Big Twin Lower Unit Reseal Question

[Doug Wilson]

make sure the shift shaft o-ring is ok they usually seem to be the weak spot

Doug

how is it motors multiply when the garage lights get
turned off?

[raglover]

Thanks for the replies. Let me give some more detail.

I completely resealed, including shift o ring. Use scotch weld 847 new prop shat drive shaft and spaghetti seal. Standard fare for the split case. Resealed quite a few but this one is troubling me.

Testing first at 8 psi under water and rotating…..no bubbles.

It will hold pressure for hours. Using the Stevens instruments gear case pressure tester and a Miley vac vacuum tester…the latter it under water. Vac test fails faster but cannot tell where.

Shafts are good, no grooves….actually a later lower unit that had zero noticeable wear but had evidence of a prior reseal with too much 847.

Here is how the leak exhibits. Fresh oil passed all pressure tests. Run it for an hour on boat. Drain and it is milky….more so than just the air bubbles. Some times there was trace amount of oil behind prop. Tore it down and resealed with new prop shaft seal and spaghetti seal and required cleaning. Ran it again after passing all pressure testing and same result but this time no oil behind prop…..looks like there is more than just tcw3 oil in exhaust cavity when I drop lu. Even ran the motor on an old tempo hose tester and got no water in oil.

Only conclusion I have is a seal is failing under water under way. Because I pass pressure testing (best I can tell) I was thinking I had water getting sucked in….thus the theory on double stacking

Got me stumped and I want to get the boat going for a meet in Chaplin next week.

Thanks for all input and suggestions. Please keep them coming!

Allen

[pappy]

If you are using alot of vacuum on a single lip seal with the seal properly oriented to keep the oil in……then you may have exactly what you are describing.
When using vacuum remember it is in inches, not pounds. Pretty powerful stuff. Would prob. use no more than a few inches of vacuum for that test.
You can do a visual vacuum test on the bench by using soapy water and watch the water bubbles get sucked into the seal in question.

[jeff-register]

I’m with you Pappy. I seat the seal & retainer after the shaft is in place as well to get the correct friction feel on the shaft & o-ring as well. Not tight but a firm fit.

[fleetwin]

Keep trying to pinpoint the leak in the bucket of water, twist the shafts/pull the shift rod up and down, use the low and high pressure settings as others have described.
PS- I mean no offense, I’m sure you have checked, but does each gearcase lube plug have one, and only one gasket? It is surely easy enough to mix them up putting two gaskets on one screw and none on the other. Have you probed the screw cavities in the gearcase to ensure there are no remnants of the old gaskets left in the holes?

[raglover]

I found it, finally. Spaghetti seal. Started leaking at 10 psi. Had some trouble with this one. Lapped surfaces new seal, 847 sealer.

Oh well. Back apart we go.

Is there a better sealer than 3m 847? I have seen listings for loctite, anyone tried it. D if so what type?

I am also going to switch to hex socket stainless screws. Those flat heads are getting too beat up.

[chris-p]

Im assuming it is leaking where it abuts the prop shaft seal housing carrier?

Ensure that the seal overhangs 1/16", not too short or it will shrink and leave a gap, not too long or it will buckle.

Before cutting it, ensure you push the seal to the outside edge of the groove.

The 847 is a superb product, not much better than that. If it is leaking, not the 847s fault, something else is going on.

[raglover]

It is actually leaking in the straight sections about secon screw from rear and one from front.

Will know more about his week after dismantling

Thanks

Allen

[jeff-register]

Allen,
When I resealed my 53 Evinrude 15HP 1954 it had the same mechanics. The new spaghetti was dipped into the sealer & mating surfaces were precoated. The end cuts were done with a razor & were cut very square & seated against the end. I also let the sealer harden overnight to start the curing process before adding oil. Check all threads to be sure to be clean & seat well. Hope this helps,
Jeff

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