Logo
FULL SITE MENU

Volvo Penta sterndrive 290 SP-A – Vacuum test.

M

moresparks

Regular Contributor
hi ... not sure if I should bother??
Have my sterndrive off and at home for overhaul and painting etc.
I have drained the oil and it’s as clean as it went in. I have pressure and vacuum tested.
Will hold 17Psi pressure for hours no problem.
However the vacuum test worries me. I can evacuate the drive to around 7 Hga (25kpa approx) and it will hold for hours. But if I increase to recommended of say 11hga (47kpa) it will slowly slip back to around 7Hga after about 15mins and hold. Believe to be in specification but.... Looking back at my notes it hasn’t changed much in the last few seasons.
I have twin sterndrives and the other one is spot on pressure and vacuum tests.
With such a minor “leak” it will be difficult to trace.
I am thinking of replacing the gear selector seal and retesting as that is probably 6 seasons old and probably wouldn’t hurt.
Anyone had anything similar and could point me in the right direction, rather than replace the seals one by one till I find the cause?
Or should I leave well alone?
 
..................
moresparks said:
hi ... not sure if I should bother??
Have my sterndrive off and at home for overhaul and painting etc.
I have drained the oil and it’s as clean as it went in. I have pressure and vacuum tested.
Will hold 17Psi pressure for hours no problem.
However the vacuum test worries me. I can evacuate the drive to around 7 Hga (25kpa approx) and it will hold for hours. But if I increase to recommended of say 11hga (47kpa) it will slowly slip back to around 7Hga after about 15mins and hold. Believe to be in specification but.... Looking back at my notes it hasn’t changed much in the last few seasons.
Due to the nature of the seal lips, the seals in the drive hold against pressure much more effectively than against vacuum.

I have twin sterndrives and the other one is spot on pressure and vacuum tests.
With such a minor “leak” it will be difficult to trace.
Believe it or not, shaving cream works fairly well to pinpoint a vacuum leak.
When placed on the suspect area, and while under vacuum, it will disappear if there is a leak.


I am thinking of replacing the gear selector seal and retesting as that is probably 6 seasons old and probably wouldn’t hurt.
That would be your "eccentric piston" seal.
Good call.
These are prone to leaking after several years of service.
Do a search using my user name before doing so.
There is a trick to use for certain eccentric piston detent retaining "spring" pins.
The spring pin that runs parallel to the piston must be retrieved.

Anyone had anything similar and could point me in the right direction, rather than replace the seals one by one till I find the cause?
Or should I leave well alone?
I would begin with the eccentric piston seal.

NOTE: the eccentric piston seals are directional, and will prematurely fail if installed incorrectly.
Click to expand...
 
Many thanks for your speedy response..
It is bothering me so I am ordering the seal etc.
Have already removed the selector unit and removed the roll pin etc - no problem.
Just have to remove the lip seal without damage to the casting.
Have done this before but its not easy.

I will report back when its all refitted.
 
moresparks said:
Just have to remove the lip seal without damage to the casting.
Have done this before but its not easy.
Click to expand...

Years ago I bought a surgical gouging tool. I reversed the profile at the gouging area so that the new profile will allow it to go in between the seal casing and the seal bore without causing any damage to the bore.
It works very well.
I do need to re-sharpen it occasionally.



seal removal tool.jpg



As they say...... "the mother of invention is necessity".



.
 
Last edited:
Just an update..
Completely overhauled the gear selector plate with new eccentric piston seal and O ring,but no improvement.
Tried the shaving foam test and that does not give any clues.
I am leaving it under pressure overnight to see if that will give a clue. I have some leak detector fluid and although not conclusive it shows some disturbance on the seal under the plate where the permatex sealant is used. Possibly need to re finish and smooth off where it all joins.
If I need to remove the Bearing Carrier.. to replace the prop-shaft seals, I will make the prop removal tool.
Quick question .. can you confirm the thread of the long threaded rods is it 7/16 UNC thread.
“(290 SP-A Drive)" .. Only someone mentioned it may be 5/8.
Many Thanks.
 
..........
moresparks said:
I have some leak detector fluid and although not conclusive it shows some disturbance on the seal under the plate where the permatex sealant is used.
I use grease only around the O-ring between the shift mechanism housing and the main gear case.
You must be careful that any excessive grease between the O-ring and its groove does not become trapped and cause a hydro-lock.
Yes.... hydro-lock. (that was not a typo!)

I use Perfect Seal on the seal and it's bore.


If I need to remove the Bearing Carrier.. to replace the prop-shaft seals, I will make the prop removal tool.
My tool design is used to pull the prop shaft bearing carrier out...... it will not remove a prop.
Quick question .. can you confirm the thread of the long threaded rods is it 7/16 UNC thread.
“(290 SP-A Drive)" .. Only someone mentioned it may be 5/8.
Yes, those threads are 7/16” NC.
Use grade #8 threaded rods and nuts.
Click to expand...






.
 
Many thanks for that..
Apologies - my typo ... meant Prop Shaft Bearing Carrier removal Tool.
I did fit the “whole mechanism” exactly as stated in the workshop manual.
I will remove, clean the whole area up and try refitting again.. any luck I may see some shaving foam or leak detection fluid to give a clue..
 
Back
Top