Wiseco 89.00mm Piston?

[Steven]

This is the piston that came in my 440 big bore kit.

On the box it reads:
4667M08900
89mm honda xr/trx400 f/top
3504XC-89.00mm
04242MK/001A CW20/S553
CLEARANCE: 0020 in (.051mm)
REPLACES 4667PS

What is the actual displacement of my engine with this piston?

This piston was advertised by Wiseco to yield an 11:1 compression ratio. Is this the piston that really yields 9.5:1 compression ratio?

Thanks-Steve

[F-16Guy]

Your actual displacement is 435.48cc (borexborexstrokex.00314 divided by 4). Your actual CR is a little trickier to find (but not too bad w/ a flat top piston). Go to:
www.greatplainsas.com/icompratio.html
You'll only be able to figure this out if you have all of the measurements, take measurements BEFORE you put your motor together. You'll need compressed gasket thickness (head=0.025, base=0.014 if you used standard cometic big bore gaskets), deck height in thousandths (top of piston center to top of cylinder deck), cylinder head volume (stock=38cc). Input this stuff into the formula and you'll get your actual CR. If it's not what you want, alter gasket thickness, or have the cylinder decked to achieve the desired CR.

[MIKE400EX]

Steve, how about measuring and posting the dim. from the piston; from the top of the pin bore to the top of the piston. Let's see if Wiseco has changed anything on the "new" piston. Is it a flat top also? Thanks!

[quadman21]

I just measured from the top of the piston pin hole to the top of the piston on both my weisco 440 and a stock piston a few days ago and they were the same. If memory serves me right they were both @ 16mm or 17mm. either way, they were the exact same.

[MIKE400EX]

I wonder what they changed on the "new" piston. That's the same as the old "440" piston --- which would mean that the CR is still not right!

[quadman21]

I just bought the piston this month from White Bros. Maybe they didn't send me the "new" style piston?

[Steven]

Guys, this piston is already in the bike so I can't measure it.

Is this the new or old model piston?

I presume it is a flat top because it says "f/top" on the box. Why is this a point of focus for everyone.

Agian, is this the piston with the improperly advertised compressio ratio? Does anybody know?

Thanks, Steve.

[Extremeracer167]

When i got my actual 11:1 piston for the 425 kit. My piston was a domed top. And from what i always thought, thats where the extra compression came in. Th only other way i know of to raise compression with a flat top piston. is to 1) Shave material off the head. or 2)new crank. so if its a flat top piston, i dont think its 11:1 but i could be wrong

[MIKE400EX]

Steve, it seems as though its only the Wiseco 89mm (~440) pistons, but the 11:1 flat tops actually yield about 9.5-9.8:1 if installed as per the instructions. In other words, w/o decking, changing gaskets etc... Probably the reason that many argue (adamantly) that a 416 will out perform a 440.

[Steven]

This is sad.

What reason would Wiseco have to advertise a piston as 11:1 compression ratio and provide directions that will create a 9.5:1 compression ratio?

If this is the case, wouldn't Wiseo be open to a class action suit for false advertising?

This is a sad and expensive mistake...

[MIKE400EX]

Not too expensive though. Take the cylinder off and deck it , the compression can be brought up to where it ought to be. Then you'll really appreciate all those other mods you have.

[Steven]

Ok then, what does it cost to deck the cylinder?

What sort of shop performs this sort of service on a local basis?

Steve

[MIKE400EX]

Most any machine shop with a decent lathe should be able to deck it. Probably $25-$35.