single port intake leak and related questions

[StefansBus]

Hi there,

After fitting a new stock exhaust on which the preheat plumbing didn't quite line up requiring some brute force during install, I now have an intake leak around the right cylinder head intake area. I have the crush metal ring gaskets and will attempt the fix in the next few days. Hoping to be able to replace the gasket without having to remove too much stuff. I also hope I don't have a cracked intake manifold.

Would it not be a good idea to modify the pre-heat pipes on the intake manifold by making a part of it on each side from flexible metal tubing? This should make installing exhausts very easy in the future, at least as far as the pre-heat is concerned.

Also, If I do have a cracked intake manifold, I was considering ordering the aftermarket three piece manifold which is similar to those used on the dual port engines. In fact the center section is a universal part for 30, 31 and 34 carbs and the end pieces are sold as either SP or DP. The thing is: The internal diameter of these is apparently larger than the stock single port manifold. Will this be detrimental to torque? Of course the intake port and valves in the heads remain unchanged as does the stock 30 PICT 2 carb. So will the larger diameter between carb and heads make any difference at all (good or bad)? This is the kind of part I'm talking about: https://www.csp-shop.com/en/?func=detailcall&artnr=12379a

Cheers

Stefan

 

[atafonso]

If you chop the tubes and install flexi pipes you run the risk of the manifold coming loose on the heads and/or having vaccum leaks. It's quite a heavy assembly for being suported only by two 6mm nuts on each side. The pipes also perform the function of making the assembly sturdy. If you compare with the dual port manifold, you can see the DP has a support in the middle attached to the case.
The difference in torque will exist due to lower air velocity on the larger tubes, but IMHO i think it will not be really noticeable.
Abel

 

[StefansBus]

Thanks Abel. I appreciate the input. Will report back once I have had time to work on this. If in the meantime anyone else here has any thoughts, please let's hear them. Cheers. Stefan

 

[Happystamps]

I'd save modifications for when you really need them. You've got an issue with your existing part, sure, but I'd simply replace any broken parts with good quality standard originals since they're cheap, effective, and not detrimental to vehicle value. Modifications should be for functional improvements.
I would suggest that if you wanted to make a good job of it, your best bet would be to adjust the exhaust to fit properly so that it doesn't pull the inlet manifold out of position. Might require cutting and welding it but shouldn't be an insurmountable problem, and it'll reduce stress on the exhaust too, so hopefully it'll last a bit longer.
Flexible exhaust tubing isn't capable of withstanding the temperatures that the area in question is subjected to, and if it leaks it leaks into the cabin heater air, so I'd stay away from that. And the split single port manifold might make lining up the ports a little simpler, but it introduces two new (4 if you include the brazed pre-heat pipes) potential leaks, it will effect torque (probably not by much, but still) and it's likely to be as well made as most new parts, which is to say stay away if at all possible.

 

[StefansBus]

Hi Happystamps,

Thank you for your valuable input. Last Friday I did remove the intake manifold and found it cracked on the right hand side where the pipe goes into the flange that connects to the head. I had it repaired and re-installed it. To move the tension I mentioned I did cut the right side of the the pre-heat pipe and installed a short piece of silicone tube. The right side is the "cold side" as the pre-heat air runs from left to right. Even after reaching operating temperature the right side can still be touched (barely), so the silicone should easily withstand the temperatures. I did not have to cut the left, hot side which is good as the entire manifold installation remains very rigid that way. By the way, the manifold in question is a reproduction part so it's not like I cut up a good OEM part. So far so good. If anyone is interested I can post some pictures these days.

I found that unsurprisingly the nuts for the manifold needed retorquing after the first couple of heat cycles. I hope they stay tight now. A first leak test with brake clean was successful.

Cheers

Stefan