VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 '40 chevy engine"blow-by"

HELP !!!-have a "blow-by " on my 40 .pulled the intake/exhaust ,yup --not even so I had it milled --checked the block and that was striaght .went through 4 sets of gaskets and 4 times on and off an I still have that *** **** "blow -by" and its always the same place --the forth exhaust port from the front of the engine.Any suggestions ??????

I am assuming that you have an exhaust leak at that point. (blow-by is something else)....Are the three rings, one in each of the round intake ports bent or distorted or preventing the manifold from pulling up to the head completely?Have you tried loosening the bolts slightly that hold the two manifolds together, installing the gaskets, and then retighten the bolts?

Confused-the forth ex.port from the front is the very rear one as there are only four exhaust.

The forth port from the front is the center intake (round hole)

Is the gasket material actually burning away at the point of leakage?

Your right Gene--I have an exhaust leak ,and not 4th exhaust port -but 3rd one . No the gasket isn't burned away --I can just feel the hot gases blowing directly up from the 3rd.exhaust port ! the intake and exhaust are almost "welded " together, I'm afraid to really get aggresive in trying to seperate them fearing I'll break something .checked the rings --lightly taping with a hammer --no movement .

I went thru a similiar situation on my "40 - 216, after I seperated the manifolds, replaced the gasket, re-installed with the manifolds snugged up but not tight, mounted the manifolds to the head and lastly tightened the manifolds together.
All was well, no more leaks........

John.That is what I would recommend.Soak the bolts that hold the manifolds together and they usually come out and apart with out any problem.The gasket comes in the engine rebuild set-if thats what you had.Infact usually both the 216 and 235 gaskets come in the set.
If the manifold to head gaskets are new you could reuse them.When removing the manifold check to be sure the intake rings are entering the head and block-if one is twisted it will prevent the mainfold from seating and you will have an intake leak also.
Is the interior in now???

Gene--yes --FINALLY !! The interior is in place --the guy did a super job !! I'll pull the manifold tomorrow and drown it in wd-40 hope that will seperate the two sections .Ordered two new gasket sets (manifold) from N.A.P.A. will pick them up monday .thank you and whmarquis for your help --keep your (collective ) fingers crossed !!

I feel for you, I had one on a 57 engine that would not come apart easily, I had to do an extended job with lots of PB Blaster and a bunch of choice words. Then I spent a while getting the heat rizer flapper working too.

Followed this forum's advice and took the intake/exhaust apart this morning --finally got the two pc.'s and had about 3/4 of an orginal gasket there----with a soot line following the bend of the exhaust manifold to right where I was feeling it by the valve cover .Wasn't leeking around the head a I guessed . Now I get the fun of playing with the heat rizer flapper as you did Mr.Mack ---ain't one thing it another !!!

He John,
Was your head rizer flapper stuck in the open position?

YES !!!---Seems to be actually solidified in position . Have drowned it in wd-40 as we speak .

BigBob--just came in from the garage --shaft on the heat rizer still "lock" in position however the "flapper" moves but only with a very heavy finger and a lot of squeaking on the shaft--looks kinda like the weld "flapper to shaft " is broken.

John,
Thanks for the information. Along with WD-40, I found some stuff called PB Blaster, and the stuff really works. If you haven't used PB, you should give it a try. When you use the stuff it kind of foams and seeps into hard to get places.

Checked locally and no one seems to have heard of PB Blaster ---is that something out on the west coast ?? Will be going to N.A.P.A. tuesday but will check the auto supply stores around here tomorrow .

John,
Our local NAPA happens to carry it. It is not a NAPA labeled product. Here is a link to see what it looks like.
PB Blaster

I buy it in the local discount type auto parts stores here in Florida.

Let your fingers do the walking and call around.

Good luck...

I get my P B Blaster at the local Walmart Super Center. Also at Advance Auto Parts.

Our local NAPA store has it too!

John,To free-up the heat riser DO NOT try to turn it.Tap back and forth from front to back.A brass or other soft hammer or a black of wood is less damaging.

Gene --have an old brass hammer from way back when and I'm using it --got about 1/16 or 3/32 movement (front to back on the shaft) ,however in doing so the flapper moves by itself as the hammer hits the shaft looks like the flapper weld is broken .Have a friend who can tig or mig (always get them confused)weld ---BUT --how much from to back movement (or ) spin on the shaft should I expect when it's "free"

The shaft will have at least 1/8" front to back movement.When the heat riser is in the cold position the flat part of the weight will be horizontal.When in the hot position will turn about 30 degrees - clock wise when viewed from the front.Should rotate freely....do you have the thermostatic spring??

Gene--yes I've got the old bi-metal spring --looks kinda ugh so I've ordered a new one from chevy of the 40's ( also the oversized shaft as this is really a bear to move --just in case I've got to resort to "plan 'b" and replace the whole thing . With the part of the gasket missing and the flapper in the winter position I think that was the cause of my trubles ---at least I hope so .

Wow! What a great source of information and knowledge this forum is !! Although I am a few weeks ( or more ) from reinstalling the manifold on my 40 town sedan, I am quite sure I would have installed without loosening the two parts first. I have sprayed mine with Liqiud Wrench penetrant and when the time comes will break the two sections loose before installing. I have found WD-40 to be a poor penetrant also. Evaporates too quickly- I heard it was developed as a water displacement spray developed to "dry" out points ignitions and electronics. I get my Liquid Wrench at my local Farm and Fleet.- probably a midwest operation. Thanks again and I'll keep reading ! Chevy40

Farm&Fleet also sells PB Blaster-cheap.Also see it in other parts stores around here.It the only product that WORKS

Checked on the confuzer for BP Blaster (thanks BigBob) and found tha N.A.P.A.handles it --stoped there today and picked up a can !! it's medicating the parts as we speak --hope it works ----will let you guy's know -----stay tuned --video at 11 !!!

PB Blaster is good , but you will still have to put a wrench on it and put out a little leverage, don't expect the tap to screw off by itself! or in your case the flapper shaft...Ha!