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MG MGB Technical - Head's out, now what?

So now that the head is at the shop, what should I be doing to prep the engine for reassembly?

After what I put the head studs through, it looks like I'll be replacing all of them. I know I should roll the push rods to test them for straightness. I have heard that I should remove and buildup and gasket remnants from the engine surface with a straight razor and some laquer thinner. I was also told it might be good to clean off the buildup on the piston heads.

Any recommendations?

Jeremy
1974.5
J. Palgon

Get a set of ARP head studs. They are available from Moss or APT.

http://www.mossmotors.com
http://www.aptfast.com

Yes, clean the block mating surfaces and decarbon the tops of the pistons. Use a shop-vac while doing the latter to prevent any bits from falling down and scoring the cylinder walls. Rotate the engine so the piston is at the top of the bores while cleaning them off. If you can get the tappets out, take a good look at them and check for pitting on the wear surface. If there is any, it's almost a certainty the corresponding cam lobe is worn. If they look good, put them back into the same hole they came out of!! I'm a big fan of ziplock bags and Sharpie markers to make sure everything is labeled and goes back where it came from.

Paul K

Paul,
Thanks for your confirmation. My local British shop has the moss studs. I'm definitely going to clean the mating surfaces. What's the best way to decarbon the tops of the pistons?

Jeremy
J. Palgon

Hi Jeremy.

It is best to scrape the coke off the piston tops with something that is harder than coke but softer than the piston top, I use a hard plastic decorator's spatula.

Don't be tempted to use emery cloth or abrasive paste, the risk of some of it not being cleaned away afterwards is too great.

Check that the rockers aren't wobbling about on their shaft and that the ends of the rockers are not worn.

Don
Don

I would also recomend that you, chamfer the tops of the headstud holes in block and clean threads, before fitting new studs neverseize on threads and to about 15lb/ft.
Make sure to give all the headstud holes through head a good cleaning, especially centre one distributer side (this is the guide stud and hole in head is smaller) small round wire/nylon brush is the best thing I have found for this.
While I have the head off I make sure to check and clean other threads/studs etc, easier to do any work while it is on the bench.
When I refit the head I give the studs a smear of neverseize, not too much dont want it to get dragged down onto the gasket.
Make sure the head and block are straight and true.
Good luck
cheers Ric
R.A Willis

Hey guys,
Good news. My head isn't cracked. The shop is just going to do the usual hardened seats and such. The rocker ends are fine. I'm replacing the rocker shaft. So it looks as though I'll have my car back together for the show on Saturday.

As for the cleanup while the head is off, I've cleaned up the mating surface of the engine pretty well. I haven't manage to make much progress on hard carbon build-up on the piston heads though.

Don, I tried the hard plastic spatula and it scraped some carbon off a little here and there but was largely insufficient (even with laquer thinner). All that stuff is really stuck on there good after 30 years.

So I'm wondering how important it is to take all this stuff off the pistons? I have heard that it's better to leave it than to scrape some of the stuff off and end up having it floating around in the engine.

Any other suggesions on how to decarbonize the pistons?

Thanks,
Jeremy
J. Palgon

Oh I don't know, maybe browse eBay and see if some guy's wife is selling off one of his cars piece by piece :-) ?
Maybe you find a replacement for that broken rear side marker lens you got?

Safety Fast,
David
David Deutsch

Hey David,
But of course. Thanks so much for the lenses. I really needed one after I clipped the egde of the garage and exploded my driver's side lens into a handful of pieces. Luckily, I didn't dent the car as well.

But seriously, any suggestions for cleaning the piston heads?

Jeremy

J. Palgon

It's been a while since I've dealt w/ carbon removal. Paul & R A gave you good advice. I'd just add that you may want to use some wide masking tape across the entire surface and over the bores you are not working on, to keep krud from getting places you don't want it. A shop vac and a wire brush, would be my weapons of choice here.

I hope you plan on using a good composite head gasket. I like the Payen ones best.
David Deutsch

Hi Jeremy.

Is the coke thick, lumpy and layered, or is it just a film, like a single thin coat of paint ?.
If it has lumps and ridges it needs to come off, as these will provide a potential 'hot spot' for triggering pinking / pinging.

The piston tops are relatively soft and will scratch badly if you get carried away, and these scratches will theoretically encourage new coke to stick quickly, though in my experience it seems to get a grip fairly quickly in any case.

If you need to use a more aggressive scraper I would go for one that doesn't have edges that will dig in (eg the corners on a chisel blade), but go for a scraper with rounded edges, maybe an old, wide (at least 1") chisel with the corners ground off.
Hold it with the whole width of the blade in contact with the piston top at a shallow angle and it shouldn't dig in.

Whn you get the head back I suggest that you gently radius the edges where the combustion chamber meets the face of the head, especially if it has been skimmed, as a sharp edge here are another potential trigger for pinking / pinging.
Be sure to clean up any filings afterwards.

Don
Don

Jeremy;; Try a little power steering fluid or ATF and it will soften all the carbon on the piston tops.
Sandy
Sandy Sanders

David,
Thanks for the tip about the masking tape. Definitely a good idea. I'm not sure which head gasket I'll be using. It'll probably be whichever head gasket Brian at O'Connor Classics recommends.

Don,
Ths consistency is generally just a thin film across most of the piston heads. But at the edges, near the cylinder wall, it's a bit lumpy.

I've posted some pictures of the engine with the head out (before and after clean-up) in the Engine Head Removal album at photos.yahoo.com/jeremysmgb. Perhaps the pictures can better show what I'm dealing with.

Jeremy
J. Palgon

Hey everyone,
I just wanted to say that I eventually managed to decoke the piston heads. I ended up repeatedly drenching the heads in laquer thinner while scrubbing away with the plastic putty knife. The piston tops are now very clean (although the putty knife is worn down to a nub). Thanks again.

Jeremy
J. Palgon

You can get ARP studs significantly cheaper from JEGS. I ordered all my ARP stuff from them and saved around a $100 total over the Moss prices. They don't list them if look by vehicle make, but if you will go to ARPs site and look in their catalog for your part number, and then do a search on JEGS website for that part number, they will have them listed for a BMC B series engine, and can purchase online. I think I paid about $100 a set or less for head studs and main bearing studs from JEGS. I just stumbled on this while trying to find a cheaper source for them than Moss. Not knocking Moss mind you. They get plenty of my business (through Moss resellers).
Greg Bowman

Hi Jeremy.

So, you are heading towards putting it all back together. There are no real snags to avoid, just take your time. I would do an engine oil change more-or-less immediately, to clear any lacquer thinner that found its way past the piston rings into the sump. I would also flush out the cooling system.

When you have the head and valve gear in place (but before you put the rocker cover back on or the spark plugs in) turn the engine over manually until you can see oil ooozing from all of the rockers. This proves that the oilways are clear and that the bearing surfaces are lubricated before you start the engine for the first time.

Don

Don

This thread was discussed between 07/05/2006 and 11/05/2006

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