbrella seals I have were from the first rebuild. As far as I know the latest ones are likely the viton type Don C mentioned. As for what was done to the guides, no idea. I trusted their expertise. Unfortunately that shop has since closed due to the owner's ill health, so I have no way of trying to find out from their records.
First, I'm going to check out the PCV tubing I made up. It could well be full of oil. If it is, I'll redirect it.
Next, I'll pull the v/covers and see if there is anything obvious. It will be a process of elimination for sure and I'll keep this updated as I go.
Thanks for your ongoing input.

 

[71ProjectJunk]

Good luck, hopefully it is something simple.

 

[mrgmhale]

I suspect the valve seals are having some issues (also). I am not certain what to make of your description ot the valve seals (using Viton), Here is what I do know, especially for a head with canted valve angles... I would be (also) using a hardened steel seat for the valve seats - good move. Rather than merely knurl the valve guides I strongly recommend Bronze Wall valve guides be used, even though they are costly. And I also like to use Perfect Circle valve guide seals as opposed to the umbrella style oil deflectors that are often called valve seals (a misnomer if ever there was one).

On a side note, for anyone running a flat tappet valvetrain, please be certain your engine oil has Zinc in it, or as an alternative you can add Zinc to the oil you use if it does not have Zinc in it. Otherwise you risk wearing out your cam lobes and lifters badly, and very quickly. Zinc is not added to many modern engine oils because it fouls catalytic converters. Engine designs now use roller lifters as a result, as they do not wear badly in the absence of Zinc. We use AmsOil Z-Rod, with Zinc in its blend, in all of our vintage, flat tappet equipped engines (10/30).



https://mgaguru.com/mgtech/engine/ch102.htm

 

[Roland]

Did you check the oil level? does it really burning and consuming oil?

 

[Stanglover]

I suspect the valve seals are having some issues (also). I am not certain what to make of your description ot the valve seals (using Viton), Here is what I do know, especially for a head with canted valve angles... I would be (also) using a hardened steel seat for the valve seats - good move. Rather than merely knurl the valve guides I strongly recommend Bronze Wall valve guides be used, even though they are costly. And I also like to use Perfect Circle valve guide seals as opposed to the umbrella style oil deflectors that are often called valve seals (a misnomer if ever there was one).

On a side note, for anyone running a flat tappet valvetrain, please be certain your engine oil has Zinc in it, or as an alternative you can add Zinc to the oil you use if it does not have Zinc in it. Otherwise you risk wearing out your cam lobes and lifters badly, and very quickly. Zinc is not added to many modern engine oils because it fouls catalytic converters. Engine designs now use roller lifters as a result, as they do not wear badly in the absence of Zinc. We use AmsOil Z-Rod, with Zinc in its blend, in all of our vintage, flat tappet equipped engines (10/30).



https://mgaguru.com/mgtech/engine/ch102.htm

Thanks for your reply.
I did mention that the exhaust valves are SS, but I did not mention that the seat were changed to hardened. Also as mentioned, I do not know what if anything was done to the valve guides and as the shop has since closed, I have no way to go back and ask. I also mentioned I do not know for sure what name or brand of seals were used other than being told at the shop, they were a type with a spring like coil around the valve stem, I assume, to hold the rubber in closer contact. Other than that, I'm in the dark.
As for oil, yes I use zinc additive, always have.

 

[Stanglover]

Did you check the oil level? does it really burning and consuming oil?

Oil was just changed and to be honest, it's a bit on the high side for a stock 351C. If it were a Boss that uses a different dip-stick, it would likely be right on the mark.
This car is a 4 speed and I do engine brake quite a bit. That alone tends to use some oil. Oil usage is not a concern, maybe 1 pint in a summer's driving of about 1500 miles.
Again, I would like to stress that this occasional smoke on start up, is not so bad it needs to be addressed right now, but it is something I am keeping an eye on. If it worsens, then I'll have to pull the heads or at least have the seals changed with heads on.
Thanks to all for your input and suggestions.

 

[Steve McMahan]

In the late 1970’s, I rebuilt a motor for a small block Pinto swap. Used all quality parts and the machine shop was top of the line, very respected. I assembled the motor with no issues, installed, owner happy, 2 years go by. Came back to me with startup and very hard acceleration bluish smoke. Valve train looked great, no visible signs of why. So, I pulled it apart and found cyl 1 with frozen oil control ring set. Why did I check that one first, spark plug was a bit darker than the rest. I purchased a complete replacement ring set, put them on, no more smoke and not for the next 7 years. I moved after that, so . It could be lots of things.

 

[Stanglover]

I pulled it apart and found cyl 1 with frozen oil control ring set. Why did I check that one first, spark plug was a bit darker than the rest. I purchased a complete replacement ring set, put them on, no more smoke and not for the next 7 years. I moved after that, so . It could be lots of things.

Steve, good thought on the oil ring stuck. I hope it's not, but a good clue.
On my engine and going back to 2016's rebuild, it was using a lot of oil. I took videos of the bores and at the time, thought I could see score lines in more than one cylinder, especially #1. when the motor was torn down, those lines turned out to be oil lines (?) not score marks. As I wanted to fit new dish top pistons, the cylinders were re-honed. I saw the block before it was assembled and it looked good.
#1 cylinder was the worst and as the original problem was apparently caused by a mistake made by the shop owner, I might suspect that cylinder to still be an issue as it had the darker plug, but not oiled.
As said, I hope not. I don't have the funs these days for yet another rebuild.

 

[Stanglover]

Stanglover,
The next time you go for a drive (drive like you NORMALLY do, when you are done remove your PCV valve and hose at the carb, hang the assembly so it can hang and drain from the carb end into a clean container and see what you collect overnight.
When you re-install, look for that occasional smoke on start up.
Too much pcv flow could be laying in the bottom of the hose causing the smoke on start up.
your engine may not like the brand or part number of the pcv valve you have.

Boilermaster.
Yesterday, I removed my custom PCV tube and there was no oil in it, i.e. none dripped out of it. That rules that out. but I will install a new PCV with a new air cleaner element. An air cleaner element does NOT need to be that dirty to affect the amount of air and upping the restriction. That also can cause it to suck oil.
One thing at a time.

 

[Stanglover]

Well, here's the bad news. It still smokes a bit on start up and a puff on acceleration.
It's not the PCV tube, although I suppose I could pull the PCV and try again just to be sure, so I'm guessing the valve stem seals. As I said before, I'm not too worried about this right now, so if need be it will be a winter job. Damned annoying!