1970 chrysler 120hp no reverse

Everything works great in neutral and forward, I simply have no reverse. There is no grinding sound or anything like that. When I move the throttle into the reverse position, the linkage moves. Any ideas out there?

Re: 1970 chrysler 120hp no reverse

When in reverse is the prop in neutral? Have someone slowly advance the shifter towards forward. While they are doing that slowly turn the prop with your finger(In neutral it should spin freely in both directions) As soon as the prop locks have the person shifting stop and see how much more forward room you have on the shifter. I dont know about yours but the older chryslers had an adjustment nut in the motor leg (hidden by covers) that is about 2 inches long and has reverse threads on one side and regular threads on the other. By adjusting this you might be able to center the adjustment better in order to reach reverse. Chryslers can be real touchy on this and it is always better to have a good forward gear then a reverse gear.

Re: 1970 chrysler 120hp no reverse

Like eurolarva said, you need to check to see if you have equal throw in both directions. It is possible to bias the shift so far in either direction that it will not go into the other gear. First you need to check the cable and be sure it is adjusted properly in the clamp at the engine. Next, the lower shift rod goes through the mid leg just below the shroud. Mark it with a pencil when in neutral, them mark in forward and reverse. The marks should be equally spaced. Look under the lower carb to find the shift plate/neutral interlock. The upper shift rod goes through this plate and is held by two locking nuts--sometimes 1/2, sometimes 9/16. Adjusting these nuts will shift the upper shift rod upwards or downwards to bias the throw.

Also, disconnect the lower shift rod cotter and pin (just below the shroud) and be sure the lower rod is screwed all the way in (clockwise) then backed out just enough to line up with the holes in the connector between it and the upper shift rod.

All the big Chryslers and Forces used the same shift arrangement up until the early 90s. They changed the lower unit to a one piece but the internals are the same for shift.

Re: 1970 chrysler 120hp no reverse

Thanks to both of you. I'll check these things out and post the outcome. Last question. What is the gap spacing for spark plugs on this engine? Model number 1207HB. Thanks again.

Re: 1970 chrysler 120hp no reverse

I just checked all that you both said. All is good. Here is a strange one, to me anyhow. I just ran the motor out of water (I have the proper equipment to do so), so I could watch the prop. It, the prop, actually turns the opposite way as when in forward, and just as fast. So why doesn't the boat go in reverse when its in the water? The prop is old but appears in good shape. Is it possible that there could be some kind of problem with the prop? I'm really confused now that I have seen the thing run good and fast in both directions.

I have also reset the gap on the spark plugs to 40, they were at 28.
The motor doesn't stall out now and also starts much easier. Is 40 correct?

Re: 1970 chrysler 120hp no reverse

According to my clymer manual three cylinder motors ran an L20V plug which should be a gapless plug. For plugs that are adjustable I would go with .030 inch

The torque inside your lower unit may be causing the prop to spin in the reverse direction. The clutch dogs may be kissing the reverse gear which will allow it to spin but not with enough force to move the boat. I would move the adjustment a hair toward the reverse if it is possible till you loose forward then find a happy medium.

Re: 1970 chrysler 120hp no reverse

Understand that on all lower units, the pinion gear constantly turns both the forward gear and the reverse gear at the same time in opposite directions. That 2 piece lower unit has a bronze bushing inside the reverse gear hub, riding on the shaft. The shaft itself carries the gear. It is not uncommon for there to be enough drag on that bushing to turn the shaft with no load on the prop. I think you will find that in the water, the prop will turn very much slower, if at all. The newer 1 piece lower units do not have that bushing but instead, have a gap between the gear hub and the shaft. The gear is carried in two separate bearings--not the shaft. They usually don't spin the prop, and if they do it at all, it is very much slower.

Now, I don't remember my engine years well, but if you have a points ignition with what looks like a regular auto coil sitting up near the top of the engine on the bypass side, then you use regular plugs. That ignition only puts out about 10,000 volts. .040 with that ignition will be a bit wide --as you put age on the plugs they may tend to misfire. .030 might be better, but go with whatever works for you. If you have the Motorola Magna Power ignition--It will be a large, black, finned aluminum box-- then you use L20V plugs and there is no gap to set. These are surface gap plugs and need the 20-30,000 volts the Magna Power puts out. Champion changed the numbering system and these plugs now have a three digit number. I forget what it is.