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MG TD TF 1500 - Misfire - I am starting to lose hope

I am a mg td newbie and have owned my present car for 14 months and have steadily worked to improve her. I am a "tapets and points" level mechanic, anything more scares me a bit.

Please help as I am stumped and starting to lose hope.

I have had a good look through the archives but see nothing that has helped my problem.

I get a mis fire on revs over about 2000. She starts and idles really well. I have replaced the points for an accuspark electronic system and that has been running well for 12 months. There is no arcing across leads or on the cap visible in the dark. I have renewed the rotor, the plugs, plug caps, HT leads and those horrible HT connectors at the cap and and on the coil.
Opening up the distributor the advance weights seem very sticky and dont always close in the same place but I am assuming that engibe vibration will shake them shut. I can rotate the rotor clockwise and counter clockwise about 1/4 inch each way which makes me wonder of the gear is worn. The rotor also has some slight side to side play and up and down play.
I have never taken a distributor out an engine and feel nervous in doing so.
Does it sound like a worn distributor to you? Will new bushes fix it? Are they easy to remove, Can I change the distributor gear at the same time? Have I missed something?

Thanks chaps
Ray

R Coyte

Ray,
Frist,,, WELCOME TO THE FORUM!!!!!!!! I think we need some history,,,, Was there a problem befor you changed over to the Accuspark System???

SPW
STEVE WINCZE

Thanks for the welcome Steve

Yes there was a problem before I took the points out - they were pretty well worn and burnt and she was "a reluctant starter". That said she did not misfire once she decided to fire up.

The installation of the elctronic ignition system made a positive difference with instant starting and smooth running for 11 months. A month ago this wretched misfire began.

Let me know if you have any more questions that might help the diagnosis.

Regards

Ray



R Coyte

Ray,
Was there play up and down with the old rotor? You didn't mention that you replaced the Distributor Cap..
With the rotor off, can the shaft move up and down and side to side??
SPW
STEVE WINCZE

Hello Ray May I suggest you complete a continuity check on the leads . When performing this check lightly bend the wires to insure no interruptions occur . You may have a fracture lead. John
J .R.C Cavey

From experience, I would look at two lines of enquiry:

worn bushes in the distributor causing the rotor to track erratically. Removing the distributor is not a high risk item. Ideally scratch a mark in the engine side and on the distributor (or put a piece of coloured stick paper across the join and mark that). This will help to relocate the distributor back where it came on replacement. You need to ensure that the rotor is in the same orientation on return as it was on removal. If the bearings are worn it is pretty obvious since the spindle will move sideways when it shouldn't. Send to Jeff Schlimmer in the USA or The Distributor Doctor in the UK for repair or rebuild.

Alternatively the electronics are playing up at higher revs. Try replacing the old points and see if the problem disappears, if it does you know who to blame.

If none of these report back, and the team will put their combined heads together and sort it!

IanB
Ian Bowers

ray, perhaps i am reading it wrong..if so, my apologies..but the arcing in the cap could easily be on the inside of the cap.
hmmm..ran great for 12 months and now you have an issue on the ignition side..i am not familiar with the electronic ignition system you installed.(.in my opinion points, with regular maintenance, are pretty trouble free with the use we give these cars.) what troubleshooting tests have you done so far and what are the results of those tests?. just a shotgun idea here..don't rule out a failure of your electronic system.

regards, tom
tom peterson

Ray, I had a similar problem last year and found that there was excessive play in the distributor bushes, in fact there was so much the rotor arm was catching the pick ups on the distributor and causing a ticking sound. A reconditioned distributor sorted the problem. However be aware the distributor doctor usually has a 4 month lead time.
You could also try renewing the low tension cable from the coil to the points it can sometimes have a break and cause intermittent faults.

Cheers Chris
C A Pick

Try a different ignition coil.
George Butz

Thanks everyone for the questions and ideas I do appreciate it.
Ian - thanks for the advice on the distributor removal it is now out and I have a ruddy great hole in the side of my lovely XPAG and can see the bowels of the engine which is a disconcerting sight for me!
J R C C - Thanks for the tip on checking continuity of the leads I had not done that. Done it now all OK.
Tom - Yes you are probably right I should revert to some new points to rule out the electronic unit. But I sort of figure if the electronic unit fails it should completely pack up not work fine at tick over - Do you agree? Also Tom, as far as I can judge there is no evidence of tracking inside the distributor cap.

