Rubber Bumper MGB - What Should I Do With It?

So a friend is selling me a 1978 or so MGB that's an unfinished project. It's mostly there and mostly rustfree but the head is probably warped, the interior is half-stripped, it needs new wiring, and needs paint.

First step will be to remove the rubber bumpers and make a cheapie Sebring-style front end such as this: http://www.mgexperience.net/phorum/read.php?1,1891627

Probably will add a Sebring rear as well when I get better at welding.

I'm not restoring it but I want to retain the original British flavor of the car so I'm keeping the engine, which I'll tune. The plan is to have something fun for the street and autocross, probably in ST. Thankfully most of the parts are there, as a baby's on the way and I don't want to put a lot of money into this.

Any grassrootsy ideas?

ST rules are not really meant for carburetor equipped cars. The inability to remove the smog-strangled carbs would really kill any chance of them being fun. Street Prepared would be better, although a cam really wakes these engines up and again - not allowed.

These cars are literally PERFECT for V8 swaps. The engine bay swallows them easily. SBF swaps are especially popular. Rover V8 swaps are obviously popular since they were available that way.

I like rubber-bumper B's. Especially when the bumpers are painted to match the body.

http://www.flowspeed.com/cracked.htm - Check the head for cracks. The late castings aren't very good; so if you have problems with the head, there is a good chance it's cracked.

Assuming the engine is of the same vintage as the car, and assuming you're in the States you have the deeper dished pistons, and pretty low compression ratio of about 8.0:1. You could throw a supercharger at a refreshed engine and the car would be a decently fun weekend cruiser.

I haven't yet been able to get into autocross so I don't know the limitations of given classes. I can't help you there.

I have MGBs. If I wanted an MG as any kind of a competition car it would have to be a Midget. The A Series has an aftermarket to rival small block V8s. The B series does not.

Oh, also RB cars sit an inch higher than an MGB ever should. Plan on fixing that. You really have the perfect candidate for a V8 or V6 swap.

Rubber baby buggy bumper B's sit too high to handle properly IMHO. It's not overly difficult to fix it, a front crossmember from a chrome bumper car (or you can notch the original crossmember and accomplish the same thing), this will get the nose down. The rack shaft will not line up properly after this is done, either get a chrome bumper car rack or have a machine shop cut/respline the original shaft. The rear can be easily lowered with blocks. Being a '78, it's already got the front and rear sway bars which is a good thing and you now have a nice handling car that doesn't feel like it's on stilts. Otherwise, there's not a whole lot of difference between chrome and rubber B bodys.

I just got through doing a rework of a late 18V motor like yours, so I can impart some information (wisdom is not in my repetoire ).

The smog motor has 8:1 compression, way too low for any reasonable performance. That's easily fixed with early style pistons. Don't go overboard; on a streetable motor somewhere around 9:5-1 is about as far as you can go without detonation problems. A 6cc dish is probably about right if you will be using the 39cc chamber head Do not surface the head unless it's absolutely neccessary. If you have this done, see if the machine shop can machine another couple of cc's out of the piston crown (not difficult).

The 'warped head' may be a 'cracked head', if so that can get pricey. The cheapest way out is a used head, the early heads (pre-'75) are a drop on swap. Either way, if your engine has single valve springs a set of duals is a good idea. Make sure to get the retainers and the bottom spring cups at the same time.

These engines tend to wear camshafts pretty quickly, for whatever reason. There are all sorts of regrinds and new billet cams out there. If you want to keep the motor sounding stock with a decent power range, uise the early 5 main cam. The lift and duration are the same between the early and late versions but the late cam has the timing advanced 4 degrees for emissions reasons.

You can certainly replace the stock single row timing chain and gears with a double row, but there is no real need to do it. The single rows last just fine.

B's like better carburetion and free flow exhaust. Any set of headers with any Weber or a dual SU setup will run rings around the stock 1 piece intake/exhaust with the single Stromberg. Don't just chunk the old one piece manifold out, though; there is a market for them in states where these cars are still covered by emissions regulations. That's assuming it hasn't cracked like a LOT of them did!

About cylinder heads again: there are replacement aluminum heads out there. I've never used one myself but I've heard good things. The direct bolt on piece uses the stock intake and exhaust setup, the crossflow has a completely different intake port design meaning a different intake and carbs, which can get pretty pricey. There are new cast iron heads around also but they are not much different $ wise than the direct bolt on aluminium piece.

Since you asked about Grassroots approach.....

....as opposed to throwing the baby out with the bathwater.

