Are OEM cylinder head bolts stainless?

[BarryK3]

Hi all,

My 1991 90hp was rebuilt a number of years ago for a previous owner. The power head bolts (for the cylinder head, exhaust plate, transfer port plates) are painted black. The paint is peeling off now and the bolt heads are a bit rusty. The boat is in salt water about once a week lately.

Is the black paint from the factory or did the rebuilder paint it? I'm not sure if these are the factory bolts or if they were replaced during the rebuild. Are the OEM bolts regular steel or stainless?

What should I do now?

1. Remove rust and repaint.
2. Replace bolts with stainless steel (316).
3. Do nothing. I don't want to cause more problems, the engine is running great now.

Thanks,
Barry

 

[jerryjerry05]

The black is the wrong color.
Forces were blue/

They are not stainless.

Just wire brush and then paint, they're gonna do it again.

Why mess with a good running motor?

Once you loosen the port covers, they tend to suck air if the seal has been broken.

The best thing you can do for a salt water motor is: flush it after each use.
WD on the moving parts.
Keep the tank full between trips.
And install a water/ fuel separating filter.

 

[Scott Danforth]

stainless is no where near strong enough

 

[jerryjerry05]

The tuorqe is only 20#

 

[dingbat]

stainless is no where near strong enough

I chuckle every time this comes up...
Unless your talking hardened, grade X hardware, stainless is generally “stronger” than carbon steel hardware. The issue with stainless is elongation, not strength.

Here is a good side by side comparison of mechanical properties of A36 and 304

https://www.makeitfrom.com/compare/...l/ASTM-A36-SS400-S275-Structural-Carbon-Steel

 

[Scott Danforth]

op was talking 316, not 304. standard hardware are not made from A36, they are made from medium carbon steel. Reference SAE J429. ASTM A307 is used for Grad 2 hardware, A325 is used for grade 5 hardware and ASTM A354 are used for grade 8 hardware

Head bolts are generally Grade 5 on small engines and Grade 8 on larger engines

Grade	Nominal size, inches	Full size proofload, psi	Yield strength, min, psi	Tensile strength, min, psi	Elong, min, %	RA, min, %	Core hardness, Rockwell
2	¼ - ¾ inch	55,000	57,000	74,000	18	35	B80 to B100
¾ - 11/2 inch	33,000	36,000	60,000	18	35	B70 to B100
5	¼ - 1 inch	85,000	92,000	120,000	14	35	C25 to C34
1 - 1-1/2 inches	74,000	81,000	105,000	14	35	C19 to C30
8	¼ - 1-1/2 inches	120,000	130,000	150,000	12	35	C33 to C39

most stainless hardware found in your local hardware store are 18-8 which unless you get certified hardware, you can only take the lowest value of the range of 20,000 - 65,000 yield and 65,000-100,000 tensile since most hardware store hardware comes from off-shore suppliers.

dont believe me, take two grad 8 bolts, any size, chuck them in a vice. take one grade 2 fastener and one stainless fastener, thread them in the nuts, then use a beam type torque wrench and see when the heads pop off. hardware store stainless breaks about 80% of the torque of grade 2.

316 is more corrosion resistant than 18-8 due to the lower carbon, however a bit lower tensile strength than 18-8 in the smaller fasteners.

as a side note, at work, most of our A36 is coming in at about 50ksi based on the material certs. the 316L is coming in 35ksi. we have to have certs on everything, including our critical fasteners.

 

[BarryK3]

Thanks everyone! Great info. I will wire brush and repaint.

 

[dingbat]

standard hardware are not made from A36, they are made from medium carbon steel.

C1010 and C1018, both low carbon steels, are the two most common alloys used for fasteners, shafts, etc.

A36 and C1018 are so close in chemistry that you typically don't need to differentiate between the two when measuring both products during production.

The difference in properties primarily comes from downstream processing of the materials. A36 is typically produced as hot band or billets and C1010 and C1018 are typically cold rolled or drawn.

Fasteners made from either material are suitable to mount the seat on my tractor....lol

 

[Scott Danforth]

glass filled nylon would be enough to hold a tractor seat. I used zip ties for about a year