The Distributor Doctor here in the UK cant work on it for another 10 weeks and I am a bit glum I will lose the chance of using her in the summer.

I enclose a photo of the distributor. Does the gear look worn to you or does it look normal?

As I metioned I can move the (red) rotor arm from side to side and indeed if I shake it hard the whole distrbutor moved a tad in its position on the engine.

Now I have the distributor out the engine if I grasp the gear with one hand and the rotor cam with another I can wiglle it...ie the gear pin is loose. Is this normal?

Am I on the right track it is electrical and probably the distributor?

Finally anyone know how I remove the bushes? I cant figure it.

Thanks everyone - you are being most kind.

Ray

R Coyte

ray, i cannot comment on the gear being loose on the shaft..it should not be, but i do not think that is the source of your trouble. from what i see on the drive gear..there is some wear, but i do not believe the level of wear it shows would cause it to be the source of any trouble for you either.
now worn counterweights..that is something else.
i am not sure of your round trip postage costs to the states..but advance distributors would have a much quicker turn time..even considering shipping..there must be another good distributor shop in your part of the world.
to answer your question..the bushings page C.10 in the service manual shows the mandrel required to press fit them into place. they are oilite bushings so you do NOT hone them after installation.

regards, tom
tom peterson

I would think one could send the distributor to Jeff here in the states and get it back inside of 2 1/2 months.
Tom Maine

While I would defer to the much greater wisdom of the group, I thing George Butz is on the correct path.

I have had the LUCAS coil on my TD fail. For the cost I would try a new one before giving into the distributer rebuild.

Jim B.
JA Benjamin

Ray, as others have suggested I would take out that electronic ignition and try it with the old style points. This would be a quick job and makes more sense than messing with a possibly unnecessary rebuild.
Hugh Pite
H.D. Pite

I heard the suggestion to check the coil. I'm surely no expert, but I found that to be the solution to a problem I had several years ago.

Regarding continuity tests... the engine runs ok at lower rpm, but stumbles above 2k. At 2k, the "spark system" is firing 4 thousand times a second. Any component, coil, wires, distributor, points, electronics could check out ok with a meter but stumble at higher rpm. (i.e. Correctly gapped points that run ok at idle could float or not close effectively at higher rpm.)

This makes it so elusive and frustrating. Do you know anyone with an analyzer or scope to see what is going on electrically?
Best of luck,
Bob;
RwB Brown

Ray,
I learned more on engines from my 500cc single BSA than anything else. The first things I'd check back then are the same things I check now.
Voltage & gas! Make sure battery is up and system is charging!!!
Pull plugs and check porcelain colors. Are any pair realy black or really white? if so, go to
http://www.dbraun99.com/
and see how to work with SU carbs!
BY the way, what are the points & plugs gaps???
Replacements caps are known to crack. Look inside the cap to search for cracks or carbon tracks leading down from posts.
I'm with the others, try restoring old ignition. Too late to spends hours reviewing Accuspark, but did it eliminate the condenser? Usually condensers don't crap out, but they DO get installed crooked where the cap does not sit down right!
Get back with us!
Jim
JIM NORTHRUP SR

Hi Ray,
as a temp measure try a dizzy from a late Metro ( "A" series Metro ) you will have to fit the drive gear from your old one to it.
If you are a member of a T Type club then I am sure someone will loan you one until yours is fixed.
If you are not a member then I recommend MG Octagon Car Club who cater for pre 1955 cars.
Ray TF 2884
Ray Lee

Many years ago when I was running my TD with points I would get a misfire at about 3000 to 3500 RPM. Turned out the cam to the distributor shaft contact was worn and the distributor would not hold dwell at that RPM. A change to electronic ignition cured the problem as a slight wobble of the distributor cam did not affect the slotted disc that triggered the electronic system.

John F. Quilter
Eugene Oregon USA
John Quilter (TD8986)

Steve / JRC / Ian / Tom P / George / Chris Tom M / Jim B / Hugh / Bob / Jim N / Ray Lee / John

Thanks for all your helpful advice - very much appreciated.

Having looked at the distributor carefully now it is removed from the engine. It is slightly worn but I am faily sure it is fit for purpose. The bushes are (I think) OK and I now think the slop I felt was because the whole unit wasnt tightened firmly to the engine block.

Looking at the workshop manual replacing the bushes is a bit beyond my ability as I dont have a mandral or a press. They seem OK so I am going to leave them.

