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valve to piston clearance

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Posted by: ochster

With the 13:1 piston and oversize valves, I have .035-.040 clearance when claying. I know this is not optimal, but is it problematic? I also never reuse headgaskets when claying. I have been told this is a waste of $$ if the machine is not braught to temp. Any opinions? Not that I would think it should matter much, this is on a XR300.


Posted by: jib

.035-.040 is to close for a dirt bike application. You should be looking for a min clearence of .085 or maybe .100 to be on the safe side. My advice would be to fly cut the valve reliefs. We are talking valve to piston clearance correct, and not piston to combustion chamber ?


Posted by: Rich Rohrich

Ochster are you getting this measurement at TDC, or ATDC on the intake? What about the exhaust?


Posted by: ochster

Rich, I have not specifically paid attention. I have simply been putting small patches of clay, around the valve reliefs. And then gently and slowly turning the motor over with a breaker bar. Should I be doing a TDC, and ATDC measurement? Could you run through a quick 1,2,3, on claying for me. By the nature of your question, I would assume the TDC is what I should be concerned with? Thanx


Posted by: Rich Rohrich

I've never trusted clay because it's so difficult to get consistently accurate results. I use light checking springs and a dial indicator on the valve.

Depending on the cam you're running the intake valve will be closest to the piston somewhere in the range of 2-12 degrees ATDC. The exhaust valve will be closest in the 10 BTDC - TDC range, but it's rarely an issue on pentroof chambers. Obviously because the exhaust is closing it should have considerably more available clearance than the opening intake. Using an indicator and a degree wheel is more of a hassle, but with the clearances you are talking about it seems warranted.

Steel rods don't see much stretch so you might be able to get away with .040" but I think it would require good cam dynamics and a really stable valve train. Feeeling lucky? http://dirtrider.net/ubb2/smile.gif


Posted by: ochster

I was originally going to use the indicator method, but lost patience with the set-up. I will however retest.

When I had the oversize seats installed, they left them high. I'm sure there is .010-.015, to be gained by just making the seats flush. I guess it may be time to buy a couple carbide seat cutters.

I also was surprised by how thick they made the face of the stainless valves. Not nearly as trim as most O.E.M., and they feel quite heavy, wich bothered me running a R&D spring set for the stock valves. These are 2mm larger on intake, and 1mm larger on exhaust, should I expect a trimmer valve design if I was to go with Ti. These were made by Black Diamond. My biggest reason for considering the Ti, would be for weight, having them be trimmer in design would be a bonus. Do you have an opinion on this?

The reliefs in the 13:1 J&E are already fairly deep. Would you consider it better for chamber efficiency, to try to deal with creating more tolerance via the valves and seats?

I am running a shortened Hot-Rod, with the crank pin relocated, to achieve a 3.1mm stroke increase.

Thanx for your input


Posted by: SFO

Quote:
Originally posted by ochster:
I was originally going to use the indicator method, but lost patience with the set-up. I will however retest.

When I had the oversize seats installed, they left them high. I'm sure there is .010-.015, to be gained by just making the seats flush. I guess it may be time to buy a couple carbide seat cutters.

I also was surprised by how thick they made the face of the stainless valves. Not nearly as trim as most O.E.M., and they feel quite heavy, wich bothered me running a R&D spring set for the stock valves. These are 2mm larger on intake, and 1mm larger on exhaust, should I expect a trimmer valve design if I was to go with Ti. These were made by Black Diamond. My biggest reason for considering the Ti, would be for weight, having them be trimmer in design would be a bonus. Do you have an opinion on this?

The reliefs in the 13:1 J&E are already fairly deep. Would you consider it better for chamber efficiency, to try to deal with creating more tolerance via the valves and seats?

I am running a shortened Hot-Rod, with the crank pin relocated, to achieve a 3.1mm stroke increase.

Thanx for your input

I used to run the custom department at Kibblewhite, if there are questiuons regarding the dimensions of your custom valves, be assured that they will help you.
Your valve pockets could be deep enough, they just aren't big enough for the os valves.
Be carefull with R&D spring kits, what kind of seat pressure are you running?
Did you get the rockers reworked?
The os seats being installed proud will alter your installed height on your springs, you are on the right path checking everything, this is the only way to avoid exspensive tangles.



Posted by: ochster

SFO,

The reliefs in the piston are sufficient for the o.s. valves.

What do you know about R&D spring kits? can you reccomend a better quality? Yes, I did have the rockers reworked, and replated.

The most frustrating part of relying on othere people, is that more often than not, there claimed quality and expertise is not reflected in thier work. The valve job done to this head, and the amount of tolereance in the guides/stem is disgusting. I was dealing with a large well reputed company. It's time to take things into my own hands.


Posted by: SFO

Quote:
Originally posted by ochster:
SFO,

The reliefs in the piston are sufficient for the o.s. valves.

What do you know about R&D spring kits? can you reccomend a better quality? Yes, I did have the rockers reworked, and replated.

The most frustrating part of relying on othere people, is that more often than not, there claimed quality and expertise is not reflected in thier work. The valve job done to this head, and the amount of tolereance in the guides/stem is disgusting. I was dealing with a large well reputed company. It's time to take things into my own hands.


Kibblewhite also does cylinder head work with a serdi machine. I, even as a former employee, still have them do all my engine machine work, the stuff that requires specialized tools.
They also make a xr spring kit that white bros repackages as there own. I have had great results with all of their products, a real no-hype company that delivers.
R&D was a competitor of ours, I believe we had proven results that spoke for themselves.
I would not use R&D springs after seeing the aftermath in a few cylinder heads.
E-mail me if you have more questions regarding your head, it seems this thread could be leaving the realm of this forum.
It is not my intention to talk s*** about any aftermarket manufacturer, these are just my experiences...


Posted by: ochster

SFO,

I also do not wan't to intentionally product bash. Judging from your comment on the aforementioned componet, I was thinking you may be able to substantiate something that DID, happen to me.

There is not alot "experiences" out there with people experimenting with these mod's. I do appreciate you voicing yours. It is also the reason this board is so powerful.




Posted by: Rich Rohrich

Quote:
Originally posted by ochster:
When I had the oversize seats installed, they left them high. I'm sure there is .010-.015, to be gained by just making the seats flush. I guess it may be time to buy a couple carbide seat cutters.


Ochster - Have you checked valve to seat contact with prussian blue, or lapping compound? Generally speaking, sinking the valves deeper will disrupt flow and compromise the port short side to seat transition. If the backside of the valve is already larger than stock then low lift flow will be very poor and the engine will tend to feel like it has too much cam. On the flipside, making the valve reliefs too large will kill tumble and limit charge motion at lower speeds. This is wil tend to kill torque and mileage in the low to mid rpm range and require additional ignition advance along with a higher octane requirement.

It's likely you can strike a balance midway between to two. As Bill suggested take a close look at the valve/seat interface and if need be take it to a pro to have it finished properly.

Once you get it sorted it sounds like it should be a fun bike http://dirtrider.net/ubb2/smile.gif




Posted by: ochster

Thank you Rich, I believe I will take your advice, and atleast have some one look at it. I know there is not alot of room for error, before I end up with a really expensive door stop,


Posted by: SFO

When I first started building motors, some kind sage commented, "You can tell who can build a motor by how many he has blown up".
So welcome to the jungle dude...
There is a pile of blowed up s*** in my foreground...



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