Piston design?
Miscellaneous,Etc.
I have before me my stock Yamaha Piston (1978 dt175e) and a new
wiseco piston to replace it.
I was immediately struck by a difference in the piston ports that
interact with the intake port. The wiseco features two perfectly round
ports; nicely machined and all but just simple holes in the piston
skirt. They measure about 0.612 inches diameter.
The stock piston has a pair of ports that are vertical rectangles
with rounded corners. They measure 0.562 inch wide and 0.9inch tall. The
bottom of the ports is essentially the same distance from the bottom of
the piston skirt on both pistons. Therefor, the extra port hieght on the
stock piston is all above the wiseco piston.
Now, I'm certainly not an expert on 2stroke theory (but this
teardown certainly helped me visualize the whole process). I'm thinking
that this port difference will affect the duration of the intake event,
and well, that's gotta do something. What, I don't know. Could it create
a dangerous lean condition? Will it alter the color of the (currently
blue) powerband? What?
Also, the relief area around the wristpin id dramatically different.
At first I was concerned that this area was supposed to interact with
the transfer ports, but upon further thought, I'm guessing they are just
regulating the wall thickness of the piston for cooling purposes. They
are below the rings, so they are out of play.
Any insight would be comforting.
Thanks,
dean h
1978 dt175e
1970 cb175k4
Vintage Dave
intake event, and well, that's gotta do something. What, I don't know. Could it
create a dangerous lean condition?
I would say that the jetting will not change, and the motor will run the same
as stock. I would guess that with the piston at top dead center and BDC the
holes will still line up with the intake port? If they do then the read valve
will be controlling the fuel flow and not the "timing" of the holes in the
piston. If I understand this engine the holes in the piston just let the reed
valve do it's thing and control the fuel mixture flow. They don't time the
intake, like the bottom of the skirt on a piston port engine. Said another way
the port is always open....the read valve controls the flow. When you get
negative pressure in the bottom end the fuel goes in, when its positive the
valve closes and no fuel goes in. I'll bet that a round hole is less prone to
cracking the piston and has about the same area as a rectangle hole. I would
try the bike. If it runs different (which I wouldn't expect) and you don't
like it, take it appart and file the hole more like the original.
The relief area will not effect the port timing, the timing is controlled the
top of the pisotn and the ring. I would think that its an improvement over the
stock piston.
Vintage Dave
Aaron Swarvar
design is likely attributed to making the piston easier to manufacture while
still giving hte bike the same performance...or the way Wiseco did it may
actually make piston stronger. there is a reason for what Wiseco did and if it
hurt the engine in any way Wiseco wouln't have manufactured it this way.
Piston design in itself will not change your jetting in any way...having a
fresh top end and a motor with more compression may have an effect though.
Don't worry though, it shouldn't make it run lean enough to burn up an engine,
if it changes the jetting at all. The change in the wristpin area is to make
the piston lighter, facilitating easier change of direction of the piston when
it's running, giving you better throttle response and more over-rev. It's a
good design. It's hard to OEM to duplicate because they cast their pistons
which makes it hard to get Wisecos design, or they could machine it increasing
manufacturing time...neither of which is acceptable to the manufacturers. With
their design they get a good piston design with the quckest manufacturing time
they can. Don't worry about the Wiseco, it will be fine.
Aaron
1999 YZ125 (hibernating)
#691
Redline Race Team
Rot 13
Aaron Swarvar <mxrac...@aol.com> wrote:
>I wouldn't worry about the Wiseco piston hurting your bike. The change in
>design is likely attributed to making the piston easier to manufacture while
>still giving hte bike the same performance...or the way Wiseco did it may
>actually make piston stronger. there is a reason for what Wiseco did and if it
>hurt the engine in any way Wiseco wouln't have manufactured it this way.
>Piston design in itself will not change your jetting in any way...
Depends on the bike. If this was a piston-port engine then it
sure would change the jetting. But it shouldn't for the DT.
>having a
>fresh top end and a motor with more compression may have an effect though.
>Don't worry though, it shouldn't make it run lean enough to burn up an engine,
>if it changes the jetting at all. The change in the wristpin area is to make
>the piston lighter, facilitating easier change of direction of the piston when
>it's running, giving you better throttle response and more over-rev. It's a
>good design. It's hard to OEM to duplicate because they cast their pistons
>which makes it hard to get Wisecos design, or they could machine it increasing
>manufacturing time...neither of which is acceptable to the manufacturers.
