Force 75 HP 1996 Gear Problems

[force75pk]

I'm from Holland so please don't mind some bad written questions.
So in short after I purchased a 14 feet boat for my sons wich we had to restorate. We finaly could get it to the water about a month ago it came with a Johnson 60HP after 10 min. the motor blew up. So we had to purchase a new motor. So we now have a Force 75 HP 1996.
Everything looked great and we mounted it on the boat. Firts time out I heard a strange noise comming from the Lower unit. So we took it out of the water and I thought it was the prop on one side had wearing signs. So mounted it back up and at first the noise seemed disappeared. After a while we heard the noise again but not as strong as the first time. We took back home and I inspected the carrier gear assembly. I noticed it was coming out of the housing and was on the brink of disrupter. I purchased a manual and drained the oil which was not much and saw some chunks of iron and wanted to get the gear assembly off. Well I had more luck than wisdom because of yoke gear shift. The manual was unclear how to take it off so I just pulled it out not knowing if the gear must in reverse, neutral or forward. When the gear assembly was out I noticed also that the bearing of the reverse gear was that good anymore. I took the assembly to a Merc dealer who ordered a new assembly and bearing. When I got back home and waited for the parts I took another look at the lower unit. Because it is hard to see exactly how the pinion gear end the forward gear was looking I took the lower unit down. Then when I rotated the shaft I almost got an heart attack. The pinion gear had ripped 2 teeth on two sides. Also In Europa Force parts are hard to get by and expensive. I got some luck and got the pinion gear from France. So I went to the Merc dealer with the lower unit and the pinion gear so he could mount everything together. Well the first thing he said he had no experience with these kind of motors and just mounting everything together is not an good option. I thought the lower unit was from Mercury. I need to replace the forward gear also and all bearings in the lower unit need to be replaced all shimming must be done and that is a specialized job and I would need to give him the correct measurements. The forward gear has some signs of wear but in my view still usable. So I asked him to take the pinion gear of and look at the bearing on the forward gear if it looks ok and don?t take it apart. Because of a lack time he cannot replace all the parts before his and my holydays. Besides that it is a steep price for all that. The parts delivered by the Merc dealer would be around $ 700 and additional the hours for repairing and I suspect that would be around $ 500. Well I already spent about $ 500.
It would be disappointing to my sons if the boat cannot go with us on the holydays. The worked really hard on the boat. They will use the boat for water-skiing at that kind of fun probably for 2 hours a day and for three weeks after that the boat will not be used much over here in Holland.
Well now I have a few questions:
What will happen if only the pinion gear is replaced in the worst case scenario?
I also found a Forward gear from the USA if something would go wrong so I?m about to order that one and I also can buy a pinion gear from France again.
What is correct gear ratio, the manual doesn?t state that for 75 HP only for a 70 HP, 1.64:1 , I assume these are the same.
How can I find out the correct measurements for shimming?
How do you measure the gear linkage of this motor?
I would be grateful for your advice.

 

[pnwboat]

What will happen if only the pinion gear is replaced in the worst case scenario?
Worse case scenario is that the pinion gear and or the corresponding main gear will suffer damage. How long will it last? That's a good question.

What is correct gear ratio, the manual doesn?t state that for 75 HP only for a 70 HP, 1.64:1 , I assume these are the same.
My manual shows that the gear ratio is 1.64:1, so looks like your assumption is correct.

How can I find out the correct measurements for shimming?
The factory service manual may have the shimming information, however, you may need special tools to do so. I know on the older gear cases, the shims are no longer available. I don't know if they are available for your particular gear case.

How do you measure the gear linkage of this motor?
If you are referring to the external gear linkage, then you adjust the linkage so that you get good engagement in Forward, Neutral, and Reverse. No measuring is involved.

I have found that it's often much less costly and easier, to replace the complete lower unit with a good used one rather than try to repair a damaged one. The gears are very expensive and the special tooling and shims can be difficult to find. I believe that in 1996 they started using Mercury style gear cases, so you may be able to find a Mercury style lower unit or parts which may be more common than the Force units.

 

[Frank Acampora]

Well, first off, welcome. I always enjoy hearing from people in other countries than the USA and Canada. It shows that this forum is truly international.

The lower unit is the same for a 70 and a 75 HP Force. The engine is made by Brunswick and uses many Mercury designed parts, including the lower unit. As you already know, parts are very expensive and yes, the gears need to be shimmed. There needs to be .005 inch backlash otherwise the gears, even new ones will self destruct. There is a special tool to shim and brass shims for the top bearing which may or may not be available.

I would not install only a pinion. if the teeth broke on the old one there is a very good chance that the other two gears are damaged and service life will be reduced. In your case it really would be best to try and find a complete used lower unit in working condition. I know this is difficult but any other option will be costly . As you know, labor charges are high in addition to parts.

