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Old 08-16-2003, 02:37 PM   #1
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Default Problem with Mugen MR-12

I have had the MR-12 for some time. I estimate I have used about 1 to 1.5 gals of fuel on it. I live in a high humidity environment (Puerto Rico) and it ususally runs around 250-270 degrees.

I disassembled it today and the conrod bushing fell off. I put it back on but it seems to be loose. I assume I need a new conrod. I have various MT-12's and never had this problem.

Any ideas on what could cause this? I would like to take measures to avoid ruining a new conrod.

Thanks

Jose
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Old 08-16-2003, 04:02 PM   #2
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Consider yourself lucky that it didn't break in pieces and destroy your sleeve/piston/case/button head. That's what happened to me with my RS12. Just get a new conrod and you should be fine. The failure of a rod bushing is inevitable. Consider it routine maintenance after a gallon or more.
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Old 08-16-2003, 04:40 PM   #3
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I've seen some oilites from the conrod to break and create a hell of mess (imagine it breaking at WOT - lucky to saw it before it went to wrong).

I cannot do a fix for it rather than putting a new conrod (get at the same time, the clips that fix the piston and the piston pin on the place, better to change it each time you disassemble the piston pin).

Some argue that is cause by using WD40 on the engines like After Run. Unique I can say is that never happened to me, but I use ATF oil as after run.
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Old 08-16-2003, 04:44 PM   #4
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250 TO 270 SOUNDS KINDA HIGH TO ME ,BUT IF STILL BLOWS SMOKE OFF CORNERS AND GOOD TOP END,KEEP ON GOING""JUST A THOUGHT
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Old 08-17-2003, 09:14 AM   #5
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Old 08-17-2003, 09:15 AM   #6
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Old 08-17-2003, 09:39 AM   #7
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Quote:
Originally posted by EVOLUTION
Whoa! scary hole into an expensive hole. Each time I run mine MRX3 I disassemble the engine to examine the conrod and change if I see a minimum amount of some into the conrod and crank pin. Is cheaper than needing to by a complete engine.

BTW: How ended the crankshaft? the conrod is gouged and seems to receive an impact from the crankshaft. Have more photos about this?
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Old 08-17-2003, 09:51 AM   #8
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Quote:
Originally posted by Corse-R
Whoa! scary hole into an expensive hole. Each time I run mine MRX3 I disassemble the engine to examine the conrod and change if I see a minimum amount of some into the conrod and crank pin. Is cheaper than needing to by a complete engine.

BTW: How ended the crankshaft? the conrod is gouged and seems to receive an impact from the crankshaft. Have more photos about this?
Sorry dude,don't have any more pics.I found them a while back on the zone forum and it's the first time i've seen part of a conrod come straight out of the block!

What do you think caused this,is it too much play in the bushing/crankshaft or maybe the engine revved to long without any additional load(runaway)?
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Old 08-17-2003, 10:10 AM   #9
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Quote:
Originally posted by EVOLUTION
the engine needs some fresh air !
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Old 08-17-2003, 10:27 AM   #10
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Quote:
Originally posted by EVOLUTION
What do you think caused this,is it too much play in the bushing/crankshaft or maybe the engine revved to long without any additional load(runaway)?
When a conrod blows like this is for too much slope in the bushing of the conrod with the crank pin (take attention on this if you appreciate your engines). I safer to spend 20$ on a new conrod from time to time than burn a lot of bucks in a new engine due a blown conrod.

Saw some of those and almost were by a worn conrod.
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Old 08-17-2003, 11:56 AM   #11
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Quote:
Originally posted by EVOLUTION
Sorry dude,don't have any more pics.I found them a while back on the zone forum and it's the first time i've seen part of a conrod come straight out of the block!

What do you think caused this,is it too much play in the bushing/crankshaft or maybe the engine revved to long without any additional load(runaway)?
I had that happen to me years ago with a Paris Rex .21 Turbo. The conrod snapped and blew a hole in the bottom of the case. My dad used some Araldite and repaired the hole. The engine ran good for a long time after that. Like Corse R said it is mainly caused by a worn Conrod end bushing finally giving up. This usually happens just as the engine peaks at Top RPM on the straight or when you give it heavy throttle out of a tight hairpin corner.
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Old 08-18-2003, 09:29 AM   #12
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Quote:
Originally posted by Corse-R
I've seen some oilites from the conrod to break and create a hell of mess (imagine it breaking at WOT - lucky to saw it before it went to wrong).

