This is rather disturbing given that we have all invested in what we believe to be a 'premier' product. I must say, this has made me wonder whether I will ever be able to fly this engine with complete confidence. Anyway, I suppose that at some point my disappointment will be minimized when it does carp itself....I would have seen it coming.
I am glad that there are enough people here to provide input on their thoughts and experiences, maybe we will be able to find a way to minimize the chance of failure, even if we cannot avoid it all together.
I thought I would chime in with some of my findings, maybe all the pieces of the puzzle will lead us to an answer that will save our investment.
I agree that the hydrolock potential is there, especially if it is in the lower cylinders all the time, but as people have said, the chances of the cylinder filling with oil, is not really a consideration. Fuel, yes, but not likely to be oil. We all know that the induction system of these engines has been a factory/design problem, and whether it is possible to redesign or create a fix, is available with many people with the skills, such as Ray English. I have not really followed up on his recommendations (if any) from him regarding this engine. I know the 84 has received a lot of upgrades to minimize failure. THis engine was supposed to have received the upgraded inlet and bushing scenario, but since I bought mine from rcjapan, I don't know whether I got these or not. Are all the failures happening on the new and the old version, or is it just one of the two?
Ok, so here are some things i have noticed on the engine, since I got it. I followed the break in procedure where I was running the engine as per the manual, with 15:1 redline oil mix. During the break in procedure, I was tilting the stand in order to get the lower cylinders rotated up, and it was clear that they only fired in the 'rich' state, when they were in the upper position. You can see clearly through the smoke coming from the pipes, and the cyl temps. After a litre of gas through it, I mounted it inverted on the stand, and did another litre that way. In order to heat cycle it, I was removing plugs alternately (probably not good for the ignition, but I would rather replace that than cylinders and internals). After the 2 litres of fuel, I mounted it in the plane, and leaned it up to good idle, transition and HS. It runs beautifully. Added the Keleo exhaust for 'that' noise. Love it.
I checked the cylinder bolts after the first two flights, and got a SLIGHT 'click' from them, just cinched them down. I did it again yesterday, and again, just a click. I am afraid to over tighten now, so will leave them for a few flights.
So, now on to engine temps......I installed a Spektrum TM1000 and put the probe on cyl 1, one fin down, directly under the exhaust port. I know it might not be the ideal place as it will be affected by EGT, but since I started there, and I have multiple flight data, it is my control and I will leave it there for now.
The engine is mounted in an El Cheapo Yak-55M as I wanted a stable platform to test it. Running in an engine on a heavy warbird is not ideal.
As you know, the Yak-55M cowl is like a big bucket, and I installed some louvres to help remove air coming into it. Before I went down this route, I flew it without the cowl for max cooling effect. I recorded temps as follows, all in Deg C.
Idling on tarmac - 110 to117
Mid Stick on tarmac - 115 to 138 (continuous for around 30 secs)
Full bore on tarmac - 125 to 147 (continuous for around 30 secs)
Its interesting to note that as soon as you back off the throttle, it takes around 8 secs before the temps drop down sharply to the idle range.
For flight, with a 22x8 Xoar wooden prop, the following
Mid to 3/4 throttle cruising: 120 - 130
Full bore continuous around the circuit 125 to 143
Full bore vertical - 145 to 155.
Its under propped for sure, there is not enough pitch speed on this prop, so will do a 22x10 on the next flight. There are a few things to consider here.
This plane will not prop hang without over-heating....any lack of airflow over the cylinders will see sharp temp rises.
The temps fluctuate a LOT and temp changes are RAPID. For example, after the vertical, up to a hang, I put her in a steep dive, and by the time I had pulled out of the dive, the temps were back at 130 Deg C. The changes are steep and quick!!
I then mounted the cowl and although there was no baffle, there were three small louvres installed behind each cyl, and I 'assumed' enough air going out, I have come to the conclusion, that assumption was wrong.
So temps were:
Idling on tarmac - 117 to 135
Mid Stick on tarmac - 125 to 140 (continuous for around 30 secs)
Full bore on tarmac - 138 to 155 (continuous for around 30 secs)
Again, temp drops were very quick
In flight we got:
Mid to 3/4 throttle cruising: 135 to 145
Full bore continuous around the circuit 145 to 150
Full bore vertical - 155 to 160 (it crossed the 160 mark briefly, and I immediately put her in a dive to cool down.)
From this I can see that regardless of where I have the temp sensor, this engine seems to have VERY rapid heat cycles from cooler to hot. I also took the time to get her to fly around for a circuit every now and again, completely inverted, to make sure those lower cyl's are seeing some action. I don't want to do too much inverted as the Keleo ring will probably fill up with oil.
I was thinking of finishing the 3 liters of fuel that I have, and then changing the ratio to 18:1 from 15. The plugs are burning a little oily, and although I am running it on what I think is a little rich, I would rather reduce the oil content and keep it rich a little, than lean the hell out of it.
I am not sure if any of this is any use but given that parts are breaking, there may be some connection between that and the big temp fluctuations that I am finding. Metal behaves very differently at different temps and these parts are seeing big variations in temps. Well, mine does anyway.
Regards to all,
Andy