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Distributor caps

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Distributor caps

Postby Kai Lyche » Wed Jul 15, 2015 7:57 pm

I had a 22A engine on my hands the other day that had started showing the signs of ignition detoriation. Would´nt you know it, the cap had its center electrode completely worn away- just as the SB said it might.

So I get hold of a new set of distributor caps from my usual certified Jab representative and put them on the engine: to put it mildly, that was an unpleasant surprise! The engine became hard to start and ran eratically: no chance of safe flight with that kind of performance :-(

I recall that both the connectors from the plug leads and the coils were kind of hard to press down in the cap sockets, so everything comes off again for a closer investigation.

I find that the metal connectors in the cap sockets are positioned so deep in their sockets that the contacts from plug leads and coils will hardly touch them: in my opinion not very conductive to satisfactory ignition! And yes, the ignition harness and the coils are original Jab and less than two years/50 hrs old.

The question is, has anybody else experienced this, and what could be done to rectify the problem?
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Re: Distributor caps

Postby Steevo » Wed Jul 15, 2015 9:20 pm

I have certainly had the problem of faulty distributor caps where the centre electrode stays pushed in. There was a period a little while ago where Jab had sourced caps from a source in China and they were sub-standard (as detailed in the UK LAA magazine). These were purchased from the official UK Jab distributor Skycraft. The problem was meant to have been fixed and were replaced. The replacements, also Jab supplied, still caused issues. In the end I managed to find original Bosch ones and have not had problems since.

From what I have heard, the distributor caps are still being supplied from the same Chinese source but have been re-designed. Personally, I would not use the Jab supplied ones but instead try and source some compatible ones. The compatible ones are half the price and do not seem to suffer these problems. The ideal would be to find some original Bosch ones but these are few and far between now.
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Re: Distributor caps

Postby SEQFTA » Sat Sep 24, 2016 8:10 am

Hi All
"mag drop" on a 2200 solid lifter 4 cylinder Jab engine
One Jab i fly has a CDI drop that is hardly noticeable when one side switch or the other is isolated .
Another Jab i fly "was" the same until I removed a distributor cap to check for oil seepage through the shaft , no oil leakage into the cap but when I refitted the cap i got a rough 200RPM drop when I isolated the other side switch .
Put new dizzy caps and rotor buttons on both sides.
Now I get an even and consistent 90 RPM drop on both sides and the motor runs beautifully on both , "but"
I can't seem to get the drop back to how it used to be before I touched the dizzy cap on the left side , which was that you could barely notice any drop at all originally .
Could anyone advise me possibly ?
I've put new plugs in and gapped them to 0.22 thou
gapped the coils to 0.10 thou on both magnets on both sides
I haven't put new CDI's in as the maintenance bulletin says a max of 100RPM drop and mine is within that .
Is there any possible adjustment on the dizzy caps or rotor buttons ???????
Has the 25 degree's BTDC alignment possibly got anything to do with it ?????
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Re: Distributor caps

Postby Garyo » Sun Sep 25, 2016 5:14 pm

I have had the centre pin issue, the answer to this is to releive the plastic around it and it will pop back out with no further issue. As for the plug leads not going right down, i removed material from the top of the dizzy holes so the leads made full contact, no issue.
For the mag drop and possible radio interfeerence you may find appears, try moving the dizzy a bit, you will find you can move it a few degrees in either direction ad not a fixed position, you need to fine tune a new cap
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Re: Distributor caps

Postby SEQFTA » Wed Oct 05, 2016 10:25 am

Thanks GaryO

May I just confirm that the way to move the dizzy cap a little would be to loosen off the 2 allen key screws "under" the cap , twist the shank of the distributor a little , do em back up and try to see if worse or better , if worse loosen again and go the other way ?
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Re: Distributor caps

Postby Garyo » Fri Oct 07, 2016 8:04 pm

Yes, exactly that
Former Owner of
G-OMER
Jabiru 450 UL
Engine serial 1041
1 CHT sensor on No 4 under plug
No Exhaust temp sensors
No glass panel
No xponder
Microair radio
No bells and whistles
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Garyo
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