i just got it back from horizon after a bearing failure. they replaced just about everything inside, but now it suddendly stalls while idling and you can spin the prop without hitting any compression stroke. after you spin it for a while it regains compression. it tried doing a valve adjustment , but it still happens. thanks for any advise.

well, i just read that the supplies (.1 mm)gauge is useless b/c the valves should be set at .04-1.0mm could the valves get so far out of adjujstment that the compression is totally lost-then regained?

This sounds like a sticking valve. Next time it happens, pop the valve-covers and see if either of the valves is sticking open.

If it is, you could try putting some oil (Mobil 1 synthetic would be about the best) directly on the stem of the offending valve (or as near as you can get to the stem).

The valve-gear of most 4-strokes doesn't get much lube (unless it's mounted inverted) so it always pays to pop the covers and give them a squirt of oil ever now and then.

If the valve still sticks you might have to pull it out and check for varnish buildup, dirt or (worst of all) a bent stem or guide. Failing that, send it back.

The .1mm gauge is the correct NO-GO gauge. The valve lash should be between 0.04mm and 0.1 mm (0.0016" and 0.004").

Ivan

i know the valve gap is very important , but can it cause complete loss of compression like a valve sticking?

Yes, a sticking valve not only can but WILL cause complete loss of compression.

Ivan

right, but will the tappet gap cause the valves to stick?

Originally Posted by txfly

right, but will the tappet gap cause the valves to stick?

No. Lack of gap will keep the valve slightly open and the engine will have reduced or no compression at all. Keep in mind that when the engine warms up the valves and the lifters (the rods between the cam and the rockers) extend and if there's insufficient gap (cold engine) the engine will end up with one (or both) valve slightly open during the compression stroke and it will lose compression. When the engine cools down it will regain compression.

Ivan

my problem is the engine (hot) will suddenly (violently) die and you can free spin the prop. after a while it will regain compression. it was just set by horizon .

the only thing i can think of is a valve is sticking then coming loose the regain the compression

if youre reving the motor this does not happen . it only happens when the engine is running at idle.

We might be steering in the wrong direction (valves). It could be just improper idle needle setting - the engine backfires which will cause it to stop. A warmed engine usually has less compression (by feel when turning the prop). Tach it to see if the engine has enough power at WOT. If it is OK at WOT you can rule valve problem out. A 4-stroke can backfire at idle if the setting is lean or way too rich.

Ivan

backfire and lose total compression?(prop free spins)