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Crankcase to Block Gasket??

K

KyPoorBoy

Member
Hello,
I have a 1972 Johnson 25HP model 25R72R. I recently got this motor and after getting it running I see gas spitting out from what appears to be a bad seal between the crankcase and the cylinder block. After looking at the shop manual and parts diagrams, I cannot see a gasket listed for this area. However, it certainly appears to be a gasket edge sticking out of the motor and it looks broken where the fuel mix was leaking. I have it tore apart with only the crankcase left to remove to access it. Also, can I remove the crankcase without worry of any internal parts being disturbed?? I appreciate anyone's help and I want to thank all who share their knowledge and experience with these old motors so I and hopefully the next-generation can appreciate these classic motors.
 
Use loc-tite 518 to seal between the crankcase halves paint both sides with it and reassemble. Make sure there are no gouges and the crank halves are in good shape. You should be able to pull the intake side off and leave the crank in. Also make sure you reinstall the seals when you reassemble it and use the correct torque and sequence.
 
Timing is everything once you apply the loctite quickly assemble the halves most all of the sealant should squish out metal to metal. I just put a light bead on one half and quickly bolt them together using a center out pattern. Do a couple dry runs and check the end play on the crank is good then install the seals and assemble the halves with the sealant. The halves are a machine fit the sealant can act as a shim and throw the bearings out of spec.
 
Thanks again for the very useful help. I already have the 3M 847. Can I use it with the same results? Also, any suggestions for how to remove the middle bolt in the front, under the intake,.that holds the powerhead
to the housing. It is proving to be difficult ,as I thought it would when I saw it. Again, many THANKS.
 
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KyPoorBoy said:
Ok, I have it broken down, so can I use the 3M 847 instead of the lock-tite . Are they the same? Thanks Again
Click to expand...

OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964 or "Loctite #518". Any of these are what's known as "Gel-Seal".
 
Use BRP gel seal or loctite 518.-------------I do not use any other product.---I would not use a " rubber adhesive " for this critical application.-----------Do not use 776964.
 
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You use the 3M 847 on crank case haves that had a groove cut in them for a o-ring type rubber seal. Motors used that for years. The Loctite 518 is used for ones without the groove.
 
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My 25R72R doesn't have a "spaghetti" seal on the crankcase halves. It's metal to metal except for the oil seal on top of the crank. I don't use it on the oil seal do I? Also, just to clarify, should I only use the 3M #847 only where there is a rubber seal? Thanks Gentleman
 
KyPoorBoy said:
My 25R72R doesn't have a "spaghetti" seal on the crankcase halves. It's metal to metal except for the oil seal on top of the crank. I don't use it on the oil seal do I? Also, just to clarify, should I only use the 3M #847 only where there is a rubber seal? Thanks Gentleman
Click to expand...

No, don't use it on the oil seal, a little oil will be fine on that item.
 
That makes perfect sense to me Joe to put oil on the oil seal with the same principle as putting oil around the seal on an oil filter. Also, looking forward, I don't plan to use any product on the gasket the powerhead sits on inside the motor housing or the gasket between the motor housing and the exhaust housing. Is that correct? Finally, I am forever grateful for all the help and advice from you Gentleman who take your time to share your knowledge and experience with these awesome motors. I have always enjoyed them, my first being a 1949 Ward & Montgomery 5HP . It had fins on the motor cover that reminded me of a 57 Chevy . I hope that I can help pass on my enthusiasm so the next generation will hopefully have an appreciation for these motors and their quality and the hours of enjoyment they provide. Thanks so very much.
 
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I use a light coat of permatex aviation on all gaskets except head gaskets. Just brush a light coat on both sides of the gasket. It makes it a bitch taking it back apart but I never have to take stuff apart because of a leaking gasket. Never use silicone of any type anywhere on a marine engine period!
 
So are you saying that I should use a gasket sealer on the powerhead gasket and the exhaust housing to motor housing gasket? Also, speaking of the head gasket, what is recommended for the head gasket. My shop manual isn't very clear about it. Thanks again Everyone.
 
