Sealing crankcase halves, which sealant? 1972 Johnson 6 HP

[jrs_diesel]

My service manual calls for Adhesive M for the crankcase halves (3M # 847), but i have read here that Gel Seal (Loctite 518) may be a better sealant to use.

Which one should I use?

[seahorse5]

Adhesive M is also distributed as Marpox or Boat Armour Sealer 1000 and the trade name is 3M 847

[j_k_bisson]

The 3m 847 is for rubber gaskets and belows. The 518 is flange sealant and the right stuff to use. Don't need much, only about 5-10ml bottle will do any job. Also watch out and check the expiry date. It goes bad fast.

[Joe Reeves]

If one half of the crankcase has slots that a spaghetti type seal would rest in, then use the 3M#847 adhesive. If the crankcase halves are simply a machined fit with each other and do not have the sealing slots, use the Gel Seal.

The confusion is due to the fact that before "Gel Seal" existed in the marine world, the larger horsepower engines incorporated slots in on one half of the crankcase halves (on both sides of the crankshaft). A black spaghetti type seal was laid in the slots, then the 3M sealant was spread on top and around the spaghetti seal material. This resulted in a sufficent seal with no leakage. This same 3M#847 (OMC Adhesive) sufficently sealed the smaller horsepower crankcase halves "without" the slots or spaghetti seal.

With the coming of "Gel Seal", the spaghetti seal slots were no longer needed and "Gel Seal" became the new sealant for all of the horsepower models. Gel Seal does the sealing in the absence of air........ when the two crankcase halves are torqued together.

However, the older still existing engine models that "do have" the spaghetti seal slots will still require the 3M#847 sealant.

[jrs_diesel]

Awesome information there Joe.

No spaghetti seals or slots on this little 6 HP. Like you said, it's a machined fit. I'll be using the Gel Seal.

Thank you all!