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jdc
01-12-08, 10:03
I took apart my seized 2 stroke Mercury 3.3 outboard this weekend (big end needle roller had rusted up!), and all is now well except stupidly I didn't notice which way the oil seals go. There's one either side of the crankcase.

They have a U cross section, with a flat face and a dished face; does the flat part face in or out (and is it the same for both anyway)? I also wonder whether they were the right way round in the first place since water got in there somehow and I don't think it came via the exhaust or gasket failure.

The clean side is the crankcase, but on the other hand the low pressure is on the inside (it's a 2-stroke), so I'm confused and would be grateful for advice.

james

bazza
01-12-08, 10:44
Just done my Tohatsu. If I remember one side had the flat face pointed in, the other side was the opposite! If you look carefully at the old seals (I reused mine) you should be able to make out the marks left by the semi circular thrust plates that fit inside of the seals.

vyv_cox
01-12-08, 11:01
Free workshop manual here. (http://books.google.com/books?id=LPDseE1mkT8C&pg=PA319&lpg=PA319&dq=2+stro ke+outboard+seals&source=web&ots=zuBNR039Me&sig=A8 EeEl_cC_8sHAUbWP3uEYB5X7U&hl=en&sa=X&oi=book_resul t&resnum=1&ct=result#PPA232,M1) See page 231.

earlybird
01-12-08, 11:27
The oil seals should be fitted with the lips facing in towards the main bearings, and the flat faces outward. BTW, have you split the crankshaft assembly to renew the big end? If, as I believe, it is a pressed assembly, this is no easy job for a home mechanic, hope you've got back together true. Good luck

drawp
01-12-08, 15:57
How I always remember is that the pressure acts outwards from inside the U, forcing the seal onto the surfaces either side.

Clyde_Wanderer
01-12-08, 20:57
Side with the tensioning spring around the sealing lip to the inside.

VicS
01-12-08, 22:00
[ QUOTE ]
tensioning spring around the sealing lip to the inside

[/ QUOTE ] The diagram on page 231 of Vyv's link appears to show the seals with the lips both facing down (ie top one inwards lower one outwards) but the text in paras 13 and 15 on page 269 indicates, I think that they both face inwards. However that refers to a diagram of 6 to 15 hp models in which the two seals appear to be different!

This sort of confusion is why these third party manuals are so poor. They attempt to cover too many models.

FWIW the crankshaft seals in my Evinrude both face down. ie the top one faces inwards and the lower one outwards. Clearly and specifically shown on the parts diagrams.

I would interpret the diagrams in the mercury parts list HERE (http://www.crowleymarine.com/mercury_parts/4665/60.cfm) as also showing them both facing down but it is too general to be sure.

A question on the Mercury engine forum at iBoats (http://forums.iboats.com/forumdisplay.php?f=25) would stand a good chance of an accurate reply.

earlybird
02-12-08, 08:25
To put oil seals facing different ways is illogical and incorrect. The correct way is as stated in my earlier post. This agrees with the Mercury 2.2 manual, which I have to hand, and also with proper engineering practice. The primary purpose of the oil seal, as it's name indicates, is to retain oil, and petrol mixture, in the crank-case. They are designed to achieve this by being fitted with lips facing inwards.

Startline Al
02-12-08, 08:31
[ QUOTE ]
Side with the tensioning spring around the sealing lip to the inside.

[/ QUOTE ]

Agree with you.

VicS
02-12-08, 08:53
[ QUOTE ]
To put oil seals facing different ways is illogical and incorrect

[/ QUOTE ] obviously in a Merc they go which ever way round the manufacturer's workshop manual states for the specific model concerned. Likewise I suggest for other makes.

I will leave it to you to tell BRP that the seals fitted to, some at least, Johnson and Evinrude engines are fitted illogically and incorrectly.

Evinrude 6hp (http://shop2.evinrude.com/Scripts/ImgServ.exe/convert?ilFN=E%3A%5CEmpartWeb%5CData%5C41%5C394670 %5C17.TIF&ilSC=39&ilIV=0&ilBR=0&ilIF=P&ilRE=8) items 2 and 3.

The only source for the correct info is the manufacturers manual for the specific model!

