Author Topic: New Owner needs a little help? (cut out when hot)  (Read 3547 times)

Offline bigwol

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Hi guys, recently bought my first BSA, 1959 A7.
Due to one or two factors only took it round the block a couple of times and all was fine. Used it yesterday for the first time "in anger" so to speak and after 12 miles or so she lost power and eventually came to a stop. I checked spark as best i could and didnt seem to be great to be honest but when she cooled down restarted so I headed home with the same result. Cooled her off again and got back to base and she is now on the ramp. Blue spark at plug when cold and starts ok. (flood carb no choke fores first or second kick)
There is some oil appearing at the top of the head, so my question is most likely cause? Magneto breaking down when hot? Condenser same thing? Or something more sinister like losing compression when hot?
One more thing, as she had wet sumped I topped up the oil before setting off. When hot after first breakdown the level was around an inch below the top of the tank, is this too high? Where should the level be?
Any advice will be much appreciated.

Dave
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Offline a10gf

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Re: New Owner needs a little help? (cut out when hot)
« Reply #1 on: 19.07. 2012 12:27 »
Hello & welcome. Moved the post to the lucas board, ref. your main question\problem.
Very probable you've got a heat problem with the mag, maybe open circuit in armature winding when hot and expanding, and ok when cold and contracting (...how did I learn about that :O)

About the condenser, take a look at this http://www.a7a10.net/forum/index.php/topic,5359.0.html

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Offline bigwol

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Re: New Owner needs a little help? (cut out when hot)
« Reply #2 on: 19.07. 2012 13:17 »
Thanks for the welcome a10gf, and the reply.
I have heard of the "brightsparks" external condeser (I have run a couple of AMC's for a year or so, so although new to BSA'a not a complete novice with classic brit iron) and would certainly consider it if I need to replace the condenser, however if it's a windings issue will probably send the mag away for refurbishment. Either that or look at electronic ignition although I do like the mag system, not least as you can start and run with a dead battery if needed.
I'm not 100% certain it is mag yet, will investigate further including run the thing till it plays up and check the spark hot again, but it only seems to do it after 10 to 15 miles and being made to work. Another avenue I will check is compression hot and cold and take a look at the carb to see if there are issues there.
It doesnt missfire so much as lose power which gradually gets worse. No popping back or spitting, just more and more gutless untill it stops completely. Just wondered if anyone else had similar problems so I could get a few pointers.
Regarding the oil level, while I doubt a high level would cause problems like this can you give me a clue as to correct level?
Thanks
Dave
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Offline Goldy

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Re: New Owner needs a little help? (cut out when hot)
« Reply #3 on: 19.07. 2012 13:47 »
Hi big wool, first thing I would look at for this type of fault is to see that there is a thick insulating gasket between the carb and the head to prevent heat transfer to the carb.
All. The best Goldy
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Re: New Owner needs a little help? (cut out when hot)
« Reply #4 on: 19.07. 2012 19:05 »
Oil on the head is often from the rocker box or out of the plug hole if the spark plug isn't seated properly or blowing back from the exhaust port. I'll send you a p.m. re the mag. Welcome to the board.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline nagrod

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Re: New Owner needs a little help? (cut out when hot)
« Reply #5 on: 19.07. 2012 19:23 »
regarding the oil level my "BSA Instruction manual" printed 1964 states 5 1/2 pints as the capacity of the oil tank for the A7 (and A10). Maybe you can fill the tank and mark the level before it has a chance to wet sump!

