Bolt and Nut Replacement

Hi Again

I have a question on replacing nuts and bolts on a Volvo Penta diesel I/O.

I'm stripping it all down to the repair the hull and while everything is out Ill be doing some long overdue maintenance on Motor and Leg. Many of the nuts and bolts are not stainless and show a degree of corrosion especially on the motor.

My question if I replace these with stainless will this become an issue.

I am going to Duralac any bolt that runs through the hull but what about the outdrive, or motor? Don't they suffer from dissimilar metal corrosion as well.

Thanks
Katoh

 

Cant comment on the fastenings...Use Volvo original spec.
In general Steel and aluminium like each other...stainless steel and aluminum are enemies .

Duralac is OK as a bedding compound for waterproofing metal to metal joints...its just a bit messy to use. I use Duralac for fastenings that will be over painted. If the fastening head will not be painted I use the product called TefGel to waterproof and lubricate the joint. Tefgel is effective at preventing SS "galling". Very good results. Tef Gel is widely used in the marine industry, so should be available locally. If not....BECOME THE DISTRIBUTOR

http://www.tefgel.com/contain.php?param=tefgel_infor

 

Assuming that the bolts and nuts are the original ones, it is easy to discern the strength classes by looking at the bolt heads. The ones with a trademark and a number like 08 or 09 are high tensile strength and must be replaced with identical ones. Bolts used to fasten peripherals are generally not marked - or 06 and lower- and can be replaced by stainless ones.

Use a bit of grease or copper paste when bolt and nut are both stainless, they tend to damage each others thread when tightened dry.

Galvanic corrosion is no issue unless the fasteners are under water; on the drive there should be zinc to protect the light alloy.

 

I will have to check the nuts and bolts as I go along as to tensile strength, for the life of me I cant see why they used mild steel bolts, on the engine mounts, not HT but just a pillar of rust, and on accessory brackets, just looks down right terrible and leaves a pile of rust stains on the bottom of the engine well.
The ones I cant change so be it Ill just replace and repaint them same as the motor.
I thought Duralac was the best thing recommended for dissimilar metals, so much so that its banned in some countries? all the good stuff is, is it not!

 

The engine is mostly iron and steel. The bolts are a small percentage of it. I don't see why it is a problem overall. If the engine is so rusted, it indicated poor maintenance.

 

Gonzo, your dead right! It was poor maintenance and a some terrible fitting out, not by the builder but the previous owner. Ive only had the boat for a couple of months now and I'm slowly pulling it all down, I have to remove motor and drive to roll the hull over to fix all the corrosion on the bottom. Previous owner installed some lighting and drew the neg through the hull and painted the stern drive anode, good to see some people know what there doing.
Back too my bolts and nuts, my thinking while I'm replacing I might aswell go all the way and use stainless, Ill have to replace half those nuts and bolts anyway cant hurt, or can it? that's the question?

 

Some bolts can be exchanged for stainless (A4 or 316) For example, all brackets, thermostat housing and exhaust manifold. Any others that need higher grade, like heads, etc. won't work.

 

That's really good, I wont be touching the internals of the motor, but the bolt on pieces will have to be removed and cleaned up some parts replaced, might aswell just spend a little extra and buy the stainless. Would you duralac those bolts before installing them?
Is there are difference between marine gaskets and auto gaskets, I will have to replace them also, but it is just as easy to make my own instead of buying genuine, just buy a sheet of gasket material and cut out, maybe even cnc them.

 

I can't see any harm in using duralac. Marine gaskets are usually different if there is a metal insert or layer, in which case it will be stainless or brass instead of steel.

 

Im not familiar with something called " Marine " gaskets. When you disassemble a joint, look at the gasket...it will have a number imprinted on the gasket stock.....ICP 9400....or ICP 9000 or whatever. This is the grade and rating of the gasket materiel..... oil, water, heat......simply replace with the same stock.
An engine shop should be able to advise and will generally have a good stock of typical gasket stock on hand .

Obviously some gaskets are specialized or very intricate to fabricate and should be purchased and not shop made.

Be sure to buy an adjustable rotary circle cutter , a set of hole punchs and a block of flat surfaced lead or a chunky balk of hard wood "end grain" stock to punch on.

http://www.icpcalvo.com/planchas_eng.html

Be aware that duralac is a hard compound like paint and makes a poor waterproof joint in areas were a flexible bedding compound is required.

 

Look at any engine catalog and in the section "marine" you will find the marine version of the gaskets. Any boat mechanic is familiar with them.

 

Gentlemen
Again thanks for your Knowledge and advice.
Cheers
Katoh