No Reverse

[pearson1973]

My Atomic A4 reverse failed to move the sailboat backwards yesterday for the first time and I am wondering whether I need to adjust the reverse clutch, however I noticed the drive shaft does rotate counter clockwise when the gearbox is in reverse which in my mind says to me the prop must be turning . Is it possible for the prop shaft to turn but slip when throttle is added due to incorrectly adjusted reverse clutch?
Or is it possible for a propeller to drive the boat forward just fine but become loose in reverse?

When I select reverse I can no longer feel the propeller engaging as I did before and the gear lever just moves smoothly to the full reverse position .

[Al Schober]

Fwd and reverse are separate mechanisms and separate adjustments.
If your reverse 'suddenly doesn't work', I suspect you've had a failure of the reverse actuating mechanism. You're going to have to take the lid off the transmission and have a look (engine OFF).
As you shift into reverse, the mechanism will pull a flat bar away from the engine block. This flat bar fits into a slot in a round bar - this round bar has a nut on one end and a roller (inside the slot) on the other end. The flat bar is tapered, and as you pull it, it tightens the round bar which engages reverse.
I suspect it won't tighten, and you won't find the roller - you may not even find the flat bar! But you know where they are - in the bottom of the transmission.
What happens is that reverse gets adjusted too tight, the pin holding the roller shears, the roller falls out, then you can't get into reverse at all.
This problem in not uncommon, and many A4 owners during an overhaul have had their transmission housings modified to have a 3/4" pipe plug installed (the Kaminsky modification) to facilitate removal and repair of the round bar. If your engine has a 3/4" pipe plug in the transmission housing (carb side) you're in luck.
Let us know what you find. Take off the transmission cover and take some photos (we like photos). We'll walk you through this.

[pearson1973]

Thanks

I will take some pictures this weekend, however I removed the top plate yesterday ( before seeing your reply- thank you) and I checked the lever was at full travel with the gear select cable disconnected. I then check the reverse clutch was tightening and was unable to turn the propeller shaft when the gear lever was backwards( in reverse position). I then put the gear lever in neutral and I could clearly see the clutch had released and I was able to turn the propeller shaft again. So I followed the instructions on the site and tightened the reverse get adjuster on notch and put everything back together but the problem still remains. I can see the boat does start to move backwards when reverse is engaged but very slowly and with very weak motion. Even with high RPM it hardly seems to move backwards. When in forward gear I can feel the propeller engaging and I also feel the motion of the boat surging forward so there is a big difference. I used to be able to put the boat in reverse when moving forward and it would stop the forward motion, now it just continues going forward when i have reverse engaged and with fairly high RPM. The propeller shaft is turning so knowing that the propeller shaft is turning in reverse does that still mean I have a broken reverse selector as you suggested ?
Someone suggested the propeller could be fouled but can that stop a boat in reverse and allow it to travel forward just fine?

[JOHN COOKSON]

$.02 worth here.
What kind of oil and additives do you use? Or more to the point have you recently chained the oil\additives?

TRUE GRIT

[Dave Neptune]

Are you "holding" the shift lever in reverse with some pressure? A must in reverse when applying power.

Dave Neptune

[pearson1973]

$.02 worth here.
What kind of oil and additives do you use? Or more to the point have you recently chained the oil\additives?

TRUE GRIT

I have not changed the oil as I just purchased the boat two months ago, but from your question I will do an oil change and see if it helps. Thank you

[pearson1973]

Dave N
Yes I am holding the shift down. Thank you

[Jim Booth]

Can you look under the boat and see the prop? Seems pretty strange that the shaft is turning both directions but the prop thrust isn't following along. There are only a couple parts: prop, prop shaft key. I'm voting for something fouling the prop.

[JOHN COOKSON]

I have not changed the oil as I just purchased the boat two months ago, but from your question I will do an oil change and see if it helps. Thank you

Some additives will reduce the friction between the clutch plates and allow them to slip. As I recall slick 50 is one of them. Changing the oil will probably not help the reverse problem in your case since an oil change did not precede the reverse problem.
That said it would be a good idea to change the oil on the new to you engine when it's oil change history is unknown.

TRUE GRIT

[sastanley]

P73,
First - welcome to the forum!

Where are you? Here in the Chesapeake we've had an unusually heavy year of fouling. A neighbor that had not been to his boat in a while thought reverse was 'broken' on his boat, but realized later (an after a haulout) that the prop was just so fouled he couldn't get any thrust in reverse compared to what he expected.

(The following assumes a direct drive A-4)
Keep in mind that there is also a reduction in prop speed in reverse, like ~1.4:1, so you gotta get the revs up on the motor several hundred more RPM to get the prop to spin in reverse at the same speed it would normally be going in forward for that given engine speed. In forward, there is a distinct engagement..we call it the "detent" around here that actively locks the prop shaft to the engine's output shaft for a 1:1 ratio in forward. A 'brake band' does some magic with the gearset to allow it to spin in reverse, but there is no 'engagement', this is a friction only action, and the shift lever needs to have pressure retained on it to keep the engine in reverse, as Dave Neptune mentioned earlier. Is the shift lever on the cockpit bulkhead or on a steering pedestal?

One more thought to consider is (most) prop blades are more efficient in the forward direction, further exacerbating lack of thrust in reverse.

And a question....Has anything changed from when reverse worked correctly?

[pearson1973]

Thanks to everyone for your help. Nothing has changed, the last time I docked I put her into reverse to stop and the thrust was strong and what I had come to expect. I came back two days later to go for a sail and tried to reverse out and she decided otherwise! Just RPM and only the slightest movement backwards. The gear lever is on the port side seat with the engine starter and gauges.
I am in the Hudson river NY and will be taking a dive this weekend to see if the prop is fouled. Not looking forward to jumping in that water but hey I am now out of options

I will update everyone over the weekend and thanks again to all of you as I have a lot to learn.

[ndutton]

Let's make absolutely sure the cable jacket is securely mounted at both ends.

[pearson1973]

Thanks will do. I checked the cable was secure down in the engine compartment but did not check the other end that connects to the selector handle.

[Marty Levenson]

camera

Or borrow an underwater camera?

[zellerj]

is prop on a tapered shaft

Forward rotation pushes prop against the taper, and reverse loosens the prop so the shaft spins without the prop spinning.

Just a guess.