1974 Mercury 850 Thunderbolt Shift rod play

[MatchT]

Hello everyone,

I bought an old boat last year for fishing and when I first bought it, the reverse would grind a lot before kicking into gear. I mostly avoided using reverse period. This spring I attempted to adjust the shift cable to allow more movement towards the reverse side of shift on top of motor.


I adjusted my shift cable so that forward and reverse would work properly in my yard, with water muffs of course. IN the water, reverse just grinds and engine revs up high...I have cheated the cable to reverse as much as possible...I discovered that the dog leg portion of the shift rod (upper housing area of the engine) rubs against engine housing when going to reverse...it even has a little wear... It has a up and down play..My guess is that this upper shift rod has to much play coming up into the engine housing. How do I make this dog leg/shift rod stay down? When I removed the lower unit I could not find how to make the upper shift rod come down farther and stay...I was expecting a replacable bushing. I bought the online manual from iboats link but doesn't mention how to remove or replace upper shift rod... IN the water in wont shift to reverse, mostly because I believe the rod rides up and is being prevented from shifting in reverse.

thanks for any help or suggestions.\




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[Chris1956]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

The shift rod has an upper bushing, however it is not replaceable according to the parts list. However, I do not think that is the problem. If the splines of the upper and lower shift rods are mated, the upper shift rod should not move up and down.

It would be easiest if you had a friend with experience, who could look it over for mangled/worn parts. I suspect that your reverse dog may be worn. What does the gear oil look like? Any chunks of metal? Filings?

 

[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

I did change out the oil this spring as well. It was kinda milky, but no metal chunks....I did find a tiny bit of metal shavings on plug, nothing major...I can shift the lower unit pretty easy with pliers into reverse, forward, and neutral.

I did have one heck of a time figuring out the reverse cam lock...through trial and error, I found the position that would allow it to unlock in neutral/forward and lock in reverse...it took me about 4 times:redface:

do you think that under load the lower unit can fail, but operate ok in yard no load on prop?

thanks for your response....

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[emckelvy]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

Just a random thought, is there a load of grease packed inside the coupler on the upper shift rod?

If someone had loaded the top of the shift shaft with grease, the shift shaft might be 'hydro-locking' into the coupler, which would tend to force the shift rod upwards.

Older motors had a small casting 'ear' at the bottom front of the intake cover which would keep the shift rod from riding up. If that ear was busted off, it could cause issues. I can't recall if your 4-cyl would have anything like a travel limiter for the shift rod. Except for maybe hitting the bottom of the lower carb and that wouldn't be the best idea would it!

Another thought, if the shift cam were worn, or the tip of the shift plunger, you might be able to shift manually with the L/U off, but reassembled the arm wouldn't have enough travel to get to the point where it actually would shift. Or, the giant cover nut on the gearcase has backed off, allowing the bearing carrier to slide rearwards and affecting shifting action. Hopefully not that or bad reverse cogs as mentioned, but if you can't find any real issues with the shift shaft/rod, you may be looking at a teardown.

Note some motors had an aluminum shift rod coupling pressed onto splines at the end of the shift rod, this coupling actually engages the shift shaft. So it'd be possible for the aluminum to be extremely worn or corroded; this would introduce quite a bit of slop into the shifting action. But I can't recall if your motor would have this coupler, or just one-piece all-metal at the end (non-replaceable except by replacing the entire shift rod). Just something else to check!

HTH & G'luck.........ed

 

[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

I will take a picture of the upper shift rod portion with lower unit on, and one after I remove the lower unit...I think there is a probably enough difference that might cuase the dog leg to jam against the lower carb.

I remember that when I removed the lower unit, there is a some type of plastic bushing that centers the lower portion of the upper shift rod(female) to the male end of the lower unit....

I will take a look at the up an down play once again with the Lower unit off....if its not to bad, I might have to look into the lower unit....this kinda scares me...

I read in another post that the reverse cam lock should engage in nuetral and reverse? I only lock in reverse....I will fix that as well...might not fix my reverse problem but will be in the right place...

thanks everyone...will post results whether good or bad...


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[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

Hello everyone,

I removed the LU today and I took pictures of the upper shift rod before and after

before removing LU pic 21

after revoving LU pic 28

Picture of shift shaft coupler on upper unit Pic 33

Picture of lower unit shift shaft 39

my thoughts that the play on shift rod might not be as significant as I thought. but if you look at pic 28 you can see the slop I am talking about.'

I would like any one to comment on the condition of my splines on upper and lower and if they see any culprit to my reverse shifting problem. I have read in another post that a worn coupler could be the culprit. My question, how would I remove this?

thanks everyone,

Match




after

 

[emckelvy]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

That aluminum coupler is buggered...........you can see the splines at the bottom of the coupler are all worn out.

