...That time when your crankshaft rods bearings fell apart...

What's up XJ riders!
Faced a problem a month ago....
Decided to check my xj650 Seca max speed, brought it on a straight and smooth road, pushed it to the max speed and after this I began to hear strange knocking sound in the low part of the engine, especially when it is hot..sound was not to loud but still...
So I immediately drove it a few miles to my garage and decided unmount the engine with a friend mechanic to check what have happened. When he took of the engine low cap he said that it was crankshaft rods bearings which fell apart =(
Bad, but not critical! It was the second time when I split the cases on this motorcycle this year (first time to change chain guide....common problem).
Anyway, decided to order a used crankshaft in a good shape with rods and rods bearings assembled...ordered and waiting for delivery in Kyiv now.
Cut to the chase I have a few questions :
- Do I have to order a set of new crankshaft bearings if mine are in a good condition?
- Is it possible to uninstall and install back crankshaft with pistons from under? Without uninstalling head and cylinder? (Do not want to order head, cylinder gasket and other).
- If I will be ordering gasket set, where I can find it? ( Didnt saw on ebay for YICS engine)
- What theoretically and practically could cause such problem on this engine? Changed oil and filter to Motul 10W40 semi-synthetic, 100 miles ago.

Thanks forward for ur advices!

 

there are numbers to be checked and math to do short answer no or maybe but doubtfull

xj4ever catalog

ENGINE BEARINGS:

Crankshaft Bearings:

Yamaha used a unique way of "sizing" their engine bearings, both for the crankshaft main journal bearings and the connecting rod big-end bearings.

The factory coded, via a series of numbers indicating a "size code", numbers onto the crankcase, the crankshaft, and the connecting rods.

The crankCASE has numbers hand-scrawled onto the upper (and possibly the lower, also) engine case(s) ---typically, behind/below the stamped pad where the engine ID number is, behind the clutch cover opening, but, in reality, could be anywhere on the case(s) --- that specifies the main bearing saddle sizes for that particular engine case:

http://www.xjbikes.com/forums/threads/complete-xj650-rebuild.81981/page-2#post-498539

Note that these last 2 sets of 2 numbers --- “40’ / 46” and “45 / 40” in the above examples --- are the codes used for calculating the thickness of the shims used with the middle gear drive shaft of each particular engine.


The crankSHAFT will have two grouped sets of numbers on one end. The first set of 5 numbers are the main bearing journal size numbers for that crankshaft, and the second set of 4 numbers which denote the rod bearing journal numbers for that particular crankshaft. Both sets of numbers refer to the crank journals starting at the left side of the crankshaft (the #1 cylinder side, see the last picture in the post below):

http://www.xjbikes.com/forums/threads/complete-xj650-rebuild.81981/#post-498538


Each connecting rod also has a number that is stamped (with ink) on the rod itself, right where the upper and lower shells meet.


To calculate the correct bearing sizes to use in a particular engine, you will go through the following process:

Crankshaft Main Bearings:

The correct main bearing selection is made by subtracting the crankshaft journal number from the engine case main bearing saddle size number, for each main bearing journal position.


Connecting Rod Big-End Bearings:

The correct bearing selection is made by subtracting the crankshaft journal size number from the rod size number, for each rod/crank journal position.


For both the crank main journal bearings and the rod bearings, you will then use the numbers calculated above to realize a "bearing color" as outlined in the chart below. You would then order the correct "color" bearing for each crankshaft main journal or connecting rod big-end position:

Bearing "Color Codes":

#1 = Blue
#2 = Black
#3 = Brown
#4 = Green
#5 = Yellow

A good visual of the color marking on the bearing can be seen at:

http://www.xjbikes.com/forums/threads/complete-xj650-rebuild.81981/page-2#post-498544



Example:


- Crankshaft is marked 21223 2111
- Engine case is marked 34534 48 47 (note that these last 2 sets of 2 numbers --- ’47’ and ‘48’ in this example --- are codes used for calculating the thickness of the shims used with the middle gear drive shaft)
- Rods are marked 6, 4, 3, and 3

The first set of 5 numbers on the crankshaft (21223) are the main bearing journal sizes for that crankshaft, and are sequentially #1 to #5 as read. The corresponding 5 numbers scratched onto the engine case (34534) are the main journal saddle sizes for that engine and are sequentially #5 to #1 as read. For the #1 main journal position (the far left position), we would have 4 (on the engine case) - 2 (on the crankshaft) = 2. The #1 main journal bearing is a "size" 2, which is a "black" bearing.

NOTE THAT THE HAND-SCRAWLED NUMBERS ON THE CRANKCASE READS JOURNALS #5 TO #1 as you read them left-to-right, and thus in a 5/4/3/2/1 sequence for the main journal bearing sizes! They are actually "backwards" from an intuitive approach (and "backwards" from the sequence they are coded onto the crank itself), but are "correct" in spatial orientation and sequence for the top crankcase half (since they are scrawled "reverse" in relation to the crankshaft position within the crankcase).

For the #1 con-rod, using the example above, you would use the 2nd set of numbers on the crankshaft (2111), and the ink-stamped number on the rod itself. So the #1 rod is stamped as 6, and the #1 crank rod journal is 2, and 6 - 2 = 4. Thus the #1 rod was use a "size" 4 connecting rod bearing, which is a "green" bearing.


Notice that it is NOT unusual for a single crankshaft to use a variety of different "size" or "color" bearings.


NOTE: The yellow "size" bearings are used only for crankshaft main journal bearings. Rod bearings were never made nor available in the yellow "size".

IN ALL CASES YOU SHOULD REFER TO A FACTORY SERVICE MANUAL OR A SKILLED, EXPERIENCED MACHINIST AS TO HOW AND WHAT SIZE ENGINE BEARINGS THAT NEED TO BE PURCHASED AND USED DURING AN ENGINE REBUILD! DO NOT PURCHASE ENGINE MAIN OR ROD BEARINGS BASED ON THE "NUMBERS" ALONE----ALWAYS PLAN YOUR ENGINE REBUILD PARTS NEEDED ONLY AFTER ENGINE DIS-ASSEMBLY, PARTS MEASUREMENT, AND CONSULTATION WITH A MACHINIST.

 

where to buy parts www.xj4ever.com email address on the page

link to catalog

http://www.xjbikes.com/forums/threads/xj-parts-catalog-section-e-engine.44640/

you should also check out your oil pump and passages . find out why your bearings failed

 

Fell apart!?

Pics please. I've never seen plain bearings fail in that manner.

 

Well, not literally...it was from words of the mechanic, that means that something wrong with them..

 

Thank u for ur reply, I will check all this stuff out.

But I do u know if it is possible to uninstall and install back crankshaft with pistons from under? Without uninstalling head and cylinder? (did not find it in ur reply)

 

looking at the manual it looks like you could do that. fitting the pistons back into the cylinders would be the challange. the cylinder sleeves do extend down into the upper case

 

Plane bearings can't 'fall apart' unless they BROKE. There are no ball bearings in there. Sounds like a fishy story to me.

As far as slipping them in without pulling the crank.......I know that with automobile engines, there are people who have done it, but it's considered a very cheap, inferior, and half-@$$ed way of doing it-----and they'll be back into the engine is a fairly short period of time to do it the RIGHT way.

That all said, I wouldn't recommend doing it that way-----

 

+1

The crank is heavy, and trying to refit it while also lining up the connecting rods will be a huge hassle, and likely result in damaging the new bearings.

 

Hi,
I know this is an old thread but I have a question about the numbers printed on the rods. Does the number have a letter in front of like G5?
Thank you!