The stock piston uses a very high silicon alloy, whereas the regular
Wiseco uses a low silicon alloy, so that they can forge the pistons.
High silicon alloy doesn't forge very well, because it doesn't flow
as well at forging temps. That's good for a two-stroke piston which
needs to keep its shape at high temperature (because the two-stroke
does not have an extra 360 degrees of crank rotation to let the piston
radiate heat to the cylinder walls). However the high silicon also
makes it tough to machine, which is why they don't do it.
The high silicon content also keeps the piston from expanding as much
when it reaches operating temperature. So the low-silicon Wiseco pistons
require greater piston clearance than the stock piston. You should
check the clearance and make sure that it's to the specs that came
with the Wiseco piston. If the clearance isn't enough, then you
will need to have the cylinder bored to the correct spec.
> With
>their design they get a good piston design with the quckest manufacturing time
>they can. Don't worry about the Wiseco, it will be fine.
If it's a low-silicon Wiseco (probable since it's for an old bike)
and he doesn't have enough clearance, it'll be seizure city.
Low silicon forged pistons are great for four-strokes but they
need special care for two-strokes.
--
Eric Murray www.lne.com/~ericm ericm at the site lne.com PGP keyid:E03F65E5
<IMG LOWSRC="javascript:alert('Delete C: and install Linux?')">
David E. Wilson
Vintage Dave
Peter Lambert
The bore is machined to a standard size e.g 65.00mm and the piston skirt
will be 64.92mm.The Wiseco piston maybe 64.85mm.
So unless something odd has been done if you get a Yamaha piston the
clearance should be correct .
This can be ascertained by measuring the parts and doing the calculations.
Pete
"Miscellaneous,Etc." wrote:
> Howdy folks,
>
> I have before me my stock Yamaha Piston (1978 dt175e) and a new
> wiseco piston to replace it.
>
> I was immediately struck by a difference in the piston ports that
> interact with the intake port. The wiseco features two perfectly round
> ports; nicely machined and all but just simple holes in the piston
> skirt. They measure about 0.612 inches diameter.
>
> The stock piston has a pair of ports that are vertical rectangles
> with rounded corners. They measure 0.562 inch wide and 0.9inch tall. The
> bottom of the ports is essentially the same distance from the bottom of
> the piston skirt on both pistons. Therefor, the extra port hieght on the
> stock piston is all above the wiseco piston.
>
> Now, I'm certainly not an expert on 2stroke theory (but this
> teardown certainly helped me visualize the whole process). I'm thinking
> that this port difference will affect the duration of the intake event,
> and well, that's gotta do something. What, I don't know. Could it create
Rot 13
Peter Lambert <p.la...@elec.canterbury.ac.nz> wrote:
>This is a multi-part message in MIME format.
>--------------4E587F6050B6C8174574FEF1
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>
>Generally piston clearance is assigned to the piston !
>The bore is machined to a standard size e.g 65.00mm and the piston skirt
>will be 64.92mm.The Wiseco piston maybe 64.85mm.
>So unless something odd has been done if you get a Yamaha piston the
>clearance should be correct .
>This can be ascertained by measuring the parts and doing the calculations.
>Pete
That's not always true with Wisecos. For RZ350 pistons they are
stock size (or larger, i.e. overbores up to 2mm) and you have to
bore the liners out to gain the extra clearance.
I would think that given their reputation for siezing and the
current practice of hard cylinder coatings which can't be bored, that
they would produce their pistons undersize as you suggest. But
I haven't seen one of those, since I prefer to avoid Wiseco pistons
if I can and haven't bought one for a hard-coated cylinder.
BTW, if you turn off MIME your postings won't contain as much cruft.
Rot 13
Miscellaneous,Etc. <dhy...@snet.net> wrote:
[..]
>
>So, now I have my re-bored and honed jug specifically machined to this piston (.020
>over) and it looks like the machinist pulled out the wiseco guide for piston
>clearances, which will, what, be too sloppy for a stocker? Hmmmmmmm... let me pull
>out the piston clearance info here.....for a cast iron cylinder the wiseco
>literature calls for .0025" (.06mm) and the book calls for less 0.0016-0.0018"
>(0.040-0.045mm). So yes, I now have a sloppy bore.
