Johnson 120 Jerks When On Plane Every So Often

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Author Topic:   Johnson 120 Jerks When On Plane Every So Often

rookie31 posted 07-08-2009 03:10 PM ET (US)
When planing out, and when I get to full plane, every so often my [Johnson 120-HP] motor will jerk, almost like I hit something. Any idea what this could be.
Tohsgib posted 07-08-2009 03:13 PM ET (US)
Either a dead miss or a stripped gear somewhere.
rookie31 posted 07-08-2009 03:27 PM ET (US)
ok im not sure what a dead miss is, but if it is the stripped gear, will i need to replace the entire lower unit.
Tohsgib posted 07-08-2009 03:40 PM ET (US)
Think about a miss is when the motor just cuts out but cuts back in again real quick, it can bang pretty hard.
Depends where the gear is. Usually gears are more frequent like a stutter every now and then.
rookie31 posted 07-08-2009 03:56 PM ET (US)
it is pretty consistent, I think it was kind of doing the same thing once before and I think the mechanic said it was a 3 dog clutch or something does that sound right. And how hard would that be if i wanted to replace it myself.
Peter posted 07-08-2009 04:50 PM ET (US)
Probably the gearcase is slipping. Check the shift cable to make sure its adjusted properly to fully engage the forward gear.
Whaler_bob posted 07-08-2009 05:15 PM ET (US)
Sounds like a classic case of a worn clutch dog and forward gear. The surfaces of the two components wear round after time due to shifting and when under extreme load- ie: getting up on plane- they slip with a sudden jolt. Used to scare the crap out of us when we ran engines in the test tank at full throttle to diagnose this problem. Felt like the engine wanted to jump off the brackets!
Not a super expensive repair, but special tools and knowledge are required to make the repair- so it's really not one a casual mechanic should attempt unless you've done it before. While out, it's good to replace the prop shaft seals in the bearing carrier too.
You didn't mention the year of your outboard, but here's a typical OMC V4 "set" (please check w/retailer before ordering to ensure correct fit!!!) with both forward and reverse gears, pinion gear and clutch dog- $315.
http://www.masonmarine.net/complete-gear-set-clutch-p-1214.html
Tohsgib posted 07-09-2009 11:23 AM ET (US)
I had worn gears/clutch dog before but it never banged it would stutter at cruise like it was missing. But I guess if it got worse enough it could.
sosmerc posted 07-09-2009 11:31 AM ET (US)
If there is air in your trim system the engine might suddenly jerk "in" when you apply thrust. Just one more thing to check.
Whaler_bob posted 07-09-2009 01:04 PM ET (US)
Tohsgib-
The old OMC 40hp's would bang so hard it was very common to see them come in with broken motor mounts due to a bad clutch dog. The common trick was to simple swap out the forward gear with a good used one and reverse the old clutch dog so that the seldom used (and usually in perfect condition) reverse side of the old clutch dog faced the new forward gear. The only new parts used was a bit of spaghetti-seal and some permatex. It was a quick 30 min repair done for under $5 in parts.
Tohsgib posted 07-09-2009 02:19 PM ET (US)
This was on my old 1982 35hp in about 1985/86 with over 1000 hours on it. Cost $400 back then I believe. I did "get away with it" for a few weeks more by adjusting the shift cable into forward more but that made docking a bit experimental.
rookie31 posted 07-10-2009 04:59 PM ET (US)
I ran the boat at the lake yesterday for a good while. [The engine] will jerk when given full throttle to plane out, and once I get [the boat] up and going [the engine] will give a small jerk every now and then. So I think that [the cause of the problem] is the clutch dog.
wilson posted 07-11-2009 07:54 AM ET (US)
torn motor mount allowing powerhead to move and pull on shift linkage when underload leads to failure of clutch dogs if not fixed as stated above fairly common on older omc,s not a big deal to fix unless its a saltwater engine
penbay01 posted 07-14-2009 12:03 PM ET (US)
I've got this going on in an old Evinrude 35hp too. What's the end result if i don't replace the clutch dog? I've just been holding the shift lever kind of forcibly into forward, and that seems to pretty much solve the issue.
Whaler_Bob I like your fix but the parts catalogue for this motor lists the forward gear as quite a bit more than $5. Suggestions on where to dig up old outboard parts?
(Parts catalogue is here: http://shop2.evinrude.com/Ext/PartList.aspx?assem=40885)
Whaler_bob posted 07-14-2009 03:17 PM ET (US)
penbay01....
Don't know the year of your outboard- the link you provided isn't up.
Check with these guys:
http://www.masonmarine.net/gears-and-clutch-dogs-c-24_39_1844_43.html?osCsid=8751736ca4548641b5b7230dab100654
If not- do a google search for "used outboard parts" and make a few inquiries. If you don't fix it- it will get progressively worse and could do some major damage to the motor mounts an/or your transom. In most cases- you need to replace the forward gear and clutch dog as they wear together. If you only replace the clutch dog- you may still have the slip problem or it will return soon enough.

