1972 45HP Chrysler lower unit died

[jdwood01]

On my last run of the season(at least it waited until the end of the summer) something very bad happened in the lower unit. It completely slipped out of gear while under power. I managed to get back to the dock but oil was leaking out like crazy and I notice a crack near one of the bolts on the propellar bearing cage. I have never done much with outboards besides general maintenance and I changed an impeller once. I have the chrysler service manual and am fairly mechanical but the manual isn't all that detailed and it calls for alot of special tools(which I don't have). Do I dare start tearing it apart and is it even worth fixing? Didn't pay much for it but the engine runs great. Any good tips on rebuilding this thing?

 

[eurolarva]

Re: 1972 45HP Chrysler lower unit died

If the bearing cage is the part that is cracked you should be okay. If the gear housing attached to the bearing cage is cracked you will probably want to keep a look out on ebay for a new lower unit. I believe Mercury still sells bearing cages and if they do it is pretty simple. Remove prop remove both screws holding the bearing cage in place and replace it will a new bearing and seals. Where is the damage? Can you post a picture?

 

[Frank Acampora]

Re: 1972 45HP Chrysler lower unit died

The special tools are for setting up a lower unit that has had components replaced. That is the correct way BUT---Chrysler lower units were set up with "loose" clearances and usually, the special tools are not necessary. Even if you are swapping in a complete gear-pak.

If the crack is in the bearing cage, it could be minor or it could be a toasted lower unit. If the crack is in the gearcase, the lower is almost certainly wasted. Typically, a gear tooth or two breaks and jams in between the gears themselves. The engine has more than sufficient power to push through the jam and the resulting forces will crack either the case or the bearing cage.

At this point, you only need hand tools to disassemble the lower and assess the damage so that is the next step. If only the bearing cage is broken, try to buy a used one. New are very expensive.

Chrysler and Force made TONS of these engines and the lower unit design remained substantially the same. SO: If your lower unit is destroyed, you can swap in a lower from anything from late 60s Chrysler to a 1994 Force, 35, 45, 50, and 55. The gear ratio is all the same in Chryslers and possibly Force. Look for an inexpensive one on ebay, but just don't buy a Chrysler 55 from a twin carb engine and be careful with a 35--Chrysler made two versions. These are different and will not fit. Late 60s Chrysler lowers have a regressive water pick-up but the gearcase and components will swap onto your middle section.

Just be aware that the front stud is about 8 inches long and frequently gets corroded into the casing. It can be a witch with a capital "B" to get off the gearcase. AND, you must remove the gearcase to get the gears out for inspection.

 

[jdwood01]

Re: 1972 45HP Chrysler lower unit died

Thanks for the info! I'm going to try taking it apart this weekend and get a better look at the damage. I'll post some pics once I get going on it.

 

[jdwood01]

Re: 1972 45HP Chrysler lower unit died

I got the lower unit all apart without major issue. The prop bearing cage is broken. The lower screw hole broke off. The drive shaft bearing is a bit chewed up but none of the teeth are missing; just a couple of small gouges on a few of the teeth(need to be replaced?). I didn't find any kind of debris inside. Prior to the failure I did notice a clunk every now and then when under power but it only happened a few times. Clutch slipping?

I do have a few other quesitons...
There is a bit of rounding on the clutch dogs. I've never worked with these before so not sure how much rounding it can handle before it is a problem. Doesn't seem very severe though to me.

There is a brass piece on the shifting mechanism that moves the clutch in and out. It seems like it is worn some and I'm wondering if this is creating to much slop in the clutch movement and this maybe caused the clunks and ulitmatley the bearing cage failure.(Picture is attached)

Any thoughts? I was really expecting things to be torn up worse than they are...not that I'm complaining. Just not sure what the ultimate problem is now.

thanks in advance

 

[Frank Acampora]

Re: 1972 45HP Chrysler lower unit died

That brass yoke is worn more than usual and probably can be replaced. bearing cage , I don't need to tell you.

As far as the drive dog clutch and gears, I really need a photo. They are only about 3/16 high, so an appreciable amount of rounding will cause them to pop out of gear.

Good news is that with a dremel and carbide bit tou can dress the edges and make them functional without spending beaucoups bucks.

 

[jdwood01]

Re: 1972 45HP Chrysler lower unit died

Here are some more pics. Hard to get the camera to focus just right but they seem good enough. First if of the chewed up teeth on the drive shaft bearing. Do you think I need to replace this? The other are of the clutch showing the rounding of the teeth. Glad to hear these can be touched up with a dremmel. Checked prices on some of these parts...ouch.

 

[Frank Acampora]

Re: 1972 45HP Chrysler lower unit died

Well, the pinion definitely needs replacing. Those teeth will continue to spall and eventually fail, ruining everything. I can't see the condition of teeth on the forward gear though. The drive dogs are rounded enough that they may or will pop out of engagement. They need to be dressed and squared.

All in all, you need a bearing cage, seals, pinion gear, shift yoke, and need to square the drive dogs on the forward gear. Note the condition of the reverse drive dogs on the clutch. Because reverse is used less and gets much less abuse, the dog clutch can be turned around and will function. ----Unless you have a junker to swap parts, new are prohiibitive-- buy a used lower unit OR buy a whole junker engine and swap lowers. I believe in a previous answer I told you what engines would swap.

 

[jdwood01]

Re: 1972 45HP Chrysler lower unit died

Thanks for all the great info. I attached a couple of pics of the forward and reverse gear teeth.. Any tricks to dressing up the drive dogs with a dremmel? Do you try and make a jig or something or just do it free hand?

I was reading some other posts on this topic and saw some talk about shimming of the gears to make sure the clearances are correct if you replace them. Is this something I need to worry when I replace the pinion gear? Don't see anything that looks like a shim...

Thanks again for all the help!

 

[Frank Acampora]

Re: 1972 45HP Chrysler lower unit died

If the pinion was shimmed, it would be a thin brass one between the pinion and bearing. The bearing is located in the housing by the top castingbut if you use the wrong thickness gasket, then nthe gears will be out of shim with the pinion. --no special tools required, just install the pinionand bearing.

As far as dressing the drive dogs, it is always better to use a jig, but I have always done them by hand. You will need to be careful, though, so that an equal amount is removed from all three dogs.