90LX toasted? (Full Version)

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Methanolover -> 90LX toasted? (8/13/2007 9:41:51 PM)

Hi Bob!


I have a 90 LX that after brake in turned apc 10*10 @ 15.500, 15% fuel with 15%Klots synth + 3%Ricin
After flying several 9-minute-flights , It really came alive and , with a lovely scream pulled my Patriot .40 like a missile. (didn't tach it then though)

Then I did a couple of lean runs, blowing plugs, finally discovered that the Jett bladder tank up front had rotated, kinking a pressureline..

After the tanks (one 12 oz and a 8oz parallelly plumbed) had been secured from rotation, I flew it again, but It doesn't reach the rpm's it did before , now only 14.900 on the ground ,same when set on the test-stand .

I can't say if there's any difference in compression .

Took some photos ,( the ones showing piston and sleeve separately is taken with oil wiped off). Do they say anything to you? (I've so far never toasted a sleeve, don't know what it looks like)



BR HT



bob27s -> RE: 90LX toasted? (8/14/2007 12:07:38 AM)

Man.. weird stuff. Of all the goofy things to happen.

Engine -- hard to tell, it may have lost the seal. But usually a lean run or two won't do that quite that fast.

My suggestion.... put it on the bench..... and put an 11x6 on it for a few runs. Let it turn up while just a bit rich (some of the break-in proceedure again - take it up to 15,500 or so). Give it 2-3 runs (6-10 minuntes) with the light prop. Then try the 10x10 again.

See if that recovers some of the rpm.

If not, and the rpm does not recover much of anythnig, its not likely the sleeve.... the piston is what gets damaged. You can have a new piston fit into the sleeve (requires sending it back) or Dub can send a new piston/sleeve combo.

Of note, more likely than not... the head came loose when the engine got hot enough to blow the plug. Compression loss may have been lost.... or the sleeve may have rotated in the case just a bit when you change the plug. In any case, as long as the engine is apart, you can ensure it goes back together aligned properly, and make sure the head bolts are tight ... especially after the first run (check when warm)

Let me know how you make out

Bob



Methanolover -> RE: 90LX toasted? (8/14/2007 10:14:37 AM)

Bob Allmighty! Thank you!

How would we make it, if it wasn't for you?

I will do what you suggests and report!

Also, the hex exh. outlet restrictor is gone... does that matter much? , (I have a 45 deg silicon extension mounted)

HT



bob27s -> RE: 90LX toasted? (8/14/2007 2:20:07 PM)

The restrictor is there to help balance the back pressure and tank pressure a bit better.

Ive never seen one of those come out before :)

See how it runs on the bench.



Methanolover -> RE: 90LX toasted? (8/19/2007 8:09:49 PM)

Bob,

Did exactly as you said, and now I get 15.200
?
Henrik




bob27s -> RE: 90LX toasted? (8/19/2007 9:25:09 PM)

If that is 15,200 with the 10x10 ....... fly it.

Its is 300-400 rpm lower than it would normally be. But I have seen that much variation sometimes between a warm day and a really cold day on some engines.

Run it like that for a while..... see how things progress. Its not usually worth swapping out parts for just a few hundered rpm if the engine is otherwise behaving properly. You may even see it recover a bit with time.

However if the engine misbahaves or starts dropping rpm beyond that point....... yeah, its going down hill, and may need to be serviced.

Bob



Methanolover -> RE: 90LX toasted? (8/20/2007 10:36:10 AM)

OK!
I'll do so.
The engine seems tighter again,forgot to mention, beeing a bit hard to turn over when cold and primed with fuel, and also emitting that hartbreaking squeeky noise ...

Thanks a lot for your replies!

H



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