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Piston size for bore 66.40?

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Hi all, have a Honda cr250 2000. Service manual says bore and stroke 66.40 x 72.0mm (2.61 x 2.83 in) ... oky so i have to buy a new piston and con rod kit. Was thinking op ProX if not then Wiseco..

So what is the correct size piston to buy guys? Im still new to all of this so your help would be much appreciated.. (rebuilding the bike- project)

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Measure the bore first for wear, taper and out-of-round.

If the bore is in spec any OEM replacement will work just fine. I'm partial to Wiseco but that's just me.

Clean the bore surface thoroughly before reassembly.

Be sure to service the power valves while you have it apart.

Edited by Chokey
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Thanks for the advise.. so is cylinder is 66.398 - 66.405 "A" , "B" is 66.390 - 66.398mm. Manuals Talk about a Piston O.D "A" : 66.33 - 66.338mm and "B" : 66.323 - 66.330mm. Service limit A is : 66.28 and B: 66.273. This make any sense to anyone?

Thanks Choky, you know alot.

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Thanks for the advise.. so is cylinder is 66.398 - 66.405 "A" , "B" is 66.390 - 66.398mm. Manuals Talk about a Piston O.D "A" : 66.33 - 66.338mm and "B" : 66.323 - 66.330mm. Service limit A is : 66.28 and B: 66.273. This make any sense to anyone?

Thanks Choky, you know alot.

 

The numbers in the manual are only the serviceable limits.You still need to measure the cylinder to know it's true size, and to make sure it's still straight and true. If you don't have the tools and/or knowledge to know how to measure it properly, any machine shop or engine shop should be able to do it for you for just a few dollars, and they might not charge you anything to just measure it.

 

Of course if after thoroughly cleaning the bore surface you don't have clearly visible cross-hatching, the plating is worn out and the cylinder needs replating. But the plating will last through many top-ends unless you have poor air filter maintenance habits.

 

If you buy an OEM replacement piston, they are going to give you a "A", the larger one. Which is fine.

 

Other brands will only come in one size.

 

For your crank, buy a 2005+ OEM crank, or a Hot-Rods crank.

Edited by Chokey

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My stock crank is still fine... luckily not damaged, shoul i replace it?

 

 

Then why did you ask about a rod kit?

 

The problem with rebuilding it is that few places still do it. They are out there, but finding a place that will do it right will likely require you to ship the crank out. And by the time you pay $100 for the rod kit and $100 to rebuild it plus shipping, you'll have almost paid for a new crank.

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See the big end bearing broke, and the con rod damaged the axle of the big end.. crank itself is fine. Just need to replce the con rod (new kit ) and piston. End of the day about 190$. See in Bloemfontein where i live there is a enjineering works that press and balance the crank for about 45$.. .. buying trough ebay. I hear what you say , but jeee crank sets are expensive... and why send money on a crank if mine is still fibe... see i bought the bike with a broken big end and piston. Only needs that and a rear wheel. Take a guess what i paid for my new project..... 380$.

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Then why did you ask about a rod kit?

The problem with rebuilding it is that few places still do it. They are out there, but finding a place that will do it right will likely require you to ship the crank out. And by the time you pay $100 for the rod kit and $100 to rebuild it plus shipping, you'll have almost paid for a new crank.

Chokey, here is my pictures of the barrel measurement, piston measurement and head shim :

1401227344816.jpg

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1401227396045.jpg

1401227426398.jpg

1401227450153.jpg

1401227477804.jpg

1401227508520.jpg

1401227536172.jpg

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Then why did you ask about a rod kit?

The problem with rebuilding it is that few places still do it. They are out there, but finding a place that will do it right will likely require you to ship the crank out. And by the time you pay $100 for the rod kit and $100 to rebuild it plus shipping, you'll have almost paid for a new crank.

Piston measurement:

1401227750185.jpg

1401227797288.jpg

1401227852380.jpg

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Then why did you ask about a rod kit?

The problem with rebuilding it is that few places still do it. They are out there, but finding a place that will do it right will likely require you to ship the crank out. And by the time you pay $100 for the rod kit and $100 to rebuild it plus shipping, you'll have almost paid for a new crank.

Here is the Wiseco con rod kit i ordered! Just waiting for your message/ emails regarding the piston? Please hurry, guys want to ship the con rod , waiting for your comment on the piston link i send in previous message...

1401228502206.jpg

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Vernier calipers won't cut it for a bore measurement. Get it measured at a machine shop.

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That cylinder looks sleeved.

Yep, looks like its sleeved. Didn't pick up on that the first time.

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Chokey, here is my pictures of the barrel measurement, piston measurement and head shim :

 

Ok, first:

 

You can not measure a cylinder that way. That will tell you the bore size, but nothing else. A cylinder has to be measured in three places, about an inch down from the top, in the middle, and about an inch up from the bottom, and it must be measured side to side and front to back. This is the only way you can tell if the bore is straight and true and within specs.

 

Second, that cylinder has been sleeved. Since it has scratches that could not be removed by honing, you should purchase the next oversize Wiseco piston, and take the piston and cylinder to a machine shop to have it bored to fit that piston.

 

If it were me, I would order a new cylinder because I despise sleeves, but I understand that you are on a budget.

 

Third, that head needs to be replaced. All those ridges will create hot spots that will cause detonation, which will kill your new top-end quickly.

 

I sent you a link with the message you sent that I responded to with an engine rebuild kit. Before you order it, you need to actually call them on the phone and see if you can get the kit with the oversized piston instead of the standard size piston.

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Ishhh... this bike is killing me.. oky thanks fir the input guys. Chokey, ill contact the place you recommended for buying a new top today. Thanks alot.. a least I'm doing it right.. last thing i wana do is strip again

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yep somebody that didnt know any better ( probly one of the many previous owners) had a sleeve installed. went to all that trouble and extra weight for +8cc that most likely wont even help performance. if anything it will probly decrease the heat transfer slightly. oh well might as well use it but it looks like you might need a bore job

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Ok, first:

You can not measure a cylinder that way. That will tell you the bore size, but nothing else. A cylinder has to be measured in three places, about an inch down from the top, in the middle, and about an inch up from the bottom, and it must be measured side to side and front to back. This is the only way you can tell if the bore is straight and true and within specs.

Second, that cylinder has been sleeved. Since it has scratches that could not be removed by honing, you should purchase the next oversize Wiseco piston, and take the piston and cylinder to a machine shop to have it bored to fit that piston.

If it were me, I would order a new cylinder because I despise sleeves, but I understand that you are on a budget.

Third, that head needs to be replaced. All those ridges will create hot spots that will cause detonation, which will kill your new top-end quickly.

I sent you a link with the message you sent that I responded to with an engine rebuild kit. Before you order it, you need to actually call them on the phone and see if you can get the kit with the oversized piston instead of the standard size piston.

Where are you Chokey? Waiting for private message response my friend...

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