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Head gaskets are already pre coated. Lightly surface the head and slowly torque it down to spec with a center out pattern in at least three steps. I use my table saw and some 220 grit paper and just swirl the head in a figure 8 pattern until it all shines the same. A glass table works well also. Use a inch pound torque wrench and torque it to 120 inch lbs.
 
fetch
 
Ok, I can do that and I absorbed your instructions much better than the manual for some reason. I guess because the manual is written by engineers who just think differently than most of us. Not to sound negative, just different that's all. One last question please, I am still unsure about the powerhead adapter gasket, that the complete powerhead sits on. and.this 25R72R has another gasket on top of.the exhaust housing which is under the motor housing, called the exhaust housing seal # 308292.. I don't know what to do about them. The last powerhead I installed on the housing I was told not to use anything on the seal. only the seal by itself. The exhaust housing seal, seems like a thin foam pad , should I "glue " it to the exhaust housing just on that side or nothing but the gasket? Thanks again All Everyone!!
 
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(Gasket Sealers)
(Usually available at any reliable automotive parts type store)
(J. Reeves)


Do Not use any type of sealer on outboard carburetor or intake manifold gaskets as this would cause blockage of various fuel/air passageways. Also, there are new type gaskets, including head gaskets, which are used through out the engines that are coated with a substance that gives a shinny appearance to them. These gaskets are coated with a self sealer and are to be installed as is.... no sealers! Older style head and fuel related gaskets that are not coated with this substance are to be simply coated with oil.... nothing else.

All other gaskets (hopefully I've not overlooked anything above) should be coated with Gasket Sealer (the type that comes in a can that has a small brush in its screw off cap). This also pertains to some water pump installations that use a gasket between the plate and the lower unit housing.

Marprox Sealer 1000 or OMC Adhesive or Boat Armor Sealer 1000 (same substance)[See Below Note] should be used on any metal to metal (Unless GelSeal Is Called For) or metal to plastic surface (such as impeller hsg to plate, and plate to lower unit surface) to eliminate air leaks. It should also be used on the Spaghetti tubing that is used on many powerhead crankcase halves, lower unit skegs, etc. I have found that this substance works quite well on various "O" Rings such as what are found on lower unit carrier and upper driveshaft bearing housings (Note that this substance is obviously not to be used on all "O" Rings). This substance also works quite well in sealing the surfaces between the lower unit and the exhaust housing to which it attaches, eliminating the unsightly water spray between the two after completing a water pump installation.

NOTE 1: I am under the impression that Marprox Sealer 1000 and Boat Armor Sealer 1000 is no longer available.

NOTE 2: OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964 or "Loctite #518".

DO NOT use any sealer on the large "O" Rings that are used on the upper and lower crankcase heads (The housing/heads that slide over the top and bottom of the crankshaft). On those "O" Rings, use only a coating of grease.

The exception of surface to surface contacts pertains to the later model matching crankcase (block) halves (which does not incorporate spaghetti tubing) which call for "Gel-Seal", or any other surface that calls for Gel-Seal. This substance seals in the absence of air, and if called for, must be used. One other form of Gel Seal that can be substituted is "Loctite #518". Nothing else that I know of will do!


I advise against using silicone or permatex on a outboard engine. It simply will not function properly. The exception to this (as per OMC's recommendation), is to use the black Permatex (heavily) on the gasket 306242 which seperates the inner exhaust tube from the exhaust housing on the 1959 35hp and 1960 to 1970 40hp OMC outboards.

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(GelSeal & LocTite 518)
(J.Reeves)


GelSeal and the equivalent substance of LocTite 518 creates a sealing condition due to the absence of air. What remains of the substance after torquing the retaining bolts, as you may have noticed during disasembly, is a very thin almost clear sheet of sealant.


There is a removing substance to remove that old sheet but I have found that it can also be removed by carefully using a sharp putty knife like tool. Just be carefull not to actually scrape into the aluminum surface.


There are various methods to applying this sealer. My method is to apply a thin bead of the sealant from one end of the crankcase to the other, then spreading it around with ones finger so that it encompasses all of the bolt holes.


Make sure that you do not apply that substance any closer than 1/4" to the Main Bearing areas or to the Taper Pin holes.


As mentioned above, the substance seals with the absence of air, meaning that as soon as you set the other half of the crankcase in place, the substance starts to slowly take effect. So plan your job so that once you start this portion of the rebuild, you follow straight thru to the finish (all bolts tight and torqued).


The sealer substance that squeezes out internally will not harden as it will still be exposed to air. This will simply blow out the exhaust as the engine runs. The excess that squeezes out externally.... simply scrape/wipe it off to eliminate the gooey appearance.


Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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