Can I anneal M8 phosphor bronze bolts?

[Oily Rag]

I've just replaced the bolts on my Beta 30's heat exchanger end caps because the old ones were about ten years old. M8 phosphor bronze, according to the Spares List.
They look fine to me, so they're now in the Spares Box. But should I have annealed them first? And if so, is it as simple as quenching from red hot as per copper washers?

 

[VicS]

I've just replaced the bolts on my Beta 30's heat exchanger end caps because the old ones were about ten years old. M8 phosphor bronze, according to the Spares List.
They look fine to me, so they're now in the Spares Box. But should I have annealed them first? And if so, is it as simple as quenching from red hot as per copper washers?

You dont have to quench them.

There is no change in crystal structure of copper with temperature so you are not trying to preserve a structure stable at high temperature. You only anneal them to allow recrystallisation of the structure deformed by cold working

 

[vyv_cox]

Why would you want to anneal them? I am guessing that they have been manufactured to have good strength by either heat treatment or mechanical work. Annealing them will reduce their strength.

 

[BabaYaga]

A related question, if I may:
I also have a pre 2011 Beta engine with single bronze bolt HE end caps. Does anyone know the reason for the requirement/recommendation to replace these bolts after 10 years or so? It appears to me that these bolts should not be subject to any particularly stressful conditions. Does bronze get weaker over time?
(Like the OP I have ordered replacement bolts for my 16 years old engine, will switch them during the winter layup).

 

[vyv_cox]

A related question, if I may:
I also have a pre 2011 Beta engine with single bronze bolt HE end caps. Does anyone know the reason for the requirement/recommendation to replace these bolts after 10 years or so? It appears to me that these bolts should not be subject to any particularly stressful conditions. Does bronze get weaker over time?
(Like the OP I have ordered replacement bolts for my 16 years old engine, will switch them during the winter layup).

A mystery to me. Traditional keels are attached with long bronze bolts, pic of one on my website. (Edit - sorry, misremembered, there is not, it is in one òf my talks ) Many will be 100 years old and still in pristine condition.

 

[penfold]

Do Beta recommend replacement? I suspect the main cause of replacement will be hamfisted overtightening, where a steel fastener might take this in its stride M8 is small enough that weaker bronze may either shear altogether or the thread strip(the hamfistedness may be a corollary of not renewing O rings or gaskets when the cooler is being serviced). The main thing to bear in mind is follow any recommendation Beta make for the torque used on the fastener, or if they don't have such a recommendation use as little force as is necessary to stop water leaking and no more.

 

[BabaYaga]

I cannot find any torque settings for these bolts in my manual, just a cautionary 'do not overtighten.'
Don't remember where I read the recommendation to replace at 10 years, probably on this forum.

 

[vyv_cox]

Phosphor bronze bolts have good strength. The phosphorus is included as a deoxidant that makes the alloy far more able to take tensile loads than standard tin bronzes. Bolts are stronger than equivalents in 300 series stainless steels and mild steel.

 

[Oily Rag]

Many thanks all. I have no experience of bronze bolts and assumed that somehow they were weakening over the years. I'll forget about heat treating the spares I now have and keep life simple.