The bottom gear of the distributor does look a tad worn and is sloppy so I will replace that.

So. Based on your advice my plan is this.

I am going to replace the bottom gear and pin.
then
Put a new set of conventional points in
then
Reinstall and fire her up.
if I still get a misfire I will swap out the coil.
If I still get a misfire I will swap out the cap.
if I still get a misfire I will replace all the leads
if I still get a misfire I will try to borrow another distributor as suggested by Ray Lee.

This will take me a few days so forgive me if I go silent for a while.

Many of you say its possibkly the coil. I think (and hope) you are right but it is fairly new and I did meter it before I fitted it and the readings were all within spec. I have another on order so we shall see.

Out of courtesy to you all I will of course let you know what happens.

Thank you everyone



R Coyte

Ray,
if you want to borrow a complete distributor than give me a mail. I can give it to you and the shipping from Germany is not so expensive.

At the other hand, I can recomment the 1-2-3 Distributor
http://www.123ignition.nl/
It is an unbelivable improvement and a good investment.
Cheers,
Guenter

Guenter

Latest update.

I swapped the sloppy bottom gear and badly worn pin. Put in new bushes (and yes I did soak them in oil beforehand). Put in brand new points, plate and condenser and sorted out the sticky advance weights. Reinstalled the whole lot fired her up and still she misfired.

Swapped the coil out for a brand new coil and still she misfired.

Changed the distributor cap for a new one and still she misfired.

Made up a complete new set of HT leads and still she misfired.

As before she still ran sweetly at tickover.

With nothing better to do I kept the revs high whilst she misfired and pulled each plug cap off one by one. With plug one removed she stumbled even more - same with plug two - but with plug three however no change!!

I know plug 3 was firing as I was getting shocks off the wretched thing. It must have been erratic firing.

I put in a brand new plug into 3 and fired her up - problem solved.

It was a simple spark plug issue all along that only manifested itself at higher revs.

I did early on check each plug...but only at tickover.

The plugs are only a few months old - and I enclose a photo of the offending plug.

Thank you everyone for your help - including Guenther in Germany for the offer of a loan of a distributor to help with diagnosis.

Not sure why a plug should give problems at higher revs seems to me they either should work or not. I have had a good look at it and cant see anything wrong, no cracks or tracks and with the correct gap for a high lift cam.

I have learnt a lot about the ignition system and my distributor and have now got a load of spare parts so the process was no so bad.

Once again everyone - thank you for your helpful advice and guidance - very much appreciated.

Warm regards

Ray Coyte
Honington
Warwickshire
England





R Coyte

Ray,
thank you very much for chasing that down and documenting it for us and the archives. What a frustrating experience. I expect most of us have gone thru something similar and just collapsed in exhaustion when it finally was solved. (I know I have).
Al

54 TF "Emma"
A W Parker

Jud,
Other than looking a bit black,,, the plug seems fine,, 'specially if it is so new,,,, Do you think it might have not have been tightened properly??? Therefor misfiring at a higher rpm??? can you do me a favor and put it back in,,, and make sure it is properly tightened and then try it at the higher revs??? Just a final test,,,, The compression ring doesn't seem squished,,,

SPW
STEVE WINCZE

Steve, that was (is) Ray gnashing his teeth but now celebrating over sparkplugs. I was gnashing and am now celebrating over voltage regulators. More importantly - It seems to be a day for celebrating problems solved through the collective wisdom and just damned good fun of this bbs. If it doesn't rain tomorrow I'm going for a 50-mile victory lap.

Jud
J K Chapin

Steve

As requested I put the plug back in another cylinder and it definately is the plug.

You mentioned if I had tightened it properly which gave me a thought.

It was over tightened by me (my fault, no excuse) and needed effort to get it out.

I wonder if I had mashed the compression ring and also damaged the plug internally?

I enclose a photo of the compression ring.

May fault...It is most unlike me as I usually am very careful when tightening bolts

In fact this morning I had to think twice about admitting to it on this forum or if I should keep quiet and hide the shame.

£158 in parts and a days work...all because of one plug :-(

R Coyte

Ray,
Thanks Ray, I appreciate the double check!!! I don't think that you could have damaged the plug by overtightening,,, (other than stripping the threads out of the head)
ALSO,,, Sorry about getting the names mixed up Jud!!! enjoy your Victory Lap !

SPW
STEVE WINCZE

This thread was discussed between 08/07/2013 and 11/07/2013

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