I cannot do a fix for it rather than putting a new conrod (get at the same time, the clips that fix the piston and the piston pin on the place, better to change it each time you disassemble the piston pin).

Some argue that is cause by using WD40 on the engines like After Run. Unique I can say is that never happened to me, but I use ATF oil as after run.
All this problem with conrods on Novas engines is happened, due to -they made brass bushing too thin, it will happened all the time till you are going to use Novas conrods. It is not due to the temperature or lubricant. Novas engines made too tight initialy and during the brak in period we just killing the shaft and conrod. It is main problem with this kind of set ups. Normaly well designed and well done conrod should last at list 6-10 galons of fuel (we never had this kind of problem in the past, but it was done differently, btw it was 32-34 KRPM, so no need to point it was slow). If you mesure you pin on conrod after run in you will find your pin isn't round any more-it is like egg. There is way to fight with this porblem, but as long as we use as it is, it will be the same.
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Old 08-18-2003, 01:24 PM   #13
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Quote:
Originally posted by Top Gun 777
Novas engines made too tight initialy and during the brak in period we just killing the shaft and conrod. It is main problem with this kind of set ups. Normaly well designed and well done conrod should last at list 6-10 galons of fuel (we never had this kind of problem in the past, but it was done differently, btw it was 32-34 KRPM, so no need to point it was slow). If you mesure you pin on conrod after run in you will find your pin isn't round any more-it is like egg. There is way to fight with this porblem, but as long as we use as it is, it will be the same.
For only information. I've run many .12's and quite .21's and ever changed mine conrods each 6 - 8 litres of fuel (on .12's as a precaution, on .21's as a necessity) and never blow a conrod.

On .12 the low mass of their pistons make this problem lighter, but think on a .21 pulling more than 2.5Hp at more than 40Krpms the conrod gets quite beaten in few time.

The key to have a healty engine is to keep conrods on prime condition and take attention to the wear. Crank pin wear is quite minimal if you pay attention to your conrod tolerances (I have a Nova R1 not WC with more than 20 gallons thru it and 4 complete P/S sets quite worn and beaten, but still is a good practice engine and runs like a champ).

If you want to keep your engines for a long time conrod atention is the key to this.

BTW: RB, Nova and some Novamegas are the SAME conrods, so saying that xxx conrod is better than Nova one is BS.
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Old 08-18-2003, 03:39 PM   #14
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Quote:
Originally posted by Corse-R
For only information. I've run many .12's and quite .21's and ever changed mine conrods each 6 - 8 litres of fuel (on .12's as a precaution, on .21's as a necessity) and never blow a conrod.

On .12 the low mass of their pistons make this problem lighter, but think on a .21 pulling more than 2.5Hp at more than 40Krpms the conrod gets quite beaten in few time.

The key to have a healty engine is to keep conrods on prime condition and take attention to the wear. Crank pin wear is quite minimal if you pay attention to your conrod tolerances (I have a Nova R1 not WC with more than 20 gallons thru it and 4 complete P/S sets quite worn and beaten, but still is a good practice engine and runs like a champ).

If you want to keep your engines for a long time conrod atention is the key to this.

BTW: RB, Nova and some Novamegas are the SAME conrods, so saying that xxx conrod is better than Nova one is BS.
Hey, very interesting! When I sad Novas I was meaning all engines made by Novarossi, including RB, Novamega, some HPI, Novamax etc. So, just mentione it as BS sound isn't right. Fortunatly there are other brands of engines and I was comparing with them.
Conrod worn out doesn't affect by rotating mass as it is affecting by abnormal counter force (during the run in period). If you put your engine together right way (All novas engines is to tight initialy), it will last much longer then 6-8 liters of fuel. I can give you one more tip which material is realy good for conrods-it is old used alloy on the impeller for real airplane, you even don't have to make bushing there-it will last for you at list 4-5 gallons ( I used that alloy before we start making conrods with needle rolling bearing in it-you saw pic in Richey tread). To have pin last 10 times longer, you can plate it by chrome and it will last you forever (new CMB doing it ).
Don't try to confront it, if you don't belive it, make what I recomend you and you will see the difference.
I try to share my expirience with you and you call it BS.
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Old 08-18-2003, 03:51 PM   #15
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I would have to agree with Top Gun!


Quote:
The key to have a healty engine is to keep conrods on prime condition and take attention to the wear. Crank pin wear is quite minimal if you pay attention to your conrod tolerances. If you want to keep your engines for a long time conrod atention is the key to this.

What do you mean by this Corse?

Tare down the motor after every run!?!?!?!

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