And the splines on the shift shaft are marred as well. Get a small file and clean up all the burrs on the steel shift shaft.

A good way to know when you've got it cleaned up enough is when the steel reverse lockout cam comes off the shift shaft smoothly. Right now I bet you couldn't pry it off of there on a bet. But don't do that either, you risk pulling the shift shaft out of the lower unit, and that's a whole new level of pain!!!

The splines on the coupler look clean farther in; what I suspect is happening is that the shift shaft isn't going in any farther than the first 1/16" or so of the coupler, then it's pushing the entire shift rod up.

I'm thinking if you clean up the burrs on the shift shaft and also the end of the coupler where those splines are buggered, you should be able to get things back together properly.

BTW if your shift shaft is positioned to where any more CCW movement shifts into Neutral, the shift cam is 1 set of splines too far CW. The reverse lockout rod should be pointing directly at the middle of the ramp in the shift cam, when the shift shaft is in the correct (Fwd Gear) position to be shifted into Neutral.

In other words, as soon as you shift to Neutral, the shift rod meets the flat spot at the top of the shift cam and then the rod is blocked from dropping, to release the lockout hook.

You can see how the flat spot on the cam is extended, so that when you shift to Reverse the lockout rod is still blocked by the flat spot.

So, I'm thinking that's your issue; the shift shaft just isn't going into the coupler, pressing upwards on the shift rod until it's stopped by the bottom of the carb or whatever it's running into. At that point only the very end of the relatively weak aluminum coupler's splines are engaging and you can see what that's done to them. Clean it all up and maybe it'll go together.

BTW that coupler is pressed onto the shift rod, with splines the same as you see on the shift shaft. Usually you have to heat the coupler with a propane or MAPP torch then pull it down. Unlikely you could get it off of there without destroying it, but if you could find a replacement (supposedly NLA but some dlrs might have in stock still), you could put a nice new coupler on there.

A few other alternatives would be to find a complete shift rod assy from a parts motor, but you'd have to pull the powerhead to replace. More Fun!

Best bet for now it to clean up the splines and give 'er a shot.

G'luck, the pics helped a lot to figure it out..............ed

 

[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

ok,

I cleaned out the spline coupler.....

I then put everything in nuetral.....engaged the LU...got jammed at the shift shaft coupler, had wife wiggle the control box between neutral and forward....slipped in...now it did not shift to reverse at all...only forward and neutral...

long story short, I was always one spline off when I attempted to engage the shift shafts to each other.

through trial and error, I moved the control box to forward as far as possible,,I nudged the dog leg on top forward as far as possible too...I put the lower unit in neutral, I engaged the LU, once again after the driveshaft lined, the shift shafts met but did not engagge, i had my wife slowly shift towards neutral while I pressed up on the LU. Once they lined up I tightened up the bolts and bam... I had forward, neutral, and reverse....this time reverse gear kicked in without grinding to long and way before revving up...I am crossing my fingers and hope to also have all three in the water...will post results in a couple of days....

on a side note, I could never get it to work if I set both control box and LU to neutral...having set them in forward on control box and neutral at the control box allowed be to maximize movement towards reverse....wife and I must have reset the LU 7-8 times before we got the shift and the reverse cam lock to work properly,,,at one point we had forward and reverse backwards

the dang reverse cam lock kicked my but too, in one way I almost locked in reverse, if i set it to lock in reverse, i did not have enough play to disengage in forward...

It seems to be good now....not much grinding at all in reverse....only the water test will tell.

I really like how the engine runs...it has great power in forward and always starts great!

thanks everyone!

 

[emckelvy]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

Cool! Glad it helped!

Most times you pull the L/U and it'll just go right back up, no problems. But then you get that pesky one that's just off enough that it won't line up no matter how you move the control box.

What I've had to do in those cases is to disconnect the shift cable, then you're free to move the shift arm all over the place until you find the right spot. It's a pain when you're expecting things to line up, and it adds a fair amount of time to what should be a pretty quick job, once you get the hang of it.

But, anything to help Git 'er Dun!

Enjoy your boating, you worked hard for it!.............ed

p.s. A tip about the grinding, the best way to tell if the preload on the shift cable is set up properly is to shift from reverse to neutral, spin the prop to make sure nothing's dragging, then shift from neutral to fwd and back to neutral again.

If you still hear nothing dragging when you spin the prop, it's perfect. If it's not quite right , adjust the threaded ferrule on the shift cable until things shift well. You may have to spin the prop a bit by hand when shifting without the motor running. Of course be sure to pull the plug wires when handling the prop!!

Best to adjust the shift cable before putting everything back together, since the throttle cable goes on top and is in the way of those adjustments.

And last tip is have a sharp motion when shifting, especially to reverse. Don't let the gears grind; that grinding sound you hear is the 'dogs' on the gear and shift clutch being worn down. You don't have to slam it, just a flick of the wrist, she's in gear and away you go.

