piston style

the496rocket · Post by **the496rocket** » Mon Nov 07, 2005 9:28 pm

my friends spree that I am working on had a broken ring, and now needs a new piston, the style that was in it was concave, and I know they also make a flat and domed. can I safely put on a flat or domed to raise compression for more power?

Post by **noiseguy** » Tue Nov 08, 2005 8:24 am

Where can you get a domed piston?

I believe flat pistons are what the Honda dealer will give you, I also believe flat pistons are preferable to the dished ones. The Spree head really wouldn't accomodate a domed piston without reworking the head. Deck the head for higher compression, you can remove more with a flat piston than dished.

the496rocket · Post by **the496rocket** » Tue Nov 08, 2005 12:02 pm

I guess they dont offer a domed piston for a spree, the stock piston on an aero like mine is domed, but the ring is thicker on the top, I dont think I would have to rework the head though, I have the 70cc kit for my aero, and I used the stock head, and the piston is domed and is quite a bit larger, seems like it would hit the head, but it is fine

Guess Ill just go with a flat, dont want any problems.

How can I make sure there are no pieces of the old rings in the crank case without taking it apart?

vette76 · Post by **vette76** » Tue Nov 08, 2005 12:24 pm

noiseguy wrote:Where can you get a domed piston?

I believe flat pistons are what the Honda dealer will give you, I also believe flat pistons are preferable to the dished ones. The Spree head really wouldn't accomodate a domed piston without reworking the head. Deck the head for higher compression, you can remove more with a flat piston than dished.

um i have an 87 spree, and the piston is domed.

darat · Post by **darat** » Tue Nov 08, 2005 1:46 pm

yeah thats what i thought to b/c 84-85 are flat toped and 86-87 are domed i really dont think it will make a big difference.

MySpree · Post by **MySpree** » Tue Nov 08, 2005 3:31 pm

i have a extra one. it looks domed to me its sheped liek this ) and yea. i have an extra cuz i hav the biggers cylinder and well u all know.

Post by **noiseguy** » Tue Nov 08, 2005 11:39 pm

Huh, that's new info. Has anyone ordered a Honda OEM piston lately? Was it dished or domed?

burnt_toast · Post by **burnt_toast** » Wed Nov 09, 2005 12:10 am

I believe mine was flat or slightly domed when i rebuilt.

the496rocket · Post by **the496rocket** » Wed Nov 09, 2005 1:15 am

picked up a piston for 85 spree from a honda dealer today, it is domed.

Also, I have several heads for a spree, and I noticed that there is a difference in the part where the top of the piston comes up to on the stroke, under the spark plug (best I can explain it)

1 is shaped like a horn, slight drop on the edges then gets more of a drop towards the plug hole, the other is a gradual drop all the way. I cant explain it any better than that, anyone else ever notice this before?

Post by **noiseguy** » Wed Nov 09, 2005 10:16 am

These are both Spree heads?

I'm betting the "horn" shaped one is an earlier version, and the more "domed" version is later. Am I right?

the496rocket · Post by **the496rocket** » Wed Nov 09, 2005 10:39 am

Yeah, i used the one with the gradual drop, because I am thinking that is is made for the domed pistons, because the horn shaped one is flatter on the edges, and maybe the domed piston could hit easier? the gradual drop one drops the same from the edges to the plug hole, and would have more clearance for a domed piston, with the same amount of volume.l

Post by **noiseguy** » Wed Nov 09, 2005 3:46 pm

The way to check clearance is to tape 4 pieces of electrical solder in a cross pattern on the top of the piston and reassemble the head with gasket to spec torque. Rotate the piston around once to squish the solder, and disassemble it. Use a caliper to measure the solder thickness. .0020" is sufficient clearance, as you can run the Spree with no head gasket and not have interferance problems. .0010" is as close as I would ever run, currently mine's around .0020 at the closest.

Anyone have thoughts on this tolerance, and what works on these little engines? Obviously the closer the tolerance the higher the compression, if it's running close uniformly over the piston face.

As for the design, the smaller "horn" should have a peakier, higher RPM power band than the wider one. This gets into "piston squish," which I don't understand that well.

darat · Post by **darat** » Thu Nov 10, 2005 11:30 am

here is a real engine for the spree lol http://www.strokeitimports.com/stroke%2 ... 20home.htm

gman75 · Post by **gman75** » Sun Nov 13, 2005 12:17 pm

My '89 Elite E engine has a domed piston....

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