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[johnnyboy]

Got a crack in the exhaust manifold, so just bought a new one from Lightys.

Andrew suggests (if I understand him correctly... ) that I shouldn't need any gaskets, just go for a metal to metal contact? Any thoughts? or did I just misunderstand?

Also, it turns out that the metal pipe that transfers hot gas up to the choke mechanism has rusted through, and I am having trouble sourcing a replacement. It has been suggested that I could go to an electric or manual choke (Carter BBD 2 barrel carb) but I have always previously been happy with the way the choke worked, so I am not keen on a change. (and I can't afford to buy a Webber)

Any suggestions on a source for a new connecting pipe? or on how to make one - it just looks like a bit of metal petrol pipe... though I cant see how it attaches to the top of the fitting that goes through the manifold...

:
See below for a couple of photos to jog your memories of what I am talking about:

[IrishKenCJ7]

I managed to source one from the US before and it was a generic one but I still haven't installed it. It was a kunifer one no different to a brake/fuel line and came with a braided cloth cover and connectors for either end but my 79 Cj7 only needed a connector at the carb end and just dropped down on the hole on the manifold.

You only need about a foot of Kunifer and use some brake line connectors, I wouldn't worry about the end at the manifold.

Ken

[eastryjeep]

To clarify for my own sanity!
Gaskets go between the two manifolds and between the head and manifold assy.
Air pipe has no sealant or whatever down near diverter.
Pipe is flared with nut fastening it to choke on carb.
You may have to reset the choke actuator for different air flow however.
Hope that helps.

[johnnyboy]

On the gasket subject, I did not explain very well... The inlet to head and the square one between the manifolds are both good.

However: The Gasket in question is the one between exhaust manifold and cylinder head.

One is supplied in the gasket kit, but Andrew is saying that I should not use it. Andrew says they were not fitted from new (on 1970's CJs that is... which leaves me wondering why one should be on mine since we have had it virtually from new and I can't remember ever taking the manifold off...) and that in the Howes Motors days they did not give them out.

The argument was that with the manifold being so much hotter than the (water cooled...) cylinder head, the differential expansion squashes the gasket and it fails - unless you clamp it up extremely tight which risks distorting / cracking the nice new manifold. On the other hand, with metal to metal a certain amount of movement is possible (in extremis...) without damage.

Having opened the gasket kit, it comes with an instruction leaflet that says "Upon dissassembly it is likely to find the absence of an exhaust manifold gasket since none was offered as original equipment. However.... we recommend that the included gasket be installed""

I am in a bit of a quandry. I have not fitted many new manifolds to cars over the years but I would never have considered putting one on without a gasket... on the other hand Andrew and co. know an awful lot more about CJ7's than I do....


,
 

[Dave69]

you can use a gasket but it all depends on what it is made from, metal ones which are double skinned pressed together are better, but if you have replaced all the bolts and studs for new or at least cleaned them so thay dont sieze then bolt the two together bare. But remember to check the torque value after you have heat cycled the engine a few times to allow for the new manifold to settle and reduce casting stresses

[eastryjeep]

Ive had two engines in my CJ7 and have had to rebuild them numerous times. Its a '77 model and had a two piece manifold gasket from new, it was a strange thing, where the inlet and exhaust had separate gaskets, but the gaskets themselves were rivetted together!
I must have had to remove my manifolds at least 5 or 6 times and have always fitted a new gasket.
See page 87 in Chilton's manual and page 90 in the Haynes, but surprisingly both illustrations only show an intake gasket. That said I have always used the one piece aluminium type with no problems.
Tightening torque is 23ft.lbs or 31Nm in new money.
Sorry about the attachments, twas my first attempt!

[johnnyboy]

Thanks for the info guys. Most helpful.


FYI, I have decided to go with the gasket.




Diverting a bit, what was the story with the "air pump"?


The holes are blanked with bolts on the old manifold, presumably when I had the emissions stuff taken off in 1980 before I shipped it over, but I have always wondered how it worked.


John

[johnnyboy]

Oh, and another thing....


Is there any point in my trying to polish up the inside of the ports in new manifold with a Dremel to improve gas flow?


Back in the day we were always polishing up heads and exhausts on fords and mini's, but I am not sure it is worth it on a CJ7?

[eastryjeep]

CJs dont really like polished inlet ports, the cast surface helps keep the fuel in the low speed air flow.
You can match the manifold size to inside of the head and ensure everything lines up nicely without the gasket poking into the airflow and go wild on the exhaust, making sure there are no steps or sudden constrictions in the gas flow, but as you still have that diverter flap in there I wouldnt fret too much.
Just concentrate on a smooth transition between the head and manifolds and call it job well done!
I recommend you pinch up the two manifolds then mount them to the head temporarily to ensure BOTH manifolds are true to the head, and only then tighten the 4 bolts that hold them toghther. Then install the manifold gasket and torque it up, new bolts are always a good idea as the previous ones may have some embrittlement, and if they fail as you are finishing the job you'll be right narked! I like to use grade 10.2 cap screws as they wont strip their threads, dont suffer from rust too much and an allen key is ideal for getting into some of the tight spots.

[Dave69]

porting on a 4.2 lump  the engine is a torque machine not a power house

[johnnyboy]

I like to use grade 10.2 cap screws as they wont strip their threads, dont suffer from rust too much and an allen key is ideal for getting into some of the tight spots.

10.2 implies Metric? - have you retapped the head?


Also, what do you use for washers? Standard CJ or something more ordinary?

[eastryjeep]

10.2 is the steel grade, nothing to do with the threads.
You can come unstuck using soft mild steel bolts (Homebase, B&Q type quality) but I'd use something better, at least a grade 8.8 engineering quality, but preferably a 10.2 as that is where your high tensile steels start, and quite often they are often less prone to rust. Just dont use stainless steel in this hot area as I think you may end up with galvanic corrosion after a while, see link if you're really interested.
http://www.engineersedge.com/galvanic_capatability.htm

As for washers Ive still got some of my originals but have also made up some specials out of 3mm sheet steel where I wanted something with a bit of shape to it.

[Jonny Jeep]

Metric are classed - Class 8.8, 10.9, 12.9 (I've never seen or heard of 10.2)
UN bolts are graded - the equivalents to the above classes are Grade 5, 8, 10.

[eastryjeep]

Dammit, I always knew the recession would get me, or maybe it's just old age.

You know, of all the things I've lost, I think I miss my mind the most!

Just use high tensile bolts and common sense and all should go well.

[johnnyboy]

The sad remains of your mind gave a link to "galvanic corrosion".

The sad remains of my mind have followed the link and:

Am I reading the table right to say that:
The cast iron head is "Iron, wrought, grey or malleable, plain carbon and low alloy steels"   and is rated .85  while...
the SS bolt will be either "18% Chromium type corrosion resistant steels" and rated at .50 (or possibly chromium plated, tin plated , 12% chromium type corrosion resistant steels", rated at .60, but I would not have thought so...)


So .85 minus -50 equals .35, which is greater than .15 (or even .25) therefore don't do it?


John

[Bubba]

i always used a gasket but much preferred the later two part manifold

[eastryjeep]

So .85 minus -50 equals .35, which is greater than .15 (or even .25) therefore don't do it?

Yup, you got it in one, and if I'm right the stainless will corrode the threads in the head and if you were to use SS washers they would chomp the manifolds too.

Therefore carbon steel bolts with high temp paint are the way to go.

[johnnyboy]

Cheers. Will do. Thanks for the help.