 

[Wingedwheel]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

I had the same problem. It looks like someone forced the coupler together out of alignment and marred the splines. I replaced mine for $42 parts and shipping from Boats.net. It made all the difference in the world.

 

[emckelvy]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

It's good to know that you can still get it somewhere. When I looked up the coupler at Mercruiserparts.com it showed as NLA.

 

[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

Thanks again everyone,

I could not wait so today I took out the old boat to a local lake and gave it a whirl...

The shifting worked! First time ever that I could actually use reverse without grinding and high rev....I could actually shift into reverse then rev it up....

a couple of small items...as I shifted to neutral to shift into forward, my idle was too low and the engine would die right as I engaged forward...I had to rev up a little then start the engine...When I shifted to neutral it would die agains as idle was too low....I brought the boat home, removed throttle cable (engine area) and give it more rpms by twisting the adjustable barrel two revolutions towards the rear...this gave it a higher idle...Hopefully next time it will stay on as I engage forward... the engine runs well and I can plain really well...

Wingedwheel and EMC,
I feel like should order the coupler and replace someday as I believe that I also forced the shifts shafts together too much today...the coupler is worn for the first 1/8" on the coupler...My question to you...If I heat up the coupler, I just pull it off with vice gripes? If I am succesfull at that, how do you press the new one back on? Heat up again? I imagine you have to press it in, and the only way to do that is bracie the top end of the shift shaft (at the dog leg) down as you hammer the new one on from the bottom???

Thanks for your help...I have confidence now to take the kids fishing monday!

This site has been great!

 

[emckelvy]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

There's probably more than enough splines engaged, the shift shaft penetrates in quite a bit farther than 1/8". In fact, probably just about as deep as the hole in the coupler. But it couldn't hurt to have a new, undamaged one in there. What you described for removal and reinstall sounds spot on. Just be sure to brace the shift rod solidly when you tap the new one in place. A wooden or plastic wedge would do nicely.

On the idle speed, yes, adjusting the cable as you did can change the speed but you're actually supposed to adjust the idle speed stop screw on the bracket at the front of the distributor.

Note there are three screws, Idle Stop, Spark Stop, and Carb Stop. You want the one that the throttle arm will rest against at lowest idle speed. And it's clearly marked with cast-in letters on the front of the bracket.

The correct way to adjust is, turn the screw CW for higher idle speed, CCW for lower speed.

Then, you adjust the throttle cable such that there's a bit of tension pushing the throttle arm into the idle stop. Just a wee bit, not a ton.

You can tell when you've got it right, just raise the fast idle lever to move the throttle arm, then return the fast idle lever to normal. The throttle arm should consistently return to rest firmly against the idle stop screw. If it doesn't quite make it to the screw, add some preload to the throttle cable adjustment and that'll press the arm against the screw.

BTW you may also benefit from adjusting the idle mixture in both carbs. Warm the motor in the water, idling in gear. Slowly turn the idle mix screw on the top carb CW until the motor begins to stall out (too lean). Then slowly turn the screw CCW, you'll note the increase in speed then it'll start to slow down again (too rich).

Set the needle about halfway between the lean-rich range you just determined. Then repeat with the bottom carb. This may raise or lower your idle speed, so you might have to adjust with the idle stop then re-set the tension on your throttle cable accordingly.

Now, the important part, after adjusting mixture try to accelerate smartly. If the motor bogs, it's a bit too lean. These guys don't have accelerator pumps, so you have to adjust the mix so (as my good buddy Dr. Frankenmerc says,) they 'slobber' a bit.

Adjust each idle mix screw 1/8 turn in the rich (CCW) direction and try the holeshot again. If it's still a bit doggy, do one more 1/8 rich adjustment. Any more tweaking past that point will likely make it too rich, but if you need to give it another 1/8 and see what happens.

These motors will tolerate running a bit rich on the idle but don't like running lean at all. What'll happen, besides bogging on acceleration, is it'll get real cranky on cold starts and you'll have to use a lot of choke upon restarts. Having the idle mix a touch on the rich side helps with this.

Well, sounds like you're real close to gettin' 'er dialed in. Enjoy!...............ed

 

[MatchT]

Re: 1974 Mercury 850 Thunderbolt Shift rod play

thanks again EMC,

I did notice the idle screw adjustment on the distributor and I was just a hair off from touching it...If it dies again on the water I will adjust the screw there...
the throttle/shifting forward worked great before (no dying on shift)until I started messing with reverse shifting...I had tried letting off of the throttle cable to allow for the shifting to occur before reving up...since the barrel on the throttle cable is the adjustment I had made before, I am undoing that action first...

I will tune up as you mentioned for mixure too....

thanks again...