What type of bolts

I am currently re fitting the exhaust elbow/injector to my SP 135 Lehman.

The four bolts are, I think, mild steel and I assume that the manifold is also steel (cast iron) The bolts are looking a bit tired - the thread looks a little worn so no problem - up to the bolt shop for some replacements.

Should I replace with mild steel, or could/should I go to Stainless Steel - is there any advantage in stainless?

"is there any advantage in stainless?"

Should rust less than mild steel., so easier removal the next time.

I still prefer mild steel bolts over stainless in most cases. Use some anti seize and they'll come out easy down the road.
Stainless steel is usually softer.
In this case I would use steel for the manifold, and either for the elbow.

Depending on the bolt shop...

Inconel A286 would be the absolute best.

ASTM A193 B16 or B7 would be great.

Acklands or Fastenal could get Inconel, and might have B7 or B16 in stock

If you want to go stainless, use 304, (or B8) I wouldn't, though.

jleonard said:

I still prefer mild steel bolts over stainless in most cases. Use some anti seize and they'll come out easy down the road.
Stainless steel is usually softer.
In this case I would use steel for the manifold, and either for the elbow.

Click to expand...

+1

Never heard of "mild steel bolts" Is that an actual classification? Or do the posters using that expression actually refering to grade 5 bolts. I would assume G5 bolts/cap screws were higher carbon content than mild steel. Perhaps "mild steel" is what Ace Hardware has.

Spy ..... What about that?

The only place for stainless steel fasteners near an internal combustion engine is hose clamps in my opinion. I'm with Northern Spy on the rest. Fastenall should have what you need in stock.

Mild steel is regular old low carbon steel.

OK. I just looked at the web view of the forum, and realize the question was asked by an Australian.

That changes things as I really don't know what Australia uses for specifications. I remember crossing over some of Rex's anchor steel specs from ISO to ASTM.

Inconel is Inconel everywhere as it is a brand name.

B7 is a chrome-moly alloy steel. Equivalent would be a 4140 alloy steel.

B16 adds vanadium. I don't know the equivalent... Maybe an 8740...

Never heard of "mild steel bolts" Is that an actual classification?

Click to expand...

I answered using the expression that the poster used. I assumed he meant "regular steel bolts" as one would find in a hardware store.
Yes I know there are different grades, just wanted to keep my answer simple.

WOW - I thought steel was steel and stainless was stainless so I thought my alternatives were to go to the chandler and ask for stainless steel, or the bolt shop and ask for regular steel.

Am I right to summarise that any steel is better than stainless? If the bolt shop has a choice of steels, the best type would be.........................?

BTW, I do appreciate the contributions (as always)


George

There are 1,000s of types of steel.

Another thought for stainless would be a 17-4ph steel. Condition A if you can get it. Fairly available.

In fact, I'll put that right below inconel.

I really would stay away from a 300 grade SS.

Note: Were there any head marks on the existing bolts?

No need for stainless there. In fact while the SS does not corrode readily, it can set up a galv cell with the mating cast iron, should it be damp. In that case the iron corrodes and the corrosion products pack the gap and now the bolt is seized. No bueno.

Grade 5 SAE fasteners used in all but high stress joints. Grade 5 fine for OP's joint.

Steel bolts will usually have a marking on their head.

Look up the equal to a SAE grade 5 in where ever you are , or just go to NAPS or Ace, in the USA.

Grade 8 will be there also, but at a higher cost.

Might be some merit to the galvanic corrosion with SS to the casting. Good point.

I'd still seek a chrome-moly stud/bolt material if possible.

A grade 5 is a medium carbon steel. Very ductile and may creep with heat cycles.

That said, I doubt Lehman put any consideration into this.

If it is not a problem, there really is no required fix...

I think those bolts are adjacent to water jackets on each end, so temp probably not an issue. If they do get hot, then grade 8 I think has better high temp performance, but never checked into that.

If temp is not an issue, than a grade 5 would be just fine.

Well, in the end I went to the bolt shop and bought grade 5 - we call them "high tensile" down here.

Maybe what would be interesting is a tutorial for boaties on what type of bolts to use where - what`s stainless good for and in what applications -ditto for regular (or not so regular) steel. There sure is some knowledge amongst our members........

Thanks again for the help

Ski in NC said:

No need for stainless there. In fact while the SS does not corrode readily, it can set up a galv cell with the mating cast iron, should it be damp. In that case the iron corrodes and the corrosion products pack the gap and now the bolt is seized. No bueno.

Grade 5 SAE fasteners used in all but high stress joints. Grade 5 fine for OP's joint.

Click to expand...

What he said.

This isn't brain surgery and it isn't a high pressure, high stress, high corrosion application.

Grade 5 fasteners with a good anti-corrosion (or Loctite) coating on the threads are all that's needed.

George, I`m not far off having mine done, were they difficult to remove? What condition were the angles in?
I got new gaskets while in Seattle recently, posted to the hotel by the ever helpful fredwarner1(ebay).

Bruce,

Remember I`m talking about a 135, but very straight forward - a socket with a 100mm extension - easy peasy - however having said that - I was luck the bolts weren`t seized.

The only complication was the run of flexible exhaust pipe from the elbow to the muffler - mine is only short (on the port engine ) and took some effort to firstly break the rubber pipe free from the elbow WD40 helped), then get it to bend enough to get the elbow free.

I took it off, more out of curiosity than anything - I had steam from that engine and found the impellor was stuffed - I know the heat exchanges are good so I thought I`d check the elbow - glad I did - it was made of mild steel and had rusted on the inside - enough that when I poked a wire down into the cavity between the inner and outer pipes to clean out some gunk - it broke through the weld, letting water into the exhaust. Raw steel and salt water aren`t great partners. That's why I had mine remade in stainless. The other side is next.

George