LO206 exhaust valve warp

T

tyreguy

New member
Well here's the question of the week. I wrapped my pipe to close to the head. Now I find out that is a bad thing.
I have removed the head and lapped the valves....they look seated. Should I have new seats put in or I am I in good shape?
 
Not sure about wrap to close to head being or causing and issue. Just lapping valves will not always guarantee a good seal but with that being said if you just had to lap lightly with fine compound you should be fine. I use a torque plate bolted to head and a concentricity gauge to check seats, I have found new heads as far out as .005 and used heads out as far as .010+ . With LO206 I feel spring pressure is pretty light so exhaust valve/seat does not clean/transfer heat as well as it could. JMO. Would be more cost effective to just replace head rather than installing new seats.
 
Wrapping "too close" to the flange does reduce the potential to dissipate heat. As is the case with any racing application, many things come into play. Returning the motor to top-dead-center each & every time the motor is turned off is key to maintaining valve seal. Occasionally checking head torque is important. If a valve job is done, make sure the head isn't warped, and the seal is good between valves & seats. The wrap being closer to the flange shouldn't have any bearing on ruining a seat.
 
TDC has the piston at the top of the compression stroke, so both valves are closed. As Bernie shared, dissipating heat is one reason, another is, with the valves closed, cool air cannot enter through the exhaust pipe, potentially warping the valve. A less than complete seal for the intake & exhaust valves is THE single biggest contributing factor in these motors that decreases performance. Returning to TDC each & every time will help extend the life of quality valve job.
 
In the flathead days, everybody I knew rolled their engines to TDC on comp. Stroke and even pluged their headers for the reasons listed. A worked down boat plug in the header was the ticket, but if you forgot to pull it when you refired, you would shoot somebody. Lol. It seems to be a lost trick. I roll these clones to TDC and tell others to do so as well as why.....:)
 
No way to put a plug in the LO206 pipe unless you remove the spec muffler. Would be a pain to do that with the safety wire and all. But yes, those plugs used to do the trick with the flatheads.
 
Sitting on the front porch, watching the grass grow, can be a tedious task.

Turning the engine over to top dead center, while not being a bad thing, (it never hurts to be cautious) can be a tedious thing with little to no benefit.

Think about this, how would you close all the valves in a V-8? Think about an F1 car, what do they do between practice sessions? Just a guess, but their valves probably get a lot hotter than yours.
 
I have to agree with Al here. The old wives tales of plugging headers and all to keep valves from warping is just that, an old wives tale. The valve has already cooled down if the engine is idling, and rapidly drops when you kill the ignition. File that one with painting your engine black to make it run cooler.....
 
I agree with with Al and makoman on this. That is why my answer above was rather ambiguous. While it wouldn't hurt to close the valves I wouldn't loose sleep if you don't. As far as springs being relaxed, I've tested springs after being removed when engines come in for work. They usually have 10 to 20 race days on them plus practice days. ( sprint karts ). I see a minimal initial drop off from a new spring but after that drop off is hardly worth noting. It's never an issue on LO206 engines that I have seen. For what they cost you may want to replace them in time but I think more as to prevent fatigue based failure rather then spring pressure loss. I've NEVER seen a broken spring in a 206.
 
Test Don't Guess
The single biggest reason for loosing valve seal is heat.
The hotter the engine gets the more chance you will have of loosing your valve seal.
The most likely valve & seat to loose its seal is the exhaust is because (duh) it gets hotter than the intake.
Aluminum melts at about 1220 degrees. http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
The exhaust gas temperature can easily get that hot.
We do not see the head melt but the aluminum will get softer and pliable around the exhaust area of the head.
This is why the head bolt looses it's tension after a while and should be occasionally re-torqued.
It is also a contributing factor for header bolt issues.
The spark plug is also installed in such a position and angel to pull on the aluminum around the exhaust valve seat.
When the aluminum deforms around the valve seat the valve seat will also deform slightly.
You can lap the valves for a very long time and it will not fix your leakage problem.
Recutting the valve seats with carbide cutters is the best way to fix a deformed valve seat. Then lap them lightly.
I prefer to refinish a used head over replacing it with a new one. It seems that once the head has been heated and cooled many times this issue is diminished. It seems that the head and valve seats settle into position and therefore it doesn't seem to happen as often or to the same degree it does on a new head.
 
K12 said:
Thanks for the info. So just the crankcase is sealed? Is there a process for refreshing it?
Click to expand...
You buy a new short block for around $300. Head can be freshened by cutting valve seats and replacing top end parts. If maintained properly the bottom will last a long time.
 
Getting the fuel mixture right is the best way to handle overheated valves, seats, or other internal engine issues.
This ought never to be a problem on a stock engine.
 
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