CT3 exhaust port is smaller than DT, but has a blowdown hole above the top edge of the port.

DT175 433 cylinders, fitted with YZ85 VForce reed block, are the best for power (outside of IT or YZ ones).

Here's CT2 porting layout from the factory sheet.
Of all the 175's i've only ever seen the early orange AG175 cylinders with the 'open' compression relief hole above exhaust port. Happy to be proved wrong.
RD400's had those holes too.
I drilled one in my YZ465 after finishing motocross & doing a bit of enduro to make it easier to start when i'd run out of energy & slid off in the mud or at the mottom of a gully haha.

Thank you. Thank you.
It's unreadable

I have 2 CT175 cylinders (one NOS), and both have holes above the exhaust ports. The hole isnt there on the only CT125 cylinder I have though. According to someone in the US who has been tuning Yamaha engines for 40 years, the CT175 cylinder, works well on TY175s.

Tried to quote your post but features broken--so copy & paste.

Yamfan post=163385 I have 2 CT175 cylinders (one NOS), and both have holes above the exhaust ports. The hole isnt there on the only CT125 cylinder I have though. According to someone in the US who has been tuning Yamaha engines for 40 years, the CT175 cylinder, works well on TY175s.

Maybe different markets [parts of the world] get different variations of motors compared to us down here.
Still stuff to learn just when i thought i knew it all haha.

daniel-jaros post=163383 Thank you. Thank you. It's unreadable


Daniel do you mean its readable [not un-readable]. The one i have up there now i thought looked readable--can see the numbers.
Or am i seeing it different to you. Cheers.




 

Yes different markets may vary. The CT cylinder looks as though it probably would be better for trials, but maybe not for road or trail use, as I would guess less power than a big port cylinder?

There is Clymer manual which shows port maps for most of the smaller capacity Yamaha motors, which seem to be suggestions for modification?

The service manuals in the Tech Library here have many porting diagrams... 

On the "compression release hole"...  there was a Service Bulletin on that...  it was done to relieve some compression to help prevent damage to kick starter due to improper starting procedures or incorrect tuning.  Bulletin applied to all CT1/CT2/CT3 models.

It's not common to have the hole on CT2/CT3 cylinders...  I've never come across one here in the US nor do I recall any member of the forum mentioning finding one on their bike...  until Yamfan just did.  (Enduronut mentioned the existence years ago...  I'm not sure if he said he had one though)

The September 1973 Bulletin does not list a serial number where this part modification took place...  which makes sense because production of the CT3 would certainly have ended by then.  Bulletin gives instructions on how to drill the hole and mentions replacement cylinders will be available with the compression release hole. 

Bulletin says the small hole makes no difference in performance after starting as the location of the hole has cylinder pressure and exhaust pressure balanced at  running speeds over 1,000 rpm.

Interesting to know for sure what the hole is for. Brand new cylinder i bought has one in it.

I believe I have a CT1 cylinder, piston and rings 1st. oversize that just got put on the shelf on Monday. No needle bearing, no wrist pin, no clips, no gaskets. It looks to have cross hatch scratches present. It might get listed in June on eBay. Send a email if someone is interested. It will be priced at $325.00 plus USPS Medium Box Priority Mail $20.00 50 states. 1969 - 1971 Piston Port Package.
No electronic payments.

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