Decision to Overhaul

[GraemeSmith]

As Aeroconversions say - No published TBO. Overhaul decision up to owner.

Last year - 390 hours. 78/78/78/78 - after lapping the valves. Honing marks still clearly visible on all cylinder walls.

This year - 473 hours. 72/70/58/69 - after lapping valves. Honing marks no longer visible on any cylinders. Decreasing performance has been somewhat masked by low density altitudes giving good performance. The engine has not been as smooth running (if you can ever call a VW smooth) and with summer and high DA's on the way that is only going to get worse.

The iron on the last oil report had ticked up a bit - nothing dramatic - but it was there.

Oil consumption has been up a bit instead of a quart ever 25 hours - more like 1 3/4 per 25 hours.

More oil on the belly.

No 3 has always been the problem child for the builder and for me. Never mind issues of keeping ii cool. Builder had problems with the head on that cylinder from the get go and finally resolved it at about 150 hours with all new EMPI head. Today it was demonstrably soft pulling the prop through. Didn't need the leak down test to tell us it was headed south.

I could probably glaze bust the cylinder walls and fit new rings. But with that amount of work involved - might as well just jump for (hopefully with peace of mind) all new pistons and cylinders.

With the jugs off - the inside of the engine is as clean as a whistle - I'll put that down to regular oil changes, TCP in the fuel to scavenge the lead and recently using Camgard.

Cam lobes show no distress. Look nice and polished and profiles are good.

And while No 3 showed more deposits and carbon than the other three cylinders and the wrist pin was a pig to get out compared to the others - it was number 1 had a broken 1st ring..... Yet it had the best leak down number. Go figure.

New cylinders and pistons on the way.

[GordonTurner]

Good thinking, and in the middle of wonter to boot.

[bvolcko38]

Any score marks due to the broken ring? That ring may have been broken fora long time. Or it may have broken one minute before your last shut down. The periodic valve lapping required to maintain compression is what bothers me.

[GraemeSmith]

Any score marks due to the broken ring? That ring may have been broken fora long time. Or it may have broken one minute before your last shut down. The periodic valve lapping required to maintain compression is what bothers me.

No scoring - for all I know it broke on the way out the cylinder - but I am pretty sure it was broken in place.

Valve lapping - well it's not exactly periodic - but those exhaust valve SEATS do seem to take a beating. No indications of distress on the valves - they are even "burnt pizza" with no green heating on a spot. Seems they are rotating OK. But the seats seem to suffer the erosion.

[karmarepair]

Graeme, what fuel are you running?

[GraemeSmith]

Graeme, what fuel are you running?

100LL

[sonex1566]

Hi Graeme,
I'll throw my two cents worth into this discussion. For years I ran 100LL in a Jab 2200, plus ran it in my AeroVee as well for nearly 80 hours. It was quite common for both engines to have a soft cylinder after 25 hours and need a quick lap of those particular valves. The club I'm in has used Jabiru aircraft for twenty plus years now with each aircraft doing around 1000 hours every year. They suffered similar problems for years, but the LAME for the club conducted an experiment last year on one of the aircraft for a few months. It was run only on Mogas 98, I'm not sure what the equivalent US fuel is as I know the 98 octanes are different from the 100LL octanes for whatever wack doodle reason. The important result was that the leaky valve problems effectively stopped. For this reason, I have only run my Jab 3300 on Mogas since I installed it almost a year ago. So far, it has behaved itself. Its got about 40 hours on it so far, when I pull it through it still 'feels' great. I know a 6 cylinder doesn't 'bounce' like a 4 does, but I am very confident that when I do a leak down at the next service that it will be in the high 70's.

So after all this dribble, I am very interested in how other people have gone using different fuels. My club installed a new Mogas 98 tank and pump setup last year, and the whole fleet runs on it now. I wasn't keen before as I really didn't want to refuel using jerry cans.

[GraemeSmith]

Richard - NOT discounting your thoughts. I think they bend the conversation in a possibly different - though still worthwhile - direction

So trying to separate a few things here.

When I lap valves on a head - I have a jig I made I bolt the head down to and I can pressure test the head only.
If the head is tight (you can usually get 80/80) then when the head is bolted to the cylinder - the next compression test is of the state of the rings. Valves were tight. So soft cylinders THIS TIME - was rings/bores. Hence the decision to overhaul.

The builder of my engine set the 8:1 high compression which needs the 91/98 octane non-autofuel. Setting aside bringing it in from the local motor racing pump 10 miles away - the reality is that if you want to fly anywhere around here - you are going to be refueling on 100LL. So dealing with lead is a way of life. Hence TCP. In my experience in other engines - TCP plus Camguard keeps lead out the valve guides and avoids stuck valves, keeps it off plugs - clean as a whistle usually, and keeps it suspended in the oil so it doesn't sludge the engine. The cleanliness of the engine on tear down, clean plugs and easy moving valves makes me think that this bit is working on the AeroVee. I don't think there is any argument that getting rid of lead is good for lots of reasons and if I could fly between Swift UL94 and GAMI100 pumps - I would. But round here - I would be stuck with just one other airport to visit (the other is so short and deep in trees that it is not an option!!)

My limited experience on this - plus a lot of club culture where O-200's are used - is that leaking valves are usually caused by the valves and guides getting gummed up - which what is now understood to be lead bromide compounds (people used to say carbon).

So for the sake of argument - let's say I have dealt with the lead and it is not a factor.

The bit that is bothering me is how fast the exhaust valves SEATS seem to erode. I'm sure the valves are rotating well. They are even and show no signs of edge distress. But the seats look almost "oval" in wear pattern. It's tough to photograph - it is very slight and you see it in the pattern of the lapping compound. It's like the exhaust gas is flowing like a torch in just one direction across the face of the seats all the time. Possibly it is. Or worn loose guides? They seem to measure dimensionally good still.