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Discussion Starter #1
Hello,

I have been reading the forum since years but that's my first post, so finally greetings everyone!

My name is Orestis and this is my beloved and abused xrv:

IMG_20190531_174921aa.jpg

My bike's main modifications are: Boano Sachs 48mm fork, Nitron ntr pro shock, jetting/pump/air/exhaust, controls/levers etc...


And to my questions:

I'm thinking of changing the pistons with the JE 82mm 11:1 for the Hawk 650 NT.
1. Are there any modifications needed on the JE piston's skirt or it's a direct fit appart from the cylinders?
2. I've read that with the Wiseco oversized pistons there is an increase of oil cosumption. Is it the same with all oversize pistons? Any experiences with the JE?
3. Are there any other modifications needed on the head/valves etc for that fit?

Any other advices on the big bore conversion or on any direction are more than wellcome!

Thank you in advance,

Orestis
 

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OVALTEENY !!!
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Welcome Orestis, nice bike

I wouldn't change the engine, I'd just change the gearing to suit what you are doing. I've left my bikes standard and have had no issues. Just changed gearing to suit. Honda OEM sprocket is available 1 more or 1 less. My front is standard and the rear is the easiest to change. Up 3 or down 3 on the rear is roughly the same as 1 up or 1 down at the front. Outside of those margins you will need to change the chain


Any change in the output will affect reliability and limit your options of maintenance and aftercare
 

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OVALTEENY !!!
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PS Can we have some of your blue sky !
 

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Discussion Starter #6
Welcome Orestis, nice bike

I wouldn't change the engine, I'd just change the gearing to suit what you are doing. I've left my bikes standard and have had no issues. Just changed gearing to suit. Honda OEM sprocket is available 1 more or 1 less. My front is standard and the rear is the easiest to change. Up 3 or down 3 on the rear is roughly the same as 1 up or 1 down at the front. Outside of those margins you will need to change the chain


Any change in the output will affect reliability and limit your options of maintenance and aftercare
Thank you Paul!
I have already experimented with 46 and 47 rear sprokets and always leave the front OEM and standard size. Together with all the other changes on fuel and air I can say that my bike runs significantly better than a stock one but I would like to experiment with some extra bhp and torque.
What I plan to do is to buy a pair of used cylinders, bore them to 82mm and use them with the JE pistons while I will store my standard cylinders and pistons.
Some extra mods I am considering (if I do the oversize conversion) are heads porting and Arrow exhaust headers installation.

Any experiences with the JE 82mm pistons fiting? Oil consumption? Other info?
For about what range of reliability/maintenance intervals reduction are we talking with such a modification (relatively)?

PS Can we have some of your blue sky !
And imagine the picture is not in Greece! I'm in north France right now with my bike for work! I wish it was sunny like that everyday too...

Orestis
 

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Discussion Starter #7
No one?

I think the member jensen has done this modification but I cannot reach him by pm. Although I try to send pms my "sent folder" is always empty for some reason.
 

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JE piston is just bore and fit. I have run different pistons, the last 40.000km, but not for so long time, that I can tell about oil consumption. You can take some material from the top of the pistons to reduce the comp. 11:1 is a little high for the shape of that combustion chamber.
 

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Discussion Starter #12
JE piston is just bore and fit. I have run different pistons, the last 40.000km, but not for so long time, that I can tell about oil consumption. You can take some material from the top of the pistons to reduce the comp. 11:1 is a little high for the shape of that combustion chamber.
Finaly got to contact you Jensen! haha! Thank you for your reply!
For what amount of material from the top are you talking about? And drop the comp from 11.:1 to 10.5? 10?
Do you consider it as a value for money mod? Reliability?
 

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Together with other cams it really wake up that lazy engine. Especially when overtaking on the road. Comp. 10.5: 1 or 10:1 you have to measure out and see how much you remove. As long as you do the same to the two pistons its no problem, just your choice.
 

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Discussion Starter #14
Together with other cams it really wake up that lazy engine. Especially when overtaking on the road. Comp. 10.5: 1 or 10:1 you have to measure out and see how much you remove. As long as you do the same to the two pistons its no problem, just your choice.
uufff... Installing and removing the pistons for measuring the comp again and again sounds really difficult though. The mechanic is elsewhear, the machinist is elsewhere and the expenses get higher and higher.
Is there any pattern for about how many mm removed would achieve a 10 to 10.5:1 comp ratio?

Thank you!
 

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Discussion Starter #16
If you cant do it yourself then just dont do it.
I don't have the knowledge, experience or machinery to do this by myself but... I have access on great mechanic and machinisht to do this. They just haven't done this work on that engine before, neither searched for these details.
So I'm searching all by myself for all the info needed for that job and hope to gather as much information as possible for what needs to be done to my beloved xrv.
After all we are not talking about nuclear submarine technology over here.. I am willing to search as much as I possibly can and try it.

Your experience and knowledge sharing are precious.
 

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Discussion Starter #18
I don't mind the high octanes as I do mind the long term stress on my rods/crank. Even if it's just in my mind, I won't be sleeping well.
I will try to gather as much info as possible and along with the machinist's advice, remove some material. From what I have read untill now 0.8 to 1.2mm might be good to start.
 
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