Starter Clutch Replacement

OK, here are some pictures of the lower half. I tried to take one using the nice camera, but the closest that I could zoom in was on the entire case, ha ha. It zooms in very nicely though. I took some individual pics using my phone as well.

I am at least owner number 3 of this bike, I can fairly confidently say no-one in my family ran it out of oil, I know in the about ~5k I have had it, it has had 5 oil changes, ha ha. 3 of them were related to diagnosing the starter clutch failure though. I typically ride in the 4-5k range on the bike, so if I just had to worry about keeping below that, it shouldn't be an issue. I'll try to get pics of the connecting rod bearing as well a little later.

Finally bit the bullet and signed up for imgur as I was having trouble uploading this round. So...:

Full lower case:


Left side rod end:


#1:

#2:


#3:

 

Pictures #4 and 5 (and possibly the last image, too) show some significant bearing damage. Something happened in there..........what do the upper main bearing shells look like?

 

I assume I will need to remove the crankshaft for this? Sorry,I didn't read much further than what I needed to do to replace the starter clutch.

 

Here is the crankshaft under the rod:


Now imgur is giving me crap, the rod bearing pictures are attached. The lateral scratches are from my fingernail, it does catch slightly.

 

Sorry, the rod bearing I took pics of above was #3, attached are #2.

 

The crankshaft main bearing that has the damage is the one I was worried about.
The damage to the con-rod bearing confirms the problem.
As Chacal said, it was run low on oil, or there is a blockage, or the oil pump is not putting out full pressure.
You need to make some choices.

Slap it back together as a light-duty rider (never go above 5,000 RPM), and hope the crank doesn't fail while someone's riding it (I'd even replace the damaged main bearing (honestly, I wouldn't even choose this option unless I had no other transportation (Honestly I'd rather walk))).

Find a replacement crank and the bearings that you will need to install it (you'll need the new crank first so you can do the math for the bearings).

Sell the parts and use the cash to help defer the cost of a replacement engine.

Part or sell the bike as-is and make it someone else's problem.

 

I appreciate you telling it to me plainly. I might have put it back together and just hoped it was fine, but I have too many people depending on me being alive. Plus,I usually keep it between 4-5k, but every once in a while everybody gets a wild hair! I guess I'll be looking for another crankshaft, I've put enough money into this bike to have bought another one at this point, but I'd just have to put more money into getting it where I want it with anything I could afford. This bike will ride (safely) again!

This just fits the day I've had; I just bought a new to me van today and one of the tires blew out on the way home. Grrrr.

Anyone have a spare 750 crankshaft laying around?

 

I found one on ebay: http://www.ebay.com/itm/190787871760
Does that look good?

 

Wow Gnat, you're not in the best spot here.

My first thought would be to try and find a used (from a low-mile engine, preferably) MATCHED CRANK/ROD set......that way you wouldn't be worrying about the rod bearing size compatibility issue.

My second thought would be to try and find a matched CRANK/ROD set with the crank's main journal dimensions (numbers cast onto the end of the crank) that are as close as possible to what you already have......even though you have some main bearings that need replacing, my thought (which may be completely unfounded, but.......) is that you want to keep the same "color" (size) bearings as what is already in there, that is how the case was machined and I'd just feel more comfortable ---- on the bike, on the freeway, at 10K rpm's or whatever ---- with replicating the factory specs as closely as possible.

 

Yes, but he's asking a bit much.
Do this.
Search for XJ750 crankshaft (they are the same for both the Maxim and Seca.
Send each seller a message asking for the nubers that are printed on the end of the crankshaft. Buy the one that is the closest match to the numbers on yours. Those numbers are half of the code that you use to figure what size bearing shells to use. The more of those numbers you see that are identical (both number and position of the number) the fewer bearings you will need to get.
There is no need to rush. Crankshafts sell relatively slowly.

 

OK, this one is cheaper and the rods say G4, which are what mine say. I am going to read through the write up on the XJ4Ever site, I glanced at it earlier and saw there are a few pieces to consider.

 

OK, I have searched over ebay and have sent out the requests for information.

Based on the few that had all the information visible, it looks like I will need to replace at least a few of the bearings, both rod and main journal. Can I swap good ones around as we do for the valve shims as long as they are of the same type (e.g. main journal vs rod, oil holes vs not)? Based on the pictures I have uploaded, do any of them stand out as needing replacement? I assume that any gouges that I can feel with my fingernail will necessitate a replacement?

Thanks!

 

Rod and main bearings are NOT interchangeable.

On crank bearings, the lower bearings MUST have the 3 oil holes in them. The upper case bearings can use either the holed or hole-less main bearings.

On rod bearings, the bottom (cap) bearing does not have an oil hole; the upper (rod beam) bearing may have an oil hole or may not. IF the rod BEAM has the drilled passage for the oil spray (onto the cylinder walls), then the upper rod beam bearing must have an oil hole. Otherwise, the upper bearing can be hole-less, too. We're sure that all of XJ750 (air-cooled) engines used rod beams with oil spray passages (thus requiring an upper bearing with the hole), but are not sure on the other models.

I would NOT recommend swapping bearing shells, even though it "may" be okay. Bearing shells develop wear patterns in them based on where they were mounted and used, and one rod (or main) bearing's wear pattern, EVEN THOUGH IT IS THE SAME "SIZE" BEARING AS IN ANOTHER POSITION, will not be the same and might cause premature oiling/wear issues.

 

Chacals warning about moving bearing shell position has merit, however if the shells maintain the correct clearance, and there is no scoring (run your thumbnail over them. if it catches on the bearing surface then discard the bearing), they can be swapped around. any bearings with scoring that is in any way perpendicular to the direction of crankshaft rotation should be discarded. Visible scoring that does not catch your thumbnail will not effect oiling, but would cause me to not use that bearing for a position swap.
Ideally you would want to use all new-bearings, but that can be cost-prohibitive.
You will need to verify bearing clearances with plastigauge and a dry assembly of the rotating bits.

 

Is there a published list of what the clearances should be? I see the different color codings, but not how to know when to move to a different size.(other than based on the numbers on the crankshaft, case, and rods. I don't even see where they mention the actual size of the shims, just the numbers and their corresponding colors.

 

The bearing sizes are not listed in anything other than color sizes; it's just how Yamaha did things. I think the goal was to make production run smoothly (colors are easier to remember than decimal values, and therefore more difficult to mess up). The bearing to bearing journal clearances are listed in the service manual.

 

i looked at those pictures several times and i just don't see a problem. The crank got hot when that gear was heat treated at the factory and the bearings show very little ware. How many miles on it?

 

The chain sprockets did not get heat treated seperately from the rest of the crank. the crank would warp if it had. Nothing on the crankshaft should be that color.

The upper #2 main bearing is absolutely roached.




That uneven reflection in the second picture is the telltale of a worn out bearing, and it's full of crap (the black flecks) and gouged all to hell.

 

K Moe, is that what they refer to as main bearing oil clearance?

Polock, it has just under 25k on the clock.

 

from looking at the colors, the sprocket was the hottest part, heat treated to be a sprocket