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Johnson 70 tilt trim rattle

O

ozboy

New member
Hi I have an 1985, 70hp johnson that has a rattling tilt trim pump.
It goes up in trim and then goes fast in tilt no problem and does not stop at all.
Half way up it starts a rattle sound coming from the pump area.
It only makes this sound when going up.
It will make the sound one time and not the next.
The oil level is full and all pivot point are lubricated.
Can anyone explain the workings of the hydraulic circuit?
The pump goes one way to go up and opposite to go down but are there valves too?
Are there internal valves to stop motor falling down?
Are there any hydraulic circuit diagrams available for tilt trims?
I am thinking the pump or maybe there are valves rattling inside that area.

It still works but I am thinking this could be the start of a bigger problem and don't want to get stuck somewhere.
Any ideas or info are appreciated.
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Hi Guys thanks for replying

It is more of a rattling sound not a banging or creakings sound and only happens when tilting up.
The engine goes up and down smoothly and it also only rattles when it is 3/4 the way up and not all the time
Sounds like it is running out of oil but the reservoir is full when the motor is tilted up all the way.

I have lubricated all pivot points on the motor.
The noise is coming from the pump area, I was told there is a shuttle valve in there that can get noisy but i have never pulled it apart before.
This seams to be a bit of a mystery area on out board motors.
 
Is this motor operated in salt water ????---------------The factory service manual has about 70 pages of detailed information , circuit diagrams of the electrical and hydraulic systems.-----step by step trouble shooting as well.------Everything you might want to know about the operation of the unit, no mystery to it at all.
 
Hi I bought a Clymer service manual about 3 years ago which is very good on most things but lacks detail on tilt and trim. It tells you how to operate it, how to fill the oil and about electrical circuits. I don't really want to buy another manual as this one is virtually brand new.

Is there any web sites that can explain more detail? Or can anyone else here tell me how the hydraulic circuit on a tilt/trim works?

The boat is operated in salt water.
 
Totally drain and re-place the tilt/trim fluid. It might be gas bubbles created from the pressure that makes the ball valves 'noisy'.
 
Ok thanks for the suggestion, there could be merit in your idea but wont the gas bubbles come back when I use it again?

Does anyone know what kind of valves are in the tilt trim hydraulic circuit on a Johnson 70hp? Plain ball valves, spring balls, shuttle valves???????
I know there is a valve that can be release to lower the motor if the system fails.
Does anyone know how a tilt trim hydraulic circuit works?
This seams to be a bit of a mystery area that not too many people know about.
Any help is appreciated
 
No big 'mystery. There are mainly simple non-spring loaded balls. If any water contamination in the oil, the noise (air-bubbles) will come back. However with clean oil, the water will not vaporize during pressure and create air bubbles. Even if no leak, the oil will absorb moisture over time and ought to be changed around every 5 years. This might depend if engine/boat is stored in water or on land. Be sure your top bushing for the tilt cylinder is not frozen!
 
Ok thanks haffiman37 for the explanation I see what you are talking about and it makes sense.
I will change the oil and see if it fixes the problem.
I also had a closer look at the top seal on the tilt rod and there is a little bit of oil on the rod so yeah it may need some attention.

I do trouble shooting on machinery at work so I am used to looking at hydraulic circuits diagrams on machinery. That kind of info is a valuable tool when diagnosing problems but I suppose I will have to buy an original johnson manual to get that kind of info. Clymer manual is limited.
Thanks again I will give your suggestion a go.
 
Leakage of the top seal is often due to the trim rod bending due to a frozen bushing for the pivot pin. The pin may be a pain in the AA to gest out!
 
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