'66 80 HP Head Bolts Needed

[riktweed]

We are putting new heads and gaskets on our 80 and want to replace the headbolts. Two had broken so those need to be replaced at minimum. Does anyone know the specs on those? I am not finding that part number (302767) online and need to try and get a good match from another source.

Thanks for any tips - Rik

 

[dew2]

Re: '66 80 HP Head Bolts Needed

Dont know where you are located,But here I just go to a box hardware store that carries stainless steel bolts,Get them to match.

 

[riktweed]

Re: '66 80 HP Head Bolts Needed

Thanks. We did not find them at our local hardware, but interesting to hear you have used stainless replacements. The old bolts were corroded onto the cylinder head and two snapped on removal. Even with the bolt caps off we still had to drill them out to get the head off.

 

[Cofe]

Re: '66 80 HP Head Bolts Needed

Dont know where you are located,But here I just go to a box hardware store that carries stainless steel bolts,Get them to match.

Do stainless steel and hardened steel head bolts have the same thermal expansion/contraction rate

 

[riktweed]

Re: '66 80 HP Head Bolts Needed

That is the big question. We are going to try and find the original spec, but if stainless can be used without causing problems in this application I would consider it to prevent corrosion.

 

[Chris1956]

Re: '66 80 HP Head Bolts Needed

I am pretty sure my old Johnny 50HP V4 has stainless head bolts. Actually, most everything on that motor was stainless, brass or aluminum. Unless the torque values for the head exceed the grade 2 strength threshold, I would think stainless would be fine. (stainless steel is about grade 2)

 

[Cofe]

Re: '66 80 HP Head Bolts Needed

I am pretty sure my old Johnny 50HP V4 has stainless head bolts. Actually, most everything on that motor was stainless, brass or aluminum. Unless the torque values for the head exceed the grade 2 strength threshold, I would think stainless would be fine. (stainless steel is about grade 2)

Lots of different grade SS bolts. I have seen plain ss bolts exceed shear strength of a grade 8 bolt.

The head bolts in my 25 are carbon steel, what grade I do not know....

 

[F_R]

Re: '66 80 HP Head Bolts Needed

Don't use stainless steel!!!! They will corrode and sieze worse than the steel bolts did. Why? Because they are more dis-similar from the aluminum. The more dis-similar, the greater the galvanic action, which is what causes the corrosion. OK, OK, so it is the aluminum that corrodes, not the stainless. Small matter when it siezes and you can't get it out and break it off. And when you do break it, stainless is much more difficult to drill out.

There is reason for using stainless below the waterline, or where they are exposed. In those cases, the corrosion is the lesser of two evils.

 

[F_R]

Re: '66 80 HP Head Bolts Needed

Following up, you have the original bolts. Take one to a hardware store and find a clerk that knows his head from a hole in the ground, and he can tell you exactly what they are just by looking at them. The things to be concerned about are the material, the "grade" or hardness, the thread size, the length, and the length of the threads. OMC truly loved to use non-stock bolts, so you may not find them at the hardware.

 

[riktweed]

Re: '66 80 HP Head Bolts Needed

Thanks for all the good advice. In fact the SS bolts at the hardware store were not of a grade to handle the torque required according to the engineering tables. While flange bolts like the originals are not stocked, the local Ace Hardware does carry a good quality SAE grade 8 hex head 5/16"x 18-thread bolt and matching hardened washer. This grade exceeds the factory torque spec of 16-18 ft lbs dry.

The only real issue was the length - stock is 2.25" (an odd length, as you suspected) and common is 2" or 2.5". After cleaning and inspection, we decided to replace only the 2 that broke. We went with the 2.5" for maximum thread and put them in the two center most holes which we found to be more than deep enough.

We reassembled the port side this morning with new gaskets and it went together just great, tight and right. Starboard side next and then on to the next thing... thanks again.