puff of blue smoke at higher rpm decel

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 »

superpursuit wrote:It could be valve stem seals, valve guides or a leaky inlet manifold gasket allowing oil to be sucked into the port. I would try checking the tension on the inlet manifold bolts first. What type of valve stem seal do you have? Viton seals are the better ones. Teflon seals don't stop the port from becoming wet. 'o' ring seals as in factory seals on SBC are pretty useless on a performance engine. Silicone on rocker studs does not seal the threads. Try using Loctite on the threads going in the head.
Fair enough and worth the try. Which Loctite would you use on them (PS, this is a shaft rocker system)
Last edited by Belgian1979 on Mon May 29, 2017 3:17 am, edited 1 time in total.
User avatar
modok
Guru
Guru
Posts: 3321
Joined: Sun Jun 06, 2010 1:50 am
Location:

Re: puff of blue smoke at higher rpm decel

Post by modok »

Belgian1979 wrote:
modok wrote:I don't know if it's guides ect..... but I do see what is common between these comments.

With no LOAD, the ring tension itself, and mainly the second ring is doing the oil control.
If the second ring is overly worn, worn barrel face, or lost tension, for whatever reason, you could get a situation like that.
Good compression, leak down test OK.. but eats oil anyhow.
In that situation there is still the first ring to prevent the oil from going up imo
Oh no, no.

Have you ever scraped anything off anything else?
A barrel faced thing, with rounded edges is of course going to work terrible, just glide over it.
To scrape anything off anything you want a sharp edge, or high contact pressure.
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 »

modok wrote:
Belgian1979 wrote:
modok wrote:I don't know if it's guides ect..... but I do see what is common between these comments.

With no LOAD, the ring tension itself, and mainly the second ring is doing the oil control.
If the second ring is overly worn, worn barrel face, or lost tension, for whatever reason, you could get a situation like that.
Good compression, leak down test OK.. but eats oil anyhow.
In that situation there is still the first ring to prevent the oil from going up imo
Oh no, no.

Have you ever scraped anything off anything else?
A barrel faced thing, with rounded edges is of course going to work terrible, just glide over it.
To scrape anything off anything you want a sharp edge, or high contact pressure.
I doubt it would only smoke during high rpm decel if it were rings.
Carnut1
Guru
Guru
Posts: 4659
Joined: Tue Jun 11, 2013 6:32 pm
Location: Melbourne fl.

Re: puff of blue smoke at higher rpm decel

Post by Carnut1 »

Care to explain ?[/quote]
On an engine that the valve stem is bathed in oil or submerged when the throttle is leaned on the change in vacuum pulls oil past the loose guides.[/quote]

I understand that but right now I cannot conclude to a loose guide. I remember they were within tolerance when built.


Any check that can be done with the heads on ?[/quote]



If you can get a scope or look down to the intake valve stem and top of the valve? If the stem that is in the bowl and top of the valve that seals the bowl are coked up that is from oil leaking through thr guide and burning right to the hot valves.
Servedio Cylinder Head Development
631-816-4911
9:00am - 9:00pm EST
fdicrasto
Expert
Expert
Posts: 780
Joined: Wed Sep 26, 2012 3:44 pm
Location:

Re: puff of blue smoke at higher rpm decel

Post by fdicrasto »

I agree with a probable valve guide issue but usually if guide problem on restart you would usually see a puff of smoke also.
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 »

fdicrasto wrote:I agree with a probable valve guide issue but usually if guide problem on restart you would usually see a puff of smoke also.
I do not see blue smoke on startup.
User avatar
ptuomov
Guru
Guru
Posts: 3587
Joined: Fri Aug 07, 2009 3:52 am
Location:

Re: puff of blue smoke at higher rpm decel

Post by ptuomov »

Novice question: how confident can one be that the smoke is from oil? Does the car have deceleration fuel cut off turned on or off?
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU
https://www.instagram.com/ptuomov/
Put Search Keywords Here
Truckedup
Guru
Guru
Posts: 2728
Joined: Mon Jan 21, 2013 2:41 pm
Location: Finger Lakes

Re: puff of blue smoke at higher rpm decel

Post by Truckedup »

Belgian1979 wrote:
fdicrasto wrote:I agree with a probable valve guide issue but usually if guide problem on restart you would usually see a puff of smoke also.
I do not see blue smoke on startup.
When the engine is fully warmed up and it idles for the few minutes, does accelerating the engine slightly blow some smoke from the tail pipes?
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 »

ptuomov wrote:Novice question: how confident can one be that the smoke is from oil? Does the car have deceleration fuel cut off turned on or off?
No decel fuel cut is not activated.

