SonexBuilders.net

Hi Jabiru maintainers,

Some of you might have followed the boring threads about the "unhappy"
3300 of mine.

Lately, I discovered that the exhaust valve of #4 was sticking open at
the 350 hours tag. This happened to me already at 125 hours, leading to
a top end overhaul plus conversion back to solid lifters.

It seems quite common, as others on this forum have experienced and this
was confirmed by a Jab dealer I've been in touch with lately.

This, I think, could be better mastered with a dirt simple tool that
I've manufactured today. This tool allows to push the valves open, while
having a good sensitive feeling whether the stem is sticking or not. The
tool is a simple high strength steel rod --I used a 8 mm diameter
rebar-- shaped in a "?". The top or the hook grabs below the thick most
outboard fin of the cylinder head. It has been forged flat to get in the
slot. The inflection point of the "?" comes into contact close to the
tip of the rocker and the bottom end of the "?" is where you carefully
applies the load while feeling any irregularities or hard spot.

Of course this has to be done with great caution, not to hit the piston
with the edge of the valve. So the prop has to be rotated perhaps 90
degrees past the TDC. I have to check on that angle in the hangar. Also,
if you go deep enough, the rod might fall down from its cavity. Note
that this check might be counter indicated for hydraulic lifters.

Knowing an exhaust valve is beginning to stick might be interesting.
Perhaps it is possible to put some drops of solvent with a syringe
fitted with a long needle and activate the valves to dissolve the crud
after some hours of chemical activation, if discovered soon enough. Kind
of preventive maintenance avoiding to remove the head when it is too bad
or even discovering the phenomenon while aloft.

My intention is to regularly check those valves at annuals or valve lash
operations.

Cheerio,

I used to get exhaust valves sticking open on a low compression (7 to 1) TCM IO-470-J engine, which could be prevented by including a quart of Marvel Mystery Oil at the 10 quart oil changes. A couple times a shop was able to free up a stuck (open) exhaust valve without removing the cylinder by using "Mouse Milk", which is a penetrating oil. Prevention was better than fixing the problem. I have since learned I contributed to the problem by taxiing with a low idle RPM, idling TCM engines below 1,000 RPM results in the lead not being scavenged, contributing to the lead buildup on the exhaust valve stem with the result of a valve sticking open. Food for thought.

Hi N190YX,

Thanks for your comment. Interesting to note that the simple act of taxiing might (contribute to) stick exhaust valves.
One more preventing action might be to swap to Mogas instead of Avgas. I'm seriously thinking about it now, since adding Decalin was not sufficient to avoid this kind of issue.

Thanks.

N190YX wrote:I used to get exhaust valves sticking open on a low compression (7 to 1) TCM IO-470-J engine, which could be prevented by including a quart of Marvel Mystery Oil at the 10 quart oil changes. A couple times a shop was able to free up a stuck (open) exhaust valve without removing the cylinder by using "Mouse Milk", which is a penetrating oil. Prevention was better than fixing the problem. I have since learned I contributed to the problem by taxiing with a low idle RPM, idling TCM engines below 1,000 RPM results in the lead not being scavenged, contributing to the lead buildup on the exhaust valve stem with the result of a valve sticking open. Food for thought.

Maybe you already did this, but aggressive leaning (as much as the engine can take without stumbling) during ground ops will also minimize the buildup of deposits, lead and otherwise.