Yamaha OEM pistons

steve speed · Post by **steve speed** » Sat Dec 22, 2007 4:16 pm

cheesie wrote:has anyone checked the weight of the pistons je versus stock, I know the je kit is bigger and of a higher comp but that dont mean it will be heavier you could end up buying an oe piston and it will be heavier than the je kit so will not rev as quick just a thought as it all sounds to good to be true

have you got a link to( je ),,thanks

Post by **phuk72** » Sun Dec 23, 2007 11:09 am

Yes, JE pistons are lighter than stock.

cheesie · Post by **cheesie** » Sun Dec 23, 2007 3:56 pm

if anyone else decides to fit the je big bore kit could they please find out the difference in weights piston skirts ect and post pics of the pistons along side one another

pwmotorsports · Post by **pwmotorsports** » Sun Dec 23, 2007 5:51 pm

anyone have any comments on how the bigger bore effects reliability or MPG ?

Post by **phuk72** » Sun Dec 23, 2007 6:11 pm

Over size standard pistons shouldn't noticably affect either.

I've heard all sorts about JE pistons ranging from needing new rings every 10,000kms to needing a complete rebuild every 15,000lms.

Mine have done over 5,000 miles (of hard use) and I expect another 15,000 miles before I even start looking. Can't comment on fuel range but frankly I don't GAS about that!

Quan-Time · Post by **Quan-Time** » Wed Dec 26, 2007 8:56 am

The difference in weight between a stock and JE item would be in the order of a few grams. You aint gonna notice any loss in rev or how your power curve looks.

Besides, higher quality, lighter gudgeon pins would be a good place to save some weight aswell.

Obviously JE pistons will last longer than a stock item (against detonation, heat warpage, etc) but im not sure about the "needs rebuilds more often" thing.

Anyone other than phuk use JE or know someone from another forum (TRX-TDM forum, or tener'e ? ) maybe they might have a bit of insight.

HansJ · Post by **HansJ** » Sat Jan 05, 2008 1:20 am

Quan-Time wrote: ...

Also note if you DO up compression, make sure you dont have a hugely lumpy cam else your valves smash into your piston.. BUT i dont this this will be a problem with the TRX. Many people use "Kent" cam grinds and thats 8.3mm lift (from 8.0mm standard) so i dont think using a thinner head gasket will be a problem at all.
BUT thinner head gasket AND a kent cam would need inspection just to be 100% safe.

I have skimmed head and cylinders, bugger me if I can recall how much though. The pressure was around 14 kgs/mm2, which is a decent value (although taken with rubber cone compression tester...)

I also have a set of Kent cams, with somewhat more lift than normal Kent specs. I measured the valve to piston distance, and it was plenty, can't recall the measurement either... Different timing would affect the clearance of course, I still had standard cam sprockets, but it looks like the timing has been delayed a bit due to the skimming.

I also measured the JE psitons, and they were a couple of grams heavier than the standard pistons, I have the numbers somewhere, but again... I am getting old I guess

HansJ · Post by **HansJ** » Sat Jan 05, 2008 1:32 am

cheesie wrote:if anyone else decides to fit the je big bore kit could they please find out the difference in weights piston skirts ect and post pics of the pistons along side one another

I knew someone would ask

The JE pistons look "meatier" than stock, or the stock pistons look more "high performance". Maybe that's why the cylinders wear out?

Quan-Time · Post by **Quan-Time** » Sat Jan 05, 2008 6:08 am

JE wouldnt design a crap piston imo, there is a reason for the skirt being huge in comparison. It actually surprised me it was a full skirt design.

Im VERY skeptical about the "rebuild more often" statement.. Maybe the origin of this was a person who forgot to change their oil and let it stay in there for way way too long, and after 15,000km and no oil change, they were forced to rebuild ? Ive heard similar stories with brand new cars and owners saying "i thought i didnt have to look at the oil on new cars, cos its all electronic now".

cheesie · Post by **cheesie** » Sat Jan 05, 2008 8:30 am

thanks for your pics hans, at first sight there looks like there is less meat on the stock pistons but look closely how thin the skirts and side walls are the je ones , did anyone notice the oil passageways look A little larger, now I wonder what the wieght difference is between the oem larger pistons and je, on racing pistons there is usely less piston rings aswell I see they have the same amount do the je ones come with thier own wrist/gudgeon pins

HansJ · Post by **HansJ** » Sat Jan 05, 2008 10:39 am

Quan, I agree, I meant that the stock pistons design probably means they're more likely to tilt. What puzzles me is the difference between my JE pistons, and the ones that are for sale on Ebay. I saw the link in the 'For sale' section on this site.

Cheesie, the JE pistons come complete with rings and pins. There was a difference in design of the pins as well, one had a tapered hole, the other one didn't. And yes, You guessed right, I've forgotten which was which, but I believe the JE ones didn't have the tapering.

Killerwhale · Post by **Killerwhale** » Sat Jan 05, 2008 11:41 am

HansJ wrote:What puzzles me is the difference between my JE pistons, and the ones that are for sale on Ebay. I saw the link in the 'For sale' section on this site.

Those on ebay where TDM900 oneÃƒâ€šÃ‚Â´s wherenÃƒâ€šÃ‚Â´t they?

youngy · Post by **youngy** » Sat Jan 05, 2008 11:43 am

I thought the pistons were 850.

Killerwhale · Post by **Killerwhale** » Sat Jan 05, 2008 11:46 am

youngy wrote:I thought the pistons were 850.

900cc on the 850? Never heard of it. JE pistons is same for TRX/TDM and 878cc me thinks.

youngy · Post by **youngy** » Sat Jan 05, 2008 12:02 pm

good point.......................someone posted some while back (or on TDM forum) about JE pistons for the 900. But that's an 850 block, with steel liners.