74mm big bore kit

[Williston]

https://aj1moto.com/products/otom-ne...raded-to-300cc

What's your opinion, 14cc/6% increase in displacement worth it?

[Megadan]

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.

[Williston]

Originally Posted by Megadan

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.

Where can I source a cam?

[Okierider]

Originally Posted by Williston

Where can I source a cam?

Joe Henner makes a cam for the 172fmm engines.

[Thumper]

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.

[alex_in_az]

Originally Posted by Thumper

I bought that kit (Otom "300cc" piston/cylinder).


Attachment 30267

Attachment 30268

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.

249.99? I thought the "250" engines were 229?

[GypsyR]

So it's not a "big bore" kit and more of a "slightly larger bore" kit then?
Good to know. If I needed a new piston and cylinder for reason anyway I'd buy it. Otherwise, nah.

[Thumper]

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!

[Thumper]

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!

[Williston]

Originally Posted by Thumper

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!

Thanks for posting this, I ordered it after seeing this

[Thumper]

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!)

[GypsyR]

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.

[Livid_Hawk250]

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.

[XLsior]

the 200cc* cg bikes will have the 163-FM


250cc* should have the 167-FM

[Thumper]

Originally Posted by XLsior

the 200cc* cg bikes will have the 163-FM


250cc* should have the 167-FM

The 167FM engines are actually 229cc. This is the common "CG250" clone in the Storm, Hawk... There is some variability in bore and stroke on these clones, but here is a good, and accurate displacement calculator to see what real displacement should be:
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