You should measure it to be sure (or ask the machinist what he did).
BTW, are you sure that the stock clearance is 0.0016-0.0018"? RZ350s
(which also use 175cc cylinders, iron liners and the same bore and
stroke but are water cooled) call for .0024-.0026" (.060-.065mm) with
stock pistons. I don't remember the Wiseco figures for the RZ
but they were quite a bit larger.... like 6 thou. An air cooled bike
would usually run slightly larger clearances.
>I'm really wishing I never took it apart. It was bulletproof with its 22 year old
>stock piston.
>
>But hey, what's a spode to do? Pick up the pieces and start thinking.
>
>What happens if I do the Vintage Dave suggestion of filing the ports to match the
>stocker?
I assume that you mean filing the hole in the piston to match the one
in the stock piston. Yes, you could do that. Be careful to radius
the corners of the holes i.e. don't make it perfectly square, and
then chamfer the edges of the hole. Chamfer the edges of the skirt too.
> Will I change the balance of the piston? (yes) Does that matter? (of
>course it would in an extreme case, but maybe not here????). I notice extra metal
>under the crown (on both the stocker and the wiseco) that looks like it might be
>compensating for the weight missing at the ports.
That's there to withstand the heat and pressure from combustion.
With the long skirts on two-stroke pistons (compared to four stroke
pistons which don't need the skirts to block ports) the piston
won't rock in the bore. So it's ok to have one side of
the piston lighter than the other. Since the crank balance isn't
100% on a single and a wide range is tolerable, the small amount of
lightening of the piston won't change the engine balance all that much.
In fact, you have about a 50% chance of making it slightly better....
>Not too many options here:
> 1) slap the wiseco in and stop bitching. What's done is done.
It's just a DT175, so this is probably the option.
> 2)start modifying the wiseco to match the stock piston. Pretty radical, but
>really good gear talk when we stop to take a rest at Nirvana Point. I see the only
>down side being a piston balance problem, but is that a legitimate concern?
>
> 3)overbore my freshly over-bored jug *another* size to get a genuine Yamaha
>piston to work.
Run the Wiseco. I ran them in an RZ350 (with the Wiseco spec'd toleraces)
and they were fine. They rattled a little at startup until they warmed
up enough to expand and take their running clearance, and the softer aluminum
seemed to pick up some superficial scratches on the exaust side, but
they were reliable in that bike until the girlfriend of the guy I sold it
to ran it out of oil.
You should check the bore for sharp edges on the ports and chamfer them
(not all machinists do this).
Miscellaneous,Etc.
> Dean,
>
> Thanks purchasing Wiseco, hopefully I can help you out some with you
> situation. The concern that you mention is a valid one and I can try to
> address each aspect of it. Boost ports are just that, a supplementary port.
> The way that the port works depends on the layout of the cylinder, since you
> are talking about a vintage bike, I don't have one to look at. The size of
> the boost ports relationship to the power curve is difficult to test, it
> seems to be different in each application. We have had engines on the dyno
> that showed no performance difference with or without the boost holes.
>
> You can however, file fit the boost hole on the Wiseco to match the OEM if
> you would like. When you do this base your measurements from the top edge of
> the piston (timing edge), not the bottom of the skirt.
>
> The relief on the side of the piston is referred to as angled boss holes. It
> is there solely to remove weight from the piston. You are correct in your
> reference to the different clearance requirements for forged pistons
> (Wiseco) versus a cast piston (typical OEM). Due to the differences in the
> expansion rates of the materials used, a forged piston requires slightly
> more clearance.
>
> The balance of the piston that you mention is just a myth. Individual
> pistons are not balanced, and are not intended to be. I think where that
> comes from is when we package kits, we refer to them as being balanced. With
> that we just mean that each piston is within 5 grams of each other. A new
> CR250 piston has a cutout at the bottom of the skirt, boost holes and
> different overall length on the intake side skirt. There is very little
> weight on the intake side, and solid skirt on the exhaust side. You can
> modify the boost holes without effecting the structural integrity of the
> piston (within reason of course).
