Author Topic: Hot engine power loss  (Read 665 times)

Offline Phil proctor

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Hot engine power loss
« on: 07.07. 2017 18:58 »
I've just bought a 1950 a10,  after some 10 miles it started to lose power in bursts then eventually all together and wouldn't start .  I also noticed the engine had got very hot and taking the cap off the oil tank showed the oil 'steaming'. I suspect the mag is the reason for power loss and non starting?  But should it be running that hot and if not any ideas on the issue?  If not the mag then what, I will check carb too as it may be distorting.  Ps it was a very hot sunny day.

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Re: Hot engine power loss
« Reply #1 on: 07.07. 2017 19:37 »
Did you fully advance the manual ignition lever?

Offline Phil proctor

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Re: Hot engine power loss
« Reply #2 on: 07.07. 2017 19:44 »
Hi it's an auto advance (at least I hope it is because there's no lever!)

Online Triton Thrasher

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Re: Hot engine power loss
« Reply #3 on: 07.07. 2017 19:56 »
Ok that's not typical bad magneto behaviour.

Test fuel flow out of the carburettor.  Try to see if the breather through the tank filler cap is clear.

Online Sluggo

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Re: Hot engine power loss
« Reply #4 on: 07.07. 2017 21:03 »
Sounds more like a partial seizure of the pistons.  Lacking full details to assess from a computer but not uncommon at all, especially with a new machine you are not familiar with or what kind of work was performed by the DPO (Dreaded previous owner).
Might be an innocent mistake, OR might be carelessly slapped together to effect a sale, dont know and cant say, But back in the day when running a shop it was common to have to give bad news to a anxious new owner that their new toy needed expensive surgery to make it right.

Of course could be wrong,, a hot bike and an old maggie neato will certainly show up the weak links.

As they say "All electrical/ignition problems are Fuel, and all fuel problems are electrical/ign"  and not exactly the case here but illustrates the conundrum.

Flow chart of diagnostics and assessments should be followed.
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Offline Phil proctor

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Re: Hot engine power loss
« Reply #5 on: 07.07. 2017 21:41 »
Not convinced on partial seizure as she turned over quite nicely off the kicker when I stopped no sticking and compression fine too.  She started up fine too when cold which is why I suspected the mag...

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Re: Hot engine power loss
« Reply #6 on: 07.07. 2017 21:56 »
G'day Phil,  *welcome*
Sounds like the tappets are set too close and retarded ignition.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

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Re: Hot engine power loss
« Reply #7 on: 07.07. 2017 22:10 »
Heat & vibration tend to be hard on the magnets that produce the electrical field in a Maggie, If you are not aware the capacitors decline with age and even NOS ones on the shelf go bad as well, plus there is the "Shellactitis" of the original wiring in the MAG, so very probable that the Mag can have issues.  That is a very common symptom that the mag fires when cold but expires when hot,, but as another poster has suggested, it sounds like your engine is way too hot.. timing, valve adjustments, fuel supply and quality? All sound like needing to be checked.

I certainly hope its not a piston/seizure issue but based on your initial description that led me to believe that was the probably case or at least a byproduct of the symptoms.

Regardless,, much trouble shooting and investigation is required.  Best wishes.
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Re: Hot engine power loss
« Reply #8 on: 07.07. 2017 22:18 »
When did they last use shellac on magneto windings?

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Re: Hot engine power loss
« Reply #9 on: 07.07. 2017 22:32 »
I am not certain about the "Shellac" but its written in many tech articles as well as have been told by many who rebuild vintage Mags and generators that the coatings on the wires can degrade or go bad and the windings short out.  So, I borrowed that term "Shellactitis" as it sums up the issue.

To be fair,, I have seen some ancient windings (The fine strand copper wire) in remarkably good nick despite age and history,, So perhaps its all a devious plot in a global conspiracy to incur higher costs by cranky old codgers eager to separate your beer slips from your wallet upon presentation of your unit for rebuild..

