79 35Hp Evin "slam" at WOT?

[HyperFox]

So as some may know, Ive acquired a boat motor and trailer from a friend of mine he described some problems he's had with the boat through an email.

First thing he mentioned was that the starter grinds when activated. I inspected the starter and noticed it was too far away from the flywheel. Simple adjustment really and I think I got that fixed up.

Other issues were wiring. A lot of it was cracked from age, so I replaced it all with fresh wiring. Fires on a boat are a sailors nightmare, right?

The third problem he mentioned is the one I'm stuck on. He claims while cruising at WOT, the engine "slams". He described it like a bunny hop. At less throttle the boat doesn't seem to have the issue.

Im not terribly sure how to approach this in the winter. I beleve perhaps the mounts on the outboard arent tight enough and as the boat skips, the engine flexes on the mount and might cause this. Or perhaps the starter gear pops back up and bogs out the engine as it hops across the water? Is there any quirk about these motors im missing?

 

[wavrider]

Re: 79 35Hp Evin "slam" at WOT?

It is possible that under load it is slipping in and out of gear. The "wham" sounds like it could be a clutch dog problem.

The advice I have read from others in the forum reccomend to check all adjustments on your shift cables to ensure correct shifting in forward and reverse.

While in the water try shifting manual, by hand, to see if the lower unit stays in gear and stops "wham" sounds.

Inspect linkage/shiftrod for secure fit , linkage may be loose and not fully engaging the clutch dog.

My 1970 33hp is starting to do the same thing at top end so I am going to tear into the lower unit this winter also and see what is happening in the clutch dog and gear areas. Good luck. WAV.

 

[jay_merrill]

Re: 79 35Hp Evin "slam" at WOT?

I am wondering if he meant the engine "slams" or the boat "slams." If the tilt is set incorrectly (tilted down too much) the motor will repeatedly try to drive the bow into the water and the bouancy of the hull will cause it to bounce back up. In that case, the hull would repeatedly slam into the water.

If he means the engine, your right - it's going to be touch to figure it out in the wintertime. If there is any way you can run the motor in a barrell that is large enough and sturdy enough to put it in gear and run the power up, that might give you some idea.

Try to get a better description of just what "slam" means.

 

[tashasdaddy]

Re: 79 35Hp Evin "slam" at WOT?

the classic description of a bad clutch dog, is, it felt like i hit a log. then kept going.

the first description, Jay gave, is called propoising, where the boat keeps bouncing.

 

[HyperFox]

Re: 79 35Hp Evin "slam" at WOT?

Dang.. Well I guess its pretty hard to diagnose without water. Up here its roughly -17'C this morning so barrel testing will just have to wait until spring.

What I was hoping for was a common issue to be pointed out but If that happened all the time, there wouldnt be much of a point for outboard mechanics. lolol.

Now about trim, is there any way to set the trim up properly without water? My instinct tells me, not likely, but I have much to learn! (Everyone starts somewhere, sometime) Maybe when Im up there at the garage this afternoon Ill snap some pics..

 

[tashasdaddy]

Re: 79 35Hp Evin "slam" at WOT?

usually the second or third hole out from the transom. it is a total experiment, between the boat hull, motor and load. takes water.

 

[DJ]

Re: 79 35Hp Evin "slam" at WOT?

Classic descripton of a slipping clutch dog. It is caused by years of EASING the shifter into gear. DO NOT do that. Shifts are to be quick and sure.

 

[HyperFox]

Re: 79 35Hp Evin "slam" at WOT?

How difficult is replacing the clutch dog? I am somewhat skilled with mechanical type work, but this is an outboard. I do have the service manual from Clymer's but those types of books always make the job look easier then what it really is.

Or is it just a simple adjustment?

 

[HighTrim]

Re: 79 35Hp Evin "slam" at WOT?

The job is not that bad, with the help of an OEM manual and this forum. Remember, as DJ said, alot of boaters feel it best to gently easseeeee the shifter into gear, and that is wrong, you are banging precisely machined edges against one another rounding them off. You have to snap that shifter into gear as quickly as possible. Here is a good diagram.

"http://www.crowleymarine.com/brp_parts/diagrams/30628.cfm"

 

[samo_ott]

Re: 79 35Hp Evin "slam" at WOT?

It sure sounds like a clutch dog to me.

And you can get parts at Laurentian Marine in Ottawa if there's nowhere up there. It's on Mac street off of Hunt Club. Clutch dogs and gears are not cheap though.

 

[tashasdaddy]

Re: 79 35Hp Evin "slam" at WOT?

if it is the clutch doq, you may find a donor lower unit, cheaper than the parts.

 

[flabum]

Re: 79 35Hp Evin "slam" at WOT?

drain the oil and see if any metal comes out.

 

[steelespike]

Re: 79 35Hp Evin "slam" at WOT?

To define shifting;Shift crisply don't slam it into gear nor drag it in.

 

[Joe Reeves]

Re: 79 35Hp Evin "slam" at WOT?

