Latest and greatest timing and deck height?

[KRProton]

Ahhhhhhhhhhhh, yes, the fit of the piston in the cylinder. I do remember reading about that in previous posts in this thread. Thanks for copying in your answer to me.

First then, my assumptions of typical deck height without shims being .188" and typical head depth of .185" are correct leading to my correct calculation of the engine with no sleeve shims and .017" head shim is set up as .188/.020.

But according to what Lonnie Finch wrote back on the first page or so, you can't really assume that all engines will have a sleeve height of .188" and a head depth of .185". According to Mike Langlois, my engine required a .001" sleeve shim to get it to .190". So my engine without sleeve shims is .189". Looks like my head is .185" though.

Okay, now to the dry fit;

Of course. Now I remember; measuring the depth of the piston in the sleeve when totally cleaned with break cleaner or whatever ("dry," no lubrication).

If most pistons are fitted deeper than Lee Vonderhey's preference of .280 to .290, and this is .100" shallow of a standard fit, then a standard fit must be around .380" - .390". Of course, the looser (shallower) fit yields less friction and more rpm (unloading) then. At first thought I would think a looser fit would last longer than a tighter fit because there will be less friction and wear. But as, apparently, this is not the case, the looser fit just has less to go before it comes too loose.

Yes, I see that the .230" would be a very loose fit. I also see where Ray wrote anything greater than .200" holds promise.

Okay, now I've put it all together and it all adds up.

Thanks guys!

Tim

[KRProton]

Another question about shimming;

Once you know your engine setup without shims, could you/do you then just do the math and add/subtract shims to get the desired setup without re measuring?

For example, I don't have a depth micrometer (yet) and haven't measured my engine myself (yet). But, again, according to the documentation from Mike Langlois with my engine, it's set up at .190/.018 with .001" sleeve shim and .013 head shim.

Then, without a sleeve shim my engine must be .189" deck height (deck height minus shim, or .190" - .001" = .189").

The head depth without shim = the deck height - piston/head clearance with shims + head shims. The head depth of my head without shims must be .190" - .018 + .013" = .185" head depth without shims.

So, if I know my base engine setup with no shims is .189 deck height and .185 head depth, do you just start adding/subtracting sleeve/head shims to get the new setup you want without re measuring?

Let me guess the answer now that I've thought about it; It's up to your personal choice and whether or not you trust your math. Might be a good idea to check by actually re measuring - especially if you're changing both the head depth/head/piston clearance and deck height at the same time. Or if you're adding/subtracting lots of shims.

In my case, where I want to make a small change from .190/.018 to .190/.019 it's easy and all I need to do is add .001" head shim and forget about it.
You wouldn't re measure then, would you?

Tim

[rocket]

Correct. The heads are ALL 185. once you have the basic numbers of the motor there never gonna change unless you change a component. The next discussion will include the degree wheel that Lee talked about. But the phins are about to whoop the jets and there's honeydoos so later.

[cbk07]

Ray, I have a couple of quick questions......when pushing piston to top of sleeve, how hard should I push? and do you have the number we should be looking for on a Jett 426 motor with piston pushed up dry?

Thx Craig

[rocket]

push it hard enough that it wont move anymore but only with your fingers. i think jett likes it around 395 but i might be wrong. we should ask him.

[cbk07]

Sounds good. Thank you

[KRProton]

Couple of flights on my Sweet Vee again today. Wasn't expecting to be flying these things this time of year, but another beautiful weekend here in the Midwest - my wife launched again for me too!

My setup is now .190/.019. Still running the gallon of fuel with castor added. Prop is 7.4 x 7.5 that measures out to 7.4 x 7.0.

First flight I launched at about 24,500rpm. New, used plug cleaned up with Mother's like Ray showed. Nice flight. Landed, pulled the plug. Element was pulled and color darker than I would prefer I think. Again, I think the residual after-run oil in the engine may have contributed to the darkening. ???

