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MG MGB Technical - Rebuilt engine comes to life

My rebuilt engine is in place...mechanic performed all the pre-start preparations, turned the ignition this afternoon and it started with absolutely no hesitation, as if it had been running only minutes before instead of weeks ago.

Much deeper tone than before, fuller and rounder, more throaty, none of the raspiness of the engine that entered the garage weeks earlier. Still running the OE exhaust manifold, because Brit-tek is back-ordered nine months on the stainless PECO. Maybe I won't even get it at all, because my exhaust system is nowhere near needing replacement and I can't imagine the exhaust sounding that much better than it does now.

Silky smooth. Sounds eager to increase the RPMs. Initial oil pressure is almost pegged on the gauge, which he says is normal for the rebuild. After the cam is bedded he will retorque the head and tune it, then I get it on Friday pm for 500 miles. He says that as the moving parts get comfortable during the break-in, expect the oil pressure over time to drop to appx 80lb at speed and 50-60 at idle. After the 500 miles, he'll again retorque, retune & re-inspect everything, change out the oil and filter and he wants to add some kind of Lucas oil additive that he recommends every fourth oil change. He also said he would be happier if I use the Castrol GTX 20-50 instead of synthetic.

Actually, I suppose I should ask what's involved in tuning it now. He dialed in the cam perfectly before the engine went into the car; the Crane XR3000 electronic ignition automatically and continuously maintains dwell at the optimum level (the distributor vacuum unit with its connection to the carburetor is completely redundant, so it no longer exists); the Weber 32/36 progressive with K&N filter couldn't be happier.

Thought we saw an oil sheen on the block, but it was merely the glossy paint. This is truly a different engine. Doesn't even sound like a 4-banger any longer. Couldn't be happier.

Details:

Retained 18GH block with non-original OE head. Both were fully inspected and usable.
Bored out cylinders +40;
P&P and skimmed the head;
hard valve seats;
Burgess angle cutting;
Rim flow style waisted valves: 1.7 intake valves, 1.34 exhaust valves;
tapered bronze alloy valve guides; HD springs;
Crane alloy push rods;
Kent HD lifters;
Crane billet 342-0010 fast street cam;
Kent vernier ajustable camshaft sprocket/dual-link timing chain kit;
New AE Hepolite +40 pistons w/Grant tapered and bevelled rings on my reconditioned connecting rods (all balanced);
Reground & polished crankshaft, resurfaced and skimmed some weight off OE cast-iron flywheel, mounted new HD clutch and balanced all three as a unit;
Crane XR3000 electronic ignition w/matching Crane PS91 coil;
Retained Weber 32/36 progressive carburetor but added K&N high-flow air filter w/chrome logo top;
New HD oil pump and relief spring, new water pump and thermostat;
Retained and serviced radiator;
All new bearings, Payen gaskets, ARP fasteners throughout.
G. Kinslow '69B roadster

Sounds great - and by your post, you sound very pleased with it. But one thing has me puzzled - (your post) "(the distributor vacuum unit with its connection to the carburetor is completely redundant, so it no longer exists)" Not so sure about that since you don't seem to have a computer-controlled ignition, just an electronic spark-trigger device.

Wayne
Wayne Pearson

Nope, along with the optical cell that one installs in the distributor to replace the points, the XR3000 actually has an extra chip that the XR700 doesn't have! It's a two part system, as the XR700, but the extra chip makes the difference! And, I'm using the matching Crane PS91 coil.

http://www.mgbexperience.com/electrical/xr3000crane.html

http://www.mgbexperience.com/electrical/coil.html
G. Kinslow '69B roadster

From the the Crane Fireball XR700 and XR3000 instruction manual, "The XR 3000 is a high performance version with a computer chip that controls coil current and dwell. When installing an XR3000 all OE ballast resistance must be bypassed."

There is nothing I see about it that replaces the vacuum advance. The computer is supposed to control dwell but the distributor has to be timed as if it still has points. The manual does not suggest removing or even mention the vacuum advance when installing the XR3000.

Clifton

Clifton Gordon

That's what I meant - nothing to control timing (advance).

