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Alpha one oil leak

by shibbs » 14 Apr 2019, 22:09

Evening all, a question for you mercruiser experts out there.
I’ve just done an impeller change and oil change and just filled it up with oil but I have a leak coming from the small hole on the lower right as you look at it..
any ideas which seal it will be passing from?
I know I’ll have to strip it again but would be good if anyone has any knowledge of what might cause it?
Stu

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by shibbs » 14 Apr 2019, 22:13

Will try and upload a picture as it won’t let me
On my phone.. :evil:
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by Ianfs » 15 Apr 2019, 18:01

This forum software definitely needs an update. :D

Oil coming from the water drain hole, is usually the lower gearshift oil seal, not a difficult job. However if it wasn't doing it before the oil change a less likely option is that oil is leaking up the drive shaft, over the impeller housing and into the front cavity which has the water drain in.


I think your is an Alpha Gen 2 but it will be similar to my Alpha 1 . I'll see if I can dig out some photos to see if we are on the same page. :)
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by Ianfs » 15 Apr 2019, 18:41

The part is actually called Shift Bushing but when you look it up sometimes, depending on which company it is, you'll get the bush in the bell housing come up which is the most common one, also know as the Shift Shaft Oil Seal.

The part I think you want is in the lower gearbox housing and is the Gearshift Bushing. Replacement part no 21015 or Original 23-815921A21, please check it first but I think I'm correct. When it has failed oil leaks into the front cavity of the gearbox housing where the water drain hole is situated.

I hope this helps.
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by betty boop » 15 Apr 2019, 18:58

definately going to need a pic, cant think of a hole but watch out gen 1 is not so alike the gen 2 in places,

Common Gen 2 seals in the lower leg are easy to fix, first off did you replace the O ring on the join lower leg to upper leg, this is not part of the standard 'change gasket ' kit. without it you will leak oil most likely from anywhere as it finds the easiest route out.

if thats all good then the speedo /shift shaft seal is very common, shift shaft and speedo is combined on the G2, - not ion the G1 if I recall its a simple screw out remove shaft/add into new unit/ C clip and replace. You could find on either muck has got between the seal

more complex but common is the carrier seal on the drive shaft under the impeller - not sure where the lube would come out.

You could find on either muck has got between the seal / shaft and will not leak after a clean. Assuming you didnt touch the upper unit theres not much else to leak thats not complex. for peace of mind make a up a pressure tester. mine is an unwanted lube filler end cable tied to a high pressure fuel hose - other hose end goes into a tyre valve -10p from any tyre fitter - you cut off the rubber rim lip to leave the valve stem - insert into hose and jubilee clip/cable tie. That goes onto a foot pump/bike pump with a gauge - pressure up to something low (cant remember how much but is easy to find online 5psi etc ) leave for 24hrs etc, assuming no leak the gauge remains as it is. assuming leak you'll see where the oil/air has burst through the seal or the seal will give as you pump it up, simple look see listen exercise.

Obviously you can do damage by increasing the pressure but if you half intelligent it will be OK, I used to use a draper carb pressure gauge in between for detailed testing but gave up on that one - it worked easy enough assuming the fault is easy to spot. this way has found 3 leaks for me £££ saved is good in my book.

good luck can post a pic if thats confusing to read and you need it .
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by shibbs » 15 Apr 2019, 19:41

Thanks for the detailed responses.
I stripped it again last night and it was the drive shaft seal below the pump housing.
Easy enough to change. It must have caught as I pushed it back into place. To be fair, I should have changed it when I had it stripped.
The only annoying hung is I’d got the full kit for the impeller change, now I’ve had to buy the exact same kit again with the added seal as it doesn’t come separately.
Oh well, lesson learnt.
On the plus side, gimbal and bellows still in tip top condition so comfortably another year out of those.
A last few jobs, well, some quite big ones really but hopefully looking to get her back in the water soonish.

Thanks again for the pointers.
Stu

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by shibbs » 15 Apr 2019, 23:07

ImageImageImage

Thought I’d add the pictures just in case it helps anyone else in the future.
Waiting on parts again now.


Sent from my iPhone using Tapatalk
Stu

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by betty boop » 16 Apr 2019, 17:59

is that G1? looks nothing like mine G2. the shaft seal is now a small unit 50mm dia sized, 3 holes to leaver out and a press gently to reinsert no nuts etc. just looking at the corner of that last pic its much different on the shift shaft to. Hmmm knackered seal though you must have been lucky, on both of mine that failed neither had any marks or damage, the first I think a line got caught under the seal as the shaft spun as a small bit of grit came out - second was just old n crispy.

I wouldnt worry about the impeller - kits in future though, havent changed an impeller for years as they are not a yearly service item just a waste of money your made to think you need to do yearly - the gaskets Ive reused as long as they come off clean from inspections - ie last year when it came apart 3 times whilst blindly chasing the wrong fault. just saying ;) if ur a tight ass like me its quiet easy to cut a new gasket from appropriate material from ebay - just stripped my left riser on the 4.3 mpi and the new dry gasket is £50 I bought one and found out on line it is a graphite covered plate, chinese sell it for £3 a 100mmx100mm sheet so for the right side im going to order some and wait for delivery and clean/reuse the plate
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