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MG MGB Technical - Engine rebuild help needed.

Alrighty here's what I got after losing my 1950 to a blown out sidewall...
(I never plan on using another 1950 again as long as I live!) Currently I've got a worn 1800 engine in need of a major overhual and was wondering what I should do to beef it up slightly in the HP department, and offset it in the reliablity department. A rebore is needed I know that from looking at the scratched sidewalls in the block and was wondering how far I should have it bored out? I'd like to make some power with the engine but don't want a repeat of last time. How much should it be bored out? I've got two choices in that department .020 and .040thou.
Also since my cam was er snapped into three parts I'll need a new one, any recommendations on cam profiles? I'm looking for something to produce power but not at the loss of reliabilty so a good mild ranged cam would be nice. The Crank is also something I'm looking at, nothing major but I plan on aquiring a good balanced crankshaft. Know of any good suppliers for this?
The head to is in need of being rebuilt quite badly as its worn out with sticking valves and what not, but is it possible to convert a standard MGB Head into a crossflow one and has it been done before? Or is it just cheaper to rebuild the head and run with that? Any good ideas on what I should do to the head to improve its flow characteristics.
The OVD tranny has been replaced with a rebuilt one since the housing on the one in my car was cracked near the engine again the blow out was the cause of this.

The engines out a same year 72 MGB, I don't have the engine numbers on hand at the moment though.

1972 MG MGB Custom.

Any help is appreciated! Thanks! CJD
CJD Dark

Get a copy of Peter Burgess's book on Power tuning for the MGB motor. It will answer your questions quite well. FWIW, I used his book and bored the GB series block on my car 60 over (greedy for a GB block but your GV series block should be fine). The .60 pistons are his favorite and are readily available. Many people are happy with 270 degree cams. I used a 272 regrind sold by Lawrie Alexander from the British Sportscar Center in California. I am very happy with the performance increase. I did not do much head work other than opening it up a bit with a three angle cut (per Mr. Burgess).
Carl W French

I have heard nothing but good about the Burgess heads. ou may consider just ordering one from him ready to go. That or have your head reworked locally byhis specifications, but be sure to magnaflux the head first to make sure it won't crack later on. I plan to do a Burgess head soon because of the 100% positive feedback on them and lots of it!

Have you considered a basic rebuild and slapping a supercharger on it? From what I understand, when installed on a stock engine it's quite reliable so ong as you don't try to bump the boost up for additional power. It's an easy 40% HP gain but will cost more than rebuilding your carbs by far. An overbore of 20 to 40 seems to work well with the supercharger as well. Check the Supercharging forum for better info than I can give.

Sorry to hear about your troubles. But look on the bright side... you can build an even better engine this time! :)
Steve Simmons

Any idea how much one of those heads from peter costs? His sites to screwed up for me to check for prices, everythings jumbled together for some reason.
CJD

Here you go...

http://www.mgcars.org.uk/peterburgess/page12.html
Steve Simmons

1950cc has aways had issues, some good some bad. About the limit on a overbore, not all blocks will go that far. Lots in the archives. Normal trouble is bore flex and excess oil usage, never heard of the sidewall blowing out. A good fast engine, .060 overbore, Piper 270 cam, 2706 large valve head ported and polished. Peter Burgess or Sean Brown in Oregon. Twin SU's, HS4 or HIF4. Lots in the archives.

Ron
RJS Smith

Sounds like you threw a rod. I would advise using ARP fasteners during the rebuild and have your rods resized and shotpeened. I had pistons, rods and my crank shotpeened and it really does relieve stress in the metal. I also had everything balanced which is another stress reducer.
Mike MaGee

I have 1950 Aldon in my GT for daily use, one fabulous engine, powerful, flexible, only one fault, only one, a huge wasteful of oil.
Regards
michel

CJ, did you replace the rods with rebuilt rods? On my 1950, I bought a set of pre 18V slip pin rods to use with Lotus TC pistons, County brand, and had three of the supposivbly rebuilt rodbolts fail while torqing them up. The failed about 20# if memory serves. I will NEVER use anything but ARP rod bolts again-just too much at risk. When a rodbolt fails, it usually destroys an engine in the process. When time permits, that engine will be pulled apart and all the rodbolts replaced with ARP. In the meatntim, it sit's on a shelf waiting. Any of you ever have this problem?
gerry masterman

no I used new rods, one of two things might have happened one a crack developed in the side wall resulting in a massive blow out, or two one of the rods wasn't properly torqued down, but since I've found the rods and there still attached leads me to believe it was the sidewall that went and tore everything up. My crankshaft you'd be surprised to know was cut completely in half. I mean completely in half.
CJD Dark

CJD,

Were the bores lined or just plain bored?

