MGB ENGINE TIMING

[Anthony Henry]

Hello
I have an 1980 mgb roadster, RHD..Bought from UK and now living with me in Stockholm. A mechanic is trying to set the timing but can not find the engine information in any of the books. The VIN number is only 14 characters long. VIN is GVADJ1AG518415. Engine number we think , not easy to see is 18V847H3415. I believe that this is one of the last MGBs built, first registered on 27/08/81. Please help and thanks.

[Vic Butler]

Afternoon Anthony.
According to my Operation Repair Manual, assuming that the engine is unmodified and is as it left the factory all 18V847 engines are timed at 10 degrees BTDC at 1000 rpm. Ignition advance check is 19/23 degrees at 3400 rpm.
. Hope this helps.
. Vic Butler.

[Vic Butler]

Afternoon again Anthony.
Omitted to say that for the advance check the vacuum advance pipe has to be disconnected.
. Vic Butler

[Anthony Henry]

Hi Vic

Thanks for the information I will give that to the mechanic, his problem was that he could not find the information for that engine number, in the Haynes manual and other ones it does not list the H engine, we are not sure if this is the original engine either. Thanks again for your help.

Anthony

[Vic Butler]

Afternoon again.
The "H" means 9 to 1 compression ratio which is standard for the 847. You should check that the correct distributor is fitted. Because these engines were built to comply with the then EU emissions ECE15, the vacuum advance take off point is on the inlet manifold, not in the usual place on the air filter side of the carburettor inlet. The incorrect distributor will give wrong advance curves. The distributor number on the body is 41610. Anything else is incorrect. The siting of the vacuum take off on rubber bumper cars made them gutless and they reverted to a head with smaller inlet valves. I ditched all that on my 1977 BGT and fitted bigger carburettors, had a bespoke cylinder head built about 3 years ago by Downton Engineering's ace cylinder head guru, to which he fitted MGC inlet valves. The distributor was rebuilt and calibrated to the state of tune and now it will rev very quickly to the red line and beyond if I am not careful. A large bore stainless steel manifold and exhaust with just a rear silencer completes the package. I now have a driveable B with good acceleration easy in traffic and more than capable of keeping up on motorways.
. Vic Butler

[Anthony Henry]

Thanks again for your help. The mechanic is fitting a new dissy with Accuspark already installed. Hope to have it back tomorrow

Anthony

[Vic Butler]

10 degrees at 1000 is quite retarded but it's due to the way the engine was set up at the factory. No static timing figures are given but if your mechanic thinks that is too retarded with the new distributor get him to try 10 degrees static which equates to about 13/14 running and see if that is too advanced. I had to guess the timing on mine.
. Vic Butler

[Dave Linkson]

According to the Clausager book your numbers tally up..
Prefix, Engine Numbers, Car numbers, Dates
18V847-F-H 101-40188. 360301-523002. Sept 74- Oct 80

The distributor No for that engine should be 41610 which if the original Lucas dissy would be marked on the side, the advance curves in that dissy would be suited to that particular B engine, but it maybe worn now giving different readings, you need have the correct one or it will "pink" best way maybe for accuracy is to have the OE dissy rebuilt by distributor doctor, new one's can be got from Moss but they're not made as good as back in the day.. when I had a refurbished exchange engine installed I wasn't sure what exact B engine I then had and how it was rebuilt so went for a CSI electronic dissy with a choice of 16 advance curves...

[Paul Hollingworth]

Hi Anthony
You are in danger of opening a right can of worms here. I agree with the other posters that the 'correct' (as in factory fitted)distributor for your car is a 45D4 with 41610 advance curve. However if you look at my post from April time (on second page of the board now) you will see its hopelessly retarded compared to other B series curves. I took Peter Cresswell's advice and read what Peter Burgess has said in his book. To paraphrase Mr Burgess agrees the 45D4 distributor is junk. If you read the earlier post you will see that various contributors have offered explanations why the factory went with this curve. I have to say I still don't understand how retarding so much can improve economy and emissions. I set my 18GG engine to 20 deg BTDC (vacuum pipe disconnected) which is the factory setting for a 25D4 with 40897 curve and the curve seems identical to the 41288 fitted to the early 18V engines. You cant simply advance to this setting with your 45D4 distributor as it would be too advanced above 3000 rpm. The 45D distributor also has no Vernier adjustment, another disadvantage.
I rang Acuspark as they are local to me but they either couldn't or wouldn't tell me what advance curve their distributor is fitted with, so I didn't buy one. I advised my friend to talk to Distributor Doctor and I think you should do the same. He can change the advance curve of your disi to something more sensible.

[Vic Butler]

Evening Paul.
Can't agree with your statement that the 45D4 distributor is junk. The standard rubber bumper B is gutless because it was built to ECE15 emissions regulations and to achieve this the vacuum advance for the distributor is taken from the inlet manifold where there is a constant vacuum and that is why the 41610 distributor is found only on the 18V 847 series of engines. If that distributor is used in conjunction with a vacuum take off in the proper place ie on the carburettor just on the air filter side of the butterfly then the advance curve will be wrong. The same will happen if a different distributor is fitted on a standard set up.
I dispensed with this set up and fitted a completely different set of carburettors and distributor. Later I had the distributor rebuilt by the Distributor Doctor to suit the state of tuning.
Fitting the wrong distributor to a rubber bumper B os likely to make the already poor performance even worse.
. Vic Butler