Now you have me thinking improperly seated or bad front bearing. Are there any rub marks on the crankcase back cover?

Andy

O K, I finally had a chance to read back a little way. I see I am re-hashing some stuff. Sorry about that!

The bearings have been looked over, I see

When I broke mine in, I tried to run a 12X6 right away. I was very dissappointed in the performance. By my 3rd tank, I put an 11X6 on it, and then things started to happen. I could litterally hear the engine go throught the transitions of break in. After a couple tanks on the 11X6, I tried the 12X6 again. It was all the difference in the world. Unfortunately, I don't remember any rattle. The performance got so good, I eventually ran it with a Zinger 14X6. I had it on a Dragon Lady. I did notice the engine was a little finicky with plugs. It liked the OS #8 the best, and I never had a flameout. I ran Omega 5%. We had a couple guy's with OS .91's and a guy with a ST.91, and the .76 outperformed them all. No competition at all. A friend bought a .76 for his trainer, and we broke it in the same way as mine. What a sweet engine! I think it even runs better than what mine did. After seeing how the guy's with the .91's lucked out, another guy talked me out of my .76. I bought the K&B to replace it, thinking it would give my Dragon Lady more life. It is probably my biggest RC mistake to date. I have the K&B running well now, but I had more verticle pull with the GMS. All the 1.00 did was allow me to take a lot of lead out of the nose.

I guess, in summary, try the #8 plug, and run a few tanks through it with an 11X6 prop. Perhaps it will let the animal lose, inside. If the rattle gets worse, I would box it up and send it back to MECOA.

Andy

Hi Andy,

I run both of mine with a Fox RC Long Idle Bar plug, the carb adjustment is close to what it is with the OS #8 adjustment. Both engines work well for me with this plug.

Hope this helps.

Fly4Fun,

Wayne Miller

Britbrat, have you ruled out crank endfloat as a possible cause of noise at idle?

If not, try loading the crank at idle by pushing the spinner toward the engine (all standard safety waivers apply).

I'd also try a few different glowplugs (OS Type F, OS #8, K&B 1L and McCoy MC-59 should all work well in that engine) to see if changing ignition parameters influences the knocking characteristic.

Good luck.

OK, I'll try that.

Thanks

If you see the rub marks on the inside of the crank case cover, you can be sure you have crank float. Unfortunately, the amount of end float needed to make noise, does not require the rub marks be there. My K&B had it real bad. Did I mention that I would never own another K&B ever again?

Andy

At the moment I feel the same way about the GMS 76. My first one was not a "knocker", but it was a performance pig. This one is both. Maybe I'll stick that 11-6 on it & let it rip its own ***** off. Who-knows, perhaps it will like the abuse.

However, I will check for end-float.

I feel for you! Unfortunately, I have seen these problems on many different makes of engines. It seems like no manufacturers are immune. My K&B had 4 separate isues. Other engines I would not own are OS .40 LA, OS .91 FX, and ASP .91. I don't want to turn this into a "what not to buy" forum, but if you see enough issues with an engine, or experience enough issues with an engine, it makes sense to stay away. My only experiences with the .76 have been positive, but you give me reason to be cautious. I wish you the best of luck!

Andy

OK guys -- I'm pretty sure the problem is end-float. There are no marks on the back-plate, but there is just a tiny bit of axial movement when I push/pull on the crankshaft (perhaps 3 - 4 thou).

Do I live with it, or replace the bearings?

Also -- does anyone have NTN bearing numbers for the GMS 76?

Hi,

If the problem is bearings, and I lean more towards muffler resonance, then go to the following site, select the bearing and you can cross reference from there.

http://www.bocabearings.com/
For “Select a Category� select “Hobby Types� then “Radio Control� and look up your engine bearings.

Hope this helps.

Fly4Fun,

Wayne Miller

Wayne, you beat me to it!

Britbrat, they have many different kits for this engine. Anywhere from $19.95 to $84.95. Awesome people to work with! Follow their installation instructions, and you won't have any problems. They will get the bearings to you in a hurry!