There is a difference between black, blue and white smoke. Plus my plugs are slightly oily.
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: puff of blue smoke at higher rpm decel

Post by Belgian1979 »

Truckedup wrote:
Belgian1979 wrote:
fdicrasto wrote:I agree with a probable valve guide issue but usually if guide problem on restart you would usually see a puff of smoke also.
I do not see blue smoke on startup.
When the engine is fully warmed up and it idles for the few minutes, does accelerating the engine slightly blow some smoke from the tail pipes?
Not that I noticed, but I would have to try and pay special attention under these circumstances.
user-23911

Re: puff of blue smoke at higher rpm decel

Post by user-23911 »

I'd say it's just a natural progression from tuning and idling issues.

Have you given your oil the sniff test for fuel?
Newold1
Guru
Guru
Posts: 1963
Joined: Fri Apr 08, 2016 9:50 am
Location:

Re: puff of blue smoke at higher rpm decel

Post by Newold1 »

I don't think that minor to moderate valve guide wear or valve seals issues tend to show themselves with oily plugs. The seals would have to be nearly non-existent or the guide wear excessive to see larger amounts of oil in the cylinders. Usually bad exhaust valve seals show up as a short oil smoke burn when the engine is first started after sitting for a while, not on decel. Bad or missing intake valve seals and excessive intake valve guide wear can allow oil to enter the cylinder under vacuum and decel vacuum. I like the newer one piece Viton spring loaded seals for intakes and an exhaust high temp Viton seal with the springs removed. If you have good heads with good bronze properly clearanced valve guides and a valve train geometry that is not causing excessive valve guide wear I am not strong on the idea that that much oil is coming from the guides. Bronze valve guides, good valve stems and decent valve train geometry do not tend to put that much wear clearances on bronze guides.

An intake port /manifold sealing issue can inject quite a bit of oil into the intake tract and then into the cylinder to burn. Under strong decel the vacuum in the intake system is the highest and most likely to draw oil in from the lifter valley.

Sometimes on high vacuum decel a PCV breather system can inject quite a bit of oil especially if a lot of crankcase pressure is present.

Are you using a catch can, header extractor or vacuum pump system for the engine crankcase pressure control?

You should take a close look at the intake tract and see if it's wet with oil as that would be an obvious tell tale and better point to the cause.

I suspect you may have an intake /valley tract leak or and issue with cylinder/ring seal. JMO

There are obviously a few other areas that can get oil into the cylinder such as ring wear, ring seal, low ring tensions especially on oil ring and damaged cylinder walls or poor finish on cylinder prep from
machining.

Have you done a compression and leak down test?
The Older I Get, The Dumber I Get :wink:
Roundybout
Pro
Pro
Posts: 396
Joined: Tue Dec 29, 2015 8:09 pm
Location: TN

Re: puff of blue smoke at higher rpm decel

Post by Roundybout »

Belgian1979 wrote:
Roundybout wrote:I had that issue with a SBC. Leakdown test turned out ok so I could rule out the rings. PVC system looked to be functioning good. Replaced the valve seals as it was the cheapest and most likely fix. Of course it turned out to be worn guides in my case.
Yes, similar here. Compression is ok, as good as it was after running in. Was also thinking on doing new seals for the same reasons.

Did it start to smoke again immediatly after new seals ?
Yes it smoked the same after the seals were installed. I couldn't notice anything obviously wrong with the guides when I was doing the seals. Apparently the wiggle test didn't work when I was in there lol. It didn't take long for it to get progressively worse either.
User avatar
BrazilianZ28Camaro
Guru
Guru
Posts: 3939
Joined: Mon Feb 09, 2009 10:52 pm
Location:

Re: puff of blue smoke at higher rpm decel

Post by BrazilianZ28Camaro »

All good suggestions here, but While you're at it, take a look into the powerbrake hose. Sometimes the master cylinder seal leak into the booster and the engine will smoke on decel.

Have your engine low tension rings installed?
'71 Z28 street strip car
Pump gas All motor SBC 427
3308 lbs-29x10.5 Hoosiers
NEW BEST ET
1.38 60' / 4.05 330' / 6.32@111.25mph

https://www.youtube.com/watch?v=99p13UK ... ture=share
496blaze
Member
Member
Posts: 69
Joined: Sat Feb 10, 2007 1:45 am
Location:

Re: puff of blue smoke at higher rpm decel

Post by 496blaze »

Belgian1979 wrote:
superpursuit wrote:It could be valve stem seals, valve guides or a leaky inlet manifold gasket allowing oil to be sucked into the port. I would try checking the tension on the inlet manifold bolts first. What type of valve stem seal do you have? Viton seals are the better ones. Teflon seals don't stop the port from becoming wet. 'o' ring seals as in factory seals on SBC are pretty useless on a performance engine. Silicone on rocker studs does not seal the threads. Try using Loctite on the threads going in the head.
Fair enough and worth the try. Which Loctite would you use on them (PS, this is a shaft rocker system)
I use red loctite on all rocker studs that go into the intake port. You will be able to tell if its leaking soon as you pull the stud out. Oil will be wicked down the threads.
Post Reply