Piston head arrow

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sboricic123

Member
Apr 15, 2013
172
3
18
Bailieboro, Ontario
I watched this video earlier this morning and he mentions that the arrow should be pointing to the exhaust port.
https://www.youtube.com/watch?v=w5npGG2Xj3Q

So, I took of the cylinder head on my 66cc Grubee Skyhawk and noticed the arrow is pointing to the intake port. It came out of the box that way. I have been noticing clicking noises when the engine is running. Will that cause failer in other areas or problems?
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Ignore the arrow and install the piston with the ring gaps towards the INTAKE side. Look for the little pins in the ring grooves and put them towards the intake side.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
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memphis Tn
Installing it backwards will DESTROY the top end when the ring snags in a port. Be SURE the gaps are towards the intake side.
 
sbest

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
Looks like a considerable factor of safety in these engines. Small ports, wide lands. Piston will run either way. The pin is likely offset slightly. That might be your noise but who knows. I`ve seen it done accidentally in snowmobiles with no problems.

Steve
 
allen standley

allen standley

Well-Known Member
Oct 22, 2011
1,126
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Bangor, Maine
Looks like a considerable factor of safety in these engines.

After doing 15 or 20 destroyed Top Ends over a 6year period it's always been broken rings , blown out wrist pins , dislocated and or falling out ring stay pins. Even the spring loaded clips holding the wrist pin will fly out and wreck things. I would have to say build quality consistancy negates "considerable factor of safety" Let's see how long before he has trouble??? Possibly he will not.
 
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Flathead

Member
Aug 8, 2015
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Glendale az
Not looking for trouble ! Just this is how it came apart and will go together / also did a test dry run and piston didn't snag !!glory to God
​
 
allen standley

allen standley

Well-Known Member
Oct 22, 2011
1,126
238
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Bangor, Maine
Example of Cylinder flake. This was a new motor. Owner had it on a bike 1 season and said It always started hard and never ran well. Well this is why.

compression check showed max 50lbs and would seep to 0 in less than 5 seconds.
 

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sbest

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
Egad, I didn`t mean to make it sound like I was recommending running it with the arrow pointing to the intake, and I didn`t mean to make it sound like these engines are built like a diesel. What I meant was the lands between the ports are plenty wide and the ports are so tiny that there is no chance of snagging a ring end on the exhaust port. The posters who talked about a ring snagging on most 2 strokes do have a valid point on most engines, especially high performance engines.

So, arrow to the exhaust is the right way to run. The reason? Because of pin offset and thrust forces on the piston skirt. There may be some ribbing or cam grinding differences on more expensive pistons but I cannot see it on these CG pistons. I have a cylinder and piston apart right now. The exhaust port has a chordal width of about 25mm and the ring ends on the piston are spread at 31.5mm. No risk of a snag.

Steve
 
crassius

crassius

Well-Known Member
Sep 30, 2012
4,032
158
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USA
the arrow makes no difference as it is sometimes on one side & other times on other side (and sometimes not there)

the locating pins should be straddling the intake port no matter where the arrow is or isn't
 
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