>
> So if you want, match the holes to the OEM and go ride. Or you can leave
> them, test the bike and see how it reacts. I apologize for any confusion or
> setback, when you get it back together get back to me and let me know how it
> went. If you have anymore questions feel free to let me know.
>
> Thanks,
>
> Joe Mossbarger
>
> Product Engineering
> Wiseco Piston, Inc.
>
> >Not too many options here:
> > 1) slap the wiseco in and stop bitching. What's done is done.
>
> It's just a DT175, so this is probably the option.
Ouch. That hurt. <G> Hey, this humble ratbike is my pride and joy. And, well, if it had
power to spare then I wouldn't be worried about losing any. But it doesn't, so I am.
Thanks for the info, ROT13.
And thanks to Wiseco for answering my obscure dementia.
I think I will probably modify the Wiseco piston. The difference is so radical when you
place them next to each other.
dean
Miscellaneous,Etc.
it. I modified the (what I now know are called) boost ports to match the OEM piston.
"Miscellaneous,Etc." wrote:
>ten Points for Wiseco for responding to my query:
I was emboldened by Wiseco's confirmation that the back of the piston can be significantly
lighter than the front of the piston, and that the piston could handle losing a little of
its structure.
I wasn't sure which tool to grab, but it was soon apparent that a file would take all
weekend. I grabbed the dremel, but found that that was also going to be slow work. So, I
grabbed the cordless drill and a pilot bit and places two pinholes above the port and then
followed with a 1/4 " drill to hog out the bulk. Then it was a little fussing with
different stones in the dremel before going to the conical metal rasp in the dremel and the
patience reservior. It worked well as long as you keep it moving along an edge. You can't
dig in, rather, you just erode the edge repeatedly and it moves along satisfactorily. The
flexible shaft option on the dremel is definately worthwile. Final chamfering was done with
a chainsaw file and with all filestrokes going *into* the piston (as opposed to dragging
it, and a burr, out).
I took pictures of before, with layout, and after; All next to the reference stock piston.
That's like real hot-rod stuff right? Hope it was worth it.
> > The way that the port works depends on the layout of the cylinder, since you
> > are talking about a vintage bike, I don't have one to look at. The size of
> > the boost ports relationship to the power curve is difficult to test, it
> > seems to be different in each application. We have had engines on the dyno
> > that showed no performance difference with or without the boost holes.
Well, some dude at Yamaha spent some time about 23 years ago, so Imatched his work.
> When you do this base your measurements from the top edge of
> > the piston (timing edge), not the bottom of the skirt.
That struck me as an important tip.>
> > The balance of the piston that you mention is just a myth. Individual
> > pistons are not balanced, and are not intended to be. I think where that
> > comes from is when we package kits, we refer to them as being balanced. With
> > that we just mean that each piston is within 5 grams of each other.
Ya baby> Some day, if I'm good, I'll get to order a set of 8 or 12.
> A new
> > CR250 piston has a cutout at the bottom of the skirt, boost holes and
> > different overall length on the intake side skirt. There is very little
> > weight on the intake side, and solid skirt on the exhaust side. You can
> > modify the boost holes without effecting the structural integrity of the
> > piston (within reason of course).
That's like permission, right? Good cause I did it and the beast is half back together.
Thanks again to> Joe Mossbarger>
> > Product Engineering
> > Wiseco Piston, Inc.
Look for rebuild update ride report. The Boyesen power reeds should add some spunk too, as
long as I get properly carbed.
Looks like I may get to try out the new tech5s on Sunday . Yee Haw
dean h
1978 dt175 ( really trick for a 22 year old POS)
1978 cb175k4 (garage jewelry, lately)
trl...@netzero.net
{snip cool things like modifying pistons...}
: Look for rebuild update ride report. The Boyesen power reeds should
: add some spunk too, as long as I get properly carbed.
Good job Dean. I'm looking forward to your ride report. I would
have been interested in a comparison of the unmodified Wiseco compared
to your modifications, but I know that would be a lot of work.
I've personally only stuck with the stock Yamaha piston for my DT125
but I do run Wiseco in my CR125. I've never really payed that close
attention to the differences so the next top end I do I'm going to
check it out.
--
Scott Aldrich