Checking Valve Clearance?

[Jeff244]

How important is it to check the valve clearance on small engines? Many of my owners manuals say to check and adjust every year. To be honest, I have never checked them on any engine from lawnmowers to atv's. Is it really necessary if the engine is running OK? I've ordered a couple of service manuals so I can learn how to do it along with other maintenance and repairs, but again, is it really necessary?



Thanks,
Jeff

 

[3RRL]

IMHO, it's one of those things that might not be a necessity if your engines are running good. On the other hand, having proper clearance set ... without a doubt... prolongs engine life and gets you optimum performance. Plus the peace of mind knowing it's correct.

 

[number two]

Correct valve clearance is important for two reasons. The time the valve is closed heat is transfered to the cylinder head,cooling the valve. If the clearance is too small,the valve will open sooner,resulting in less cooling. If the clearance is too great,the valve is not opening as far as it should,reducing the engines performance.
I would think to at least check the clearance at the first recommended interval and see how close it is. Let that be a guide as to how often you wish to check them. A set of go no-go feeler blades make valve adjustment much easier. If you aren't familiar with them,they have a .002" step on each blade. If you were setting the valve to .008",you would grab the .007"-.009" blade. Then tighten the clearance until the .007" is loose and the .009" won't fit. Voila-you have your .008" Good Luck.

 

[Jeff244]

Thanks for the replies,

I've decided to give it a try on one of my atv's. I've got the atv in pieces all over my garage now in order to get to the engine. I am not sure I am doing it correctly. I think I have everything lined up like in says in the book, although I cannot see the timing mark. I can see that the cam shaft lobes are down and the 2 raised pins on the camshaft sprocket are in the right location. I don't really know how to tell if the valves are open or closed since the book doesn't explain it. Anyway, when I checked the clearances, I got .005" on both intake valves and .007" on both exhaust valves. I am assuming that the exhaust valves are the ones on the same side as the exhaust manifold(not that it matters I guess). The proper setting for both is .006". Do the measurements I took make sense? If so I will try to reset them at .006" and try to put it back together. Also, the valve cover gasket came off with the cover and looks good, do I need to replace it?


Thanks,
Jeff

 

[number two]

Jeff,as long as your book says you can do all four valves with the engine in one position,your mark is correct,and the lobes are down,you should be there. Your measurements sound realistic-only off a little,quite common. I would assume the gasket is probably a rubber o-ring type? That would most likely be reuseable. If it looks good,I think you're safe. Enjoy!

 

[Reg]

Thanks for the replies,

I've decided to give it a try on one of my atv's. I've got the atv in pieces all over my garage now in order to get to the engine. I am not sure I am doing it correctly. I think I have everything lined up like in says in the book, although I cannot see the timing mark. I can see that the cam shaft lobes are down and the 2 raised pins on the camshaft sprocket are in the right location. I don't really know how to tell if the valves are open or closed since the book doesn't explain it. Anyway, when I checked the clearances, I got .005" on both intake valves and .007" on both exhaust valves. I am assuming that the exhaust valves are the ones on the same side as the exhaust manifold(not that it matters I guess). The proper setting for both is .006". Do the measurements I took make sense? If so I will try to reset them at .006" and try to put it back together. Also, the valve cover gasket came off with the cover and looks good, do I need to replace it?


Thanks,
Jeff

a) If they're all closed (and they must be if you can get feelers in) then you are at the correct TDC for measuring them.
b) Since you have never done this before it isn't worth the risk of doing it wrong just for ONE thou - IOW, fergettit and put it all back together.
c) If the valve cover gasket LOOKS good it IS good, even if it is slightly torn you could probably piece it together and add a bit of rtv.

 

[Jeff244]

Thanks for the help.

I checked and rechecked the clearances and am sure I got it right.


Thanks again,

Jeff

 

[john_bud]

Now don't you feel better knowing it is correct?

By the way, as the valve seat wears the valve clearance gets tighter and tighter until the valve never seats. Then it leaks hot combustion gasses, burning the valve and seat. Loose valves are safer than tight valves. Just so you know.

jb

 

[ctjstr]

Just as an aside, I've seen way more damage done when people mess with valves and foul things up, then if they'd just left them alone in the first place. If you're going to try and adjust them, here's a couple suggestions. First off, if the engine was running and you go to adjust it and find you're having to do a lot of adjustment, stop, go back and check again. The amount of adjustment on a running engine is usually quite small.
Second, make sure you know whether to check them with the engine hot or cold. Some engines, particularly air cooled ones, change quite a bit with heat.
Third, when you adjust a valve, the process of tightening up the lock nut if you have one will almost always tighten the valve adjustment somewhat, so check again.
Have fun

 

[Jeff244]

john_bud and Ctjstr,



I have always wanted to know how to do repairs and maintenance beyond oils changes and minor tuneups and now I finally have time to do it.

Ctjstr, I understand what you are saying about doing more damage than good. I almost missed a little note in the repair manual about the exhaust valves sharing a common rocker and needing to be checked at the same time using 2 gauges. Things like that worry me the most, it would be obvious to a mechanic, but very easy for me to miss. I spent about 5 or 6 hours tracking down an electrical problem on the machine and felt great when I finally found the cause of the problem(until I found out the new part is about $300.00).

Jb, that is great information about the valves being better off looser than tighter, I have a natural tendency to go tighter, kind of like when torquing bolts, I always go to the higher end of the range, or over. This is the kind of info that they don't always put in the repair manuals.

I really appreciate the help from everyone here and I feel bad that I don't have much knowledge to share with others here, but maybe someday I will.


Thanks,
Jeff