Excess Exhaust Noise

[Jim Kellett]

Have a 1930 town Sedan that I purchased in 2000. At that time I pulled the original engine out and had it redone including balancing, counter balanced crank, hardened valve seats, lightened flywheel, etc. This rebuilt engine had been stored in my garage since 2000 and was routinely turned over with a crank. I set the car up for touring with a B engine, exhaust header, downdraft carb and BF head. Also installed a synchronized transmission with overdrive. Last fall some 5,300 miles later I decided it was time to put the A engine back in the car and offer the B engine for sale.
The A head was replaced with the BF head and all visible aspects of the A engine looked good

Made the switch and then ran into a major medical problem which took up the winter and spring.
Got the engine running but have an interesting problem. The engine idles fine and sounds good at modest speeds but when I climb a hill or put a load on the engine it sounds as if it was running without a muffler. At first I thought it was the muffler clamp but found that to be OK. I ran compression on the engine and got 70# on 1, 75 #'s on 2 & 3, and 80# on 4.
This morning I decided to put the engine under load by setting the E. brake and putting it in gear (high) and letting the clutch engage enough to put a load on the engine. I removed the spark plug wire from each plug one at a time and tested each condition under load.
The excess exhaust noise was present in all cases except when plug wire 4 was removed. I conclude that the problem is associated with number 4 cylinder. Not sure what is going on here but suspect a valve may not be closing under load. Any thoughts or suggestions appreciated.

 

[BILL WILLIAMSON]

Jim, just a thought, if you're using the original distributor body, sometimes the conductor that goes to #4 will jump spark out of the top of the cap to #3 copper strap under a load. Load it and check it in the dark. Bill W.

 

[Mitch//pa]

Other than hearing an exhaust noise/// engine knock on hard load does it misfire at all when the noise is present? A stuck valve would usually give you a miss also
By stopping 4 from firing and no noise it could be a lower end knock and not an exhaust noise.

 

[pat in Santa Cruz]

#4 manifold exhaust port is notorious for sagging. If yours is just catching the gasket, it might be sealing sufficiently at idle or under a light load, but not sealing under a heavy load. You did not say what type of manifold gasket you have. The copper clad 31 style has enough meat to catch a sagging manifold fairly well, certainly better than the steel ones or the crummy composite ones that come with the engine kits.

 

[Jim Kellett]

Thanks for the responses. I think the problem is as Pat described with the gasket not sealing properly. It is one of those composite gaskets and the pictures show the carbon build up from the leak. Haven't replaced the gasket and tried it yet as I am suppose to be cleaning out the drier vent in the house. Just couldn't resist taking a look with the manifold off.
Will let you know final results after I replace the gasket. May have to have the manifolds resurfaced. Will check flatness also.
Thanks again

 

[steve s]

If sag is the problem, I don't believe that resurfacing will fix it. And, the location of your leak is consistent with sag. I can't tell from the photo, but maybe you can tell by inspection of the gasket if the manifold hole is off-center relative to the block hole.

I've only heard good things about the new manifolds that are available.

Steve

 

[Banky]

Hmmmm. So what is the best fix for this? Mine may be doing this, I thought I saw a similar scorch mark on mine. However, it was also leaking were the manifold meeds the exhaust pipe. I SHOWED IT, tightened it till it snapped in half! Not Sunday drive for me.

 

[steve s]

Hmmmm. So what is the best fix for this? Mine may be doing this, I thought I saw a similar scorch mark on mine. However, it was also leaking were the manifold meeds the exhaust pipe. I SHOWED IT, tightened it till it snapped in half! Not Sunday drive for me.

Nothing works as well as parts that fit, and nothing is as futile as trying to make do with parts that don't fit. If yours is warped off center, get a new manifold. The sagging happens when the weight of the exhaust system pulls on a manifold that's gotten red hot and soft from retarded timing--might that have ever happened in 80+ years?

The exhaust pipe leak is expected if you're using a cheap repro muffler--notoriously bad flange fit. Get a good new Aries muffler and clamp, and use a bead of muffler cement all around it. Use of an insert connector pipe narrows the flow path and invites the overheating problem.

I'm not clear on exactly what snapped in half, but it's a good idea when mounting the manifolds to leave them only loosely bolted together, so each manifold can find its own best fit to the block.


Steve