SRX / XT valve sizes, etc.

[andy230]

Hello, more anorak info!

I have just discovered that the XT600 (2KF) valves are 1mm bigger (inlet and ex) than the corresponding SRX items.

I was going to post my tecchie info on what I have, but left it at home.  Will do this tonight...

Are big valves always the way to go?  (have a stage 4 cam, springs to replace)

And if I can stretch to it, (which is most unlikely) what about Ti valves and springs??  I am looking for reliability, although an increase in performance would always be good.

Am trying to get some info on who did the cam, and what the old springs were (cos I wont be putting them in again!!)

cheers for now

a

[themoudie]

Unobtanium is all very well, BUT!!!! Do you still have a 'budget'?

1mm bigger in the valves will make a difference, but nothing eye popping.

I don't know with Yam 4valve heads, but Duke single heads have 'orrible angles in the inlet if you wish to make them breath. Those whom are really serious, weld up the whole of the inlet port and then machine a central port with revised angles and diameter.

You can increase inlet and exhaust valves diam by several mm. But there comes a point where either the valves touch each other or the flow rate can't be maintained and the volume of fuel/air mixture entering the cylinder falls below the optimum. Loss of performance. This is another reason why going for a mid to lower upper rev range torque motor might be better than a top end motor, if you go to far you either scrap the head or fill it with weld and carve again!

You may find this site with pictures about 'squish' useful even though it applies to Dukes, the principal is the same.

http://midfield.deraeve.co.uk/The_Bike/Description.htm

This site illustrates the work of a man we have sadly lost.

http://www.mez.co.uk/mezporting/

My regards, Bill.

[guest27]

Mez of Mez porting was such a great and wonderful bloke.  Did some work on the Triton head for me and a mates R100 BMW.  When you went to his 'shed' at the end of the garden there would be these lovely looking heads sat witing to have him run his hands over them - tagged HRC, Ducati WSB etc.  Of course he did not show me, I used to peek under the covers whilst he was getting something or the other.

Sad loss to us all.

R

[Steve H]

Valve shrouding is quite an interesting topic. It champions the "bigger is not always better" argument quite well.

[andy230]

Hello Bill

Unobtanium is all very well, BUT!!!! Do you still have a 'budget'?

Yes, but I paid dear for Yam washers, so I am half of the opinion that "if it needs it, it will have to get it".  I dont want to pay to gt to a race, entry for the race, and drop the valve.  Cos thats then 200 quid down the pan!

However, I think titanium is porbably out the window.  I've also been told that thermal condictivity is duff, coupled to the fact that the valve is off its seat for much longer, so runs hotter anyway.

I believe the valves that came out were standard (with 34K and 5Y1 embossed on the combustion face)- can anyone confirm?? 

If it had standard valves before, they'll be new standard ones again!

I've got a fone number for the guy who had the motor before ash.  I'll find out about who did the cam and what  springs he recommends.

SteveL- it was GRC who bored & honed the barrel to that piston, so I am fairly certain it will be right.

Bill- I think the serious head work you describe is out the question.  But I do want to get the inlets flowing better- there are *BIG* steps where they bolt onto the flowed head.  You reckon I can (carefully) open these out myself??  And what would you think I should do it with?

Am thinking about engineers bluing the head (faces) bolt on the rubbers, and then remove metal up to where the "clean bit" is.  Sound reasonable?

This may well be after xams however!

Speak soon, will post anorak valve info soon

a

[andy230]

Hello, more anorak info!

I have just discovered that the XT600 (2KF) valves are 1mm bigger (inlet and ex) than some corresponding SRX/other XT items.

I was going to post my tecchie info on what I have, but left it at home.  Will do this tonight...

Here is the valve info as measured (in mm):

IN L  35.98   **head is "hammered" by tappet**  --> replace

IN R  stuck!  **head is "hammered" by tappet**  --> replace

EX L 31.08       looks new  --> reuse

EX R 31.08       looks new  --> reuse

All other variables are within limits (as per the SRX manual I have, same as the srx600.net site).

The head is marked 2KF.  I believe this is a Tenere part?

However, a XT600 2KF manual I have lists the valves as being 1mm bigger than this...

So, I suppose, theoretically, the 2KF head is the one to go for??  Think thats whay I have and I aint chainging now!  Cos this one is nicely gas flowed and machined for the big cam.

The valves are thus not as big as they could be, but its what we are going with!  Have ruled out Ti valves.  Not sure about springs yet.

I will also measure seat diameter and post

cheers

a

[guest27]

Hi Andy

Whilst you are bored thought you would like to read this

R

[andy230]

Hi Andy

Whilst you are bored thought you would like to read this

R

Interesting Rog....  thanks.  I hear what he's saying, and agree.  But I am getting LOADS of different info from lots of different people. 

All of which is appreciated by the way!  So keep it coming!!  I've become aware that (esp in the paddock), everyone is an expert.  Because they know whats good for them.  But not necessarily good for me!

(this is ignoring the fact that some folk will actually give bum info, just to hinder.)

I think the best idea is to read books and tinternet articles, talk online, listen to what those before have done, but take into account that their circumstances may be different- different budget, different races, different bikes, different mentality, different strategy, different service intervals, etc....

I am going to keep the head as is.

I'm just going to put up a post on my latest findings!  Cheers for now, keep it coming

a

[guest27]

As to moto-man ..  Having been a canoeist in the past I think he is right but for the wrong reasons, on a river where you get a narrowing like he describes on his ports you do not get eddies and back flow - just a blasting bend.  Where you have a nice wide bend you get confused flow and backign water etc on the inside - all of this is inlet charge and energy to my mind.  Ditto the Micron Serpent exhausts - they flatten out on the bends - giving more outside bend and less inside bend - more even flow.

R