Re: Diagnosis Needed

Posted by PackardV8 On 2010/3/28 12:04:16

Compression test and air blowing bach thru the cylinder may not give evidence of sticking valve even if done rather quickly. The 2.0 F engine i mentioned above showed good compression even when warm. Intermittent erradic vacuum on road test only when missing.

The problem is that hte valve sticks ever so slightly open but when given enuf time of a few minutes the spring will draw it closed enuf for good compression reading.

Similar problem on a Tecumseh 3 hp engine. When the engine suddenly stopped and i was close enuf to the engine i could here a 'clink' noise that i did not consider thermal expansion nor contraction noise. It was the exh valve snapping back closed after the engine had stopped for about 10 minutes.

Similar problem on a m/c engine and similar diagnosis.

The F 2.0 engine fought for over 6 months off and on while driving it until i had exhausted all other non-valve related possibilities.

The only way i knew for sure it was a valve was to remove valve cover and spring and to work the valve by hand.

This sticking valve problem is something i have only ran into over the last 6 to 8 years or so. Never had it during the 70's thru 90's.

Some kind of crud is building up on either the stem very near the head of the valve or in the guide very near the head of the valve.