20 replies to this topic

[nikollou]

I have been working on porting my own cylinder head based on David Vizard's bible and unfortunately I ground a bit more than I should have near the exhaust port of the combustion chamber and now I risk head gasket failure if I don't address this issue.

 

 

I have a MIG welder can I use that to build up the chamber a bit and then re-shape it without overdoing it this time?

If yes will a standard steel wire do or do I need something special?

 

Thanks,

Nik

 

[Spider]

You can, however, the weld and the iron immediately around it will get VERY hard, eg, to deck the head, it can't be machined by normal methods, but will need to be ground finished.

[DeadSquare]

You have just found out why skill costs money !

 

A picture will help.

 

The problem with welding, is that as it cools, it leaves a slightly depressed ring round the weld, which is OK if the item can be re machined.

 

Although they are both iron, steel wire and cast iron are not really compatible.  A high nickle content wire is required, and I hate to think how much a reel of that would cost.

 

A well experienced welder might be able to help you with a 'so called' cast iron rod or maybe a phosphor bronze rod and DC welder, but the arc tends to blow away a lot before it starts depositing material.

 

A specialist firm would heat the head in a series of hotter ovens and at the critical temperature, braze it.

 

Another head would probably be cheapest in t he long run.

[dotmatrix]

I have had a engine block welded between two cylinders between cylinderhead and block and this made the headgaskets fails multiple times in that area until I finally prepared a new block. So would not recommend welding it.

[Spider]

Now I have a little more time for a more complete-ish answer here.

 

TIG and Iron filler is best along with pre- and post-heating, then burying the head in sand over night following the post-heating. By doing this it will reduce the stress set up in the casting from the welding process. There is a skill to it.

 

You can ring around and see if you can have a firm weld it for you, try an engineering company rather than an automotive repairer.

[nikollou]

Thank you all for your replies. I'm attaching a photo of the offending cylinder head to help clarify what needs to be done.

 

The red arrow points to the location where I got a bit carried away and took out some material where the head gasket locates. 

 

As you will see the amount that needs to be filled back in is minute, so maybe with this in mind a couple quick tacks with the MIG would suffice? Or maybe someone thinks I can get away with no repair at all?

 

Note that the head will be skimmed to achieve the desired CR so the "meat" where the gasket locates will grow a bit since it is thicker further down, but not by a large amount.

 

Cheers again!

Nik

 

 

Attached Files

•  IMG_7010.jpg   77.68K   24 downloads

[Spider]

The head is subject to a LOT of heat right there, in fact, it's probably about the hottest part of anything on the whole car. This is because the 2 exhaust valves are right next to each other here.

 

For this reason, I would strongly recommend you engage a professional welding service.

[nikollou]

Duly noted and it's important to realise that I will be adding a turbo to my mini so there will be even more heat/pressure....!!!

 

Darn the hidden costs of DIY are starting to show up in this build but I am still happy that I tried. :)

 

I might actually try to find another head just to have the peace of mind and do the porting all over again, being much more careful this time...

 

I'll drive by a specialist machine shop tomorrow and ask for their opinion once they have a look at the head.

 

Will post up my final decision as an FYI here.

 

Cheers

[grizzler73]

I am in the middle of porting my head as well, After doing the first chamber I got the feeling I would probably need a spare head... I have one now and haven't needed it yet, but I'm sure I will! Good luck finding someone to do the welding, when I was a welder I did a few jobs like this, only ever found the nickel based arc rods worked well enough.

[Dusky]

From a little experience with this, nickle rods and good ovens/buckets of sand are your friend.

[DeadSquare]

The iron is thin there, so I'd find someone who brazes regularly with oxy-acetylene and knows his heat and filler rods (like a French plumber) and risk running a fillet of brass along that side of the chamber.

[elf66]

I have had reasonable success with both mig and stick welding castings with standard wire/rods. The problem is the expansion and contraction rates of the casting as opposed to the welding medium. If you just cold weld it looks like a perfect penetrated weld until it starts to cool, then it will almost certainly crack. The last thing you want is a chunk of steel breaking away and bouncing around on the piston!

If you heat the casting in an oven and get it as hot as possible then apply local heat to the weld area and get it red before welding, then reduce the heat slowly until its cooled, you should be able to make a good repair.

[Cooperman]

If that is a 12G940 casting I wouldn't even consider welding it up. Those heads are plentiful and not expensive and it is easier to simply do another one.

Why take the risk when it will cost so little, apart from a bit of time, to get a satisfactory result?

Chalk it up as 'experience'.

[unburntfuelinthemorning]

Darn the hidden costs of DIY are starting to show up in this build but I am still happy that I tried. :)

 

I might actually try to find another head just to have the peace of mind and do the porting all over again, being much more careful this time...

 

I'll drive by a specialist machine shop tomorrow and ask for their opinion once they have a look at the head.

 

Will post up my final decision as an FYI here.

I imagine many of the professional head modifiers started off by getting quite a few wrong before they became good at it.  Well done for giving it a go, I hope it works out for you.  When you do get it right it'll be extremely satisfying to have done it yourself.

[DeadSquare]

The combustion chambers, while the most important, are the cheapest element of modifying a cylinder head, as it is now done with a computer programmed milling machine, whereas it used to be done by hand using a pantograph from a template.