Sometimes boring out to 1950 uncovers the mild steel straps that tie the cores together in the casting process. If this is the case with your engine and the bores were not lined then that may have been the point of failure.

Alternatively it may have been the crank that failed first - if it was regound, was a sufficient radius left in the corners of the journals?
Chris at Octarine Services

The crank was reground about .010 of a thou with appropriately reground bearings of the correct diameter.

There were no sleeves in the engine neither me nor the mechanic thought them necessory at the time.

Ah well at least I won't be making the same mistakes with the new engine at all.
I'm going with the .060 bore piston. Now where can I find info on whats done to the head for my mechanic to rebuild it to Peter's econotune spec'd heads?
CJD Dark

CJD,
So sorry to hear of your misfortune. I know that you are just sick. I don't think that you'll have any luck converting a stock head to cross-flow. If you decide to go the alloy x-flow route be prepared for big $$$. The cheapest MSX heads are available from Shadetree Motors and they are currently at $1088 plus shipping for a complete head and $209 for the manifold. Then you need to think about a pair of high flow carbs of whatever variety (more $$$), possibly having that head flowed and the learning curve associated with the tuning process. Been there, done that. I'd be tempted, under the circumstances, to call Sean Brown and talk to him about a ported head. When considering a Burgess head don't forget shipping. The freight charges from the UK will scare you to death. If originality is not an issue, a 60 degree GM V-6 conversion can be as cheap as starting over with a 4 cylinder and you'll have a genuinely fast car that is not all chopped up when you're done. I like my .060 over cross flow car (a '66), but there were times when I wished that I had either stuck with an iron head or gone the V-6 route. RJS has a pretty good recipe for an iron head engine. The superchargers are intriguing as well but gosh, you'd have a ton of cash in it. Good luck.
David
David

I am really pleased with my 1950 engine pretty much as described above. Re oil ,I would expect to top it up about 2 or 3 times in average summer mileage of about 3000 , so aprox 1000 miles per pint .
S Best

Seems like for the cost of a cross flow head and all the bits needed to make it do what it's supposed to, the Moss supercharger kit wouldn't be all that much difference in final cost--with a bigger hp boost.
R. L Carleen

I'm running .060 over, 270 cam, K&Ns, Peco and a Sean Brown head in my '67. Sweeeeettt!!!! The only thing I'd probably do different would be to stick with the smaller intake valves (I had Sean install 1.625" valves) to give me a little more torque on the low end. At the top end it pulls like a freight train, but I'd like a little more on the bottom.
Ken Lessig

Hi CJD,

You were wondering about an Xflow head. They are actually available by B&G and priced about a lesser than 500GBP, complete with studs and alloy body including exhaust valves inserts. But they require either 2 webers carbs or 2*1,75" SU + adapters .
May that help you make decision!!
Renou

Can anyone quantify the power gain from a +.60 bore out? Does this little increase really make much difference?
Terry

Terry, from what I've read, the main benefit fo going .060 over is not the displacement increase, but the fact that the distance from the edge of the opened valves to the cylinder wall increases enough to significantly unshroud the valves. This allows much better gas flow. Correct me if I'm wrong, but the dislacement at .060 is 1863cc.
David
David

I make the displacement 1868cc at 60 thou over.

The power increase from just the overbore is around 5 to 8 bhp at max but it increases mid range power by the same amount due to the bigger capacity achieving gas flow earlier as well as it increasing the CR.

The unshrouding effect is minimal, since the valves don't project into the cylinder unless you have a high lift cam or rockers.
Chris at Octarine Services

Thanks Chris.
David
David

Thanks for the explanation. 5-8 HP mid and top range is significant and I'm surprised that the gain is this much for so little. I'll definately go +.60 next rebuild.
Terry

Cylinder swept volume goes up by 3.9% to 467cc and the CR goes up 3.4% to 9.34:1 - assuming a standard high compression set up with a 43cc head to start with. Figures for an LC engine would be less.

So an increase of 5% or so in power is not unreasonable.
Chris at Octarine Services

This thread was discussed between 12/06/2004 and 17/06/2004

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