Whats the difference between 31k and 1UA barrels??

[vic6169]

As the title says??

[4l04ever]

I think it is mainly some slight porting differences.

[midlifecrisisrd]

As said porting only

Very slight

Steve

[aimdave123]

Can these barrels be interchanged. Thanks.

[midlifecrisisrd]

As a pair yes

Would not be keen on a 31k on one and a 1ua on the other

Nothing to stop it actually working though

Steve

[jon]

The power valves are also different to match the ports.

I think the 31k has a slightly lower exhaust port?

Jon

[Mr Kipling]

All power valves same throughout the range only aftermarket billet valves address this , 1ua have higher ports 1mm from old memories n slightly wider , Yamaha originally done this to keep power output similar even though other changes didn't allow higher peak hp due to emissions police being on there case !!!. for those interested I can post up pics showing the difference between new 1ua barrels with standard valve n the other one with billet valve...

[bare]

In theory (or by BS claim )
As My 1UA billet valves from the Aus Shyster did not fit /match the ports.
Top or bottom of the ex port.. Grrr.
Spent an hour apiece on them with a Burr making them fit

[antos]

I know when I bought my billet ones from Martin at mbd I had to specify 1 ua as he said there is a difference. My god that’s reminding me how much I spent on it 😂

[antos]

Sept 8, 2017 19:25:44 GMT 1 Mr Kipling said:

All power valves same throughout the range only aftermarket billet valves address this , 1ua have higher ports 1mm from old memories n slightly wider , Yamaha originally done this to keep power output similar even though other changes didn't allow higher peak hp due to emissions police being on there case !!!. for those interested I can post up pics showing the difference between new 1ua barrels with standard valve n the other one with billet valve...

id be interested if you could mate😊

[jessy03]

There you go

www.flickr.com/gp/157569945@N05/200tHb