Author Topic: Tight engine (Read 3269 times)

Steve Kientz · « **on:** June 20, 2007, 05:29:16 AM »

I have 2 GMS .32s to break in. At the top of the stroke both of these engines are VERY tight,as in you can barely turn them by hand. Should I run these to break them in the way they are or should I oil them somewhat and work them by hand to free them up? Or , is this something an engine guru needs to take care of? Really don't want to ruin one.I have a GMS .25 and it wasn't anywhere near this tight.
I'm fairly new to the hobby(father flew up until 35 years ago)so any firsthand knowledge i have is old.
Thanks in advance
Steve

Glen Wearden · « **Reply #1 on:** June 20, 2007, 07:40:22 AM »

Steve, some of the ABC engines are so tight at the top they will squeak. Go ahead and break them in per the manufacturer's instructions, and they should be OK. Even after break-in, they'll probably be pretty tight at the top when cold. Glen

Ken Deboy · « **Reply #2 on:** June 20, 2007, 09:15:14 AM »

At least one manufacturer (Brodak) recommends that you don't turn the engine over slowly by hand as the fit is so tight you can damage the engine by doing so.

cheers,
Ken

Steve Kientz · « **Reply #3 on:** June 20, 2007, 10:38:51 AM »

hanks for the info ,will follow manufacturers break in

Steve

Randy Powell · « **Reply #4 on:** June 20, 2007, 03:37:17 PM »

Reminds me of the brand new RO-Jett .65 BSE I got. Took an awful long time to start it the first time. It was so tight at the top that I couldn't turn it over by hand and a starter was useless. About a hunderd backflips later, it finally went over and a few more, it started. After that first start, it's been pretty easy. But that first one was a lou-lou.

Steve Helmick · « **Reply #5 on:** June 20, 2007, 09:11:02 PM »

One thing that will help relieve the "pinch" with a conventional ABN, ABC or AAC engine, is to pre-heat the cylinderhead with a heat gun. With conventional heads (where they stick down into the cylinder bore), this will stretch the bore a little and free up the fit. I don't know if RO-Jets or GMS engines are made that way. The new Magnum XLS series are not...the head just sits atop the liner flange, to save weight. It might still help a little, tho.

Steve

Steve Kientz · « **Reply #6 on:** June 21, 2007, 05:28:30 AM »

We have a club contest Saturday, i'll probably pack them along. That way after I plant my just rebuilt Skyray I'll have something to do.i'd take another plane with me but I've been told tearing up 1 plane a day is usually enough.
Steve

Ralph Wenzel (d) · « **Reply #7 on:** June 21, 2007, 09:23:58 PM »

I now have almost the same situation. Received a new .25LA today, which is truly squeaky-tight anywhere near TDC, and this without the plug! Oh, well, at least I'll know exactly how this one was treated, huh?!

Steve Kientz · « **Reply #8 on:** June 22, 2007, 05:20:34 AM »

I had the chance to run one of the two engines last night. I did 1oz. of fuel at a time ,ran it thru 6 cycles. seems to be loosening up .

Thanks to all
Steve

Bill Little · « **Reply #9 on:** June 22, 2007, 05:41:24 PM »

I want an ABC engine to be so tight it squeals! Those will last the longest if broken in right.

One of Derek Barry's 40s was so tight it would squeal when starting after it had been flown for a bunch of flights. I don't think it will EVER wear out!

Steve Helmick · « **Reply #10 on:** July 01, 2007, 09:13:52 PM »

I'm kinda thinking that running a NIB ABC/AAC/ABN engine with the muffler might not be a bad idea. You need to get the engine's head hot enough to stretch that sleeve at TDC and keep it round. Bench running with the muffler would add heat, and would therefore allow you to run it richer, with more oil flushing out the bad stuff. Any opinions?

FWIW, my .25LAS went straight onto the Skyray 35 with muffler, ran two tanks on the ground, and flew it. No complaints so far, tho I shortly swapped in a .25FP backplate, screws, and a K&B Universal NV assy. I finally got around to drilling out the venturi (to .272") before heading off to Reno and VSC. The idea was that I can always effectively choke it down with Bruline coarse air filter (to about .262" effective) or fine (.252" effective), so it's not like a ruined venturi, which wouldn't be all that tragic anyway, since I can always make a new one. What I could not risk was showing up in Reno with the power this thing had with the big spraybar, to fly at 4,950' elevation. I still haven't tried it with a filter, but should, soon.

