Printable View
Everytime I get my tune up a little off ie:to fat or timing retarded( I'm a new guy but I'm learning)It results in leaking exaust valves. I'm currently running Manley stainless valves.
The question is: Is there a better type of valves or coating that can be put on the valves that would be a little more forgiving in the event I get the tune a little off in the future?
P.S. I'm changing the valves anyway.
Late timing (which aggravates) rich mixture results in high exhaust temperature. That knocks the valve seats out of round and can warp valves. I suggest timing never any later than 32 degrees, nor more than 36 degrees. I don't know what heads your are running so i can't tell if you have big seats or not. Many chevy heads had little seats and if that is the case, you'll chase valve jobs all the time. Also you need to check your valve spring seat pressures are at least 220 lbs on the seat. More is preferred.
I have seen exhaust temps of 2500 degrees with late timing and rich mixture. No valve likes that.
Measure all your valves overall length to see if any are tuliping or stretching. Occasionally I catch an exhaust valve stretching .060 or more. But usually that's from a little lean in that hole.
Thanks Fiat, I'm running GM 990 heads if this helps anymore. I'm freshening the motor right now. Do you have a preference on brand of valve or material. I don't know how long these valves have been in this motor, so they are going in the garbage. Is it a waste of money to put any kind of heat coating on the new valves for this kind of application.
BTW are you planning on running with CDBA this year? If so, look me up there. I wouldn't mind putting a face with all the good advise.
I have always used the Manley Severe duty exhaust valves. I have stretched them over .100 and never broke one. The Manley exhaust valve material is different than other companys and it's the one I trust. Intakes are less critical so I have used either Feria or Manley's severe dutys. I don't know of any type of heat coating. Good idea of throwing away and starting over. Measure your length on the new ones and you'll have reference measurements.
You'll chase the valve job for a while if your tune up is off or late timing. I'd just set the timing at 34 locked out and leave it alone. Tune with the blower or fuel curve.
My bet is the seats are going out of round. To see if they are, grind one of the old valves and use some light lapping compound and lap an exhaust. Chances are you'll find the lap disappears in the area where the intake and exhaust seats get the closest. Just grind the seats to fix that.
When adjusting valves between rounds, note valves that tighten. Especially #6 cyl on BBC. Means that cylinder could be going lean.
If you want, pm me with specs of what your motor is and tune up and we'll see where your at.
We hope to make some CDBA races as I really like that group. Fiat has been parked and for sale so boat gets the attention this year.
Originally posted by Fiat48
We hope to make some CDBA races as I really like that group. Fiat has been parked and for sale so boat gets the attention this year.
:eek!: :eek!: :eek!: