Here we go again

comnoz · Sep 14, 2019

So the custom forged billet pistons at $450.00 lasted 7800 miles before I left the throttle on a little too long and seized one.

Now for the $120.00 Taiwanese cast pistons. Any bets on how long they last?
[I got a smokin' hot date in Texas next week]

rvich · Sep 14, 2019

Longer than it takes for someone to complain about foreign parts?

comnoz · Sep 14, 2019

Foreign parts? It's a foreign motorcycle.

If I lived where it was made I probably wouldn't be trying to figure out how to keep it together in the desert southwest.

Deets55 · Sep 14, 2019

comnoz said:
Foreign parts? It's a foreign motorcycle.

If I lived where it was made I probably wouldn't be trying to figure out how to keep it together in the desert southwest.

Jim,
Move to South Jersey. No hills or turns. Plenty of O2 at sea level. You couldn’t blow that engine up with a stick of dynamite down here. Most people consider it a foreign country, so you got all the bases covered. Salt water taffy and good Italian food (at my house of course). What’s not to like?
Pete

worntorn · Sep 14, 2019

That's my path too, try to use the most expensive ,best on paper item and when that fails, go El Cheapo, all the way.
My $180 Norvil sprag lasted about 4 minutes and had no warranty so I replaced it with a $17 Chinese version. It's doing quite well, I think it's been in there for 2 years now, which means it's probably been in there for 3 years.
Also batteries- my 2 ten year lifespan $200 Li batteries lasted about 18 months so I went to the cheapest EBay sealed lead acid, $25 EA.
3 years now on those ( which will turn out to be 4 when I look it up

Glen

johnm · Sep 14, 2019

I get surprisingly good results with GPMs

jbruney · Sep 14, 2019

I get surprisingly long life from cheapo batteries and short life from $$$ ones also.... Wallet talking to me. Cheapo pistons... now I'd have to chew on that one for a while to understand it fully. I think it would depend on what they were going in and the service,

Fullauto · Sep 14, 2019

rvich said:
Longer than it takes for someone to complain about foreign parts?

It's ok. You've never been to war with Taiwan.

comnoz · Sep 14, 2019

jbruney said:
I get surprisingly long life from cheapo batteries and short life from $$$ ones also.... Wallet talking to me. Cheapo pistons... now I'd have to chew on that one for a while to understand it fully. I think it would depend on what they were going in and the service,

The only reason they are cheap is because they make them in batches of 100,000 or so. It's a popular piston made for a Polaris ATV.

Now if you had to pay for a die to cast only a few hundred they would end up costing 1000 dollars each. Piston casting dies are big bucks.

Actually the majority of pistons supplied to the new vehicle manufacturers are now coming from Taiwan. It seems they have a corner on the market.

comnoz · Sep 14, 2019

johnm said:
I get surprisingly good results with GPMs

I suspect GPM's are fine nowdays. I just have a hard time with them because I remember back when you would buy a pair of GPM's and hope they were within .005 inch of each other or 20 grams. I would hope there consistency has gotten better in the last 40 years....

Nater_Potater · Sep 14, 2019

comnoz said:
So the custom forged billet pistons at $450.00 lasted 7800 miles before I left the throttle on a little too long and seized one.

Now for the $120.00 Taiwanese cast pistons. Any bets on how long they last?
[I got a smokin' hot date in Texas next week]

View attachment 12162

Are those polymer inserts on the skirts? Also, do you shave the sides of the bowl down to reduce the crown volume? Interesting looking pistons.

rvich · Sep 14, 2019

comnoz said:
Foreign parts? It's a foreign motorcycle.

Exactly!

comnoz · Sep 14, 2019

Nater_Potater said:
Are those polymer inserts on the skirts? Also, do you shave the sides of the bowl down to reduce the crown volume? Interesting looking pistons.

The skirts have a polymer coating.
The pistons are hyper-eutectic castings with a hard anodized coating in the cup. The floor of the cup is a convex dome. It is designed to make more swirl for a faster burn.

I did remove about .040 from the top rim of the piston to get my squish clearance to .020. That will bring my compression to ~ 9 to 1.

elefantrider · Sep 15, 2019

I bet they will last a lot longer. Looks like the valve reliefs are in the correct places also. Are you going to use that pin and wire clip?

Madnorton · Sep 15, 2019

After much badgering the GPM's are fine now and have been for some years.
The HC AN omegs's are made using a new unique die, and thus do not have much scope to be modified, they are also lighter than the comparable full skirt Wiseco's, and not even $500 a pair.
One racer up north had a cylinder barrel come loose and break - the Omegas were untouched and refitted.
The Taiwan items will be fine, I suspect they would have copied and improved upon others manufacturers pistons.
The pin is designed with the design of the piston in mind and then the clips.

jseng1 · Sep 15, 2019

Any piston will fail when it overheats.

Kvinnhering · Sep 15, 2019

I did remove about .040 from the top rim of the piston to get my squish clearance to .020. That will bring my compression to ~ 9 to 1.

Wow, what are I missing? Will this result in contact between the piston and the head?
I thought squash band taget was .035-.040?

comnoz · Sep 15, 2019

Kvinnhering said:
I did remove about .040 from the top rim of the piston to get my squish clearance to .020. That will bring my compression to ~ 9 to 1.

Wow, what are I missing? Will this result in contact between the piston and the head?
I thought squash band taget was .035-.040?

I run steel rods and a crank with 2 inch rod journals so it does not flex.
That along with .0045 piston clearance and I could probably go down to .010 for deck clearance and be OK. But as they wear and gain more clearance they will rock more -so I set them at .020.

comnoz · Sep 15, 2019

elefantrider said:
I bet they will last a lot longer. Looks like the valve reliefs are in the correct places also. Are you going to use that pin and wire clip?

I had to cut the valve clearance notches. And yes, wire clips along with the pin designed for them.

acotrel · Sep 15, 2019

comnoz said:
The only reason they are cheap is because they make them in batches of 100,000 or so. It's a popular piston made for a Polaris ATV.

Now if you had to pay for a die to cast only a few hundred they would end up costing 1000 dollars each. Piston casting dies are big bucks.

Actually the majority of pistons supplied to the new vehicle manufacturers are now coming from Taiwan. It seems they have a corner on the market.

Japanese two-stroke pistons are usually spun-cast, then forged - done in the one machine. That way they get the grain flow right. So when the pistons expand they do it sensibly. Years ago, here in Australia, we had 'Die Cut Y alloy' pistons. If you used them, you had to file them down every time they seized. If they seized often enough, you ended up with enough bore clearance, also the heat affected them - so eventually they became OK.
I think that even with Japanese two stroke pistons, what is (was) used in works' bikes are better than are sold to the ordinary punter. When Jack Findlay stpped racing the 500cc Suzuki twin, the factory took the trouble to recover their pistons. The Mahle pistons which are used in Jawa speedway bikes and Porsches are excellent.

Here we go again

Similar threads