capman231

Just wondering how many connecting rod bearing failures there have been with this engine?
Mine failed between 20 & 30 Hours (10 -12 Gallons). The engine was broke in on 32:1 Lawn Boy
and changed over to Amsoil at 50:1 after 5 gallons.

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I know about the post from "Pe" on this problem but haven't saw anybody post that they have
actually had a problem until this one. Anyone having any problems with this engine's bearings?


Capman 231

rmh

just wondering- I thought the fuel recommendations for this engine were specific on recommended lube and ratios .
That is - run only a 32-1 mix of a few synthetics. right from initial operation.
The reason I ask is that I recall reading something on a European site about the bearings and recommendations of lube types.

capman231

Hi Dick

The paperwork that came with this engine in November of 2002 (New) said to use a 32:1 mix of synthetic for break in
and a 50:1 mix of synthetic after that. I don't know what the new engines call for.

Capman231

Antique

My Feedback: (4)

Same thing happens to a ST3000 if someone puts a needle bearing on the rod without doing something to the crankpin...It the case of the ST3000 the crankpin is too soft and wears out...
Looks like a few more ounces in larger parts would eliminate things like this...But FAR be it from me to point this out....I just convert and race "overweight underpowered" Zenoah engines

rmh

Not to bum rap the MVVS- but the write up I saw -- made mention of the engine using a quite small bearing -- in order to reduce dimensions /weight etc..
Anyway in order to get longivity - they recommended a syn 32-1 oil mix
Now then - as we know - improper needle settings will kill any engine - even if the oil mix is 2-1.
I am a firm believer in light powerful engines - but I can see where this can get a bit dicey if all is not done correctly--------
the gasoline adaptation of the ST engines was always a non favorite of mine.
But stick ignition on one and use a wee bit of nitro to smooth things ( stir , don't shake ) on some straight grain -- woops -forgot what I was doing.

capman231

Hi Dick:

I agree with you the rod bearing is mighty small and the 50:1 Amsoil I was using might have contributed to
the failure. The one thing I can say for sure was the engine was not lean. The plug that came out of it is a
nice medium brown and the engine was running great. By the way this engine has the MVVS tuned pipe on it
and was turning an 18X8 Mejzlik prop a little over 8000 warm. I am going to run Mobil 1 MX2T at 32 to 1 in it's
replacement. That is the oil that MVVS reccommends now at a max of 40 to 1. The reason I posted this was
to find out if this was a major problem or if something I did killed the bearing.

Capman231

Diablo-RCU

My Feedback: (1)

A tuned pipe adds power and power adds more load and heat to the rod and needle bearings. I would use more oil and see how long the next one lasts.

Rudeboy

At any rate, I'd rather replace the rod on an MVVS than on a Zenoah...

Antique

My Feedback: (4)

Can't replace the rod, you buy the whole crank..IF it wears out..The helicopter versions run at 10,000 rpm all the time, BH Hanson's marine versions around 17,000..With the STOCK crank..
Underpowered ? Right....5.9 HP at 17,000 rpm..
I know, we don't run our airplane engines that fast...The fact that these hopped up engines use the stock crank speaks for itself....
If a bad rod bearing runs very long on the crank, what happens to the crank pin ? Need a crank too ? Cost for both ?

capman231

OK fellows, let me add a couple of bits of information that you can't see in the picture.
First the back side of the bearing looks just like this side. The outer bearing shell is
cracked on both sides. The crank pin looks fine and the rollers in the bearing look fine.
I am wondering if the problem is entirely in the bearing or could it possibly be that the
rod end is not strong enough to keep the bearing from expanding under the constant
beating at the top of the stroke and this expansion is allowing the bearing housing to
expand until it breaks. Once the housing cracks, the bearing develops slop at the top
and bottom of the stroke which I think can only be from the fact that the bearing and
rod end have expanded. Secondly, the crack on the back side is straight behind the
crack you see in the picture, which I think also supports the expansion theory. If the
rod end is changing size or shape what would that do to the bearing and it's housing?

Capman231

Diablo-RCU

My Feedback: (1)

If just the bearing shell is cracked, then it's likely just a bearing problem. The rod isn't designed to strengthen the bearing shell. In a two stroke engine, the rod sees mostly compressive loads. You're lucky you caught the problem before it ate the crank. Heat the rod to about 350F and cool the new bearing in the freezer, and it should just drop in place.

rmh

It might also be nice to see how the crank pin aligns with the cyl bore--
that's a bit tricky unless you can make a perfectly drilled blank to position into the case -over the crankpin- watch for run out
or yank the crank

capman231

Hi Dick, Diablo

This particular motor is an early version (single magnet ignition) and I have ordered a new one to replace it. The motor
is out of warranty, but I think I will contact MVVS and see if they would like to have it back to check. The new motors have
several improvements and is stronger RPM wise. I am going to keep better records on the new one as to time and amount
of fuel and just see how it does. I also am going to run the reccommended Mobil 1 MX2T oil at 32:1 and see if this helps.

There has to be a lot of these motors in use and I haven't saw another post about bearing failure. Maybe the people buy
them and just leave them in the box. I suspect that the major factor in this failure was The Amsoil at 50:1. I will keep a
close eye on the new one.

Capman 231

Rudeboy

Exactly....

Antique

My Feedback: (4)

Which is very rare....I have been working on Zenoah engines for 18 years..I have replaced exactly ONE crank because of big end bearing failure....It was in a 445 twin that was modified for a race plane and was turning over 11,000 rpm, and was run way too lean on mixture....It had raced for two years prior to the failure...It was still running, just loose....
I have replaced MANY A&M cranks that used the same type of bearing as used in the MVVS..A steel shell roller bearing in an aluminum rod can't take as much pressure as a proper roller bearing in a steel rod with a hardened race..A steel rod usually has holes or slots in the end for lubrication..A steel shell bearing is set up looser for the same reason, lubrication..The test for wear in a Zenoah crank is the amout of sideways play at the top of the rod..More than .006 is considered worn out..A steel shell bearing is worse than that when new....Gotta hand it to Brison, they make it work...A&M never could, we know what happened to them...

pe reivers

The oil used does make a big difference, and probably more than halved your service life. You discovered the bearing shell failure just in time, so no harm came to the engine.
Do not replace just the bearing, replace the complete rod, It is easy to do, and not expensive. Be sure to use only fully synthetic two stroke racing oil that exceeds JASO FC class, like Mobil1 2t or MX2T does.