Bigbore for 169fmm motors

ghostdancing · 09-02-2021, 03:01 PM

Any experience with bigbore kits is welcome..i know that athena kit for honda crf230 does fit..but of course is priced..there are also inexpensive kits from the peoples republic though..looking for info and knowledge on this..

ghostdancing · 09-14-2021, 01:39 PM

any of you tried this bigbore set?:

https://it.aliexpress.com/item/10050...71997298%22%7D

Dwdavis · 09-17-2021, 04:51 PM

You really don't want to replace a 67mm bore with a 67mm bore, there are 70mm and in some more rare cases, 72mm big bore kits thatll bolt up to these engines... the 70mm kit will bring you from 229cc to a true 250cc and the gain will be noticeable, the 72mm kit will bring the cc's up to 264 if I remember right....
These engines have a 65mm stroke so you can use a bore x stroke calculator to find the results of each available bore size, I still hadn't found out how big we can go without having to have the cases bored but going from 229cc to 250 or 264 will definitely put a smile on your face

XLsior · 09-17-2021, 05:38 PM

That link is a standard 67mm cylinder and piston kit with a .8 ring gap.

There is not a lot of big bore kit use on this forum as of yet. the 300cc stamped jug 70/2mm piston kit are fairly new to the western market.

It is not a direct swap, some machine work is needed to install a bigbore* the skirt will need to be made smaller to fit the case/or machine the case...

Do they work...yes.

But is it worth your time and resources...only you can answer that for yourself.

Dwdavis · 09-17-2021, 06:27 PM

I guess that answered my question on how far we can go before any case boring is needed, of course, you can also turn down the sleeve to get it to fit into a stock case, but that haslimits as well, but if it works without having to shave too much off the bottom of the sleeve that can be a good thing

XLsior · 09-17-2021, 07:51 PM

Going by the dimensions of that link the OD of the skirt is 69.5mm so no hope of getting the skirt machined down to fit a 69mm+ piston.

I was just passing on information regarding the CG250 to 300cc bigbore swap...Not personal experience. Though might consider it when the used Jug on my project bike gets oval worn beyond use.

ghostdancing · 09-19-2021, 01:43 PM

I was talking about the ohc motor, not the cg pushrod motor..it is 65,5x62,2..max bore without boring the case is 67mm..

XLsior · 09-19-2021, 04:03 PM

Appears you are as informed about the subject as anyone else on the forum.
Quality of production and materials vs consumer price. Name brand/reproduction...If you want a high strung, tight tolerance, peak efficiency outcome then a name brand with a confirmed reputaion is likely a better choice and will pay for itself.

A reproduction probably won't meet the same criteria but will get the job done and a lower entry expense.

If the products are identical...same place of manufacturer same materials but 1 is just a name*, shiny box and stickers included...then the choice to the consumer is pretty obvious.

09-02-2021, 03:01 PM	#1
ghostdancing Join Date: Jul 2021 Posts: 62	Bigbore for 169fmm motors Any experience with bigbore kits is welcome..i know that athena kit for honda crf230 does fit..but of course is priced..there are also inexpensive kits from the peoples republic though..looking for info and knowledge on this..
	0

09-17-2021, 04:51 PM	#3
Dwdavis Join Date: Aug 2021 Location: San Antonio, Texas Posts: 2	You really don't want to replace a 67mm bore with a 67mm bore, there are 70mm and in some more rare cases, 72mm big bore kits thatll bolt up to these engines... the 70mm kit will bring you from 229cc to a true 250cc and the gain will be noticeable, the 72mm kit will bring the cc's up to 264 if I remember right.... These engines have a 65mm stroke so you can use a bore x stroke calculator to find the results of each available bore size, I still hadn't found out how big we can go without having to have the cases bored but going from 229cc to 250 or 264 will definitely put a smile on your face __________________ 2021 Tbr7, lots of goodies on the way for this one, 2017 Harley Tri-Glide Ultra Classic, 1999 Suzuki Intruder 1400
	0

09-17-2021, 06:27 PM	#5
Dwdavis Join Date: Aug 2021 Location: San Antonio, Texas Posts: 2	I guess that answered my question on how far we can go before any case boring is needed, of course, you can also turn down the sleeve to get it to fit into a stock case, but that haslimits as well, but if it works without having to shave too much off the bottom of the sleeve that can be a good thing __________________ 2021 Tbr7, lots of goodies on the way for this one, 2017 Harley Tri-Glide Ultra Classic, 1999 Suzuki Intruder 1400
	0

09-14-2021, 01:39 PM	#2
ghostdancing Join Date: Jul 2021 Posts: 62	any of you tried this bigbore set?: https://it.aliexpress.com/item/10050...71997298%22%7D
	0

09-17-2021, 05:38 PM	#4
XLsior Join Date: Aug 2020 Location: Australia Posts: 1,316	That link is a standard 67mm cylinder and piston kit with a .8 ring gap. There is not a lot of big bore kit use on this forum as of yet. the 300cc stamped jug 70/2mm piston kit are fairly new to the western market. It is not a direct swap, some machine work is needed to install a bigbore* the skirt will need to be made smaller to fit the case/or machine the case... Do they work...yes. But is it worth your time and resources...only you can answer that for yourself.
	1

09-17-2021, 07:51 PM	#6
XLsior Join Date: Aug 2020 Location: Australia Posts: 1,316	Going by the dimensions of that link the OD of the skirt is 69.5mm so no hope of getting the skirt machined down to fit a 69mm+ piston. I was just passing on information regarding the CG250 to 300cc bigbore swap...Not personal experience. Though might consider it when the used Jug on my project bike gets oval worn beyond use.
	0

09-19-2021, 01:43 PM	#7
ghostdancing Join Date: Jul 2021 Posts: 62	I was talking about the ohc motor, not the cg pushrod motor..it is 65,5x62,2..max bore without boring the case is 67mm..
	0

09-19-2021, 04:03 PM	#8
XLsior Join Date: Aug 2020 Location: Australia Posts: 1,316	Appears you are as informed about the subject as anyone else on the forum. Quality of production and materials vs consumer price. Name brand/reproduction...If you want a high strung, tight tolerance, peak efficiency outcome then a name brand with a confirmed reputaion is likely a better choice and will pay for itself. A reproduction probably won't meet the same criteria but will get the job done and a lower entry expense. If the products are identical...same place of manufacturer same materials but 1 is just a name*, shiny box and stickers included...then the choice to the consumer is pretty obvious.
	1