Steve

Jerry Reider · « **Reply #11 on:** September 09, 2009, 12:39:41 AM »

My GMS 25 and my GMS 32 did the same thing. They were so tight they squeaked and could barely be turned over by hand. I felt that it was partially due to the fact that the oil used in manufacturing was not a good lubricant. I just put a few drops of fuel in the 25, mounted it, and flew it and it loosened up after one run on a 4 oz tank. After flying it about 6 times, I felt it was pretty well broken in that I could put it through as many and, any stunts that I wanted to. The 32 was even tighter than the 25 so I put a few drops of air tool oil into the glow plug hole and down the venturi before running it. After about 10 flights the 32 is pretty much broken in. I let it warm up for a few laps before I do anything more than an inside loop. It seems to make full power after a minute or so of flight.

Steve Helmick · « **Reply #12 on:** September 09, 2009, 07:28:25 PM »

A mistake I often see is for guys to get the engine running, get a quick tach reading, maybe make a little tweek, and head for the handle. MOST OFTEN the engine changes it's song while they're hotfooting it to the handle! The engine is not warmed up!

I get the engine running, wait until it sounds about up to rpm, pull the battery off. Then I'll either pinch the pressure line (muffler pressure) or block off the uniflow vent (atmospheric) with the tach on the engine. When it drops off after peaking, I release the pressure line pinch or take my finger off the uniflow vent. The engine will be nicely warmed up, and hold a steady tach reading. That's when I tweek the NV, if it needs it. Try it, you'll find it helps...

Steve

Brett Buck · « **Reply #13 on:** September 10, 2009, 09:33:08 AM »

Quote from: Ralph Wenzel on June 21, 2007, 09:23:58 PM

I now have almost the same situation. Received a new .25LA today, which is truly squeaky-tight anywhere near TDC, and this without the plug! Oh, well, at least I'll know exactly how this one was treated, huh?!

It's usually a lot worse with the plug out than with it in.

Brett

Jerry Reider · « **Reply #14 on:** September 10, 2009, 03:04:17 PM »

I guess it's better if they're real tight from new that's better than loose. I'd think it will end up being a better fit between the piston and cylinder after it's broken in. I have an Enya 35 III that I've almost given up on breaking in. It has a half a gallon or so of fuel through it and it's still real tight. At least the GMS engines break in pretty quickly.

Jim Thomerson · « **Reply #15 on:** September 10, 2009, 05:42:02 PM »

I've had a couple of Tower 40's which I could not turn over. Take the plug out and they would flip OK. I took a dremel to a spare head and made it a low compression head. This worked fine. One short run with the low compression head and the engines were fine. I happened to have some diesel fuel handy and ran it through a Tower 40 with my low compression glow head. Putt---putt---putt---putt, typical over rich low compression diesel run. I was amused.

Mike Greb · « **Reply #16 on:** October 10, 2009, 09:26:12 AM »

The fitting of an abc,abn,or aac motor is dependent on the thermal expansion of the parts. It is important for the parts to fit right for the material. Generally, tighter is better up to a point. I have had engines reworked by "experts" who got them too tight. I ended up finding other pistons and re-honing the liner. One x-36 AAC slow rat motor that Henry Nelson set up for me never did have any pinch, but re-started fine and had great power. That motor held the national slow rat record for over a decade until the rules were changed last year.
One thing I have found out about running abc or aac motors on the bench is to be sure not to get them flooded. That washes all the oil off the cylinder and the piston tends to stick hard if it is tight. I don't spend very much time on the bench with most modern motors, just enough time for me to get familiar with the motor and make sure there are no suprises.

Greg L Bahrman · « **Reply #17 on:** October 10, 2009, 04:53:21 PM »

<One thing I have found out about running abc or aac motors on the bench is to be sure not to get them flooded. That washes all the oil off the cylinder and the piston tends to stick hard if it is tight.>

Mike,
I don't think it has anything to do with washing the oil off the cylinder walls as there is oil in the fuel, but what does happen is that the flooding the motor with a lot of fuel will cool the motor quickly causing the sleeve to shrink tight on the piston thus making it hard or harder to turn over.

Brian Hampton · « **Reply #18 on:** October 11, 2009, 07:36:09 AM »

Engines that have a pinch should never be turned over slow enough to make them squeak, especially a new engine that only has preservative oil in it. Turning them over slowly gives enough time for any oil to be squeezed out from between the piston and liner giving metal to metal contact. Usually a moderately fast flick doesn't give enough time to squeeze out the oil so there's still an oil film in place. With an oil film in place the pinch generates huge (hydrodynamic) pressures in the oil film which both expand the top of the liner and compress the piston crown. That's generally speaking because some engines can have a very tight pinch much like a certain iron piston engine I've almost finished running in. That one was a bear to get running the first few times. AAC's don't seem to have much, if any, pinch. The Enya 60X has none from new and my Bluebird 28 only had a minor pinch.

