This note is sent as a special welcome to all of the new folks that have recently joined our fraternity and to elaborate a bit on their most reoccurring “FAQ of the week”. Paraphrasing just a bit, these questions boiled down to: What did the inside of my water jacket side plate look like originally (early model folks), how important is the diverter cap on the inside of the water jacket side plate (late model folks), and how do we get the side plate off when the bolts are extremely rusty (early and late model issue)?
HISTORICAL PERSPECTIVE: Universal apparently recognized that both early and late model engines with raw water cooling needed some kind of mechanism to spread out the inflow of cold raw water to avoid uneven cooling (and heating).
Early model engines have rather thick cast iron side plates with channels extending through the plates (fore and aft). These channels feed cooling water through three small holes that direct incoming water from the pump quite evenly into the block with respect to fore and aft distribution.
In the top left photo, (provided by Tim Guy), you can see from the left-hand hole, the holes started out being approximately 1/4″ in diameter. The two holes on each end directed water up slightly, and the center hole directed water downward a bit. The center hole in this plate is somewhat enlarged by corrosion, and the hole to the far right is totally washed out. Obviously, in this condition, most of the incoming water will flow out of the large hole in the back of the plate, while hardly any will find its way out the front hole, and uneven cooling will result.
On late model engines, Universal changed to thinner steel plates with single “T” fittings in the center to receive incoming water. In order to achieve a better distribution of water inside the block, Universal installed “diverter caps” on the inside threads of the “T” fittings, to direct all incoming water aft, and slightly downward.
In the early to mid 70’s, the factory used standard galvanized 3/8″ pipe caps for diverter caps. Most of these caps have corroded away by this time, but in the process, they frequently left unidentifiable hunks of calcified material that in many cases almost totally blocked the flow of incoming water.
From the mid 70’s to the end of production, Universal used square brass diverter caps with 1/2″ holes to direct incoming water. In the center top photo, you can see the latest version of the factory diverter cap.
CURRENT SITUATION: In the case of late model engines, there is a fragile consensus among the current generation of experts with whom we network that the late model factory configuration which directed all incoming water aft might have been a bit of an overkill.
There is a concern that by directing all of the incoming cooling water aft, we tend to give the rear cylinder a “cold shower”. This cool condition may explain the fact that the number 4 cylinder on many engines tends to have sootier plugs than the other three.
In our own rebuilding operation, we provide a brass hex cap with a 3/8″ hole facing aft and slightly downward, plus a 1/4″ hole facing toward the manifold (as shown in the middle photo bottom). This second hole directs some of the incoming water through the space between the center two cylinders and over to the valve side of the engine, which is also the hottest side. We believe that this configuration provides a more even distribution of incoming raw water.
In the case of early model engines, whenever the inside of a water jacket side plate reaches a point where the holes are so enlarged that providing even distribution of flow coming into the block is impossible, it is best to simply install a late model side plate (top right photo). In the case of early model engines, the “T” fitting shown in this photo will need to be replaced with a 90 degree elbow.
It should be noted that in freshwater (or “enclosed loop”) systems (early or late model engines), the incoming water is already partially heated, so directing all incoming water aft does not result in this overcooling of the fourth cylinder. However, we still like to use the second hole in the diverter cap in enclosed systems, simply to get a little more flow over to the hottest side of the engine.
BROKEN SIDE PLATE BOLTS: In cases where side plates have not been removed for many years, a few of the original (8) 5/16″ retaining bolts may twist off while removing the side plate for service or replacement. Our preferred method of dealing with broken side plate bolts is to drill out the broken bolt(s), and dress up the threads in the block using a 5/16″ coarse tap.
We offer it as good news that in the latest engines (circa 1977 and later), Universal seems to have used side plate bolts that were softer, or otherwise more prone to becoming “sacrificial anodes” with respect to the block.
These bolts twist off very easily, leaving most of the bolt behind as nothing more than hard, calcified crud. Many folks mistake this condition as the bolts twisting off; when in fact, these deposits can be dug out rather easily by tapping and twisting a small screwdriver through the hole, and then dressing up the threads with a 5/16″ coarse-threaded tap.
By comparison, when healthy bolts twist off, they will have a well defined metal fracture surface, instead of the rounded corroded look of the bolts in the latest engines. Healthy bolts will also require more force to break off. The “sacrificial anode” bolts of the latest engines will practically fall off in your hands. In fact, we have some reports of these bolts actually falling out of their holes before ever seeing a wrench.
More good news – whenever water jacket side plate bolt holes in the block do end up being beyond repair, the new stud kits in our online catalog provide a convenient method of reinstalling side plates, particularly in the case of making repairs while the engine is installed in the boat.
SEPARATE BUT RELATED ISSUE: Early model side plates had an alternator supporting lug cast into the plate itself. In the case of late model side plates, the attaching lug for the alternator support arm is a separate small piece of angle iron that is held in place by one of the lower water jacket side plate retaining bolts.
Focusing all of the stress of supporting the alternator on a single bolt frequently results in the bolt working loose, and eventually wiping out the original threads in the block. The side plates shown in our online catalog (and as shown in the preceding link) have this lug welded to the plate, so that the stress of supporting the alternator is transferred to the entire plate for more strength, as was the case in early model engines.
If your late model side plate is otherwise in good condition, you could have a local welding shop weld the small piece of angle iron in place and achieve the same benefit.
IN SUMMARY: In most cases, unless the engine is already experiencing severe overheating, water jacket side plate maintenance is usually best left to a wintertime project. In this way, contingencies dealing with broken bolts can be dealt with, without eating up a lot of your sailing season.
If you are experiencing overheating and you suspect that the diverter cap in a late model engine may be blocked; you can unscrew the “T” fitting and let the diverter cap drop to the bottom of the cooling jacket, re-install the “T”, and then press on to enjoy the rest of your season. In the meantime, having all the incoming water directed toward the center of the block is not likely to create any ill effects for a relatively short period of time.