Wiseco forged piston false??

[1983_Enduro_YAMI]

Hi all,
Let's have a discuss about this....i brought my bike into the shop and the mechanic said that i should stick with the OEM piston rather than the wiseco forged piston because it causes knocking in the engine...I don't really have any idea about the engine works. If i can't find the OEM piston..will the Wossner still do the job?? 

[pokey]

Okaaay. Im confused. Could you possibly clarify or separate the question's you would like to know the answersto and, maybe explain why or ask your shop why the wiseco knocks?

[Tomas]

Wossner and Wiseco pistons are of good qality and oversize piston kits are available. I like piston kits since you dont have to buy separate piston, rings,pin and circlips. Not sure why your mechanic does not like aftermarket pistons. You just follow instructions from manufacturer when fitting. OEM clearances may not work with aftermarket pistons.

[Momus]

Find another mechanic would  be my initial response. Both these brands are good and when fitted properly work as well as std pistons.  They don't cause knocking. Some mechanics/reborers may incorrectly fit them with too much clearance so they are at a worn out spec. from start up.
Without getting too far into the technicalities there are 2  types of aluminium used for forged pistons; a high expansion and a low expansion grade. We get the low expansion grade which runs with a tight clearance compared to the other grade: 001" per inch of bore diameter is recommended.

[Nathan S]

Forged pistons expand more as they come up to temp, so they need to be run with more clearance when cold, which means they rattle more when cold.
Whoopdee doo.

They're also heavier most of the time, which is a negative - but generally not a very big one.

But knocking? Never heard of that one. I'd be asking for a credible explanation of how a different manufacturing process can cause knocking. I'll be surprised if you get one.

[skypig]

As mentioned two totally different Pistons (construction and/or material.) need different set up.

Anyone that doesn't know this shouldn't take money for working on your bike.

Even going to water cooled engines (in 1981) required some re education of my engine machinist. (If I wanted the low clearance denoted in the manual, I had to take responsibility for any seizures.)

[KTM47]

I get all my rebores done by Serco, who sell both Wiesco and Woosner pistons they know what the correct clearance should be.

Anyway the Maico came with a forged piston standard a Mahle but they are like gold in price.

[yamaico]

I think the mechanic means rattling, not knocking, and that is quite normal on a cold forged piston.

[pokey]

Generally but there are exceptions to the rule...

.a Forged piston heats up slower than a cast piston. This is to do with the grain of the metal and the silicon content in the alloy.

 Cast pistons are forgiving that's why they are OEM, They are good for every day use and usually last ok. Forged pistons are stronger this is why they are used for high performance engines. if you race an engine with a forged piston  while its cold its not going to like it at all and will usually chuck a ring. this is because a cast piston needs a bit more tolerance on the rebore than a cast .. its looser when cold.

if your not interested in spending the time warming up the engine properly before riding then just get a cast piston... or buy a few forged kits and a few spare barrels as you will need them.

[Lozza]

Hi all,
Let's have a discuss about this....i brought my bike into the shop and the mechanic said that i should stick with the OEM piston rather than the wiseco forged piston because it causes knocking in the engine...I don't really have any idea about the engine works. If i can't find the OEM piston..will the Wossner still do the job?? 

Run away from Wossners, they are complete shit Wiseco's are not much better(ever since the Dover Group buyout). Get a Vertex, ProX or OEM if possible.

[tymes]

Forged pistons being heavier than oem give you the wonderful opportunity to trial and error your way to the best crank balance factor for the extra piston weight.
Or just throw it in and enjoy those pesky engine vibrations.
Some aftermarket crank kits have heavier crank pins than oem
But yes the forged piston is the tough nut its just that they rarely are properly balanced up for the average single engine, in high performance applications like drag engines the rotating and reciprocating masses are meticulously well balanced.
Don’t worry too much about it, I find I have to use whatever piston I can get for these old bikes, even if you have to get an old one coated like that one Nathan had done.

[sleepy]

A very large percentage of the winners at the recent Classic titles here in Qld all had either Wossner or Wiseco pistons in their bikes. If a shop tells you they are no good find a new shop that knows how to set up engines. As for the Vertex and Pro-x cast pistons, they are good also but don't make much for the classic era of bikes.
As said above, forged pistons generaly have a little more clearance than a cast piston because the materials used have a higher expansion rate. This can make them a little noisier when not at opperating temperature.   

[Lozza]

A very large percentage of the winners at the recent Classic titles here in Qld all had either Wossner or Wiseco pistons in their bikes. If a shop tells you they are no good find a new shop that knows how to set up engines. As for the Vertex and Pro-x cast pistons, they are good also but don't make much for the classic era of bikes.
As said above, forged pistons generaly have a little more clearance than a cast piston because the materials used have a higher expansion rate. This can make them a little noisier when not at opperating temperature.   

An indication of state of tune of the engine and length of time at WOT. Try get someone to use a Wossner at the Island Classic in a 2 stroke. Everyone found the same thing Wossners all work OK during break in then the moment full rpm and load occur, they seize on the skirt. Even with excessive clearance, swap the piston problem disappears.

[Momus]

I ran Wossners in both my smokers- CR125 and RM370 at the Classic Nats - both as good as gold. The little CR gets a fair workout.

Have Wossners in an SX85 KTM and an RM500 as well.


Name some names and bike types of the Wossner seizure sufferers at PI please Lozza.

[sleepy]

A very large percentage of the winners at the recent Classic titles here in Qld all had either Wossner or Wiseco pistons in their bikes. If a shop tells you they are no good find a new shop that knows how to set up engines. As for the Vertex and Pro-x cast pistons, they are good also but don't make much for the classic era of bikes.
As said above, forged pistons generaly have a little more clearance than a cast piston because the materials used have a higher expansion rate. This can make them a little noisier when not at opperating temperature.   

An indication of state of tune of the engine and length of time at WOT. Try get someone to use a Wossner at the Island Classic in a 2 stroke. Everyone found the same thing Wossners all work OK during break in then the moment full rpm and load occur, they seize on the skirt. Even with excessive clearance, swap the piston problem disappears.

If you hadn't noticed this is a Vintage MX forum.
I also now that some of the fastest KX125's powered classic road racers in Australia use Wossner piston giving them podium finishes at Oz titles.