Greg L Bahrman · « **Reply #19 on:** October 11, 2009, 05:21:30 PM »

<AAC's don't seem to have much, if any, pinch>
I don't know if this was a typo or you really believe this.........Anyway OS ABN motors have the least pinch. OS's are designed to be like this. It makes them more user friendly in terms of a shortened breakin time. AAC's which is aluminum piston and aluminum sleeve chromed tend to have the most pinch. Aluminum expands and contracts more than the others but the dimensions of the bore and the piston and the tolerance of the fit has more to do with pinch than anything. The engine designer can make the pinch whatever he wants.

Brian Hampton · « **Reply #20 on:** October 11, 2009, 08:35:59 PM »

Quote from: Greg L Bahrman on October 11, 2009, 05:21:30 PM

<AAC's don't seem to have much, if any, pinch>
I don't know if this was a typo or you really believe this.........

Not a typo. My own Enya 60X has no pinch (although I got it second hand) but this has been backed up by others who also have the 60X from new. Agreed a designer/manufacturer can use whatever pinch they like but Enya seem to know what they're doing.

On the controversial subject of getting a new ABx up to hot running conditions quickly or it'll be ruined I've always had my doubts about this so a few years ago I carried out an experiment on a brand new ABC by running it absolutely slobbering rich right from the first start. Before I started it I checked where the pinch began (no plug and using a degree wheel) and rechecked at the end of each tank. After 45 minutes of this there was no change in pinch at all. On stripping the engine the only signs it had been run was that the top of the lower rod bush was getting a polish and the chrome on the liner was polished slightly down below the top edge of the transfer ports. The piston was unmarked. After reassembling the engine I gave it a tank set at a fast but still somewhat rich 2 stroke and the pinch was then almost gone. Because of this experiment I've now changed the way I run in that type of engine. Too rich doesn't do anything so I start at the 4-2 break point then gradually increase revs to slowly build up heat (mainly in the piston from decreasing internal cooling by gradually leaning the mixture).

Greg L Bahrman · « **Reply #21 on:** October 11, 2009, 09:08:34 PM »

Interesting, I went to the ENYA site.......http://www.enya-engine.com/ListCL_E.html
and it showed the 61CSX PRO to be a ABN motor and not an AAC. What usually happens to a let's say an ABC or an AAC motor with a good pinch that is not brought up to temperature during the breakin period is that the rod will be overloaded because it can't force the piston up into the tight bore that is not expanded properly by the temperature. I have seen the rod break and I have also seen the upper end of the rod eggshaped from the practice of running a new ABC or AAC motor to rich (read that as cool). Well anyway no matter, they are good motors. I guess everyone has their own breakin system that works for them. Happy flying

Brian Hampton · « **Reply #22 on:** October 12, 2009, 11:13:10 PM »

Greg
Yes, the 61CSX is ABN but the earlier 60X-III was AAC and AFAIK the first production engine to use AAC. Enya still list the SS25 TN as being AAC. The only other mass production engine I know of that used AAC was the Bluebird (sold in the USA as Brat) with their 25, 28 and 45. My Bluebird 51 is ABC though and that's the one I used for my experiment which caused quite a stir when I reported the results in RCU at
http://www.rcuniverse.com/forum/m_2875125/mpage_1/key_/tm.htm

L0U CRANE · « **Reply #23 on:** October 14, 2009, 02:52:21 PM »

Regards break-in...

I had a project for a friend, to do initial break-in on a sizable number of one model of OS engines. What I observed has also appeared on several of my own and a few friends' OS engines since.

First start is often, mmm, shall we say "reluctant?" Exhaust oil is fairly dirty for the first two or three short, heat-up runs. Fuel usage also is pretty thirsty. After 4 or 5 brief, bench runs - to fully heated throughout, then fuel-line pinched off - exhaust oil runs cleaner, starting is easier hot or cold, and fuel 'economy' starts improving.

At about that point, I'd consider them safe to fly, provided you don't go over lean. Too rich is also a serious no-no...

Economy and power continue to improve, and starting stays easy. ...for a long time...

I figure from this that these engines need some carefully controlled initial runs to smooth off tooling marks and any overly tight fits. These are not very large, but large enough to show the symptoms, above. Polishing-in the fits at operating temperature completes the desired break-in.

I've also noticed that the smaller OS engines, often run in low-2 cycle, benefit from leaving the plug connected until they audibly 'lock-in.' A few seconds is all it needs to bring them to full heat. A premature launch sometimes seems to prevent them from 'getting on the step.'

Author Topic: Tight engine (Read 3269 times)

Steve Kientz

Steve Kientz

Steve Kientz

Steve Kientz