Wayne
Wayne Pearson

Wayne and Clifton, I see your point. I don't know the difference between vacuum, advance or dwell. Nonetheless, the vacuum unit is disconnected and the carburetor tube is capped with no ill effect that I can tell, and my mechanic says it's no longer necessary. So, I'm clueless but happy. Any further explanation would be most welcome.
G. Kinslow '69B roadster

This will affect your fuel economy. If you fire ealier you can run a slower burning weaker mixture and have time to burn it. When you open the throttle the SUs richen the mixture and the vacumn falls sparking later for the fast burning richer mixture. Leaving vacumn advance off "solves" a lot of problems , but for me when you consider how clever the old MG engineers were at squeezing out good mileage and performance using the SUs and vacumn advance it just is not true to the "Abingdon touch"
S Best

Oh , and I'm pleased that your engine turned out so well , hope you enjoy it many years.
S Best

Sounds great! I hope to send a similar email to the group one day :) My engine is rebuilt and in but it is waiting for the rest of the car to be built around it. Mainly need to sort out exhaust (will just be stock), fuel system and wiring/instruments. I set the valve clearances and filled her with oil last weekend. Found with a new gasket and new rubber bushes on the alloy rocker cover I had to do the two bolts up tight to get the gasket to seal. I had oil dripping down the block until I did that.
Simon Jansen

G, my GK engine is very similar to yours. Crane cam, 10:1 compression with ported aluminum head, total seal piston rings, full balance, HD clutch, etc... I ran an expensive Aldon distributor with no vac advance for a VERY short time. I went back to using the vacuum advance and it was worth 5-10 horsepower. It made a huge difference in throttle response. I'm actually building my 3rd distributor right now, each with a different advance curve. If you're interested in my results, email me and I could re-curve another one for you, when I'm certain that I've found the best curve, and the proper vac advance can.

By the way, congratulations! It feels great, doesn't it!
Jeff Schlemmer

Jeff and all...looks like I may want to question my mechanic about the details on vacuum advance for my setup with its Weber 32/36.

Actually, I don't even know what brand or series of distributor I have!
G. Kinslow '69B roadster

I inquired about the advance with my mechanic and he said that even though the literature for the Crane electronic ignition doesn't mention vacuum advance, "...keeping the vacuum advance connected defeats the purpose of having an electronic ignition, whatever the brand..." and noted that if I reconnected it my engine would start pinging like crazy when accelerating, especially from a stationary position.

He also told me, dwell is altogether a different matter, as it has to do with the points setting, ergo, no points no dwell to set.

I'm not making this up, as I don't know what I'm writing about. I'm just the owner and driver who leaves all the mechanical mysteries to my trusted mechanic, which is why I looked for a very long time before I found a reasonably restored B at an affordable price. I would never have the time, patience or aptitude to restore one myself! But now the engine's done, I would rate this car at a 2 to 2+ (really trying to be objective).
G. Kinslow '69B roadster

Forgot to note on the rebuild, he rebuilt the original rocker assembly.

Recommends Castrol GTX 20-50 with the addition of some kind of Lucas product that protects the surfaces every fourth oil change. He knows the name of the product, not I. I just say, "sounds alright by me!"
Gary Kinslow '69B roadster Pale Primrose

Gary; Good to hear your engine is running well and that you are happy with the results.

Regarding the comment in my post above, I printed the part in quotes from the Crane ignition manual. I'm aware that there is no dwell to adjust. I have been running a Crane XR700 on my 74 MGB for six years. My engine has some performance modifications for street use, has SU carbs and the vacuum advance is hooked to the inlet manifold just like it left the factory. No pinging and no problems. As Jeff has done, I had to do some work on my distributor to take advantage of the engine modifications.

Naturally based on my experience I don't agree with your mechanics comment ("...keeping the vacuum advance connected defeats the purpose of having an electronic ignition, whatever the brand..."). That said, if you are happy with your mechanic and have confidence in his work it looks like you need to follow his advice, you don't want to upset him until you are sure everything is ok with your engine rebuild.

Clifton

Clifton Gordon

I completely agree with the oil choice, but whole-heartedly disagree with the ignition/distributor issue. I also have the XR3000 with the PS91 coil, and that system will vary the dwell. That is COMPLETELY different from ignition timing. All you have is an electronic replacement for points and condensers. The XR300 automatically adjusts the "points gap" to provide the most power. It DOES NOT change the ignition timing throughout the rpm range, unless your mechanic figured out a way to get the new ignition system to rotate the distributor.

Trust me when I tell you that the power change was drastic when I went back to a vacuum advance distributor!!! Someday, you'll have to try it!
Jeff Schlemmer

Gary
There ain't nobody else agreeing with your mechanic. There are some pretty sharp cookies on this blog.
Barry
Barry Parkinson

This thread was discussed between 11/05/2005 and 13/05/2005

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