Kawasaki VN750 Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter · #1 ·
Well, title says it all. 01 vn750 with an 05 engine, (original engine threw rod bearings and tore up the rod, and the crank, but I was an idiot and didn't save the rest of the engine, bought a whole 05 for $600, minus the carbs, swapped it in, and 3k miles later here I am) noticed some knocking, thought I was losing the rod bearings again, decided to try and save myself some money, take the bike apart before it gets worse, and I might be screwed again,

The problem:
Right side crankshaft bearing spun in the case, the crank is good, thank God, but the aluminum case has some gouging, could easily be machined out, but I know these cases act as thrust bushings for the crank, so would machining it take away this aspect? And would I be alright running a thicker rod bearing? This really should need more than 5 thou machined off to be smooth again, is that enough tolerance for even a stock bearing?

Long story short, what's the limits for machining on the right side case to fit stock crankshaft bearings, and if oversized bearings exist how big is too big?
 

·
Registered
Joined
·
10,534 Posts
Probably need to weld and then machine the case back into spec, but I would need to check the crank specs to see if .005 is too much. Whatever the thrust clearance is, that's what you have to work with.

Finding a stock bearing might be tough, and possibly harder to get an oversized.

There's a parts bike listed on the forum right now.

I'll try to get into the manual later and see what the tolerances are, and see about bearing availability. Honestly have never looked at this for the 750.

Edit: You asked about a thicker rod bearing... Are the rod bearings also spun, or what problem is there? You can't normally use an undersized bearing without machining, but it depends on what sizes are available, sometimes there are .001, .002, etc.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #3 ·
Ope, I mean crank bearing not rod bearing for the oversizing, thankfully the only damage I've found to this engine would be that crank bearing riding in the right side case.

The "manual" that states tolerances and such, is that the infamous one that's referenced in this forum for free download all the time, or is this a different one?
 

·
Registered
Joined
·
10,534 Posts
That's the manual I'm using. Section 8-16

It shows crankshaft side clearance as .05 - .55 mm
That's the same as a thrust measurement. You would need the crank installed to take the measurements.

Manual advised replacement for damaged cases, which I've recently seen some on eBay.
 

·
Registered
Joined
·
369 Posts
I think Spockster is correct in thinking you may need a different crankcase half (or take yours have it welded oversize and machined down = $ costly). I was pretty sure the crankcase bearing is pressed into the case and then honed to fit. Why is/was the bearing seized to the crank? (You need to check the crankshaft to see if it is still perfectly round after having the bearing seize since that may have contributed to the event.) A lot of guys loose rod bearings but spinning a crank bearing would seem to indicate a specific lack of oil to that bearing. Especially if the other bearings are good.

I do virtually everything I can as far as overhauling my vehicles, but fitting the crank, crankcase and new bearings would seem to require better tools and skills than I have now. I could press in the bearing and even hone it to fit the crank but I no longer have the precise equipment needed to measure the ID of the bearing and the od of the crank with the precision needed. No way to use plastigauge here. I would not trust a Harbor Freight micrometer either and unless you are experienced at measuring with a inside mic it is real easy to get it wrong. If you do have quality micometers and are familiar with their use you are probably alright to do this but why it happened will need to be sorted out. Good luck.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #6 ·
but why it happened will need to be sorted out. Good luck.

Yeah, I'm still looking into that, the OD of bearing is definitely worn and pitted, with some gouging on the case, but the crank itself is visibly flawless, I doubt it's out of round, but I'll be sure to check.

I'm 100% the kind of person who likes to try anything once, so I might push my luck with repairing the current case, I do have a 3d printer, and am entirely too familiar with using a set of micrometers, so I'm not too worried about getting measurements right, my biggest worry would be the process of filling in the negative space currently on the case, I'm rather proficient with Flux core welding, but not with aluminum welding, so I'd have to outsource that labor.

Regardless, thank you all for your information and input! I'm shopping for cases at the moment, and it seems that that will be my best option, financially and labor wise.
 

·
Registered
Joined
·
10,534 Posts
Would a small cylinder hone fit to resurface the case?

If a new bearing fits tight in the case, .005 grooves may not be a problem. ??

I'd think oil pressure failure would be the reason for the spun bearing. Check the oil pump and it's drive chain. The fitting where the oil pressure sender threads into, is a check valve or relief valve if I'm not mistaken. Pretty sure I read there's a ball and spring in it.

Is there any discoloration on that crank journal, turned blue? Seems like it would have to seize or begin to seize before it could spin the bearing in the case .
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #8 ·
I have been having some oil pump cavitation issues with this engine for a while, it seems to scoop air somehow and needs the oil filter bleed trick every now and again, and I would frequently (I know I'm a horrible rider for this 😅) cold start it <60⁰ and ride immediately, it wasn't uncommon for the bike to throw the oil light when stopping at a traffic light less than a mile from my starting location, but when riding light was off. So I know it's had oiling issues, I'm definitely going to be deeeeeppp cleaning all the oil passages I can, cleaning the case like crazy, and checking the pump and whatnot. This engine does seem tk have either had new internal oil tubes, or repairs to these tubes as they appear to be significantly more copper in color than the stock ones I've seen, and the silver(?) welding material used on the tabs is distinctly visible despite an other wise dirty and oily case. The case does show signs of a previous rebuild. So I wouldn't be surprised if a previous owner of this engine had oiling issues and also damaged the crank bearing.

But as far as my crank goes, absolutely no discoloration, fading, fogginess, scratching, scoring, etc. Crank looks good, and the ID of the crank bearing looks good, natural wear, but good. As I was splitting the case, the bearing popped out with the crank, so it sounds like the case may have been previously damaged.
 

·
Registered
Joined
·
10,534 Posts
Is there an oil hole in the case and crank journal? Edit: I see it in the manual now. Red Loctite can hold a bearing, but the holes can't be plugged up. There's another product dedicated to bearings, but I forget the name.

I wonder if the pump is cavitation or leaking, pulling air? I've not seen how the oil pickup is laid out. Any of the tubing could leak.

Do you know about the "air entrainment" these engines have when they're cold? Soon after startup, your oil looks like a blown head gasket until it fully warms up, then the oil color returns to normal. The oil literally gets air bubbles in it.
 

·
Registered
Joined
·
369 Posts
I think the crankshaft main bearings get their oil through the crankshaft so any blockage that stopped the oil from getting to the right side could have caused the failure if it is starvation that is the cause.. In reading my Clymer's I see that it sets forth the main bearings are to be pressed in and out with a hydraulic press. Since it does not instruct one to be aware of the alignment of any oiling holes I think they are oiled just like the rod bearings. Of course there could be grooves all around the backside of the bearing that provides the oil. I have a Ford Cleveland that has camshaft bearings available like that.

It then goes on the discuss how all the other bearings that are held in place with retainers can be replaced by heating the case in a oven and freezing the bearings in a freezer then driving then in place by hand (along with Red Locktite). If the prior owner replaced the mains in the case using this method, after driving them out by hand, they would eventually spin. That would account for the fact you do not see the heat damage usually seen when a bearing goes out like you describe. Also the lack of scoring on the crankcase between the bearing and the crankcase.

I recall from tearing down my son's engine the tabs on the oil tubes looked to soldered in place. That could be the "silver" look you are seeing. His is a 2005 and I would guess they might have used different material for the oil tubes over the years the more brass in the tubes the less likely they would be to break from vibration compared to high steel content tubes.

Since you mentioned your prior motor also had "issues" what kind of oil do you use, if you don't mind my asking?
 
1 - 10 of 10 Posts
Top