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Author Topic: Should I get a JE Piston?  (Read 322 times)

Offline Bajafanboy

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Should I get a JE Piston?
« on: March 04, 2018, 05:05:58 PM »
So I’m planning on rebuilding my engine and am considering getting a JE 11.5 Ratio piston.
Is it worth it or should I just get new OEM rings,
can I run 91 pomp gas,
will it be reliable,
what else would I have to change to make it work properly,
Is there really any performance gains.
Any info is greatly appreciated.



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Offline Dirk1616

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Re: Should I get a JE Piston?
« Reply #1 on: March 05, 2018, 03:42:49 AM »
You might as well if you are thinking about it. I got mine for $180 w/rings. But the potential draw back is that you probably need to send your cylinder out to Millennium Technologies with your new piston to have them match the bore to it. The first time I rebuilt my top end, the cylinder wall had some wear from the original rings going bad, and I never sent it out for recoating. This was a bad decision on my part, the new piston had too much slop inside the cylinder and ruined the piston and made my cylinder worse. So if you do order a JE piston, do it right and send your cylinder and piston to Millennium. They cost me about $250 with shipping and stuff. So a total of about $430.

Would I do it over again, but do it right the first time? Yes, most definitely! There is a good amount of power added to it. I would also recommend doing OMR carb mods, and doing the modified end cap if you can. You would need to run premium fuel for the JE Piston, which isn't a bad thing. Premium fuel is a better, cleaner fuel. All of those together is a lot more power. The end cap mod isn't expensive, just takes a little time and you can be creative with it. I made mine to look like an orange shark's mouth, really cool actually.

Just a tid bit of advice too, with more power, your clutch has the potential to slip. Mine did at first, but, it was only because of the oil I was using, not because the clutch was bad (clutch is still good, I checked it). I was using what I thought was good oil, Mobil1 Racing 4T Motorcycle Oil (Expensive), but the clutch will slip, guaranteed. I would recommend using Rotella T6 Diesel oil. I KNOW! I was skeptical too! After I started using that, I had NO clutch slippage at all. I had all the bite in the world and I could put all the power to the ground. There are several guys on here that have been using it for a very long time and haven't had any problems what so ever from it. Neither have I. But the big jug of it. It's like $50 or $60, but actually really cheap because that jug will give you about 2 and a half oil changes, depending on how much spillage you have. Haha
« Last Edit: March 05, 2018, 03:45:40 AM by Dirk1616 »
2003 DS Baja         Riding at Bundy Hill and Silver Lake
Big Gun CDI, 11.5 JE Piston, Port/Polish, OMR Carb Mods,
Custom Mod End Cap, UNI Filter, More To Come?

Offline Bajafanboy

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Should I get a JE Piston?
« Reply #2 on: March 05, 2018, 05:54:52 PM »
Do I have to send the cylinder in even if it’s in space? I’m only rebuilding my engine to do preventative maintenance,
change out all the seals reseat the valvesI and make sure everything works as it should, don’t think I even need to replace the rings,
but generally speaking it’s good practice to change them even if they’re still in spec.


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« Last Edit: March 05, 2018, 09:05:20 PM by Bajafanboy »

Offline Dirk1616

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Re: Should I get a JE Piston?
« Reply #3 on: March 06, 2018, 04:03:33 AM »
The only way to know if you are good with your cylinder and rings is to take a look at them. If you download the 2001 Shop Manual on the side bar, look at Section 3, Subsection 6. It will tell you the allowed tolerances for wear on your rings, piston, and your cylinder. It's not as scary as it all sounds and looks. A pair of calipers work well too if you don't have mics. All the tools needed can be found at Harbor Freight if you don't want to spend a lot of money on tools.

