1969 Chris Craft Roamer 46 Refit: Cummins Engine Install – Shaft Alignment and Front Engine Mount

I’m getting closer to having the starboard engine and gear finally aligned with the prop shaft coupler. But even with the locknut removed from the front vibration isolator and the adjuster nut completely bottomed out, I still have a 0.005″ gap between the couplers on the bottom. So the engine has to drop even lower at the front, which means the front engine mount needs modifying.

Cut off the original engine mount landing pads

Cut off the original engine mount landing pads

Weld in a 3/4" spacer and new landing pad

Weld in a 3/4″ spacer and new landing pad (the vibration isolator is installed upside-down)

With the 3/4″ spacer welded on top of the remainder of the 3/8″ landing pad that was still attached to the mount, the bottom of the new landing pad  is 1-1/8″ higher than the original. That should give me plenty of room to reinstall the vibration isolator locknut and still have lots of adjustment to lower the front of the engine.

Ready for paint

Ready for paint

Reconfigured engine mount looks good

Reconfigured engine mount looks good

Vibration isolators land in the right spot and the locknuts are installed

Vibration isolators land in the right spot and the locknuts are installed

When I lowered the front of the engine to align the prop shaft and gear couplers, it became obvious that something was hanging up. The rear of the engine went up as the front went down!

Need more material removed from the transverse frame under the oil pan

Need more material removed from the transverse frame under the oil pan

After trimming off another 1/4″ of material from the top of the frame I now have all the clearance I need to get the couplers aligned. But first, I need to center the prop shaft in the log and lock it down.

A hole saw and some scrap lumber maintain shaft position

A hole saw and some scrap lumber make a jig that maintains shaft position

Clamps keep everything locked down

Clamps keep everything locked down

Aluminum scrap wedge from the stringer I trimmed works as a gauge

Aluminum scrap wedge from the transverse frame I trimmed works as a gauge

Align the shaft in the log

Insert the gauge…need to raise the shaft so the gauge goes in to the mark

I tried using a dial caliper to align the shaft, but it was a real pain. The tapered gauge approach worked much better.

Right to the line on top

Right to the line on the top left

To the line on the bottom

Close to the line on the top-right…split the difference by moving the shaft left just a touch

Right to the line...the shaft is centered in the log

Right to the line…the shaft is centered in the log

Couplers line up longitudinally

Couplers don’t quite line up longitudinally…the rear vibration isolators need to drop a bit

Perfect fit...zero gap at the couplers

Nearly perfect fit.

There’s a 0.003″ gap on the right side of the coupler, but that’s well within tolerance for the DriveSaver. I still have to drill the holes for the vibration isolator bolts and then use the gantry to lift the engine out of the way so I can coat all of the bare aluminum with Devoe 235 epoxy. When I put the engine back in place, I’ll close up that gap. The hard work on this starboard engine install is just about a wrap. It’ll be much easier doing the port side now that I know what to do.

Next up on our 1969 Chris Craft Roamer 46 Refit: Cummins Engine Install — Coating the Stringers & Final Fit

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2 comments on “1969 Chris Craft Roamer 46 Refit: Cummins Engine Install – Shaft Alignment and Front Engine Mount

  1. kent says:

    You could just lock down the top adjusting mount nut by double nutting it– Maybe a squash nut if you don’t have room for a lock nut on top..

    • 1969roamer46 says:

      The fundamental problem was that the engine mount didn’t fit the boat and had to be modified. With that done, all of the other problems got resolved. I’m not sure what purpose a locknut on top of the top nut would serve.
      Cheers
      Q

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