any reason not to use stainless head bolts in outboards?

**derekfl** · 04-30-2023, 01:42 PM

they are plain jane steel. i think a little better than home depot quality, but still just steel bolts. i know a busted stainless bolt is way harder to get out, but odds of one snapping i think would be a lot lower. i posted in the for sale section by accident. so deleted and moved it here.

**H2OPERF** · 04-30-2023, 05:57 PM

Not really except in places like head bolts/main case bolts where torque/bolt strenth matters... if you want stainless there you need to go with ARP. Brush the theads on all bolts with gasket sealing compound and they will usuall come right out even on the gearcase/water pump.

**Capt j** · 04-30-2023, 11:25 PM

Stainless will weld itself into an aluminum block. 2 dissimilar metals.

**rgsauger** · 05-01-2023, 12:04 AM

Originally Posted by Capt j

Stainless will weld itself into an aluminum block. 2 dissimilar metals.

even with antiseize?

**H2OPERF** · 05-01-2023, 06:02 AM

Salt is the issue we have not galvanic corrosion, you cant get the bolt out if the heads rusted off either. The sealnt on threads cures both of those problems anyway...

**Revenge22** · 05-02-2023, 10:30 PM

in my view stainless is they way to go for head screws and powerhead / adapter mounting screws. obviously with sealant. its the shoulder that gets crusty and seizes anyway, not the threads in 90% of cases. i wonder if fully threaded screws would actually be better, or would that compromise stability somehow?

**fatlenny** · 05-03-2023, 03:42 AM

Other than the obvious issues that will occur with SS in aluminum, you may have to retorque a few times. I dont believe SS bolts will stretch when torqued. This stretch that head bolts do is to compensate for the heating and cooling and casket compression. This is just my opinion, coming from small engine repair education from 30 years ago.

**derekfl** · 05-03-2023, 07:55 AM

so the consensus is stay with grade 5 steel?

**LakeFever** · 05-03-2023, 08:08 AM

Critical fasteners all need to be carbon steel and they need to be torqued properly for the right amount of stretch. Stainless is gummy and doesnt have much carbon so this is why stainless is not used for critical fasteners. Stock bolts are best. Search out jsre member on here who offers the best advice on bolts and torque specs what lube to use etc

**H2OPERF** · 05-03-2023, 08:54 AM

Yea go with steel... factory steel fasteners are best especially around salt water and make sure you get that torque wrench calibrated for the proper bolt stretch.

**cali kid** · 05-05-2023, 02:49 PM

[QUOTE=H2OPERF;3387328]Yea go with steel... factory steel fasteners are best especially around salt water and make sure you get that torque wrench calibrated for the proper bolt stretch.[/QUOTE Half the outboards in production use stainless for headbolts as well as for most of the fasteners on the motor. Put steel bolts in a lower unit, or water pump housing and see how that goes.

**Aaronhl** · 05-22-2023, 02:30 PM

Steel head bolts non merc do they stretch? What about titanium bolts?

**derekfl** · 05-22-2023, 06:39 PM

i don't think any steel bolt stretches when it is 5/16 or 3/8 and bolted into aluminum. i think you will stretch the threads outta the aluminum first...

**Aaronhl** · 05-22-2023, 07:26 PM

Originally Posted by derekfl

i don't think any steel bolt stretches when it is 5/16 or 3/8 and bolted into aluminum. i think you will stretch the threads outta the aluminum first...

OK but do the steel bolts need to stretch because the aluminum heads heats up or is the stretch only for the initial torque, and since the steel doesnt stretch is that ok?, I might try steel or titanium bolts in some longer thermostat bolts...

And merc 3.0 liter head bolts arnt stainless ???

**BarryStrawn** · 05-22-2023, 07:28 PM

Originally Posted by derekfl

i don't think any steel bolt stretches when it is 5/16 or 3/8 and bolted into aluminum. i think you will stretch the threads outta the aluminum first...

That isn't correct. If any metal bolt is torqued or loaded at all, it is stretching. How much torque or load will determine how much elastic stretch, if it yields, breaks, or fails the threads in the block.