Topic: Japauto 1000vx build

[sanchezorr123]

Hi, i am building a Japauto 1000vx, thats a french modified cb750 bored up to 1000 cc with special JPX cylinder block.

I had to order custom made pistons 70mm diameter and now i am not sure the correct orientation of the piston. They have an arrow on the top that it is suposed to point to the exhaust but i am not sure, because the shape of the valve gap on the piston head.
 
So i apreciate any help.

Sorry for my poor english, its dificult to express my self. Hope it can be understood.

[sanchezorr123]

Sorry, this is the right picture of my engine.

[MRieck]

Those pistons can go in any cylinder

[sanchezorr123]

I know that the piston can go in any  cylinder. My dubut is if it goes with the arrow pointing to the ex side or the intake side.
And i also know that the arrow is suposed to point to the EX side of the engine but the gap inn the piston head is what is confusing me. It seems that the intake gap wich clear the intake valves is smaller than the EX gap as i have mounted them with that arrow pointing to the front.

Thank you.

[MRieck]

 Sorry about misunderstanding. The arrow does look like it is pointing to the intake valve relief. For reference here are JE piston instructions
http://www.dynoman.net/engine/pistons/piston-install/68-70mmF2.pdf
It doesn't matter that the instructions are for the F2.....same valve placement.
 And yes.....the arrow should point to the exhaust side.

[sanchezorr123]

Ok, so looking that JE instructions seems like my pistons are mounted backwards and the manufacturer did put that arrow in the wrong side.
Lets see if anybody else have other sugestion before i turn those pistons 180º

Thanks a lot for your help

[jgger]

My guess, and only a guess is that the exhaust relief would be deeper because that valve is open as the piston approaches TDC. While on the intake side the valve is just beginning to open  after TDC. I base this on my feeble understand of how valve timing is related to stroke and Piston position. THIS IS ONLY MY $0.02.

[madmtnmotors]

Can you contact the custom piston manufacturer for clarification? If anyone would know, they should know for sure.

[Old Scrambler]

I'm with jggr..............measure the width of the intake valve-pocket.....it appears to be wider to accommodate a larger valve.......Yes, on the overlap the rising piston is literally chasing the exhaust valve when a long-duration cam is installed with narrow lobe-centers.......wide centers tend to bring the piston 'real close' to the intake valve.

[Scott S]

 Why does the one relief have that little notch in the middle? Won't a valve hit that? Almost reminds me of a dual intake valve set up.

[rickmoore24]

I pulled these out of a CB750 engine I rebuilt, though I deemed them unusable because of the scoring I uncovered after cleaning them. Similar looking reliefs but the arrow was pointing to them and were installed pointing to the exhaust side.

[sanchezorr123]

Ok, it seems to me that the relieve on your piston is in the opposite side than mines. But what is supossed to be the exhaust relieve in my piston, the one is pointing the Arrow looks deeper  wich should be for the ex.
I also should say that my pistons are made so it fit the F2 larger valves.
Sorry,  i am so confused And very hard to express my self in english

Thanks fot your help

[sanchezorr123]

In the Honda workshop manual you can find the pistons mounted either the arrow pointing to the EX and also pointing to the IN in different ilustrations.

[sanchezorr123]

I like to share those pictures of my engine.

[754]

Don't worry about the middle of the double notch it works like this.
 The valve will centre over one side... OR the other. .
 If they did not have the double notch, they would then be right side and left side and it would matter where they went..