Alignment of Twins

[BobP]

Earlier in April about a zillion subjects ago, there was a thread on tht about aligning twins, how to.
They get wild at THT. Guys talking about running one engine free. Woa!
I guess I can drive my FWD car with one tie rod disconnected, probably steer fine but don't think I'll get the same steering performance as with both wheels steering.

I figured out a way to do it two years ago when I rigged my own, didn't see anyone suggest it at THT, close but not the same, so for the DIYers out there ONLY - may save you some time and bucks.

My dealer said: for engines on transom, toe in, for engines on bracket tow out, then he gave me a spec, which I forgot in a second since there was no reference to where to measure it. The dealer must have a marked tool for this task.

I figured if I could get them parrallel, then I'd just add a noticable toe out, and be done.

Nothing down there but curved surfaces, except the prop shafts, not long enough though, so I used the props. The trailing edge of the prop hub is purpendicular to the shaft varying only slightly around the circumference.

I positioned a metal straight edge across the two props half way up, and worked the tie rod adjuster and engines to get them even, spin the prop 1 turn to average out the slight hub tolerance. Disconnected the engine from the steering (I have one cylinder) so I coud jog the engines at the stern, otherwise need a helper at the bridge.

With even contact averaged at 4 points on the straight edge, the engines were parrallel to each other and the ship's centerline. Now I took 1/2 turn of adjuster at a time to just break into a toe out, didn't take much. That's it. There is some play in the tie rod, I averaged that out too by pulling and pushing apart the engines and taking the average.

Can't say if performance matters or doesn't how they are aligned with respect to toe, don't have the time to experiment.

Have fun.

 

[Boats Rock]

I have a 98 272 Sailfish and spoke to the factory last week about this very subject. The guy told me parallel no toe. The easiest way to check them is to measure the center of the steering arm bolts and then measure the center to center of the prop shafts. I taped a piece of heavy wire to the end of a tape measure and put that end in the center of the port engine prop and held it and slide another piece of wire to the other shaft and got my measurement.

 

[Twisted28]

With the printed page in hand of the above two posts, I aligned my twins last night and found a few things to watch for. I also added a step which worked out perfect for me.

I needed to replace the tie rod ball joints so after replacing the first one and locking it in place, I undid the second one. My motors were way out of alignment and the following procedure made easy work of it.

With the one tie rod disconnected, I found when you move one motor by pushing on it, the other motor moves in the opposite direction due to the hydraulic fluid.

Since I was working alone and had no one to move the steering wheel, I simply loosened the bleed screws on one of the steering cylinders.
Then by pushing against one motor while bracing the other motor I was able to get them to adjust by squeezing out the fluid from the bleed screws. Just put a rag under the bleed screws to catch the oil.

The measurement I used was a two step process.
First I measured down by the prop shaft housing in the front of the motor opposite the prop where the housing goes from the bulb shape to a point / edge which is the Center of the motor. Eyeball a common distance above the shaft bump as the skeg may be bent so I did not want to use that.

Then the "check measurement was taken at the edge of the bolt hole for the anode above the prop just make sure to measure from left side of the bolt hole to left side of bolt hole or visa-versa. It is much more accurate than trying to guess the center and provides the same measurement.
When these two distances are the same, (the forward edge and bolt hole edge) I then adjusted the tie bar into position until the bolt fell right into place.

This I feel is very accurate due to the fact the axis the motor pivots between the two measurement points taken.

When I put a straight edge across the edge of the props, PERFECT!

Don't forget to tighten the bleed screws.

 

[BobP]

Good points.

You may have to bleed the hydraulic system if any air entered it when teh screw was open when you were not pushing in a direction to force fluid out.

 

[BobP]

By the way if anyone is measuring between two point say of the shafts, no need to get exact center, just measure from the same point on one shaft to the same point on the other. For shafts, you can use the leading edge of the shaft to leading edge. Same measurements come of it.

And once you get it to zero toe, no matter the method, you can experiment with toe in or toe out, just keep a written log of how many turns or part turns of the tie rod adjuster and in what directioin, so that you can always return to zero toe without doing alignment again.

Can't help the guys with the liquid tie bars!

 

[Workdog]

Earlier in April about a zillion subjects ago, there was a thread on tht about aligning twins, how to. They get wild at THT. Guys talking about running one engine free. Woa! I guess I can drive my FWD car with one tie rod disconnected, probably steer fine but don't think I'll get the same steering performance as with both wheels steering... My dealer said: for engines on transom, toe in, for engines on bracket tow out... Can't say if performance matters or doesn't how they are aligned with respect to toe, don't have the time to experiment.

Ironically, I just aligned my engines this past Sunday by disconnecting the tiebar while running. I had heard the above technique for several years and thought, what the hell. I had set my engines at zero toe-in when I hung em a couple years ago, but wanted to see where they wanted to run at. I have a 1989 230 Gulfstream (open transom) with twin 2003 Merc 150 EFIs. I had a driver put the boat on plane at my normal cruise speed of 4200 rpm. I then disconnected the tie bar and readjusted to the new position. While the tiebar was disconnected, the disconnected engine was rock steady. I couldn't push it more than an inch from where it wanted to run. The end result was, the engines like 15/16ths of an inch toe-in on my boat at that speed.

Workdog

 

[BobP]

at what point are you measuring the 15/16ths of an inch?

And do you have engines on transom or bracket?

 

[Workdog]

Bob,
Engines are mounted on the transom.The center of the bullets on the leading edge of the lower units are 15/16" closer than the centers of the prop shafts on the back of the motors.

Workdog

 

[BobP]

Thanks, that's a lot of toe in, and considering another member posted his dealer advising to run with zero toe.

 

[seabob4]

1/2" toe-in. It's worked for 15 years. 27" engine centers, 27 1/2" at the prop shafts. Forces all the thrust of both motors towards the center of the boat, but doesn't scrub off spped because of excessive drag. Each motor is only 1/4" out of true to the hull.