Rick D
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Offline stu.andrews

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Re: New Owner needs a little help? (cut out when hot)
« Reply #6 on: 19.07. 2012 20:45 »
Sounds very much like the magneto. My A7 was playing up in a similar fashion. Have picked up the bike today after having the magneto reconditioned & all's well. It is a different bike altogether.
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Re: New Owner needs a little help? (cut out when hot)
« Reply #7 on: 19.07. 2012 20:46 »
 G'day bigwol, welcome,
                                to throw another possible cause is the tappet clearance too close. They close up when hot and prop the valves open a tad = loss of power. Stop and cool down, all fine again till hot.
 Cheers
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Offline bigwol

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Re: New Owner needs a little help? (cut out when hot)
« Reply #8 on: 19.07. 2012 23:53 »
Hi big wool, first thing I would look at for this type of fault is to see that there is a thick insulating gasket between the carb and the head to prevent heat transfer to the carb.
All. The best Goldy

Hi Goldy, the manifold has a fairly long neck which may do that job like some of the amal carb models but i'll check the gasket situation, without looking I can't recall if there is a "bakelite" type spacer as on my AMC's. Again, i need to check and see if it should have one of those?
I have a few things to look into, will keep the forum informed as to progress.

Bigwol
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Offline bigwol

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Re: New Owner needs a little help? (cut out when hot)
« Reply #9 on: 19.07. 2012 23:55 »
regarding the oil level my "BSA Instruction manual" printed 1964 states 5 1/2 pints as the capacity of the oil tank for the A7 (and A10). Maybe you can fill the tank and mark the level before it has a chance to wet sump!

Rick D

Thanks Rick, 5 1/2 pints seems a lot for that little tank but i'll give it a try.

Bigwol
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Offline bigwol

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Re: New Owner needs a little help? (cut out when hot)
« Reply #10 on: 19.07. 2012 23:58 »
Sounds very much like the magneto. My A7 was playing up in a similar fashion. Have picked up the bike today after having the magneto reconditioned & all's well. It is a different bike altogether.

Hi Stu, yes it does sound like a mag winding breaking down. Where did you have your one refurbished?

Bigwol
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Offline bigwol

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Re: New Owner needs a little help? (cut out when hot)
« Reply #11 on: 20.07. 2012 00:00 »
G'day bigwol, welcome,
                                to throw another possible cause is the tappet clearance too close. They close up when hot and prop the valves open a tad = loss of power. Stop and cool down, all fine again till hot.
 Cheers

Yes muskrat, someone else has suggested tight tappets may be to blame. Don't suppose you know what the clearances should be?

Bigwol
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Offline BSA_54A10

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Re: New Owner needs a little help? (cut out when hot)
« Reply #12 on: 20.07. 2012 12:38 »
Funny you should mention this.
My first A 10 did exactly the same thing.
I would get off, clean the carb, clean the points, clean the slip ring ,dither around a bit then it would go off like a rocket only to repeat the same performance about an hour or so latter.
A bit latter on I found out that if I did nothing for 20 minutes I got exactly the same results.
Meanwhile My friends thought that I was an "Ace" mechanic because I could always fix the thing and when it did go it went with a capital W.
One day on the way to the surf it did its usual but would not start after the usual milk shake & fag break.
When I pulled out the brushes they did look a little past it & as I was a short walk from a sparkie I went down & got a new pair of brushes .
He assures me that they were correct but when I went to put them in they were totally different to what was in there so I took them back complaining that they were wrong this time armed with an original for comarison.

He looked at these and laughed " Usually Lucas maggys don't run very well with Bosh brushes in them ".
Luck I was by my self.
Bike Beesa
Trevor

Offline squidlydit

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Re: New Owner needs a little help? (cut out when hot)
« Reply #13 on: 23.07. 2012 17:08 »
Hi all.

One more option to throw into the debate, tight valve guides. Had a customer once who's A10 was doing the same thing as yours. Fine and dandy when cold but after about 20 miles, and normally after a good thrash, would start to lose power and finally grind to a halt. Fag break for 20 minutes and away she would go again. Turned out to be the exhaust valve guide was too tight on tolerance, as the engine got hot the valve started to nip up in the guide.

Regards Chris.


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Re: New Owner needs a little help? (cut out when hot)
« Reply #14 on: 23.07. 2012 20:51 »
 G'day Bigwol, tappet clearances cold, iron head 10 in 16 ex, alloy head 8 in 12 ex.
I run my alloy head A7 at 8 and 12 but the alloy head A10 needs 10 and 14 to stop it happening.
Cheers
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