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CRF150RB Bigbore and stroker kit? How and what to do? :)

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Hi guys,

I just bought a 09 150RB with a broken valve, so it needs complete rebuild, new head, valves, piston, cylinder i prefer to change and a new crank.
Im building it for mini motard, and I'm thinking about the option of going to buy and big bore kit and stroker crank, when I'm going to buy new parts anyway.
So my question is. who has experience with this, something to be aware of?
Can i use a normal cylinder or big bore cylinder for the stroker crank? can i use the stock head with out mods, for big bore ?

Hope you guys can give me some tips and tricks :)

Christian

 

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Hi guys,

I just bought a 09 150RB with a broken valve, so it needs complete rebuild, new head, valves, piston, cylinder i prefer to change and a new crank.

Im building it for mini motard, and I'm thinking about the option of going to buy and big bore kit and stroker crank, when I'm going to buy new parts anyway.

So my question is. who has experience with this, something to be aware of?

Can i use a normal cylinder or big bore cylinder for the stroker crank? can i use the stock head with out mods, for big bore ?

Hope you guys can give me some tips and tricks :)

Christian

good your doing a crank at the same time or you would grenade the old with the big bore. The 170 big bore kit comes with a new head. From there it's up to you but I would highly recommend stage 2 cam, Stock 150 cams are pretty lame so you see huge improvements there. Bike will rip...

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Im trying to keep this at a level where it fair.
Ive looked at the Athena 163cc (69mm) Bigbore kit. Is a bolt on kit? I mean does the cylinder head require any modification to use this?

And if one were to add the 2mm+ crank, will this require any modification to cylinder og head?

Thanks

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I have a Cylinder Works 160 kit that does not require a different head. The piston is only 11.7:1 compression ratio, so it would go well with the stroker crank which will boost compression ratio, but I can't say by how much. I wouldn't mix a high compression piston with a stroker crank if the resulting ratio were greater than 13.5:1.

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The Athena BB kit is a bolt on but if you put a stroker crank in it you will need a piston with a different compression height or a spacer, without doing this your piston will stick out of the bore by 1mm with the 2mm stroker crank.

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The Athena BB kit is a bolt on but if you put a stroker crank in it you will need a piston with a different compression height or a spacer, without doing this your piston will stick out of the bore by 1mm with the 2mm stroker crank.

 

Do you know this for a fact? I ask because the Powroll stroker cranks I used in the day used a reforged rod, shortened half the stroke increase, and used the stock height barrel. They worked with any piston that worked with the stock stroke (except, of course, for the compression ratio problem with high-compression pistons).

 

Christian_83, it sounds like it is time to contact your sources with some specific questions. They will have definitive answers for you. Who would you be sourcing your stoker crank from? I'll be interested when its time for a bottom-end rebuild. I'm a trail rider and the possibility of extra torque has my attention.

 

By the way, all the head builders I've read on TT fill the ports because they find that the stock head doesn't provide enough flow velocity. Usually a bored and stroked engine moves power down in the rev range because the ports wind up not having sufficient capacity for the demands of the increased displacement. But the CRF150R/Bs should flow very well with the increased displacement. If anybody has experience with this, please chime in.

Edited by Old Plonker

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Yes, the rod length can be shortened to make a stock piston work. I was thinking more in line with a car engine, shorter rods with more stroke make for a bad rod ratio, but we are talking about a stroke increase of an inch in car engines not 2mm.

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Yes, the rod length can be shortened to make a stock piston work. I was thinking more in line with a car engine, shorter rods with more stroke make for a bad rod ratio, but we are talking about a stroke increase of an inch in car engines not 2mm.

 

Upon reflection, it would be very intelligent to use a stock length rod, because then you could tune the compression ratio with spacer and/or gasket thickness. Who makes the 2mm stroker? I'd like to ask them some of these questions. 

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Hi guys,

I just bought a 09 150RB with a broken valve, so it needs complete rebuild, new head, valves, piston, cylinder i prefer to change and a new crank.

Im building it for mini motard, and I'm thinking about the option of going to buy and big bore kit and stroker crank, when I'm going to buy new parts anyway.

So my question is. who has experience with this, something to be aware of?

Can i use a normal cylinder or big bore cylinder for the stroker crank? can i use the stock head with out mods, for big bore ?

Hope you guys can give me some tips and tricks :)

Christian

 

Came across kits in the past for a 2mm stroke increase, may be Hot Rods?

 

Thanks 418Stroker. Found it here:

 

http://www.hotrodsproducts.com/ProductInfo.aspx?item_id=687

 

Christian, no problem with Hot Rods stroker crank and big bore kit combo (2mm stroke and 2mm bore = 166cc). Just keep the compression ratio sane.

Edited by Old Plonker

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