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MG MGB Technical - It finally bloody runs!

Finally, after 2 years the first engine I ever rebuilt is running! You may have seen my other thread about the disaster. Well today I carefully plugged the hole with a clean rag and using a small grinding stone on my Dremmel I removed a small amount of the front plate. Only needed a few mm. Just enough I could get the plug in. I carefully removed the rag and that pulled all the grinding dust with it. To be sure I turned the engine over and let the oil wash out anything left. I am pretty sure that wasn't really needed but there was oil everywhere anyway so a bit more wouldn't hurt. I looked in my box of engine parts and what do you know. Lurking right at the bottom was the missing plug. Probably why I missed it. I would have just gone through my bag of bits and put them all in. I didn't realise one had dropped out. I froze it and then had to really belt it home so I am hoping it won't come out since the front plate isn't now sitting in front of it to hold it in?

After checking everything and building up oil pressure with the plugs out (and no leaks this time) I put the plugs back in and hit the starter and she fired right up! No problem getting her to start.

I do have some problems though. The coolant explosion was interesting. The fan switch blew. Coolant everywhere except on me funnily enough. Oh well, washed all the oil off. I stopped and let it cool a bit. I put the switch back and a bigger cable tie around it and refilled the coolant. Even with the fan running all the time it is running way too hot. I could only run for 5 minutes at a time then had to stop a bit. I did about 20 minutes in total with the revs at 2000 - 2500 (I varied it a little from time to time) to bed in the cam. The other problem I has was fuel overflow (after all my fuel pump testing) so I did have to plumb in the regulator which I set to 2PSI and that fixed the problem.

Car starts so easily. Seems to run OK although I haven't really done the timing or carbs yet. I pulled the plugs and they look quite good. Light brown but with a little black soot. Stopping is a problem. It runs on really badly. I stopped after 20 minutes running and retorqued the head and checked the valve clearances. I'd set them cold and now hot they were all fine at the smaller clearance except one with needed a slight tweak.

So I need to figure out why it runs hot (maybe it will get better when I actually set the timing and carbs up properly?) and I might plug the stupid fan switch hole and get something better but I am so pleased. Got the biggest grin now!
Simon Jansen

Simon. Check the timing using a timing light. Often, if the timing is retarded, the engine will run on and overheat.

The blowing out of the thermocouple in the radiator is a known problem. I have the hole patched and use an aftermarket switch having a probe which is fitted to the back of the radiator. This was a known problem when the cars were new. (Had to have the thermocouple and gasket replaced twice in five and one half years.)

Make sure the cooling system is really full. Best method is to remove the upper radiator hose at the water elbow/thermostat housing, and fill it until the coolant begins to flow out of the thermostat housing. Then, attach the hose to the thermostat housing, fill the expansion tank to half full, and run the engine. Let it cool and refill the expansion tank as necessary.

Glad you got it running.

Les
Les Bengtson

Simon, great that you have it going now despite a few gremlins. I guess that you had an air lock and that's what caused the system to blow off. As Les says make sure that the system is really full and stays full. Check that the heater is blowing hot air because if its not then it is still airlocked. That will certainly settle down. Don't worry about the running on. It will do so and quite violently as well if the motor is not turned off from an idle speed of about 7/800rpm. Set the timing and then synchronise the carbs and adjust the mixtures and I would then suggest that you pretty well leave the settings abone until the engine has a minimum of 500 miles under its belt. Then you can tinker with it and fine tune as much as you like.
Iain MacKintosh

Simon - congrats!!! Its about time! (Just kidding. mine took 3 years!)
Once you sort out the tuning it WILL run cooler. You also have to remember that all the extra friction from bedding in new rings, bearings, etc. will initially add to the heat.
The running on will also get better when you fine tune the engine and get the idle set lower.

Now, how long until you get out for a drive?
Jeff Schlemmer

Mechanically I still need to do the front brakes and brake pipes. Also a little more body work on front wings, doors, etc (but I guess that wouldn't stop me driving it.....).

Biggest job still to do is all the wiring.

I was worried about my gallery plug I put in to fix my oil leak but I think it will be fine. I think brass expands more than cast iron when hot so it should remain nice and snug in the block.

Is there an easy way I can plug the fan switch hole in the radiatior? Or should I just pull it out and have it patched and repressure tested?

Tonight I will come home and look at the dynamic timing and try to get the carbs set up. I am still using my original filters. Once it is all running nicely I will switch to the K&Ns then see if I need to change needles too. It should be easier now I have that 20 minutes out of the way so I can run at idle speeds to do the timing.

As someone told me now I have heard it run (and it sounded GOOD) I really am motivated to finish the rest of her off. I'll have to be good and not run it until I can actually drive it under load.

Thanks to everyone who offered advice and tips over the last couple of years. Especially Chris Betson whose engine building site was absolutely brilliant when I was assembling the engine.

Simon
Simon Jansen

Simon. I have always had a radiator shop do the patch. They have the experience and equipment to do the job correctly, then, test it under pressure. Not all that expensive and, to me, worth it.

I was running AAA needles in the carbs on my 68 when I switched to the K&N filters. Did not need to change the needles myself.

Les
Les Bengtson

Les, I know I could probably solder it up myself but then I would always wonder about it under pressure so I was thinking I would just pull it and take it back to the place I had rebuild it. Is it possible to get an adjust freeze plug or something to fill the hole temporarily?

