As we completed our previous attempt at changing the engine mounts, we still had two major issues. The first was the front mount material seemed thicker than what originally was on the boat, and the second issue was we couldn’t jack the engine up far enough to remove the old rear mounts. We spoke with the general manager of Poly Flex, the engine mount manufacturer, and he immediately proposed good solutions to both.
When our engine left the engine distributor in Seattle, it had the standard Poly Flex mounts as shown in the first picture below. But when the boat was delivered, the mounts were far lower profile, as shown in the second picture below. What must have happened was the boat yard had trouble getting the engine low enough, and replaced the normal Poly Flex mounts with the low-profile variant. Poly Flex said “no problem” and air-freighted the correct low-profile mount inserts to us.
We also described the problem of not being able to easily lift the engine high enough to get the old rear mounts out and the new ones in. The challenge is that the engine won’t lift high enough at the rear, without disconnecting the prop shaft and possibly the exhaust, to remove the old mounts. Again, we got the same “no problem” from the Poly Flex general manager. He said we could just cut the old studs off and he’d send us a mount package with a removable central stud, and those parts went out in the same shipment. That’s impressive service.
The parts arrived quickly and, since we were planning to be in Southwest Harbor, Maine for a few days, we got going on “take two” of changing the engine mounts. The front ones came off quickly using the same approach as before with the hydraulic jack. We lifted each front corner of the engine, removed the old mounts, disassembled them, swapped out the mount insert, and then reinstalled the mount in under thirty minutes total for both mounts.
On the rear mounts, the first challenge we ran into was the under-engine clearance is so tight that we couldn’t get the hydraulic bottle jack under the rear. We contemplated lifting the engine using an engine hoist attached the the deck above, but this looked challenging.
The solution was surprisingly simple. Rather than lift the engine, we left the engine in place and lowered the rear mount to be changed such that it was no longer bearing any weight. All the engine weight was supported by the other three mounts. This worked super well and unloaded the mount to be changed in seconds. Then we cut off the stud using a large Milwaukee cut-off saw and slid out the old mounts. It felt crazy to be cutting off the engine mount, but it made for an easier change. And with the new removable-stud mount hardware, the mount inserts can now be changed in minutes rather than hours.
This job took less then five minutes. But, we ran into another problem. In the picture immediately above, looking at the bottom of the engine mount you can see two large nut and spacers that need to come off to replace the mount insert. They appear to have been welded in place, excessive Loctite had been applied, or potentially they had rusted in place, although there’s no evidence of water or rust. It’s hard to know the exact problem, but we applied hundreds of foot-pounds of torque and they simply were not coming off.
The solution to this one was surprisingly simple as well: use an impact wrench with one of our new jumbo sockets to undo them, knowing they will eventually either unscrew or the stud will shear off. If they unscrew, great. If not, it doesn’t really matter since we’re replacing the mount bridge which includes these studs. All four broke rather than unscrewing, so we were right that they were not coming off. But the good news is that it didn’t take long. The impact wrench delivers progressively more force trying to unscrew the bolt until each eventually sheared.
The rear mounts weren’t in quite as bad shape as the front mounts, but definitely in need of replacement. They had already started to disintegrate and drop chunks.
The easy part was taking the mount bases and the new parts and reassembling the mount package and reinstalling it. With the new configuration we could change the mounts in under an hour and then only have to align the engines. Future jobs will be easy. But, we don’t expect to have to replace these mounts for another 8,000 hours. And since Poly Flex has made some materials improvements over the last seven years, it won’t surprise us a bit if these new mounts last even longer.
Once the mounts were replaced, it was time to align the engine and transmission assembly. This is considered by many to be a difficult job but it’s really not that hard. It does require accurate measurement and patience, but it’s not difficult.
The first step of engine alignment is to loosen off the large 24mm wrench sized bolts that attach the flange on the end of the prop shaft to the flange on the transmission output shaft. Once this has been loosened up, we did the alignment in two phases. Phase one is to adjust the aft end of the engine such that the prop shaft is central in the prop shaft opening. For this phase, we just returned the engine to exactly where it was when the boat was delivered from the yard measured using calipers. The rear mount adjustment procedure is similar to the front mount adjustment procedure described below.
At this point, phase one is complete. The prop shaft is central in the shaft tunnel when mated up to the transmission flange, but the engine and transmission assembly is not in line with the prop shaft. Phase two is getting the engine and transmission assembly exactly inline with the prop shaft. And, when we say exactly, it needs to be within 0.001″ per inch of shaft diameter. That’s within 0.00225″ for our 2 1/4-inch prop shaft. We prefer to be somewhat more precise so aimed to get as close as we possibly could to 0.001″ of run out.
The actual alignment measurement is made using feeler gauges between the transmission output shaft flange and the prop shaft flange. We measured at each of four quadrants ninety degrees apart. The quadrant with the most space is the direction the engine needs to move. If the bottom quadrant is largest, then the front of the engine needs to go down or the rear of the engine up. These fine adjustments we did only by moving the front mounts up and down and for these we’re only turning the mount stud nuts by a fraction of a turn. Initially we were turning 1/4 turn but, as it got close to correct, we were adjusting by as little as a 1/2 a nut flat which is only 1/12 of a turn.
In the example above, when the bottom quadrant has the most clearance, we need to move the front of the engine down. If the top had the most clearance, we would do the opposite. Up and down is fairly easy. But, if the left or right quadrant had the most clearance, the engine would need to be slide slightly sideways which is a lot less precise that adjusting screws on a mount stud. We loosened the bolts holding the engine mounts to the bulkhead and and used a pry bar to move the engine in the direction we wanted to rotate it.
If the left quadrant facing the transmission showed the largest gap, then the engine and transmission needs to rotate very slightly with the front moving left and the rear of the engine moving right. It turns out it’s actually fairly easy to move the 2,000 lb engine/transmission assembly using a pry bar once the mounts are all loose. What’s hard is keeping the motion small enough. Even tiny shifts have a huge impact on shaft alignment. Small amounts of force do nothing and then just a bit more force moves the assembly too much. The trick is to listen carefully and apply the smallest amount necessary such that you can hear slight clunk as the assembly just slightly shifts.
Once it shifted in the desired direction, we bolted everything back down, turned the shaft a couple of times by hand and remeasured the gap at the four quadrants. Again, we found the largest and repeated the process. Eventually, the process converged.
We chose to keep adjusting until the gaps only differed by one thousandth of an inch (0.001″). That’s a bit more precise than absolutely required and, if the prop shaft is not absolutely straight, it won’t even be possible. Once the four clearances measured sufficiently close to each other, we re-torqued the bolts holding the transmission flange to the prop shaft flange and the job was done.
We’re slow at this process and it’ll take us around three hours but it’s not a complex nor difficult process. Having changed parts to allow the engine mounts to be serviced more easily, we could now change all four mounts and align the engine in under four hours.
Dirona now is running as smoothly as we can ever remember, possibly better than since new.