(Jumping Out Of Gear - Manual Type)
(J. Reeves)

This pertains to lower units on all OMC manual shift outboard engines, or any OMC engine with lower units defined as a Shift Assist or a Hydro Electric Shift unit which incorporates a "Shifter Clutch Dog".

Within the lower unit, splined to the prop shaft is what is most often referred to as a clutch dog, hereafter simply called dog. The dog has at least two lobes protruding from it on both ends, facing both forward and reverse gear. The forward and reverse gears also have lobes built into them near their center area. When the engine is running, in neutral, the gears are spinning constantly via the driveshaft being connected directly to the powerhead crankshaft, but the propeller does not turn due to the fact that the dog is centered between the two gears, and the dog lobes are not touching either of the gear lobes.

When the unit is put into either gear, shift linkages force the dog (and its lobes of course) to engage the lobes of the gear. The lobes of the spinning gear grab the lobes of the dog, and since the dog is splined to the prop shaft, the propeller turns.

The lobes of the dog and gears are precisely machined, most with right angled edges that could be installed in either direction, and some with angles slightly varied that must be installed in one direction only (one end only must face the propeller). Dogs that can be installed in one direction only, if reversed, even if the dog and both gears were new.... would jump out of gear almost immediately. Keep in mind that the lobes are precisely machined with sharp angles!

Due to improper adjustment or worn shift linkages, but usually due to improper slow shifting, those precisely machined sharp edges of the lobes become slightly rounded. Now, with those lobes rounded, as the rpms increase, the pressure of the gear lobes upon the dog lobes increases to a point whereas they are forced apart (jumping out of gear), and due (usually) to the shift cable keeping tension on the engines shift linkages..... the unit is forced back into gear giving one the sensation that the engine has hit something, and the cycle continues.

Some boaters have the mistaken belief that shifting slowly is taking ixt easy on all of the shifting components..... Wrong! Shifting slowly allows those precisely machined sharp edges of the dog and gears to click, clank, bang, slam against each other many times before they are finally forced into alignment with each other..... and this is what rounds those edges off! The proper way to shift is to snap the unit into gear as quickly as possible.

When time permits, visit my store (copy/paste) at: stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

 

[HyperFox]

Re: 79 35Hp Evin "slam" at WOT?

Well fellas.. the digital camera isnt working at the moment..

So. I went up to the garage anyway.. Did a better inspection.. Trim was set up interestingly, with the trim all the way to the rear... (As if to lift the nose of the boat way up when in travel.) I noticed there was a lot of junk like 30 some cannon ball sinkers in the front, coolers full of water and such.. Im guessing the PO (previous owner) carried a lot of stuff in the front of the boat. Ive removed all of this and set the trim in the middle for now. Ill have to adjust when Its all out on the water.. And loaded with what I bring.. Now I understand why electric trim is popular in larger boats..

At the stern of the boat is a plywood insert that holds the outboard on. The outboard is secured with 2 screws kinda like a big "C" clamp. These were very loose to the point where I could move the engine around fore and aft enough that the lower would strike the bottom of the boat. There is a small dent showing me this has happened a few times.. After replacing the wood and retightening the engine (man are those heavy!!!) the outboard now sits firmly, but at a completely different angle.. Reset the trim again.. Argh!

I also checked out the forward/reverse system, and it wasn't working right at all. Reverse engages nicely.. Forward doesn't, it felt like I was pushing it into a bowl of jelly. Replaced the cable and it seems good to go. I figure you guys are most likely right, that the dog is most likely dead.. or the boat was porpoising... I'm really hoping for the latter..

But incase I'm not right.. After looking at the diagrams I figure the gear set is most likely damaged as well, especially with that damaged cable. Looking on ebay, I cant see too many lower sets for it. Any other models fit this engine? I think the costs for a new gearset, dog, and whatever else has been damaged might make it worthwhile to source out an old one.. Anyone know of an outboard boneyard in ontario?

I wont know for sure what the problem is until I can experience this myself which will most likely be in march sometime..

 

[tashasdaddy]

Re: 79 35Hp Evin "slam" at WOT?

as you said there is not much on ebay right now. there will be more in a month or 2. and prices will probably be lower.

 

[jay_merrill]

Re: 79 35Hp Evin "slam" at WOT?

I was thinking clutch dog too, except that the description is that it slams at WOT at cruise. While I have had them slip a little at low loads and then "lock in" with pressure, that usually happens in the beginning of the failure period. Once they get to the point where they repeatedly "slam," which occurs because the edges of the recesses in the gears and the tabs on the dog are pretty much completely rounded off, they fail well before you get out of the bow wave to achieve planing speed.

Then again, the description that you were given could be wrong and the dog might be exactly what the problem is. It does kinda sound like it. If so, IMO the condition of the gears is going to be the main issue in terms of cost. If they can be cut and you do the tear down/reassembly yourself, you are probably looking at a couple of hundred dollars in parts and machine shop charges. If you have to replace the gears I would say, yup, its time to go looking for a used LU. If so, be careful not to buy one with the same problem!