One thing I just realised is I may have had the alternator not wired up correctly. Well, not completely. I attached the big brown wires but left off the warning light. That's actually needed isn't it to allow the alternator to work properly?
Simon Jansen

Simon. Have not tried an expandable freeze plug, so I do not know how well it would work in the soft metal of the header tank. I have seen several of the thermocouples blow out over the years, hence, my suspicion of the factory system. Many people seem to get by using a cable tie or a piece of soft iron wire to hold the thermocouple in place. My worry is that it might still allow the thermocouple to move slightly and cause a loss of system pressure, at the least, and loss of coolant at worst. Since my cars are daily drivers, the use of an alternative fan triggering system and patching the radiator opening made sense.

If you do decide to use an expandable freeze plug as a short term solution, let us know how it works. It might, for those who use the original system, be a good thing to carry in the trunk.

Les
Les Bengtson

I need to find out where I can get one! I will probably just get the radiator patched at the shop though and go with a more modern fan switch.

Tonight I went and tried the engine again to see that it wasn't a fluke yesterday and to check out the dynamic timing. I also wired in the alternator warning light. At first the alternator didn't seem to work but then after a while it started working fine and measuring the battery voltage does show it is charging.

I tried lowering the idle speed and I can get it idling at 600 rpm OK. It is a little rough but not bad at all really. At that speed I measured the dynamic timing at about 8 degrees. At 1000 rpm it was about 10 degrees.

I still haven't tried setting up the carbs yet. I am going to borrow a proper tach/dwell meter off a workmate and make sure that is all right first.

I don't know what I should really be aiming for with the timing. The distributor is a 25D marked 40768F then 867. I know the first is the service number and the second means it was made in 67. I don't think it is a MG spec one though. Anyone able to look up the numbers. I couldn't find it on the web. The sites I found listing them didn't have that number. The vacuum can on it is marked 5-13-10.

Oh, at the lower idle speed the engine shuts off fine adn the temperature isn't so bad. Still too hot though. I am pretty sure all the air is out of the system. With the overflow cap off I squeezed the top hose which made bubble appear in the overflow tank then letting go would suck fresh coolant itno the hose. I kept doing that until it didn't sound like air was moving about.
Simon Jansen

"I attached the big brown wires but left off the warning light. That's actually needed isn't it to allow the alternator to work properly?"

Yes and no. Most used (and possibly reconditioned out of the box) alternators will probably charge without the warning light connected, but will probably have to be revved to about 3k before they will start. Once they have started, they should charge right down to the normal 600rpm or so. A new alt out of the box may not charge at all without the warning light connected.

The warning light current acts as a pump-primer for the field windings, without it they have to rely on any residual magnetism that may be in the iron parts to generate the initial current, which is then fed back to the field windings to generate full current. used alts usually contain this residual magnetism as they will have experienced the appropriate magnetic fields for some time, new alts not so.

A dynamo *always* used residual magnetism to generate the initial current, which is why they have to be polarised when new or repolarised when changing polarity. However *do not* attampt to polarise an alternator, you may well destroy it.
Paul Hunt 2

Simon. The 40768 is the specification number with the F suffix indicating some for of change to the distributor which does not affect the basic specification. It was made in the 8th week of 1967. I cannot find an advance curve listed. The only reference is that it was used by BMC on the Mini Moke. Thus, you might want to check the curve at various engine speeds (vacuum advance disconnected and the line plugged) and see what it shows. About 32 deg advance at 3,000 rpm might work well for your engine. Then, drop the engine speed back to 1,000-1,500 rpm and see what it reads. That will become your basic dynamic timing specification.

The early distributor, which many recommend as being as close to perfect as can be had without developing a custom advance curve, was the specification number 40897. It was dynamically timed at 20 deg BTDC at 1,000 rpm. My chart shows:

10 deg at 400 to 600 rpm
24 deg at 1,500 to 1,750 rpm
30 deg , plus or minus two deg, at 3,000 rpm

You might see what your dissy is displaying. All readings with the vacuum advance disconnected and the line plugged.

As to the fans, the switch I use is a box with a rheostat in the face, two prong type electrical connectors and a probe to be fitted behind the radiator, held in place with some soft iron wire or a cable connector. Such systems are available from a number of sources. Until you can find one, simply running a toggle switch into the cockpit will allow you to switch the fans on and off.

Running the engine until it is hot, then allowing the system to fill itself from the expansion tank should get the system filled shortly. The method of filling I was shown was to remove the upper radiator hose at the thermostat housing, fill the cooling system through the upper radiator hose until coolant began to leak from the thermostat housing, then, quickly reattach the upper hose to it. Fill the expansion tank about one half full, run the engine until it is hot, allow it to cool and fill the expansion tank as necessary. Works well.

Les
Les Bengtson

Thanks Paul, mine was rebuilt and has been sitting for the last 2 years unused so that explains the bahaviour I saw I guess. It works fine now. I guess once it is kicked into life it is good from then on in.
Simon Jansen

Les, I will try that with my dizzy and see what numbers I actually get. I've been doing all the readings with the vacuum line removed and plugged as you mention. I'll post what I get here.
Simon Jansen

I haven't finished tuning my engine yet but I found this page for minis that lists some distributors and numbers. The PDF lists what the curves are.

http://www.minimania.com/web/Item/123DIST-A/AddedFrom/Specials/InvDetail.cfm

Apparently mine is from a 850 Mini. If I am reading their data correctly it should be giving me something close to 10 degrees at 500-1000rpm, 23.9 at 2000 and 34 at 5000.

Pretty close to what you say is good Les. I will have to see what I actually get when I get the car running nicely.

I also bought a pertronix ignition to put on the dizzy when that arrives.

Simon
Simon Jansen

This thread was discussed between 12/02/2006 and 21/02/2006

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