Smoke on start up

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Superbond

Well-known member
Joined
Sep 6, 2017
Messages
129
Reaction score
41
Location
Thunder Bay
My Car
72 mustang
So
I rebuilt my 72 351c 2v a few years ago. Run great but I have alway had an issue. When I sits for awhile (a day or more) and I start it up. It always sound congested and smokes. ( light blue smoke).
When it runs for a few minutes no more blue smoke and all is well.
The heads were professionally done. Compression is good
Any ideas?
 
Superbond,
Dual exhaust ?, does it smoke from both pipes, or just one side ?
Were valve guides replaced or just knureled ?
Factory cast iron intake manifold or aluminum aftermarket ?
Exactly what type and manufacturer of intake manifold gaskets were used?
Stock pcv system and rocker covers ?
Just getting you warmed up for the big guns.
Boilermaster
 
Oh boy, this sounds familiar!! This is what I was welcomed with this year after 6 months hibernation. So far, I have not had time to delve into what's going on with my motor, but I too suspect valve guides because of why this motor had to be rebuilt a second time back in 2016. I'll not go further about my situation here as I'll start my own post later.
Here, I'll just say this " I feel your pain!"
 
dual exhaust
Aluminum intake holly
Valve seals all replace
Smoke coming from both
Ford aluminum valley pan
 
Lol
You haven’t even heard anything when I came to this engine rebuild. But it runs great! It just the smoke at start up. And maybe it is my holly 600 vacuum secondary carb. The first one I bought was bad. Who’s to say this isn’t loading up with gas. I know when it sits for a couple weeks. I have to pump it about 6-7 times to get it it start.
 
Superbond,
What do the spark plugs look like ? any evidence of oil?.
the reason I asked about pcv system and valve covers is does the rocker cover that contains the pcv valve have a proper baffle and breather ? is it twist on (OEM) or push in (aftermarket)
 
As much as I don’t like it. All the work to correct this. Removal of the carb, intake manifold, headers, heads then replacing the valley pan! ( pain in the you know what). Unless I buy some nice aluminum assuie heads. If it not hurting anything but my pride. I guess I can live with it. 😩
 
When the heads were rebuilt were valve guide liners installed or were the guides knurled? The first build that I did (26 years ago) with less funds, the guides were just knurled and I reused 15 out of 16 of the OE valves (Bad idea ,I know) and by 25 thousand miles the guides were loose. The second time around with more funds I went all in and replaced all the valves and put in silicon/bronze guides. 30 thousand miles later so far so good. If you have a bunch of crust built up on the intake valves your guides might be wasted. That is what happened to mine.
Ron
 
What kind of valve seals? Umbrellas or Viton positive stop seals?
What kind of oil pump? A high volume/high pressure pump can send too much oil onto the valves and splash onto the stems and run down them with the umbrellas.
The turkey pan gasket can be a PITA to get sealed, especially with an aluminum intake. The steel turkey pan and heads have a different expansion rate than the aluminum intake, so the there will always be some tiny bit of movement at the interface between them. It's also critical that the intake manifold sits squarely on the heads, and not have one side or end higher than the other.

Boilermaster's comments about the PCV valve and baffle is spot on, if your valve cover doesn't have a baffle under the PCV valve it will suck oil.
 
So
I rebuilt my 72 351c 2v a few years ago. Run great but I have alway had an issue. When I sits for awhile (a day or more) and I start it up. It always sound congested and smokes. ( light blue smoke).
When it runs for a few minutes no more blue smoke and all is well.
The heads were professionally done. Compression is good
Any ideas?
How often do you need to add oil? How long ago were the heads done? Did the shop replace the guides or just the seals? Sure sounds like guides or seals based on your symptoms.
 
9 times out of 10, the valve stem seals are leaking.. When the engine sits, oil seeps past the seal and into the combustion chamber.. When the cylinders fire up, the oil burns off. As the engine heats up, the valve stems and seals expand which stops the process. We've had brand new Ford engines smoke on start up from the factory and all that was needed was to replace the valve seals. Also, if the valve guides are not within tolerance, the intake stroke will draw any stagnant oil past the seals and cause the same problem when the engine is cold.. Even valve stem guide replacement sleeves can be oversized if not reamed correctly.. IMHO, install new valve stem seals (hopefully the oem style) and you should be ok..
 
When the heads were rebuilt were valve guide liners installed or were the guides knurled? The first build that I did (26 years ago) with less funds, the guides were just knurled and I reused 15 out of 16 of the OE valves (Bad idea ,I know) and by 25 thousand miles the guides were loose. The second time around with more funds I went all in and replaced all the valves and put in silicon/bronze guides. 30 thousand miles later so far so good. If you have a bunch of crust built up on the intake valves your guides might be wasted. That is what happened to mine.
Ron
Y
I sorry I don’t know. Never looked. It was my first motor that I had ever rebuilt ( or put back together).
I’ll probably just leave it unless it gets way worse
 
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