Heat exchanger repair

[MagicalArmchair]

once the bolts are out, then a gentle knock with a rubber mallet should do it, and then perhaps a poke with progressively more aggressive tools as needed. I have some nice plastic cold chisels but they are little specialist for a one off!

as long as where the oring sits is clean and unmarked your good.

Thanks for the tip - I'm not happy with some of the little nicks in the copper gasket that houses the rubber gaskets (I'll need to gently remove a couple of small burrs I've created), so I've invested in some of these: Expert by Facom 4 Piece Composite Plastic Scraper Kit | Interior & Trim Tools to get the other end off.

The tightening sequence and method posted by jwfrary is sound. Personally, i would not use a torque wrench on these, there is no need and you could do more harm than good.

"snug them up by hand based on experience" is the best way

Leave torque wrenches for this type of job to the armchair experts.

I find they are either perfect or knackered! Had an engine in not long ago where the customer tried to take the unit off and broke every stud! But it’s rare. - safe than-sorry!

Thanks for the tips, I'll inspect the studs carefully once I have cleaned them all up. They look pretty good, however, if I am in any doubt I will replace them. On refitting all these bolts should I use copper slip on them? Some of these are steel into aluminium, some are steel into steel (those that fit the exchanger back on to the engine), and all will be subject to large amounts of heat. Apologies if I have asked this before above!

 

[superheat6k]

A face seal onto an O ring is less fussy about torque, just tight enough to stop the bolt or nut rattling looses, and perhaps a bit of medium grade loctite e.g. 243. The O ring seals under fairly light compression. Volvo penta use O rings extensively on their cooling systems and these simply push in to assemble.

 

[jwfrary]

No to the copper slip, that’s one to many metals in the joint!

normally nothing is required assuming everything’s all nice and clean. But if you find somethings tight a little machine oil can help with assembling

 

[jwfrary]

A face seal onto an O ring is less fussy about torque, just tight enough to stop the bolt or nut rattling looses, and perhaps a bit of medium grade loctite e.g. 243. The O ring seals under fairly light compression. Volvo penta use O rings extensively on their cooling systems and these simply push in to assemble.

best to grease the o rings with marine grease helps things seat and makes disassembly in the future somewhat easier!

 

[superheat6k]

best to grease the o rings with marine grease helps things seat and makes disassembly in the future somewhat easier!

I find Loctite 577 works very well for bedding in O rings, and is very good if you need to re-use a seal.

 

[rogerthebodger]

I find Loctite 577 works very well for bedding in O rings, and is very good if you need to re-use a seal.

I tend to use silicone grease on O rings to help aid water tightness.

When looking at steel studs into aluminum and the load needed to strip the thread in the aluminum you must consider the thread depth in the aluminium.

The thickness of a nut( 0.8 x thread diameter) is designed based on the shear load strpping the thread in the nut for steel nuts/studs.

So look at the depth of the tapped hole in the aluminum if significantly more than the diameter of the stud the design has compensated for the lower shear strength of the aluminium.

Also the pitch of the thread in softer material like aluminium should be causer than the steel nut on the steel stud. This also compensated for the lower shear strength of the softer material.

 

[superheat6k]

I tend to use silicone grease on O rings to help aid water tightness.

When looking at steel studs into aluminum and the load needed to strip the thread in the aluminum you must consider the thread depth in the aluminium.

The thickness of a nut( 0.8 x thread diameter) is designed based on the shear load strpping the thread in the nut for steel nuts/studs.

So look at the depth of the tapped hole in the aluminum if significantly more than the diameter of the stud the design has compensated for the lower shear strength of the aluminium.

Also the pitch of the thread in softer material like aluminium should be causer than the steel nut on the steel stud. This also compensated for the lower shear strength of the softer material.

In my business repairing large fridge compressors we use the rule of thumb of 1.5x diameter as minimum depth of an effective thread.

 

[rogerthebodger]

In my business repairing large fridge compressors we use the rule of thumb of 1.5x diameter as minimum depth of an effective thread.

Yes a reasonable rule of thumb as a minimum

What is the material the tapped hole in and what is the stud material?

 

[superheat6k]

Yes a reasonable rule of thumb as a minimum

What is the material the tapped hole in and what is the stud material?

