![]() |
#1 |
Join Date: Sep 2023
Location: WNY
Posts: 31
|
74mm big bore kit
https://aj1moto.com/products/otom-ne...raded-to-300cc
What's your opinion, 14cc/6% increase in displacement worth it? |
![]() |
![]() |
#2 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,100
|
Being "worth it" or not would be entirely up to you.
It will have a benefit, but on its own it may not impress you a ton. If you are after power a cam will provide more bang for your buck.
__________________
Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124 |
![]() |
![]() |
#3 |
Join Date: Sep 2023
Location: WNY
Posts: 31
|
Where can I source a cam?
|
![]() |
![]() |
#4 |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,594
|
I bought that kit (Otom "300cc" piston/cylinder).
Oh it is a NICE kit. Complete, and the machining and parts look excellent. All gaskets, orings, gudgeon pin/circlamps, piston rings. Very nice kit. But I was dismayed when I found out it was just a 74mm bore. YUP, that increases displacement by 14cc (249.99 to 264.07). I wouldn't call that a 300cc kit, even though 300cc is cast into the cylinder (see it in the photo). At least the advert you found admits it is a 264cc kit! For me, it's NOT worth it unless I also add the cam, port the head and maybe get a slightly larger diameter carb. All together, it would probably make a big difference (maybe up to 24hp). The most noticable difference might be in the midrange torque feel, and off the start torque would probably feel spunkier and more willing. So my kit will sit on the shelf until I have time to really work on it. I also got a new head and was willing to do it, but it did not come with the valves and cam (listing showed the valves/cam included). Disappointment.
__________________
-NOS 2020 KTM 250SX (2-stroke motocross) Last edited by Thumper; 10-24-2023 at 05:37 PM. |
![]() |
![]() |
#6 |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,594
|
I posted comments about the empty head I got from a vendor on AliExpress. Today. See post #5, last paragraph... above
My son left for work this afternoon and apparently found this on our doorstep: I can't believe it. This cleared customs back in the Spring sometime, AliExpress got notified by the vendor that it was returned, and AliExpress refunded my payment in full. Thank you ! ![]() But somehow, it came back, 8 months after I sent it off. Cool. The package is pummeled but I packed it thickly padded, double boxed. Nice to have it back. I ended up just paying the shipping. Not bad!
__________________
-NOS 2020 KTM 250SX (2-stroke motocross) Last edited by Thumper; 10-24-2023 at 08:10 PM. |
![]() |
![]() |
#7 |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,594
|
I wish I waited until XPro had the Zuma Templar X X7-250 head with Valve ass'y in stock. I think it is OEM. $100 on ebay!
I posted in the web deals section with a picture of the listing. I just had to buy one from a vendor on AliExpress. Impatience... Doohhh!
__________________
-NOS 2020 KTM 250SX (2-stroke motocross) |
![]() |
![]() |
#8 | |
Join Date: Sep 2023
Location: WNY
Posts: 31
|
Quote:
|
|
![]() |
![]() |
#9 |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,594
|
FYI, I got the complete head with cam, rockers, valves and springs installed for $100 as a replacement part from XPro so I will go ahead with the porting at some point (so busy now, no time!)
__________________
-NOS 2020 KTM 250SX (2-stroke motocross) |
![]() |
![]() |
#10 | |
Join Date: Aug 2013
Location: Goodyear, Arizona
Posts: 412
|
Quote:
__________________
2020 Tao TBR7 9.3:1 PnP head CRF230F exhaust 4 degree advance key 290 degree cam Nibbi PE30 and cone filter Front fork brace |
|
![]() |
![]() |
#11 |
Join Date: Feb 2023
Location: Upstate SC
Posts: 320
|
One reason I picked mine. No problem with a 230 but not when it has 250 stickers all over it. Just me being picky though. 250 cc stickers on a 249cc (or 230 on a 229cc) I don't have an issue with.
|
![]() |
![]() |
#12 |
Join Date: Oct 2021
Posts: 5
|
Playing devils advocate here, but couldn't you purchase this kit and then have it bored out by approximately 81.06mm?
Displacement=π(pi)×( 2/Bore ) 2 ×Stroke 1. Calculate the original bore size. 2. Calculate the bore size needed for 249.99cc (74mm). 3. Calculate the bore size needed for 300cc. Might be worth it for some people. |
![]() |
![]() |
#13 |
Join Date: Aug 2020
Location: Australia
Posts: 1,376
|
the 200cc* cg bikes will have the 163-FM
250cc* should have the 167-FM |
![]() |
![]() |
#14 | |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,594
|
Quote:
https://spicerparts.com/calculators/...ent-calculator Select metric, then enter these bore and stroke numbers from various listings for engines. I copied the info from 2 engines from AJ1, and 2 listings from ebay. I was surprised to find that they were all accurate claims when I entered the bore and stroke numbers on the listings. But I noticed something interesting. The Zongshen ZS174MN watercooled engine at AJ1... 74mm bore is like the OTOM kit I got, and if you use my stroke (61.4mm for the ZS172FM) you get 265cc, but if you use the stroke from the ZS174MN (65mm), you get 280cc. I think the OTOM kit assumes a 65mm stroke! Here they are: AJ1 Zongshen CB250F, ZS172FMM-3, 20hp bore x stroke 72mm x 61.4mm 249.9cc Spicer 249.99 AJ1 Zongshen CBS300, ZS174MN watercooled, 25hp bore x stroke 74mm x 65mm 279.5cc Spicer 279.56 Ebay lifan (Cleveland Cycleworks) 14hp 167FMM 67mm x 65mm 229cc Spicer 229.17 Ebay lifan 163FML bore x stroke 63.5mm x 62.2mm 197cc Spicer 196.98
__________________
-NOS 2020 KTM 250SX (2-stroke motocross) Last edited by Thumper; 02-27-2024 at 08:49 AM. |
|
![]() |
![]() |
#15 |
Join Date: May 2024
Location: Minnesota
Posts: 1
|
Is aj1moto legit? I'm new to the group, and have been using my 172fm-3a for a dirtbike project. Wouldn't mind exploring to other zs dirtbike motors for more power, but I've never heard of the aj1 until I stumbled upon this forum last week. Has anyone ordered an engine from them? Are they based in US or China? How does shipping work? Is it worth it?
|
![]() |
|
![]() |
![]() |
|
|