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Author	Topic: Johnson 120 Jerks When On Plane Every So Often
rookie31	posted 07-08-2009 03:10 PM ET (US) When planing out, and when I get to full plane, every so often my [Johnson 120-HP] motor will jerk, almost like I hit something. Any idea what this could be.
Tohsgib	posted 07-08-2009 03:13 PM ET (US) Either a dead miss or a stripped gear somewhere.
rookie31	posted 07-08-2009 03:27 PM ET (US) ok im not sure what a dead miss is, but if it is the stripped gear, will i need to replace the entire lower unit.
Tohsgib	posted 07-08-2009 03:40 PM ET (US) Think about a miss is when the motor just cuts out but cuts back in again real quick, it can bang pretty hard. Depends where the gear is. Usually gears are more frequent like a stutter every now and then.
rookie31	posted 07-08-2009 03:56 PM ET (US) it is pretty consistent, I think it was kind of doing the same thing once before and I think the mechanic said it was a 3 dog clutch or something does that sound right. And how hard would that be if i wanted to replace it myself.
Peter	posted 07-08-2009 04:50 PM ET (US) Probably the gearcase is slipping. Check the shift cable to make sure its adjusted properly to fully engage the forward gear.
Whaler_bob	posted 07-08-2009 05:15 PM ET (US) Sounds like a classic case of a worn clutch dog and forward gear. The surfaces of the two components wear round after time due to shifting and when under extreme load- ie: getting up on plane- they slip with a sudden jolt. Used to scare the crap out of us when we ran engines in the test tank at full throttle to diagnose this problem. Felt like the engine wanted to jump off the brackets! Not a super expensive repair, but special tools and knowledge are required to make the repair- so it's really not one a casual mechanic should attempt unless you've done it before. While out, it's good to replace the prop shaft seals in the bearing carrier too. You didn't mention the year of your outboard, but here's a typical OMC V4 "set" (please check w/retailer before ordering to ensure correct fit!!!) with both forward and reverse gears, pinion gear and clutch dog- $315. http://www.masonmarine.net/complete-gear-set-clutch-p-1214.html
Tohsgib	posted 07-09-2009 11:23 AM ET (US) I had worn gears/clutch dog before but it never banged it would stutter at cruise like it was missing. But I guess if it got worse enough it could.
sosmerc	posted 07-09-2009 11:31 AM ET (US) If there is air in your trim system the engine might suddenly jerk "in" when you apply thrust. Just one more thing to check.
Whaler_bob	posted 07-09-2009 01:04 PM ET (US) Tohsgib- The old OMC 40hp's would bang so hard it was very common to see them come in with broken motor mounts due to a bad clutch dog. The common trick was to simple swap out the forward gear with a good used one and reverse the old clutch dog so that the seldom used (and usually in perfect condition) reverse side of the old clutch dog faced the new forward gear. The only new parts used was a bit of spaghetti-seal and some permatex. It was a quick 30 min repair done for under $5 in parts.
Tohsgib	posted 07-09-2009 02:19 PM ET (US) This was on my old 1982 35hp in about 1985/86 with over 1000 hours on it. Cost $400 back then I believe. I did "get away with it" for a few weeks more by adjusting the shift cable into forward more but that made docking a bit experimental.
rookie31	posted 07-10-2009 04:59 PM ET (US) I ran the boat at the lake yesterday for a good while. [The engine] will jerk when given full throttle to plane out, and once I get [the boat] up and going [the engine] will give a small jerk every now and then. So I think that [the cause of the problem] is the clutch dog.
wilson	posted 07-11-2009 07:54 AM ET (US) torn motor mount allowing powerhead to move and pull on shift linkage when underload leads to failure of clutch dogs if not fixed as stated above fairly common on older omc,s not a big deal to fix unless its a saltwater engine
penbay01	posted 07-14-2009 12:03 PM ET (US) I've got this going on in an old Evinrude 35hp too. What's the end result if i don't replace the clutch dog? I've just been holding the shift lever kind of forcibly into forward, and that seems to pretty much solve the issue. Whaler_Bob I like your fix but the parts catalogue for this motor lists the forward gear as quite a bit more than $5. Suggestions on where to dig up old outboard parts? (Parts catalogue is here: http://shop2.evinrude.com/Ext/PartList.aspx?assem=40885)
Whaler_bob	posted 07-14-2009 03:17 PM ET (US) penbay01.... Don't know the year of your outboard- the link you provided isn't up. Check with these guys: http://www.masonmarine.net/gears-and-clutch-dogs-c-24_39_1844_43.html?osCsid=8751736ca4548641b5b7230dab100654 If not- do a google search for "used outboard parts" and make a few inquiries. If you don't fix it- it will get progressively worse and could do some major damage to the motor mounts an/or your transom. In most cases- you need to replace the forward gear and clutch dog as they wear together. If you only replace the clutch dog- you may still have the slip problem or it will return soon enough.