 

[force75pk]

Thanks to you both for your quick reply. I know that the best way to go forward would be replacing or buy a used one, my problem is time. I just want to go boating with the boys these Holydays and I'm not looking for a futureproof solution. I only have 2 choices let it stay at home or maybe spend around 40 hours on the water. If something happens i will see that at home. What are your thoughts on the 40 hours would it last. I have to drag the boat for about 1200 miles.

 

[Frank Acampora]

It is not possible to predict how long the lower unit will last if you simply swap in a couple of gears.

Given those two choices I would decide to leave it home! I know it is disappointing but consider that you are towing 1200 miles and not knowing if the engine will leave you stranded on the water. It is simple risk versus reward

In this case, in my opinion, the risk outweighs the reward.

In fact, as an example, in August I am going to the New Jersey shore to visit relatives. I want to take my 21 foot cuddy cabin with a 150 Force but the engine is not running quite right. Unless I can get it perfect by then, I am not willing to tow the 100 miles with it, go out on the bay and have the day ruined by a malfunctioning engine.

 

[force75pk]

Frank, first off al I appreciate your advice. I saw a couple of videos on YouTube so I know that you know something about Force/Chrysler, we from Holland are not complete ignorant. I won’t dispute your knowledge. But if I ask it directly to you what would 40 hrs of boating with a new pinion end up with:
1: Strand on a beach
2: Have to row for a couple of hours
Would it wear out in 40 hrs in your opinion, as pnwboat says who knows. I think you can make some assumption. I don’t need it to be perfect I want to use it.

 

[Frank Acampora]

As I said, it is not possible to predict the gear life. It all depends upon how much the gear lash is incorrect. If by some chance the gear lash turns out to be correct with the existing shim package AND if the forward and reverse gears are not damaged the life is indefinite.

I understand that you do not want to be perfect but lower units do require perfection to last.

If you are willing to row for a couple of hours OR if you have a kicker engine for emergencies, you may want to take a chance.

If you are set on replacing the gears then try this.

Now, it is possible to get close on the gears. You look at the old gears and there will be a slight wear pattern on them Set up the lower unit so the gears mesh as close as possible to the wear pattern. Without the water pump turn the drive shaft and depending upon the shim location either push down or pull up. I forget exactly which needs to be done on the 70 but I think you pull up.. While loading the shaft and turning it listen and feel. If it is silky smooth with no noise, yeah you should get some hours out of it. If it grumbles--you will hear and feel the gear teeth meshing-- then don't use it . it will self destruct in a short period of time.

Understand also that I don't like to instruct in this procedure--It is very sloppy and poor workmanship. However since I believe that you are going to replace the gears no matter what anyone says, you might as well have at least a fighting chance.

 

[force75pk]

Thanks Frank, for your advice.
Turns out that someone had some other thoughts. Someone has fussed with the water pump base so it lets water in the gears. To order the necessary parts we?re going to be few weeks further to mount it up.
So after all I will not take the boat with me.
Could you inform me how the proper way is. I ordered the forward gear from the States. I will order new shims also.
Are there any issues involving a rebuild. Is the shimming very hard to do it yourself? Are the any tips and advices.

 

[Frank Acampora]

Understand that I have never shimmed a 75 lower unit. There are special tools to shim various lower units to set gear lash.without the tool specific to your lower unit you can only approximate correct gear lash as I described in the answer above.

Understand that I do not have the tools so I did use this method on a 125 HP lower unit. It lasted about four seasons before self destructing. The gear teeth were completely gone on both the forward gear and pinion. In addition there was so much junk wedged into the gearcase that it took me many hours to get it apart.

Now, here is a little explanation because knowledge never hurts but remember that a LITTLE knowledge is dangerous. SO. In order to mesh correctly gears MUST have a little clearance. This clearance is called gear lash. To much is no good and too little is equally bad. You can demonstrate this with an old set of gears and pinion. Move the pinion in towards the center of the forward gear and roll it along the teeth. It will make a rumbling sound. Move it outward a good bit and do the same. Again it will make a rumbling sound. Now look closely at the wear pattern on the gear teeth and move the pinion so that it approximates this position. It will move without a sound.

Now, apparently the position of the forward gear in relation to the drive shaft is set and tolerance held very tightly by the manufacturer. Since the forward gear and pinion are both tapered, moving the pinion up or down will increase or decrease the clearance between the teeth. THUS: On the older Force engines there is a calibrated tool that plugs into the forward gear hole. It has a flat machined surface and by using a feeler gauge and shims on the top drive shaft bearing you raise or lower the pinion until the correct feeler gauge (I forget the size) will just slip between the pinion and the tool's top surface.

Understand that I am not certain that this is the same method used in the 70-75 horsepower engines.Some lower units will actually shim the bearing on the forward gear to set lash and some engines also require setting clearance on the reverse gear. So, you can see it is a very precise procedure and not at all simple for the garage mechanic.