If you look at your cylinder, it should be completely smooth all the way up and down the wall, if you can feel or see a little step or variation towards the top of the cylinder wall, you need to get it recoated regardless of what you do. But if you weren't burning oil prior to your rebuild, you are probably okay with your cylinder and rings.
If you get new stock rings, and your cylinder is still in good shape without any deep scratches or bad scoring on the walls...
Take the cylinder off.
Use a medium scratch pad to give the cylinder a light hone, they are rectangular, about 4"x6", and usually a maroon color.
Move the scratch pad up and down the cylinder wall in a diagonal/twist motion. The cylinder coating is very strong, so you may need to work at it a little bit. You could even attach the pad to a drill to have it spin around the entire cylinder.
Use soap and warm water while doing this.
Once you see little marks on the cylinder, move to a different spot, don't work one spot too much.
This is only if you don't want to send your cylinder out to get it recoated, doing this is at your own risk though. It has worked for me in the past, that's all I'll say.

If you have your motor apart already with it at Top Dead Center, and you are using a crank stop bolt on the clutch side of the motor. It is okay to take it out and move your piston down to look at the cylinder, just know it will take a little time and finesse to get it back to TDC. Use a crescent wrench or whatever size wrench the nut is on the sprocket shaft to turn the motor while it's in gear to move your piston up and down. Use a flashlight to look inside the crank stop hole and wait until you see the very little groove on the crank, then put your bolt back in. Then when you go to put it all back together, have the cam lobes pointing away from each other (exhaust cam points towards the front, intake cams point towards the carb). Then line up the markings on the cam sprockets, then take out your crank stop bolt and you're good to go.
2003 DS Baja         Riding at Bundy Hill and Silver Lake
Big Gun CDI, 11.5 JE Piston, Port/Polish, OMR Carb Mods,
Custom Mod End Cap, UNI Filter, More To Come?

Offline Bajafanboy

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Re: Should I get a JE Piston?
« Reply #4 on: March 06, 2018, 10:53:32 PM »
Thanks for all the info!
Never would have thought diesel oil was the way to go, also good to know I don’t have to use race gas or e85 with the JE Piston.
I have some experience with engines from rebuilding my brothers 01 Yamaha YZ426F, changed the transmission crank and piston on that bike and everything is fairly similar as far as procedures go.
I’ll probably start working on the DS650 in a couple days I should have everything I need to do it including a stone cylinder hone for the crosshatching the only thing I don’t have is a magneto puller but I don’t think I’ll have to take that off to split the case.
I’ll post some pictures and updates of the rebuild in a separate post.
Thank again


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Offline Dirk1616

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Re: Should I get a JE Piston?
« Reply #5 on: March 07, 2018, 04:03:38 AM »
You don't need to split the case to do a top end rebuild or to take the cylinder off. Are you planning on doing a shift fork replacement too?
2003 DS Baja         Riding at Bundy Hill and Silver Lake
Big Gun CDI, 11.5 JE Piston, Port/Polish, OMR Carb Mods,
Custom Mod End Cap, UNI Filter, More To Come?

Offline Bajafanboy

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Re: Should I get a JE Piston?
« Reply #6 on: March 07, 2018, 09:29:40 AM »
No but I do need to fix The oil pressure regulator. Oil doesn’t stay in the reservoirtay



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Offline Oldmanracing

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Re: Should I get a JE Piston?
« Reply #7 on: March 07, 2018, 11:26:14 AM »
JE 11.5 Stock Bore Piston

Piston  dome specifications as measured by OMR:
Dome Height- .260
Valve Pockets - 1.5cc X 4 = 6cc
.260 volume = 3.165cu. in  or 52cc
Piston cc in bore = 42cc
52cc - 42cc= 10cc + 6cc(valve pockets)= 16cc total dome displacement

Head cc’d and found to measure 66cc
OEM head gasket compressed .058
Gasket Bore 3.977
Bore 3.937
Stoke 3.27
Deck .010 below
Base gasket .020

Compression -
Static compression - 11.23

If you purchase stock Cometic Gaskets
Cometic compressed is .027
Static compression - 12.35

If you also install a base gasket from Cometic
Base gasket is  .012
Static Compression - 12.68

The piston is based on using stock head and base gasket.

OMR

 

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