Second flight, another cleaned, used plug. Backed it down a bit and launched at about 24,000. After starting the engine and ready to launch, I inadvertently hit the kill switch and shut the engine off before launch. I fueled it up, richened the needle just a "click," started and launched. Another nice flight, nice landing and all.

This time the plug was good.

Maybe in the cooler, less humid air (heavy air) I need to back away on the rpm a bit.

Well, tonight I'll break-down the engine and oil it all up until Phoenix I suppose. I'm pleased with everything now. (Gotta add the checkers to the other side of the wing and the stab too!)

Tim

[KRProton]

Breaking down my engine to clean out any residual glow fuel, have a look-see and lube it up - piston and liner look fantastic. Any light (and I mean VERY light) browning/coloring washed right off with some brake cleaner and a paper towel.

But say, how do you get the crankshaft out of a Nelson? A few good taps with something friendly like a little wood mallet or something?

Thank you.

Tim

[fizzwater2]

I've started using my drill press as just that - a press. Either close the chuck completely, or put in a dowel & chuck it up tight, put the back end of the case on a wood block and press the crank rearward - after removing the prop drive and collet, of course.

I don't like the idea of beating on the front of the crank with a hammer..

[KRProton]

Hmm, so then, this sounds like a procedure you would do only when replacing parts (such as bearings or the crank) - the crank doesn't just drop out like a regular 2-stroke glow engine. I was simply breaking down my engine to clean and oil it up for storage. Crank removal shouldn't be necessary in this situation,then, yes? I'll just thoroughly spray the inside with brake cleaner to flush out any residual glow fuel, then follow up with lubricating oil (and castor on the piston/liner, both ends of the rod).

That how you do it?

Tim

[fizzwater2]

I wouldn't pull a crank just to clean it, no. That's me, though - others may feel differently.

I figure if it's not broke, don't fix it...

[rocket]

its the front bearing holding the crank back. its due to machining. some snap in some don't. put the threaded end of the crank through the front bearing from the front and you can see where it binds. I chuck the crank up in a drill, turn it with some 1500 a little at a time until the shaft "snaps in place by hand." it wont take much. you absolutely have to feel endplay after assembly, if you don't the front bearing is the culprit.

[rocket]

I wouldn't pull a crank just to clean it, no. That's me, though - others may feel differently.

I figure if it's not broke, don't fix it...

its a good idea to remove the rust on the crank where the front bearing meets the front of the shaft. jima believes this is the cause of the shaft leaving the crank. the rust starts a crack, the crack festers into a frontend saying seeya to the rest of the motor. I have to agree. seen it first hand with a rust ring around the newly broken metal. the other reason the shaft departs is there's no radius between the crank and shaft. meaning there's a 90* between the face of the crank where the bearing meets the shaft. you have agree with this too.

[KRProton]

Well, this brings up a whole ‘nother topic; How do you care for/clean up an engine? And what procedure for just after a weekend’s racing, and after the season for long-term storage for a couple of months? After Wichita I saw Duane Hulen completely tear down his engine and was cleaning it up/lubing it before he even put away the rest of his stuff. I’m on-board with that (probably wait until I get home though).

If you can get the crank to drop out by hand, then it would be easy to do so after each weekend’s worth of racing – drop the crank and flush out the entire engine, lube/oil up for next time.

Sorry to need so much hand-holding, but if the information is out there...and this is my only source. I’m sure there’s no single, right way either.

In my case, I think I will press out the crank and have a look-see. Maybe there’s just some rust holding up the crank on the front bearing. If so, that’ll clean up easily. Or, if necessary, do as Ray suggested and clean it up with some 1500.

Tim

[rocket]

you want it to snap in. just built another N motor and the crank snapped in w/o any help. others need a hammer, you shouldn't need a hammer to install a crank. no tools other than the allen to break it down to the case with bearings.