Call it "Murph'y Law" or BumLuck or any other saying regarding mechanical difficulties, but recently I have encountered not one, but TWO problems with V4 Ford/Saab cylinder heads for high performance engines.
Take a look at my exploded view drawing above. Note the exhaust valve hard valve SEAT. Today's unleaded fuel will cause early exhaust valve failure without hardened exhaust valves and valve seats. So far so good...
I install larger diameter valves and of course larger exhaust valve hard seats. I've rebuilt dozens of V4 engines with these big valve cylinder heads, with no problems. Still, so far so good.
A couple of weeks ago, my machinist found a "pocket"--a casting flaw--in a cylinder head, where he had machined the head to accept a larger diameter hard valve seat. Result? the head was instant junk. Kauput.
This week, another bad cylinder head....
This head [shown above, before installation] was on an engine installed in a customer's Sonett III, and I discovered--during the 500 mile drive-off--that the right side exhaust pipe was putting out WHITE smoke. Not a lot at first, but it got worse as the end of the 500 miles approached, it was obvious that it was not going to get better. A compression check showed equal compression in all four cylinders and a vacuum gauge check showed steady--and correct--manifold vacuum for this elevation [1350 feet above sea level].
I retorque the cylinder heads and intake manifold to factory spec's 3 times during the 500 mile drive-off runs. The drive-off period allow correction of [usually] small glitches that always appear--in any number of areas--when a car has undergone a full restoration.
I removed the carburetor, intake manifold and right hand cylinder head. Close examination of the head and intake manifold gaskets showed no damage to either, but it was clear that there was a big problem in the forward [No. 1] combustion chamber. The exhaust valve was VERY white, indicating a lot of heat, and there was a bit of fluid around the intake valve. I had certainly found the area of the problem.
NOTE: White smoke in the exhaust means coolant is being sucked into the combustion chamber. Blue smoke means OIL is being sucked into the combustion chamber, either past the valve guides or past the piston rings, or both. Black smoke means the engine carburetion is WAY too RICH. Smoke of ANY kind from the exhaust means further investigation is needed, and soon.
The reason for the problem was a crack in the cylinder head at the intake valve seat, where apparently the machining of the head to accept a larger valve had either come close to another pocket in the head casting, or was simply because after machining, the wall thickness between the seat area and the water jacket was thin enough that it cracked with the heat of combustion. NOTE: both head were magnefluxed after machining and showed NO cracks.
Well...shit happens. Particularly when you are trying to get a quart's worth of work out of, essentially, a pint pot. My modified V4 engines produce 115 to 140 horsepower, depending on how thick the customer's wallet is, but the more power you produce
the more possible are the unexpected results. Usually....everything is just fine and the customer gets a really nice engine that will be as reliable as a factory engine.
But sometimes...shit happens. That's why we ALWAYS do a 500 mile drive-off before we deliver a restored Saab to it's owner, and why we insist that the owner of one of our reconditioned V4 engines follow the instructions we include with the engine when we ship it to him.
City Car Design
7 years ago