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Discussion Starter · #1 ·
I started assembling my Z50 project motor and it didn't take long at all to realize the the new piston wasn't gonna work. Its a 79 bottom end, and a 79 piston with an 84 head. The piston is hitting the head. I was told that this configuration would work without a hitch. Now i'm getting fed up with mixing and matching parts. The 79 head and 84 head appear to be identical. The piston is from www.dratv.com Who has some insight on this one?? The piston seems to be sticking out like 2-3mm's too far. that seems like far too much to shave off the top of the piston. Stacking gaskets seems pretty ghetto? WHAT TO DO??
 

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If the piston is sticking out 2-3mm's too far, then it's not the head, it's the stroke of the crank. How did the original piston look in the cylinder before you ordered a new piston?
 

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Discussion Starter · #3 ·
The edge of the piston was a couple mm's away from the edge of the top of the cylinder at TDC. I don't get it z88r. The 84 piston is too short, and the 79 is too long. Is it possible that the piston is wrong for some reason? The rod in this motor i'm building is definately the short rod, because the '84 piston didn't travel as far up the cylinder in this one as it did in the 84 bottom end. STUMPED
 

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Finding your way around Dr. ATV's website is like finding a needle in a haystack. Also, honda is notorious for switching around parts in the late 70 and early 80's to get rid of stock lying around.



One would have to think you received the wrong piston, but who knows.



Shaving the piston depends on how much meat the crown of the piston has. How close is your top compression ring to the top of the cylinder?



Sounds to me like you received the wrong piston.



Take some pictures, and let me know which part you ordered, and we can go from there.
 

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I had essentially the same problem when I tried to update the top end on a '76 Z50. I had to change the crank, then the ignition as the original woodruff key wouldn't fit the new crank. Then the new ignition wouldn't fit the cases so had to grind some case material away for the late style ignition to fit.I feel your pain.
 

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Quoted from the Dr. ATV website:



SO FAR STANDARD IS THE ONLY SIZE WE CAN GET THESE COMPLETE PISTON KITS IN. THESE WILL FIT 69 THRU 78 Z50A'S YOU GET THE PISTON, PISTON RING SET, PISTON PIN AND PISTON PIN CLIPS WITH THIS KIT. WILL ALSO WORK IN 1979 TO 1981 Z50R'S



Talk to Dr. ATV and explain your situation and see what they will do for you.



Here's what I would do if you want to continue on with this project:



1. verify the motor is a 1979 model. If you are sure, go down to your local Honda dealer, and get the honda part number for the correct piston and rings and either order it up from them, or with the part numbers, contact some of the bigger Honda parts dealers (servicehonda.com) and order up the correct part. Classic, TB, Hondanuts may also have these on hand.



Truth be told, it looks like you got the wrong piston by a possible misinformation from Dr. atv. We won't know that until you talk with them, so withhold judgement and see if they will make it right.
 

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Discussion Starter · #9 ·
Today I noticed that there is a chamfer around the edge of the '84 piston, but not on the '79. That would definately have an effect on how to piston travels within the head (or in this case how it doesn't). I have to go ship some stuff, but i will post pictures to better explain later.
 

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take pictures with the piston in the cylinder before you install the head.



Have you test fitted your new piston in the cylinder, installed the head and verified the piston does indeed come in contact with the valves?



the dome of the piston will stick up above the top of the cylinder, but the area just above the top compression ring will not.



I need more information here to work with.
 

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Discussion Starter · #12 ·
The new piston hits not the valves...but the head when I try to turn the motor over by hand. Therefore i'm pretty sure its too tall. My camera crapped out...but i will try to get some pics of the new piston in the cylinder at TDC. The outside edge sticks out a little past the head gasket even.
 

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I think you have the wrong piston for the crank. That's the exact type of piston that came out of my '76. To use a later model piston, I had to change the crank and the cylinder. I had them lying around thogh so no more $$. But then there was the ignition. The problem is the wrist pin placement is not the same on the 2 pistons. That's why one is hitting the head. Turn both pistons upside down next to each other and you'll see what I mean.
 

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u need the piston for the newer 50, i had the same problem with my 50, all the 50s and ct 70s have the same stroke and stuff but i have a 78 ct 70 cylinder and head on mine, and when i have the ct piston it would hit the head so i got a xr 70 piston and it works perfect



mud pumper is right
 
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