sj 50.problem?
 

I got a used sj 50.but it looks new very little run time.copression is very tight.the piston squeeks at the top.I put it on my viper.with a 9x8 apc.started it up.tached it and it will only hit 14,800 peak.Im very pissed right now.any ideas????

RE: sj 50.problem?
 

Take the exhaust off and make sure the sleeve is aligned properly. It should turn a APC 9x8 close to 18,000 rpm.

RE: sj 50.problem?
 

mike you were right.the sleve is not lined up right.how do I fix it?

RE: sj 50.problem?
 

Just take the head off and turn the sleeve so it is symmetrical when looking into the exhaust port. Re torque the head bolts and you will be ready to go. This may have been caused my a lean run but that does not necessarily mean your engine is damaged. The last owner may have thought he was unloading a problem but it may be a very good engine.

RE: sj 50.problem?
 

If so 0-cool may be the recipient of a very good deal! I'm putting my SJ .50 in the SD now, after the West exhaust header came apart right by the weld on the flange last night. It will be nice to have some midrange.

MJD

RE: sj 50.problem?
 

Don't forget to re balance the plane.

RE: sj 50.problem?
 

It will probably be corrrect now.. ;). Last night I took it way up high for engine kill, and played with the glide. I am very pleased with the glide slope, not at all hard to set up and not a brick at all if you don't crank on the elevator of course.

Mike D.

RE: sj 50.problem?
 

How does a liner get turned out of place in an engine?
One of those mysteries in life right up there with how some of those desks in grade school had holes drilled in the desk tops by ball point pens...some went all the way through.

I wonder what method West uses to weld their headers? If it's done right, the weld should be stronger and more crack resistant than the parent metal.....in this application nothing [TIKO]beats gas welding with hydrogen.

RE: sj 50.problem?
 

Not my strong area here - doesn't the aluminum anneal during welding, and require heat treating afterwards to bring back the mechanicals?

MJD

RE: sj 50.problem?
 

I tig weld alum at work and I always preheat it first, then let it cool together,I havedone a few mufflers that way also salvaged from various mishaps.

RE: sj 50.problem?
 

In this case annealing is good, it will never fatigue crack. Certain items on real planes are best done by torch instead of the TIG process, too.
I have never mastered it, the trick is having blue lenses that can see through the yellow cloud of flux into the puddle of aluminum as it forms.

RE: sj 50.problem?
 

A lean run causes the engine to get hot which can cause the head bolts to be loose. Loose head bolts can let the liner turn. That is what I was told and it sounded good to me. :) I never had it happen to one of my engines though. I can't think of any other explanation unless it was just put together wrong.

RE: sj 50.problem?
 

That sounds plausible......man, now that's hot!
I thought it might be a way for some sleazeball to restore compression to an engine he was trying to unload.....but no one in our fraternity would do anything like that?

RE: sj 50.problem?
 

Here's Bob's explanation from the Jett forum to one exasperated customer:

"Look at this first before you adjust anything else..... (this is something we have seen in the past a few times)

Did you get the engine hot along the way? A hot/lean run will cause the head bolts to come loose. Usually will blow a plug too.

Remove the muffler - look into the exhaust port. Make sure the sleeve port lines up proprely in the crankcase. They should center left to right (dont worry about up and down).

If you get a hot run the head bolts can/will come loose. If you change the glow plug with the bolts loose, the liner will rotate when you tighten the new glow plug in place. A mis-aligned sleeve will make the engine either not run, or will make it run VERY poorly.

If the sleeve is not lined up, loosen the head clamp bolts (head bolts) put the piston at the bottom of the stroke. Then use a glow plug wrench on the glow plug to turn the sleeve and head button so it lines up properly in the crankcase.

(if this happened, go over the fuel system again - chance are it went way lean in flight - maybe fuel foam - be sure the tank is padded and not touching the airframe)

..."

MJD

RE: sj 50.problem?
 

Back in the day, switching to a quality after market P/L set for an engine like a Fox Combat Special was a special ocassion. The parts didn't grow on trees, you had to be there at the right time to get those precious pieces. Pinning the liner to the case was user mod numero uno.

RE: sj 50.problem?
 

The Jetts don't have a pin keeping the liner aligned. With the button style head, if the button turns, so does the cylinder. It happened to me the first time I had a lean run. Just as Bob explained, it blew the plug and when I installed a new plug I turned the cylinder. I try not to have lean runs, but if I do, I check the head bolts first thing.

RE: sj 50.problem?
 

Thanks for helping out mike......

Thats basically it. Steel bolts - aluminum case. If the engine gets hot (realllllly hot) .... the bolts will loosen up. And, usually the glow plug gets toasted. So when you go to change the glow plug, the entire head button and sleeve rotates when you try to tighten a new plug in place.

Tends to happen more with the bar stock engines, but does happen with the other engines as well.

Fix is fairly easy. After re-aligning the sleeve, Tighten the bolts back down (gently, this is still an aluminium case). Run the engine for a few minutes, shut it down, and then check the bolts again with the engine still just slightly warm.

Also........ first run afterwards, use a 9x7 prop to let the engine unload, and to ensure it dose not get hot again.

Bob

RE: sj 50.problem?
 

So you mean, I could mail you my flange and header for repair..? :D What's the going bribe rate?

Mike D

RE: sj 50.problem?
 

He he, it would probably be cheaper for you to buy a new one I think.

I'm also not really into welding right now with my injury and all, see( Juno f-20 progress) thread.