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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

Cat Pony Motor Question (old D4 5T CAT)


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  #1  
Old 10-06-2017, 09:03:45 AM
Burt Lade Burt Lade is offline
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Default Cat Pony Motor Question (old D4 5T CAT)

Hello all,

Having just acquired an old D4 5T Caterpillar and looking over the magneto
on the pony motor, I have uncovered something strange. The magneto is a
Bosch MJK 360C-47 and looks like a newer unit to me. What I discovered
is that the magneto fires with 360 degree rotation but the distributor cover
distributes on 90 degrees. Therefore, either the magneto is not the correct
one OR the distributor cover is wrong. Another way to explain this for clarity
is that the magneto fires on each 360 degree rotation causing the rotor to be
90 degrees out of phase so I only get spark on one cylinder. I would get spark
on both plugs if I used a rotor cover opposed 180 rather than 90 degrees.
Does the pony motor on these old CATS fire with a full rotation of the magneto
or on 180 degrees of rotation? If I knew that, I would know how to make it run.
I'm sure someone knows the answer to this dilemma but at the moment I am
unsure.
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  #2  
Old 10-06-2017, 09:35:39 AM
TomA TomA is offline
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

One cylinder fires at 360 degrees and the other fires at 720 degrees.
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Old 10-06-2017, 09:39:51 AM
Burt Lade Burt Lade is offline
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

Quote:
Originally Posted by TomA View Post
One cylinder fires at 360 degrees and the other fires at 720 degrees.
OK, Thanks a bunch! That's what I needed to know. That means the distributor cover is
the wrong one.
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  #4  
Old 10-06-2017, 01:37:34 PM
Gary Barber
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

now I am going to have to go out and look at mine to see if there is enough offset on the cylinders to allow separate crankshaft journals for each cylinder otherwise if both rods are on the same journal like most V type engines and with only 1 crank journal they can not fire at 360 and 720 I am kind of in favor of not changing a lot of things and trying to figure out how what is in place actually worked before condemning parts as wrong
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Old 10-06-2017, 02:39:25 PM
Heins Heins is offline
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

If you could remove the cover over the valve springs and cam followers you could tell how the engine fires by watching the valve overlap.
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Old 10-06-2017, 07:03:44 PM
Burt Lade Burt Lade is offline
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

Gary,

My pony motor is an opposed engine similar to half of a Volkswagen engine. I couldn't tell for
sure but after some testing it seems that when I have compression on one cylinder, the other
cylinder has compression after 360 degrees of rotation. I see there are several versions of
2 cylinder pony motors ( some with side by side cylinders ). If you have the opposed type, I
would be interested to know what your distributor cover looks like. Thanks.
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Old 10-06-2017, 07:43:46 PM
Gary Barber
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Default Re: Cat Pony Motor Question (old D4 5T CAT)

yep mine on my d4 are horizontally opposed more like an onan than a volkswagen yeah i get it just 2 of the cylinders of the vw 4 and if they are on the same crank journal which I highly suspect they are then there is NO WAY they can fire separated by 360 degrees of crankshaft revolution

---------- Post added at 04:43:46 PM ---------- Previous post was at 04:24:52 PM ----------

I found some pix of a crank for a d4 pony motor and it appears there ARE 2 separate journals for the rods and being separate journals the pistons would be at tdc at the same time 1 on compression and the other midway between exhaust and intake allowing them to fire evenly separated by 360 degrees of crank rotation
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