I have always had my Lucas and BTH units rebuilt and serviced by a number of trusted experts,, I will clean them, adjust the points and brushs, but have always farmed out that task for full overhaul on British bikes.   (I hear Stihl Chainsaw capacitors are a hot upgrade)

But I am a lic FAA tech and used to rebuild acft maggies,,  I got in trouble for saying that maggies are an inferior design.  (Its a simple fact that the have low spark and power at start and low RPM and only really produce good performance at high RPMS.. IE: Good for a race bike, bad for the street).  I was roundly ridiculed for this view point despite my point of redundancy and safety of modern EI ignitions.  Years back I sent some ads and an article from Acft Mechanics news to some of these people showing the now common practice of EI Retrofit kits for many common piston type acft..
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Re: Hot engine power loss
« Reply #10 on: 07.07. 2017 23:06 »
This might illustrate the issue better than my rambling and disjointed drivel....

See: http://www.brufnut.de/WORKSHOP/LUCAS/lucas.htm    (its for a Brough, but same difference)

" What you find is a great number of layers wound with a very fine (0.07mm dia.) wire, separated from each other with very fine insulation paper.

Below this, you will find 4-5 layers of thicker wire (0.7 ... 0.85mm) which make up the primary winding. These are separated from each other by a thin shellac impregnated cotton insulation; the primary winding has between 160 and 180 turns."

But then he goes on and discusses a Lacquer insulation,, but it IS an informative article,,

Another gentleman,, who DOES know a thing or 2 is Bob Kizer, of PODTRONICS,, I find him disagreeable personally, but I bow to his great knowledge and experience.  YRMV

See: http://www.podtronics.net/magnetos.htm

Very informative, although I disagree with his assessment that there is only ONE person left in the US who knows how to rebuild a maggie or generator.
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Online JulianS

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Re: Hot engine power loss
« Reply #11 on: 08.07. 2017 09:43 »
I always first suspect lubrication with a hot engine which slows. Partial seizure which losens off very quickly when engine stops.

Check tank filter clean and that there are no obstructions in oilways to impede flow from tank to engine.

If you have not changed the oil since you aquired it I suggest a change.

Next I suspect ignition timing .

Check the a/r unit is working - remove points cover and check you can move the points block against the stops on the a/r.

Check the timing.

I have found mag faults are either very sudden - the engine stops - or only come to light when hot and engine wont restart until things cool.

You can learn a bit from the plugs - if to lean a mixture I would suspect them to show it.

Online Triton Thrasher

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Re: Hot engine power loss
« Reply #12 on: 08.07. 2017 10:16 »
There's nothing disjointed about your drivel Sluggo lol.

You're right, magnetos are not fantastic.  Lucas bike magnetos are ramshackle and flimsy.

On an A10, the K2F still appears to be one of the better options for ignition. 

Offline Phil proctor

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Re: Hot engine power loss
« Reply #13 on: 08.07. 2017 18:22 »
Thanks all.  Re mag fault yes normally sudden but I have had a condensor failure in my old Morris minor which resulted in power loss before cut out?  Lubrication wise I changed the oil before going and the filter was clean and plenty of oil seemed to be pumping when observing in the oil tank so don't think that is it.  It seems I should have to hit the lot as she is new to me, a reasonably local firm refurbishes mags and say they check all before quoting for any work so at least this would tell me what if anything needs doing before I shell out, I'll then retime the refurbished mag and check tappets and breakers, change the plugs leads and pickups whilst I'm at it and then keep my fingers crossed on the next run!!


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Re: Hot engine power loss
« Reply #14 on: 08.07. 2017 19:27 »
If the condenser goes open circuit on a coil ignition, such as your Morris, it might idle ok and then miss and splutter when you give it any throttle.

Usually, on these magnetos, a failing condenser causes bad hot starting.  I don't know why.