Dead external crankshaft bearing

[dinogt]

Some bearings are die because the crankshaft turn wrong, by exemple more than 0.06mm , we tell in France "faux rond" => "wrong round" ?

If you insist with a too much wrong crankshaft, with gooooods biiiiiigs viiiiiibraaations...you willl have that.
There, the crankcase is also dead, he has the same mades.
I can't do new external bearing with a bush so bad.
The worst is that this bearing can turn about well in the fingers , when we hold it in the hand and do it turn

[rbond]

Oldjapanesebikes we need a translation please!!

[tz375]

Loosely translated:

Sometimes the end of a crank is out of true and causes the bearing to damage the crankcases as well - see the photo to see metal transferred to the bearing from fretting.

When the crank is out of round like that a bearing cannot fix the problem. It needs a new crank end or the shaft to be straightened.

I think.

[oldjapanesebikes]

Loosely translated:

Sometimes the end of a crank is out of true and causes the bearing to damage the crankcases as well - see the photo to see metal transferred to the bearing from fretting.

When the crank is out of round like that a bearing cannot fix the problem. It needs a new crank end or the shaft to be straightened.

I think.

+1

[dinogt]

Loosely translated:
Sometimes the end of a crank is out of true and causes the bearing to damage the crankcases as well - see the photo to see metal transferred to the bearing from fretting.

Yes and no, the metal do not transferred, it is not fretting.
Fretting is when there is no bore between bearing and his shaft, both are welding (like tig or mig).
Here the balls of the bearing give hammer and leave big scratches, the same at negatif are in the crankcase

When the crank is out of round like that a bearing cannot fix the problem. It needs a new crank end or the shaft to be straightened.

there, the bearing and crankshaft are game over...the crank end can be good, it does not hurt, but the con rod can have too hurt...with vibrations.
Just change crankcase, bearings and do crankshaft "true"...straightened good...about 0.02 - 0.02 - 0.02 mm turn oval
I know my english bad but I try to explane good things but as Michel Jackson said "whose baad"....I'm baad...need a dancing smiley :banane:

[Joiseygirl]

[quote I know my english bad but I try to explane good things but as Michel Jackson said "whose baad"....I'm baad...need a dancing smiley [/quote]

Hey Dinogt, no need to excuse yourself....I'm sure your English is far superior to the French or Spanish that others here can't even attempt to tackle. So, you have my full admiration for trying your best.

[dinogt]

I think a little different.
I have put off 3 crankshaft with those default.
each has about 0.9mm wrong round.
The worst in pic had biggsvibrations (worst machnined crancshaft) and 9000rpm...if we insist more and more, crankcase deform. They are very strong but like on a 250RS they can deform.
you are true when you speak about accelerations but a crankshaft must turn at 0.02 - 0.02 - 0.02 or less to during long time, powered or not.

[tz375]

This was proved time and again with Yamaha TZ's, you could gain 5-10 bhp by rebuilding a brand new engine to the factory specification/tolerances, rather than as it came from the factory with out any tuning except minor tidying of ports and castings and would include REBUILDING and balancing the brand new crank.

That sir does not seem credible.

I have and have owned and raced many TZ parallel twins and there is no way that rebuilding a crank yields 10HP in my experience. That's an old myth from articles back in the day and mentioned by AG Bell. The real problem is ports that don't match and rods of different lengths etc. Blueprinting a worst case scenario new engine would give a couple of HP. Not 5-10.

That said, your experience could be different to mine. If you bought a TZ back in 72-76 ish and put it on a dyno and then stripped and rebuilt the crank and found 5-10HP and have the proof, I'll happily accept that as a fact. Until then, it seems to me to be an exaggeration.

The transfer of metal in those shots of Dino are caused by vibration or or out of balance forces or an out of round crank. I personally don't believe you can tell which unless you measure the crank. Dino did that in his samples and found it to be out of round crank ends. You found loose case bolts. I have stripped motors and found that situation where the cases were fine and all bolted up nice and snug.

