What motor did I just recieve?

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chris8686

New Member
May 2, 2013
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I just got a new 40mm crank motor from dax on friday. I have 3 other motors from dax. i have one on my bench and on my 2 bikes. This motor seems to be the odd ball of the 4 motors I now have. I would like to get some input from any other dax owners out there.

Specs on new motor:

-6mm cylinder studs
-Studs have 1.0mm threads on one end and 1.25mm threads on the other
-8mm stud holes in cylinder
-Connecting rod marked ZAF80
-Piston has high wrist pin hole
-Piston marked #2
-Caged bottom end bearing

Old Motors:

-8mm studs with 1.25mm threads
-Low wrist pin hole
-Unmarked Connecting rod
-Caged bottom end bearing

What motor did I get? The specs of this new motor matches some of the GT5's out there. I've boughtall my motors from dax because I've gotten a consistent engine that I can swap parts from without a second thought. I don't know if I am bummed out or not yet. I am curious to know if it has the 6202 or the 6203 ball bearings in it.

Here is a video explaining the different rod and piston combinations:
https://www.youtube.com/watch?v=rzLWYSlpFEg
 
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Theon

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Jan 20, 2014
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I'd be curious of the stroke,
and I wouldn't be impressed by the 6mm studs either.
I have had long and short rod motors with either 38mm or 40mm stroke even a 39mm stroke crank! (not from DAX), depends what they had at the time I guess, but the type b (high wrist pin) piston seems to be a pain to find. However apparently it could have slight benefits in respect to the angle of rod to barrel wall.
 
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Theon

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Jan 20, 2014
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I thought 6mm studs were on motors under 66cc, The largest having a 45mm bore rather than the usual 47mm.
But I'm sure any combination of parts is possible?
 
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Theon

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Jan 20, 2014
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In my 'noob' days, I ordered a '70'cc kit thinking that well, they are 69cc, right?
It had the 45mm bore but with a 'narrow case' with 6mm studs, from the 50cc. It had the 45mm bore, I drilled the studs to 8mm, fitted a 47mm barrel, and it's one of my smoothest motors?
 
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chris8686

New Member
May 2, 2013
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Bellingham
I considered drilling out the stud holes out to 8mm but as you can see in the picture the stud holes are way to close to the edge of the case as is. So I may get the 6mm stud kit from sbp that will at least have the same thread on both ends.

The crank has a lot of rolling resistance. There may be a tiny bit of case misalignment. This motor will definitely be stripped down and have all the bearings swapped out. Also it seems that the case gasket was not lined up properly around the clutch shaft and I can see grease squirting out of there like one of my other motors.

Also the transfer ports are half blocked.. the intake and exhaust are completely free
 
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Theon

New Member
Jan 20, 2014
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Studs look 8mm from here?
If the piston is a TDC in the second shot of the second group, I'd say you got a 38mm stroke (a80/GT5).
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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from measurements I took many years ago on some #3 & #4 pistons, I'd say you had 2nd oversized piston at 40micrometers larger than usual (they seem to go up by 20micrometers per number)
 
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chris8686

New Member
May 2, 2013
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Bellingham
How will I go about getting a new top end for this motor? If I order a new top end kit from dax I could get either of the pistons.

I finished tearing down the rest of the motor and will post pics of the things I found.

The crank bearing on the magneto is stuck on. I've posted about this before with a different motor. How do I remove the bearing without damaging the crank?
 
F_Rod81

F_Rod81

Dealer
Jan 1, 2011
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Denver, CO
That is a GT5 style engine. It has the type B piston & long rod combo giving you a 38mm stroke. Looks like it has the newer 1 piece flywheels rather than the older 2 piece style. This setup has "slightly" better balance, but not as much primary compression as the 2 piece wheels. Just do the necessary mods for reliability and your engine will do just fine.
 
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chris8686

New Member
May 2, 2013
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Bellingham
F_Rod81 said:
That is a GT5 style engine. It has the type B piston & long rod combo giving you a 38mm stroke. Looks like it has the newer 1 piece flywheels rather than the older 2 piece style. This setup has "slightly" better balance, but not as much primary compression as the 2 piece wheels. Just do the necessary mods for reliability and your engine will do just fine.
Click to expand...
What mods do you recommend for reliability? I have a pair of skf bearings for the crank. I will also be putting it a bronze bushing for the wrist pin.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Here's some pics of a 40mm intake engine I recently got.


As you can see, the casting on this bigger port cylinder is nothing to write home about.
 
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Theon

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Jan 20, 2014
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All those 'bigger' barrels seem to come that way, a flap disc on the angle grinder makes them look a little neater, But in my experience, the port timing is better, and the transfers larger, All of my motors run this barrel now, as they are superior.
 
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