You can cut a coil out of the front springs (Sawzall works), but you should heat and reform the cut end afterwords. Moss motors sells lowered springs if you want to spend the money.

If you lower the car a lot, you may need to adjust bump steer. Best way is to replace the tie rod ends with regular big rod ends and bolts. Bore out the steering arms (to the size of the bolt) and add spacers to get the tie rods ends more level.

You can add spacer blocks between the rear axle and leaf spring, but you may have to get / make / buy longer U-bolts. You can also "re-arc" the springs. A truck spring repair shop can do it, but you can also do it yourself. This is done with the springs cold. I did one set buy placing the springs over the bores of an old engine block and hitting them until I "flattened out" the curve in them, bit by bit. Use a 5 lb sledge hammer. It's a lot of exercise. Here's more ideas on this.

Throw away the rubber bumpers and fill in area with sheet aluminum. You'll probably have to figure out turn signals in front.

Have the head planed and ask the machine shop to look for cracks. Worst case, a used head is pretty cheap. The aluminum heads are expensive and my racing pals tell me they aren't as good as the iron heads. I have a '69 MGB I drive several times a week. These engines are pretty tolerant of less than perfect parts. My cam is somewhat worn (see comment above) but I keep an eye on things and change the oil every 3K.

aeronca65t wrote: Have the head planed and ask the machine shop to look for cracks. Worst case, a used head is pretty cheap. The aluminum heads are expensive and my racing pals tell me they aren't as good as the iron heads. I have a '69 MGB I drive several times a week. These engines are pretty tolerant of less than perfect parts. My cam is somewhat worn (see comment above) but I keep an eye on things and change the oil every 3K.

I'd go as far as to say these engines barely care what the parts look like as long as they fit. My '66 had an estimated compression ratio 7.4:1 or something like that (I'd have to redo the math to be sure). One of the rod bearings was spun, the cam is extremely worn, the valve guides and seats are all in poor condition, the valve seals leaked, and the #3 piston had two broken rings. The damn thing still ran and was enough to get me around for a month until the damn previous owner's hack wiring caught fire.

I wouldn't bother with aluminum heads unless you've found a cross-flow that's already ported and the casting's been proven to be good.

A well ported head is worth the money if you want to see any kind of performance out of the B series.

On the grassroots side - I made my own sebring kit. A rubber bumper car is an easier v8/v6 swap than earlier cars. A rover v8 is close to drop-in. The ford has some issues with the front crossmember (it needs to be notched) - and the chassis rail gets a notch for a remote oil filter adapter. A gm v6 (3.4) pretty much drops in. I suspect an LSx is in the range of the SBF in tweaks needed. Since I did a ford swap I also made my own crossmember - that's about 80lbs lighter than stock

I built a very successful D/SP autocross car out of my 79. I used Moss Motors performance parts and Addco sway bars. American Racing wheels and Hoosier AutoX tires. That car was a lot of fun for both the road and track.

Thanks, these are all great replies. If I asked for the same things in an MG-specific forum they'd hunt me down and beat me with rubber hoses.

The owner tells me that it runs but he keeps losing head gaskets. We will see.

Graefin10, what did you do with the engine in yours?

What part of the country are you in? If you're close and end up need spares I may be able to help.

I obvious answer is to get a Triumph instead.

'Keeps losing head gaskets' sounds like something is warped. The blocks generally don't but heads will. If it has the stock low compression pistons, you could probably chop a half inch off the head and still be OK. But if you want to bump the compression with new pistons, watch out: if you remove over .010 and then bore the block, say, .030 you can unintentionally wind up in the 10's very easily. At that high of a compression, they will very likely detonate on pump premium. If you are willing to run race gas etc then that might not be a problem, but most people aren't willing to do that on a street motor.

On the last motor I built, I used this calculator: http://www.rbracing-rsr.com/compstaticcalc.html and with 39cc chamber, 6cc piston chamber, 3.500 stroke, 3.190 bore (.030 overbore), .040 head gasket thickness and .025 deck height we wound up with 9.67-1 pretty quick. The machine shop guy and I calculated that another .010 off the head would have brought it down to ~38.5 cc chamber volume and that would have bumped it to around 9.8-1.

alleghenyman wrote: Thanks, these are all great replies. If I asked for the same things in an MG-specific forum they'd hunt me down and beat me with rubber hoses. The owner tells me that it runs but he keeps losing head gaskets. We will see. Graefin10, what did you do with the engine in yours?

Try here...

http://www.mgexperience.net/phorum/list.php?40

If it is possible, it has been done. Ecotec is the latest hot topic for this swap.