How risky is it to reduce valve clearances?
Registered User
Joined: Feb 2001
Posts: 2,895
Likes: 1
From: You wish
Yeah, I redyno'd but couldn't really tell much of a difference. The bottom end seemed to be better pretty consistently (on the order of 1-2 lbs-ft), but I couldn't tell anything up top. I say that it's probably not worth it for most people.
Burning valves usually tends to occur when you don't have enough clearance. The valve remains slightly open all the time. This is really relevant on the exhaust valve, where the valve loses the vast majority of the heat it absorbs though valve/seat contact.
Honda has put in plenty of slop in the tolerances to avoid any longevity issues. If you adjust the valves every 10k-15k miles (as I do), you can go tighter. I usually don't mess with the exhaust side, but I do go 0.002" tighter on the intake on most Hondas and haven't had any problems.
If you're really worried, you could always try to adjust clearances when hot (say to 0.002") and then see what the return to when cold. This is the only real way to get a feel for how tight you can go on the cold adjustment.
UL
Burning valves usually tends to occur when you don't have enough clearance. The valve remains slightly open all the time. This is really relevant on the exhaust valve, where the valve loses the vast majority of the heat it absorbs though valve/seat contact.
Honda has put in plenty of slop in the tolerances to avoid any longevity issues. If you adjust the valves every 10k-15k miles (as I do), you can go tighter. I usually don't mess with the exhaust side, but I do go 0.002" tighter on the intake on most Hondas and haven't had any problems.
If you're really worried, you could always try to adjust clearances when hot (say to 0.002") and then see what the return to when cold. This is the only real way to get a feel for how tight you can go on the cold adjustment.
UL
Thread Starter
Former Sponsor
Joined: Mar 2002
Posts: 15,526
Likes: 19
The thinnest feeler guage I've been able to find is a .005". How could I measure a clearance of only .002"?
It seems odd to me that the valve clearances should be measured / adjusted cold instead of hot. Why wouldn't it be better to adjust them hot (other than the difficulty of dealing with burnt flesh...)?
It seems odd to me that the valve clearances should be measured / adjusted cold instead of hot. Why wouldn't it be better to adjust them hot (other than the difficulty of dealing with burnt flesh...)?
Registered User
Joined: Feb 2001
Posts: 2,895
Likes: 1
From: You wish
You can get thinner feeler gauges, just look around (my smallest is 0.002").
As for the other stuff, yep, adjusting hot engine parts bathed in hot oil is not fun. Additionally, the engine will be cooling the whole time you're working, which will cause clearances to change as you work.
UL
As for the other stuff, yep, adjusting hot engine parts bathed in hot oil is not fun. Additionally, the engine will be cooling the whole time you're working, which will cause clearances to change as you work.
UL
Thread Starter
Former Sponsor
Joined: Mar 2002
Posts: 15,526
Likes: 19
[QUOTE]Originally posted by marcucci
[B]
I would love to see any data to this effect- I do not doubt that there is a cooling effect from the contact, but I would be surprised if it were appreciable. At least, I would be surprised if increasing the "duty cycle" that the valve is in contact with the head by 10% would have an appreciable effect on it's temperature or reliability.
[B]
I would love to see any data to this effect- I do not doubt that there is a cooling effect from the contact, but I would be surprised if it were appreciable. At least, I would be surprised if increasing the "duty cycle" that the valve is in contact with the head by 10% would have an appreciable effect on it's temperature or reliability.
Thread
Thread Starter
Forum
Replies
Last Post