Thanks a ton guys. [sm=thumbup.gif]

.If this is a new engine , send it back and let the manufacturer figure out what's wrong. You may have a problem you can fix . GL

PS I wish I took my own advice with my MAG .28. I would have saved a bunch of money and not from GEICO insurance

I agree with RC-Fiend. Unless you like the challenge, I would let MECOA fix their own mistake. I like challenges, but I think my K&B cured me of taking it to an extreem.

I would do that, but like the bonehead that I am, I lost the bill of sale. I'm going to have to deal with it myself.

It wouldn't hurt to give them a call. I have talked to them on the phone, and they seemed easy to work with. Your engine has a serial number. Provided it was not on a shelf in a warehouse for two years, it may show it to be a recent production model. Ya never know....

Good idea -- thanks.

I have always had the best luck with K&B 1L plugs in GMS engines. I used to be a dealer for them until Tower got them and dropped the prices too low.

Another thing to remember about the larger ringed engines is that they take a LONG time to break in. You can't expect full performance until you have a couple of gallons through them. Also, 11K with a 12X8 APC isn't all that bad. A YS 91FZ will barely do that and it isn't considered a poor performer!

An update on my GMS 76, complete with knock & erratic tuning. The knock at idle is still there but seems to be subsiding (don't ask me why) & drilling the fuel inlet hole in the NV assembly has actually cured the erratic tuning -- now it holds a steady 11,000 RPM with an APC 12-8, without sagging or flame-out. I'll let you know if the knock is ultimately terminal, or just an annoyance.

Wayne. I have a couple Gms engines..One is a Tower 46 the other a Gms 47. I installed a front carb on the tower & the engine did not shut down w/ radio trim. Remove the engine, used a pair of slip joint pliers and forcefully seated the carb. Fixed..Runs great..The gms engine was installed the same manner, good idle runs great.. The front bearing does have a seal. No slop , pretty well machined. I did clean out the muffler tap & made sure the carb nipple was also clear. The engine will tach..~ 14,700 with a master air screw Gf3 prop. It is a late issue engine, received from tower early April 2006. I use 15% cool power.. No over heating problems..Seem's to be a good $65.00 engine ! The Tower 46 tunes better w/ a gms front mounted carb. The low end adjustment's are important, changing the low end requires a re adjustment of the Hi end. Bounce back & forth untill a quick smooth transition is achived. Make small changes & don't let the fuel tank get to low when involved in the calibration process.. I Am a tinker and don't mind dis...assembling a new engine..My tower 46 is as reliable as My Os four stroker or the Saito 56.. The Gms 47 is a much better buy than an Os 46 la. ( IMO )..~ same $$$ Good luck..

Be careful, with a GMS carb on the Tower .46. There is a bore size difference, or at least there was. Maybe they changed it. Anyway, it can be hard to get a good seal.

Hi Woofen100,

Thanks for the update. I was looking at this thread the other day and was wondering how many people may have helped. I personally am very happy with the GMS and have no hesitation in picking up "deals" from other modellers who can't get them running and are reluctant to do the mods that were listed here.

Again, thanks for the feedback.

Are there any other success stories?

Fly4Fun,

Wayne Miller

On one of my GMS .32's it helped, the other one it didn't help:-(


I have (2) GMS .32's on a Hobbico TwinStar {just a weee bit overpowered}
One improved with adjusting the LSI, while that did nothing on the other.

I drilled out the muffler pressure taps slightly larger, and put Hobbico muffler extensions on both engines.
Tried different brands of fuel & percentages of nitro, and different glow plugs.

At WOT/horizontal both run fine, but vertical & one dies while the other keeps on keeping on.

Would drilling out that brass insert help on mine, with remote needle valves?

Jim

A buddy and I both have TwinStars with GMS .32s. We had trouble running 9-6 props or any other that let the rpm go up. I think it may be a sympathetic vibration problem and fuel foaming, but I can't be sure. Our problems went away when we went to 10-6 props and got the rpm down. The 10-6 Master Airscrews run fine. With 9-6 APCs we landed single engine about half the time.

You guys think you've got problems -- just try running a GMS32 on a pipe -- there's just no way with the standard LS needle.

The problem is that even at full thruttle, the LS needle still protrudes into the spraybar -- when the engine is set up for a decent idle/transistion.

I made a new low-speed needle up for mine (it's shorter) so that when the throttle is open, the needle ends up about 1mm away and that allows *much* more fuel to flow.