Arrow On Top Of Piston

[MichaelS693]

hey guys you know the arrow that is on top of the wiseco pistons......which way does it need to point...the front of the motor or the back??? im pretty sure its the back but i wanna make sure

[MIKE400EX]

The arrow is supposed to point towards the exhaust side, or front of your EX.

[AtvMxRider]

Yep towards the exhaust.

[MichaelS693]

thats what i thought this is on my blaster tho......thanks:D

[AtvMxRider]

Towards exhaust.

[quadman21]

What would happen if you put the arrow towards your intake?

[MIKE400EX]

Some piston slap noise (maybe), because some of the pins are off-set. Possible decreased valve clearance as the intake and exhaust pockets are not always the same shape/depth or in the same position.

[oynot400]

Originally posted by quadman21
What would happen if you put the arrow towards your intake?
I can tell you from experiece. The valve placement is different from the intake and exhaust valves. So there would be some piston/valve slap. I put mine together yesterday and there was no arrow on it. When I got it all together and rolled it over by hand the intake valves hit the piston. :(
No big deal, I just had to take the piston out and turn it around. Granted I am running a 13:1 compression so, it has a high dome on it. I guess it would not be a slap, more of a dead stop. :huh

[433rd]

Originally posted by quadman21
What would happen if you put the arrow towards your intake?

quadman21,

As Mike mentioned, the piston pin location on the piston is not center, it is offset. What this does is off set the timing of your rod and piston at top dead center, they both actually do not get there at the same time. It helps aid in the proper down thrust angle of the piston & rod on the power stroke. If it is backwards, it can create some problems.

Generally, in a nut shell, your piston will get to TDC before the rod. As the spark ignites the fuel, your crank finishes the upward stroke and the rod is just arriving at TDC ready to take on the full brunt of the power stroke. If you think about it, if the wrist pin was on center (even more so if you installed the piston backwards), your rod would be actually "pulling" the piston down the bore, so to speak, before the air/fuel mixture would have enough time to ignite. Hence the reason that the spark is actually ignited before TDC to get the mixture lit at the perfect time so when the piston reaches true TDC, "everything" has already started and you get a complete, efficient, strong power stroke.

If you install the piston backwards, you will have a rod that has already past TDC when the engine gets the spark and it will get a much less efficient burn and power stroke. In short, it will loose both torque and power across the RPM operating range of the engine and not be nearly as efficient as it should be. Will it hurt anything??, most likely not. But it will be like having a 416 bore with the power & torque of a stock bore engine.

Make sense???? :huh :huh

[quadman21]

Thanks a lot for your help! I know this was micheals69 post but I still appreciate your help. I just put my piston in saturday "in backwards as I now know" but in my favor I have only started and ran it twice. Twice for about 15 minutes and it's still on the quad stand. I did hear what you guys were saying about the piston slap so I'll just tear it down and turn my piston back around the right way. I should be fine right?

[quadman21]

I have another question, in the Honda manual the piston has IN but the Wiesco piston has an arrow, but it shows the IN pointing toward the intake in the illustration, so wouldn't that mean the same for either piston?

[433rd]

Unfortunately, Honda does mark them towards the intake and most all of the aftermarket manufactures point the arrow towards the front of the engine. They do make it confusing that way huh...

As far as swapping your piston around, I've never had to do it but I really don't see a problem with it. You have very little run time on it so, you most likely could do it without a problem, kind of sucks going through all that extra work though being how you just got it all back together.

As far as "slap", you really wouldn't notice more or less either way. Piston slap is from a loose bore to piston fit and really has not much to do with the direction the piston is installed.

[quadman21]

Thanks for the reply 433rd, But I DEFINITELY need to swap right? It's a weisco flat top 11:1 440 89piston.

[MIKE400EX]

Yes, you DO need to turn it around.

433rd, many engines will slap/knock a little if the offset is in the wrong direction, sounds like the old forged pistons in cars. I've seen it, and heard it, but am not sayng that every engine will.

[quadman21]

Thanks guys!

[MichaelS693]

thanks guys

[MIKE400EX]

The IN on the OEM Honda piston is short for INtake side.

[400ex99]

i have a 416 je piston, im pretty sure iv put the arrow towards the intake. when i turn the pison around, do i need new piston rings and head gaskets? or i can use them over. i only have break in time, 3 15-20 min run times on them. thanks

[quadman21]

I did and I only had about 20 minutes worth of idling time.