Rogershaw
02-12-08, 08:59
[ QUOTE ]
How I always remember is that the pressure acts outwards from inside the U, forcing the seal onto

This is always how the seal manufactures recommended it when I worked as a mechanical designer, but in the crank case of a 2 stroke engine the pressure alternates between above then below atmospheric depending which part of the cycle thew engine is in.

To be correct the single lip seal is not quite correct it should be a double lip seal, which is more costly, but as the pressure differences are small it should not make too much difference but I woulf fit the seal with the spring inside for both seals

vyv_cox
02-12-08, 09:44
I'm not going to argue with your manual, which I assume is for the two-stroke? However, it is confusing because, as has already been said, the pressure in a two-stroke crankcase can be less than atmospheric and there is oil on its outside on the transmission side. So there is some logic in installing the seals facing opposite ways.

Startline Al
02-12-08, 10:43
So long since we did any two stroke work I thought I'd check with a friend of mine, he's got pretty good two stroke credentials having started mechanicing with a certain Mr B Sheen and finishing up as crew chief for Kevin Shwantz.
He said.....unless its an unusual design (tapered) it should work either way. If it was running in oil on the outside he'd tend to stick the spring side there.

earlybird
02-12-08, 11:21
I admit ignorance of the engines used by Barry Sheene, but, AFAIK, in 2 stroke design, the positive pressure differential in the crankcase considerably exceeds any negative differential. Also, since the prime purpose of the seals is to retain petrol mixture, they should be fitted with the garter spring inwards. Many seals do have an additional wiper lip on the outer face. This is principally intended to exclude dirt etc from the main seal surface, it will enable the seal to work either way round, after a fashion, but it will be less efficient. I can't remember seeing a 2-stroke where the crankcase seal doubles as a transmission oil seal. They may exist, but it seems poor design. on reflection, was my old Villiers engine like that, and look what happened to them!

Startline Al
02-12-08, 11:27
Square four 500cc two stroke.

From memory I think the majority of bike stroker engines run one side (clutch) in transmission oil and the other side dry.

Example (http://www.trials.com.au/absolut/files/articles/trialtech-article-20081122-crankshaft-seals.pdf)

Whether this has any relevance to outboards, I've no idea. /forums/images/graemlins/smile.gif

vyv_cox
02-12-08, 11:59
That's quite a good link. It clearly shows the crankcase oil seals facing opposite ways.

I trust that the original poster is now so confused that he wishes he'd never asked the question! /forums/images/graemlins/smile.gif

earlybird
02-12-08, 12:42
[ QUOTE ]


I trust that the original poster is now so confused that he wishes he'd never asked the question! /forums/images/graemlins/smile.gif

[/ QUOTE ]
I must agree. However, if it helps him, my Mercury 2.2 manual is absolutely clear, with specific diagrams for each seal, that the oil seal lips face towards the bearings.
I am now off to get a life!

VicS
02-12-08, 12:56
[ QUOTE ]
my Mercury 2.2 manual is absolutely clear, with specific diagrams for each seal, that the oil seal lips face towards the bearings.

[/ QUOTE ] Thats fine. you presumably have a 2.2 merc and you manual is hopefully for the same year model.

The original question was about a 3.3 merc the age of which was not specified. It may or may not be the same as your 2.2.

The only place to get the correct answer is the manufacturers manual for the specific model concerned but if I was JDC I would put the question on iBoats as already suggested

Best place for 3rd party manuals is known as trash can.

jdc
05-12-08, 18:15
[ QUOTE ]
I trust that the original poster is now so confused that he wishes he'd never asked the question!

[/ QUOTE ]

Not at all - I'm very grateful for all the advice, and rather glad that it wasn't such a dumb question after-all!

What I have decided to do is:

fit the top one. which is between the crankcase and open air, with the flat side out and the lipped side (ie where the spring would be were there one in these small seals) in; and

fit the bottom one. which is between the crankcase and the exhaust, with the flat side facing the crankcase and the lipped side facing the exhaust.

My reasons are:

1. That's what the exploded diagram implies, although not categorically;
2. As several have pointed out, the lips/spring should face the higher pressure which is perhaps in the exhaust; and
3. (cheating this one!) I think I remember it was this way, but can't be 100% sure.

Anyway, many thanks.