Join Date: May 2010
Location: Ancaster, Ontario
exhaust leak solution
Thought I would share a (possibly) temporary remedy born of frustration over an exhaust leak at the area in the intake manifold where the heating tubes are attached which run to the choke. The engine runs OK but my truck sounded like an old lump with that one cylinder exhaust puffing and leaking sound.
This seems to be a common problem, and I have not yet been able to find anyone who reproduces this tube assembly (I did find a guy in the US who was making them at one time but he does not do so any longer).
The situation is that there is a heat stove built into the intake manifold on older ('70's) Ford engines (351M and 400 ) which contains a c. 1" diameter coil of tubing which sits inside the manifold and is heated by exhaust gas which is running through the the intake manifold. Two tubes run from there to the choke. Frequently, these tubes rot out and/or the plate which holds the tubes and coil to the manifold develop exhaust leaks.
I finally went and bought a sheet of 1/8th" exhaust gasket material - Mr. Gasket part # 5960 (10"X10") or #5961 (5"X24") at Performance Improvements at a cost of $20.00 and made a gasket using the plate which holds the tubing to the manifold as a template (cut the heat tubes level with the top of the plate using a hacksaw if necessary). The gasket material can be cut with regular scissors, and the holes for the bolts can be drilled through the gasket material - put a piece of wood under the gasket when drilling to avoid distortion of the gasket and to keep the edges of the holes clean cut.
I then turned the plate upside down (exposing the coiled tubing which usually sits inside the intake) and reinstalled it using the gasket. The leak was gone but the coils were exposed, however this is not a problem because the coil almost invisible under the choke assembly.
The length of the coiled tube is approximately equal to the two tubes which used to run to the choke, so there is no more heat lost to the engine bay than previously (the gasket also cuts down the heat transfer). Also, the coil throws some heat under the choke, helping with warm up, although most of these engines have electric chokes and don't need heat to release the choke. I did place a length of vaccuum hose between the two ports on the choke assembly, joining them together.
If/when I find or make the replacement tubes I will replace them (and braze them to the plate) but if the engine continues to run well as is I may simply make a plate from 1/8th steel stock in the shape of the mounting plate and eliminate the exposed coils. In the interim, the truck runs completely quietly without any exhaust leaks.
BTW, access to the plate is easiest if the carb is removed (and socket is used), but the job can be done with the carb on the engine using a wrench).