MGB & GT Forum

Hey guys,
So I have an extra 67 GB cylinder head that I would like to rebuild, and port and polish, basically just use as something to tinker and experiment with. The only problem is that the previous owner had stored it in a moist area, so there is a good deal of surface rust. I know I could take it to the machine shop and have them jet wash it, but as this an extra, I don't really want to spend the fifty bucks. What should I do to get rid of this loose rust? I know I will have to sand alot of it out, but is there a soak or spray that would at least help a little?
Thanks in advance,
Chris Seely

If you have a tub soak it in white vinegar for a few days (stir), then with a electric drill and various wire wheels (NAPA) brush the rust off. Then consider having it hot tanked (not pressure washed) to remove the residue from the water passages. After that a Magnaflux crack inspection is appropriate.

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Be safe out there.
Kenny

Chris-
Use Naval Jelly, which contains phosphoric acid. You can get it at most any home improvement store, such as Lowes or Home Depot. Be sure to wear rubber gloves when you use it. Being a thick gel, it will cling to the surface being treated instead of running everywhere as would happen with an acid that is in liquid form. Phosphoric acid reacts very slowly with iron, thus hydrogen emission is much lower and hydrogen embrittlement of the metal is insufficient to present a significant structural problem that can result in the formation of cracks. Note that it will also react with the iron in the metal to form a dark-purple-hued, thin passivated layer of ferric chloride. This is a natural result of chemical interaction. This protects the surface and also slows down the chemical reaction, so it is more or less self-limiting.

After removing the rust, rinse the naval jelly off thoroughly with water, and then blow the metal dry with compressed air or your wife’s hairdryer (she will not mind you borrowing it for such a noble purpose, of course). To remove carbon deposits, use Sea Foam. In order to prevent corrosion, apply a coat of pure antifreeze to the coolant passages inside of the cylinder head, and inside of the coolant jacket. All of the oil passageways should be coated with engine oil.

I had a rusty head that I cleaned up with a brass wire brush. It did a good enough job so I could get it crack tested.

A friend of mine has cleaned / degreased aluminium cylinder heads in a domestic dishwasher. He puts in a couple of detergent tablets and the head and the results are very good. The first time he tried it was when his wife was on holiday which was a good job since although the head came up immaculate it had left an oily film in the dishwasher and also marked the plastic parts. It took a couple of bottles of dishwasher cleaner to restore it to a suitable condition before she arrived back. She still doesn't know!

The other question I had is that a friend of mine has an extra cylinder head from a 75 mgb. Is this a head that has the larger valve openings? Would it run better than a gb head on my 67?

If it was UK spec the big valve head was fitted from 72 to 74 and has the numbers 2708 or 2709 on the casting. (I've got one fitted to my 1979 car). I've also got an earlier cylinder block (long story!) and the earlier block requires cut outs to allow extra clearance for the bigger valves. The cutouts are easy to add with a file but are required.

Well if I can get this one cleaned up, I would like to shave the head down a bit for higher compression, port and polish, and install hardened seats. Then I can just keep my other head completely stock.

Christopher-
No the cylinder head has the same size valves as yours does, but due to the smaller combustion chambers your compression ratio will jump to about 9.3:1, so you'd be best off if you got the spark advance curve of your distributor altered in order to compensate for it. You'd get a small increase in power and fuel economy, but the use of high test fuel would be mandatory.

75 head has a smaller combustion chamber which puts the valves closer to the block. On MGB engines the exhaust valve overhangs the outside of the cylinders, so you'd need to cut valve reliefs to allow for exhaust valve-to-block clearance. Intake valves are not a problem as they are completely contained within the bore of the cylinders, and neither intake nor exhaust valves pose any danger of contacting the pistons...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Even if the earlier cylinder head has the deep combustion chambers sometimes block deck eyebrows are required to maintain exhaust valve to block deck clearance, I like .080" including valve/rocker clearance in case the head needs to be resurfaced in the future. Eyebrow requirements depend on how much material has been removed from the head, cam lobe lift, exhaust valve installed height, exhaust valve diameter, rocker ratio, head gasket thickness, and piston dome height. Yes, it is rocket science even for an "old iron tractor engine" as some call it, get this wrong and the valve train will comprehensively disintegrate.

The eyebrows cannot be too deep into the cylinder, if too deep the top piston ring will hook on the eyebrow and break. I do the final grinding with a small ball carbide bit on the outside perimeter of the eyebrow but no deeper on the cylinder side.

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Be safe out there.
Kenny

Chris,
If there's any dairy ranching in your area, c all the local feed/supply store and ask how much a gallon of "milk scale remover" is. Get a rubbermaid container just big enough for your head and pour in the liquid. It will clean it inside and out. Best of luck. Basil 707.762.0974 basiladams@yahoo.com

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Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

Great Tip Basil- How does it work? I thought the eyebrow was about exhaust valve deshrouding as well as clearancing. Vem

I clean all my heads the same way, first they go into a chemical bath and soak, the chemical is good enough to get all the grease off, and exterior paint, it is called Super Clean, it is amazing stuff, you can get it at O'Reilly's, and it is safe water based degreaser I put 5 gallons of it in my soak tank and add a couple of gallon of water to it. Then the heads are washed in hot water, compressed air blow dried. I then have a cylinder head stand in my bead blast cabinet and media blast the head with fine glass bead inside and out. I then take the head back to the soak tank where I immerse in and out of soak tank many times letting all the media flow out of the water jackets and such, then clean it again hot water, blow dry, spray with WD40, then blow dry again. You end up with a result of like a new cast iron casting.

A typical machine shop caustic cleaning will not remove will not remove rust scale.

I also use a a braided wire brush on a side grinder for machined surface, pretty typical for most machine shops.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com

Hap, will this method work with surface rust as well?

I have a small tub filled with a product called Evaporust that does an amazing job of removing rust and scale. Drop it in and 24-48 hours later they come out as bare metal.

I used to do the same with apple cider vinegar. It's very effective, but smelly.