In the case of most of the machines we overhaul cast iron, but occasionally aluminium alloy. Certain makes you just know present a real awful grade of cast iron, and we have had certain machines requiring half the holes helicoiling.

 

[rogerthebodger]

In the case of most of the machines we overhaul cast iron, but occasionally aluminium alloy. Certain makes you just know present a real awful grade of cast iron, and we have had certain machines requiring half the holes helicoiling.

This is a cylinder head stud for my MGB

The right hand thread is a coarser thread than the left had thread. The right hand thread screws into the cast iron block with the steel nut on the left hand thread.

In my view a thread into aluminium should have a longer thread than into cast iron due to the lower shear strength

 

[jwfrary]

This is a cylinder head stud for my MGB

The right hand thread is a coarser thread than the left had thread. The right hand thread screws into the cast iron block with the steel nut on the left hand thread.

In my view a thread into aluminium should have a longer thread than into cast iron due to the lower shear strength

The length of thread in the head is of course comparative to the length of thread in the nut!

D2’s have bolts on the cylinder head....seems a lot more common these days. from memory your supposed to use moly grease on the threads...easier than stretching them with Jack’s and then torquing down!

 

[superheat6k]

This is a cylinder head stud for my MGB

The right hand thread is a coarser thread than the left had thread. The right hand thread screws into the cast iron block with the steel nut on the left hand thread.

In my view a thread into aluminium should have a longer thread than into cast iron due to the lower shear strength

During my recent engine rebuild I discovered short studs with different threads between the engine transition plate and gearbox. One end had a nut on so I could understand why they needed different threads. I had to make two news ones, which was an interesting task.

 

[MagicalArmchair]

Bit of an update here. I got my plastic chisels through, and they were very useful for safely prising the cooling stack safely out of the raw water compartment of the Heat Exchanger.

It was pretty well stuck in there, so I altered a piece of scrap timber so it would fit, and gently tapped the stack out.

And out it came, nice and clean.

Gratifying, it's nearly completely clear, with very few deposits on it:

I'll give it a soak in warm Rydlyme anyway and then refit this evening

Process for refitting it grease it up with marine grease, put in the new O rings and reassemble?

 

[MagicalArmchair]

p.s. Old Keenol from stocks good enough grease to put on the o rings and to grease the stack before putting it back in? It may be old, but it hasn’t separated!

 

[MagicalArmchair]

Update here, I have the last of the parts and the raw water compartment is back together. I have masked it up and re-enamelled it all, so hopefully it'll come up like new and I'll be able to identify any leaks early with it nice and clean.

I'll bring it in and put it in the airing cupboard (even the first mate has given me blessing for this!) to give it time to set up. That should be good to fit then I hope.

I'd like to pressure test the raw water compartment before I fit it. It was a very fine balancing act of torquing those bolts up enough into the soft aluminum to form a seal without stripping them. I resisted the urge to lean on them too hard...

 

[Bobc]

Nice job, well done.

Pressure testing before fitting it is a good idea. You'll then be able to rest easy knowing that the raw water can't escape anywhere and start corroding things again.

 

[MagicalArmchair]

I'll try and cobble something together. I have a pushchairs duff inner tube with a valve I'll take, then I just need to reduce the hoses at each end, dial the compressor down to 15psi, and it should be quite easy... so long as I have enough pipe and reducers in the bat cave. This is what the engineering shop did:

 

[vas]

I'll try and cobble something together. I have a pushchairs duff inner tube with a valve I'll take, then I just need to reduce the hoses at each end, dial the compressor down to 15psi, and it should be quite easy... so long as I have enough pipe and reducers in the bat cave. This is what the engineering shop did:

lol, very professional
My setup is slightly better as I once found a tire valve on a 3/8 or whatever threaded ending and then got a few step downs/ups all bolted together with teflon tape, works fine up to a point then the final bit will be flexhose.

V.

 

[MagicalArmchair]

lol, very professional

I was expecting pressure testing (something I have never had to do before) equipment to be pricey, complex and professional - not quite so cobbled together . As with anything, the acid test is whether it does the job! The good thing is that I can put that together myself and get that test done since I've had it apart.

 

[vas]

ah, and don't forget in all these pieces bolted together to fit a tee so that you can get a boost gauge in there as well!
Tire valve means it's a close system, you pump it up, just note pressure registering on the gauge and see if it drops and after how long and judge it yourself.