[dinogt]

my answer at your question is there
http://www.dinogt.fr/refection-de-vilbr ... in---video" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
if I can, at the end of the shaft,as far as I can, at left and at right, then in the video I can't at right because the cone axis is damaged.
When my crankchaft turn well, I put bearings and, sometimes I must mouve the shaft a little to turn ok, for men on a twin cylinder, ok with 4 bearings is maximum 0.02 - 0.02 - 0.02 - 0.02 = 0.08 total, on a T500, there are 3 bearings,so I try 0.06 total maximum.
You are true with the idiots who did not align...but...the crankshaft bearing in the pic (at the beginnig) has been doing by a French professionnal, he has his web site, very knowly whith HIS 500 T re builit !!!!! a real looser...he built again now for how whant....incredible

[dinogt]

The transfer of metal in those shots of Dino are caused by vibration or or out of balance forces or an out of round crank.

I repete, it is not transfer metal, it is hurt hammer when the rod is down....down because it is the down case whitch deform, the top can't because it is too near the cylinders and fixed at them.
Transfer metal is fretting, when there is no bore, no spacement between shaft and bearing small bush

[tz375]

Dino,

In the photo the bearing appears to have raised bumps which i am interpreting as metal from the lower case which has transferred to the outer. Is it really metal on there?

One thing that is not always apparent is that cases flex and allow movement. Bearings should be slightly larger than the hole into which they fit to provide a degree of "crush". The harder a motor runs, or vibrates, the more the cases flex and become oval. Of course the aluminum cases also want to expand more than the steel bearings and that has to be allowed for.

[tz375]

Yep, I assumed we were talking twins not 4's. Wrong assumption on my part.

And you are right I haven't built motors for any world champs, only local US champions. I'm not claiming to have more experience, but I've also built parallel TZ twins, V twin TZs as well as TD3s, TR3s, and any number of RD twins as road and race bikes, so all I'm saying is that I'm not a complete beginner either. I have also read SAE papers but this isn't a contest as to who has the biggest you know what.

And I don't do this for a living. It takes far too many hours to build a motor right to charge what is needed, I'd be making a very low hourly wage. I do this for fun and to keep learning.

It's good to have you here and more experience. that adds to the pool of knowledge and hopefully some of it can be transferred and passed on.

And yes I understand that T500 and other motors such as TZ twins have steel inserts and they can still suffer main bearing damage.

As to the cause, you have some ideas that I'm not convinced about, Dino has others and I 'm not convinced he's 100% right either, but I'm not going to test the theories, so I'm happy to leave it as something that happens that needs to be fixed by putting a well trued and balanced crank into a good set of cases which are correctly torqued.

I do understand your frustration at being questioned by people with half of your experience though. That happens to all of us and I'm the same age as you and I see this in the business world sometimes and it can be very annoying.

Peace and thanks for the input and insight.

[dinogt]

but I'm not going to test the theories, so I'm happy to leave it as something that happens that needs to be fixed by putting a well trued and balanced crank into a good set of cases which are correctly torqued.

I think that to know or not if the crankcase is michmach (possibleafter 40years...), we must see them a few moment..
There are 3 bigs holes, 1° for shaft, 2° for clutch and the 3° for ending transmission.
Take the crankcase empty....see the 2° and 3°...measure well the holes, at left, right, high, low....if the measures are good and the alignment high and low are also good, the 2 crankcase are not mich mach, they are origine but deformed at the 1° down one
I hope every one understand.
This deform can be doing by a vibration we tell in french "lacet", it is a vibration we found most on a bi cylinder and it has about this form (((( I )))) ...I is the con rod in his position.

[dinogt]

For more understanding, see a crankshaft like in my video...in front or you, pistons at high.
the "the " lacet " give a mouvement rotation alternative, at left high when right down and inverse so at left down ant right high.
The lacet is very important on a 3 cylinders.
We can see it on a T500 when the engine at 1000rpm and clow accelerations....see the cylinders and the cylinders top how they vibrate (((((((((I)))))))))
It is also frequent on the 350 rdlc (rz ?) and we can also see it on those motors.
This vibrate deform the bottom of the cylinders, more external screw than internals
I never see this vibration in a single